Lamotrigine Extended-Release

1 INDICATIONS AND USAGE Lamotrigine Extended-Release Tablets are indicated for: • adjunctive therapy for primary generalized tonic-clonic seizures and partial-onset seizures with or without secondary generalization in patients aged 13 years and older. ( 1.1 ) • conversion to monotherapy in patients aged 13 years and older with partial-onset seizures who are receiving treatment with a single antiepileptic drug. ( 1.2 ) Limitation of use: Safety and effectiveness in patients younger than 13 years have not been established. ( 1.3 ) 1.1 Adjunctive Therapy Lamotrigine Extended-Release Tablets are indicated as adjunctive therapy for primary generalized tonic-clonic (PGTC) seizures and partial-onset seizures with or without secondary generalization in patients aged 13 years and older. 1.2 Monotherapy Lamotrigine Extended-Release Tablets are indicated for conversion to monotherapy in patients aged 13 years and older with partial-onset seizures who are receiving treatment with a single antiepileptic drug (AED). Safety and effectiveness of Lamotrigine Extended-Release Tablets have not been established (1) as initial monotherapy or (2) for simultaneous conversion to monotherapy from 2 or more concomitant AEDs. 1.3 Limitation of Use Safety and effectiveness of Lamotrigine Extended-Release Tablets for use in patients younger than 13 years have not been established.

2 DOSAGE AND ADMINISTRATION Lamotrigine Extended-Release Tablets are taken once daily, with or without food. Tablets must be swallowed whole and must not be chewed, crushed, or divided. • Do not exceed the recommended initial dosage and subsequent dose escalation. ( 2.1 ) • Initiation of adjunctive therapy and conversion to monotherapy requires slow titration dependent on concomitant AEDs; the prescriber must refer to the appropriate algorithm in Dosage and Administration. ( 2.2 , 2.3 ) · Adjunctive therapy: Target therapeutic dosage range is 200 to 600 mg daily and is dependent on concomitant AEDs. ( 2.2 ) · Conversion to monotherapy: Target therapeutic dosage range is 250 to 300 mg daily. ( 2.3 ) • Conversion from immediate-release lamotrigine to Lamotrigine Extended-Release Tablets: The initial dose of Lamotrigine Extended-Release Tablets should match the total daily dose of the immediate-release lamotrigine. Patients should be closely monitored for seizure control after conversion. ( 2.4 ) • Do not restart Lamotrigine Extended-Release Tablets in patients who discontinued due to rash unless the potential benefits clearly outweigh the risks. ( 2.1 , 5.1 ) • Adjustments to maintenance doses will be necessary in most patients starting or stopping estrogen-containing oral contraceptives. ( 2.1 , 5.9 ) • Discontinuation: Taper over a period of at least 2 weeks (approximately 50% dose reduction per week). ( 2.1 , 5.10 ) 2.1 General Dosing Considerations Rash There are suggestions, yet to be proven, that the risk of severe, potentially life-threatening rash may be increased by (1) coadministration of Lamotrigine Extended-Release Tablets with valproate, (2) exceeding the recommended initial dose of Lamotrigine Extended-Release Tablets, or (3) exceeding the recommended dose escalation for Lamotrigine Extended-Release Tablets. However, cases have occurred in the absence of these factors [see Boxed Warning] . Therefore, it is important that the dosing recommendations be followed closely. The risk of nonserious rash may be increased when the recommended initial dose and/or the rate of dose escalation for Lamotrigine Extended-Release Tablets is exceeded and in patients with a history of allergy or rash to other AEDs. It is recommended that Lamotrigine Extended-Release Tablets not be restarted in patients who discontinued due to rash associated with prior treatment with lamotrigine unless the potential benefits clearly outweigh the risks. If the decision is made to restart a patient who has discontinued Lamotrigine Extended-Release Tablets, the need to restart with the initial dosing recommendations should be assessed. The greater the interval of time since the previous dose, the greater consideration should be given to restarting with the initial dosing recommendations. If a patient has discontinued lamotrigine for a period of more than 5 half-lives, it is recommended that initial dosing recommendations and guidelines be followed. The half-life of lamotrigine is affected by other concomitant medications [see Clinical Pharmacology (12.3)]. Lamotrigine Extended-Release Tablets Added to Drugs Known to Induce or Inhibit Glucuronidation Because lamotrigine is metabolized predominantly by glucuronic acid conjugation, drugs that are known to induce or inhibit glucuronidation may affect the apparent clearance of lamotrigine. Drugs that induce glucuronidation include carbamazepine, phenytoin, phenobarbital, primidone, rifampin, estrogen-containing oral contraceptives, and the protease inhibitors lopinavir/ritonavir and atazanavir/ritonavir. Valproate inhibits glucuronidation. For dosing considerations for Lamotrigine Extended-Release Tablets in patients on estrogen-containing contraceptives and atazanavir/ritonavir, see below and Table 5. For dosing considerations for Lamotrigine Extended-Release Tablets in patients on other drugs known to induce or inhibit glucuronidation, see Table 1 and Table 5. Target Plasma Levels A therapeutic plasma concentration range has not been established for lamotrigine. Dosing of Lamotrigine Extended-Release Tablets should be based on therapeutic response [see Clinical Pharmacology (12.3)] . Women Taking Estrogen-Containing Oral Contraceptives Starting Lamotrigine Extended-Release Tablets in Women Taking Estrogen-Containing Oral Contraceptives: Although estrogen-containing oral contraceptives have been shown to increase the clearance of lamotrigine [see Clinical Pharmacology (12.3)] , no adjustments to the recommended dose-escalation guidelines for Lamotrigine Extended-Release Tablets should be necessary solely based on the use of estrogen‑-containing oral contraceptives. Therefore, dose escalation should follow the recommended guidelines for initiating adjunctive therapy with Lamotrigine Extended-Release Tablets based on the concomitant AED or other concomitant medications (see Table 1). See below for adjustments to maintenance doses of Lamotrigine Extended-Release Tablets in women taking estrogen-containing oral contraceptives. Adjustments to the Maintenance Dose of Lamotrigine Extended-Release Tablets in Women Taking Estrogen-Containing Oral Contraceptives: (1) Taking Estrogen-Containing Oral Contraceptives: In women not taking carbamazepine, phenytoin, phenobarbital, primidone, or other drugs such as rifampin and the protease inhibitors lopinavir/ritonavir and atazanavir/ritonavir that induce lamotrigine glucuronidation [see Drug Interactions (7), Clinical Pharmacology (12.3)] , the maintenance dose of Lamotrigine Extended-Release Tablets will in most cases need to be increased by as much as 2-fold over the recommended target maintenance dose to maintain a consistent lamotrigine plasma level. (2) Starting Estrogen-Containing Oral Contraceptives: In women taking a stable dose of Lamotrigine Extended-Release Tablets and not taking carbamazepine, phenytoin, phenobarbital, primidone, or other drugs such as rifampin and the protease inhibitors lopinavir/ritonavir and atazanavir/ritonavir that induce lamotrigine glucuronidation [see Drug Interactions (7), Clinical Pharmacology (12.3)] , the maintenance dose will in most cases need to be increased by as much as 2-fold to maintain a consistent lamotrigine plasma level. The dose increases should begin at the same time that the oral contraceptive is introduced and continue, based on clinical response, no more rapidly than 50 to 100 mg/day every week. Dose increases should not exceed the recommended rate (see Table 1) unless lamotrigine plasma levels or clinical response support larger increases. Gradual transient increases in lamotrigine plasma levels may occur during the week of inactive hormonal preparation (pill-free week), and these increases will be greater if dose increases are made in the days before or during the week of inactive hormonal preparation. Increased lamotrigine plasma levels could result in additional adverse reactions, such as dizziness, ataxia, and diplopia. If adverse reactions attributable to Lamotrigine Extended-Release Tablets consistently occur during the pill-free week, dose adjustments to the overall maintenance dose may be necessary. Dose adjustments limited to the pill-free week are not recommended. For women taking Lamotrigine Extended-Release Tablets in addition to carbamazepine, phenytoin, phenobarbital, primidone, or other drugs such as rifampin and the protease inhibitors lopinavir/ritonavir and atazanavir/ritonavir that induce lamotrigine glucuronidation [see Drug Interactions (7), Clinical Pharmacology (12.3)] , no adjustment to the dose of Lamotrigine Extended-Release Tablets should be necessary. (3) Stopping Estrogen-Containing Oral Contraceptives: In women not taking carbamazepine, phenytoin, phenobarbital, primidone, or other drugs such as rifampin and the protease inhibitors lopinavir/ritonavir and atazanavir/ritonavir that induce lamotrigine glucuronidation [see Drug Interactions (7), Clinical Pharmacology (12.3)] , the maintenance dose of Lamotrigine Extended-Release Tablets will in most cases need to be decreased by as much as 50% in order to maintain a consistent lamotrigine plasma level. The decrease in dose of Lamotrigine Extended-Release Tablets should not exceed 25% of the total daily dose per week over a 2-week period, unless clinical response or lamotrigine plasma levels indicate otherwise [see Clinical Pharmacology (12.3)] . In women taking Lamotrigine Extended-Release Tablets in addition to carbamazepine, phenytoin, phenobarbital, primidone, or other drugs such as rifampin and the protease inhibitors lopinavir/ritonavir and atazanavir/ritonavir that induce lamotrigine glucuronidation [see Drug Interactions (7), Clinical Pharmacology (12.3)] , no adjustment to the dose of Lamotrigine Extended-Release Tablets should be necessary. Women and Other Hormonal Contraceptive Preparations or Hormone Replacement Therapy The effect of other hormonal contraceptive preparations or hormone replacement therapy on the pharmacokinetics of lamotrigine has not been systematically evaluated. It has been reported that ethinylestradiol, not progestogens, increased the clearance of lamotrigine up to 2-fold, and the progestin-only pills had no effect on lamotrigine plasma levels. Therefore, adjustments to the dosage of Lamotrigine Extended-Release Tablets in the presence of progestogens alone will likely not be needed. Patients Taking Atazanavir/Ritonavir While atazanavir/ritonavir does reduce the lamotrigine plasma concentration, no adjustments to the recommended dose-escalation guidelines for Lamotrigine Extended-Release Tablets should be necessary solely based on the use of atazanavir/ritonavir. Dose escalation should follow the recommended guidelines for initiating adjunctive therapy with Lamotrigine Extended-Release Tablets based on concomitant AED or other concomitant medications (see Tables 1 and 5). In patients already taking maintenance doses of Lamotrigine Extended-Release Tablets and not taking glucuronidation inducers, the dose of Lamotrigine Extended-Release Tablets may need to be increased if atazanavir/ritonavir is added or decreased if atazanavir/ritonavir is discontinued [see Clinical Pharmacology (12.3)] . Patients with Hepatic Impairment Experience in patients with hepatic impairment is limited. Based on a clinical pharmacology study in 24 subjects with mild, moderate, and severe liver impairment [see Use in Specific Populations (8.6), Clinical Pharmacology (12.3)] , the following general recommendations can be made. No dosage adjustment is needed in patients with mild liver impairment. Initial, escalation, and maintenance doses should generally be reduced by approximately 25% in patients with moderate and severe liver impairment without ascites and 50% in patients with severe liver impairment with ascites. Escalation and maintenance doses may be adjusted according to clinical response. Patients with Renal Impairment Initial doses of Lamotrigine Extended-Release Tablets should be based on patients’ concomitant medications (see Table 1); reduced maintenance doses may be effective for patients with significant renal impairment [see Use in Specific Populations (8.7), Clinical Pharmacology (12.3)] . Few patients with severe renal impairment have been evaluated during chronic treatment with immediate- release lamotrigine. Because there is inadequate experience in this population, Lamotrigine Extended-Release Tablets should be used with caution in these patients. Discontinuation Strategy For patients receiving Lamotrigine Extended-Release Tablets in combination with other AEDs, a re-evaluation of all AEDs in the regimen should be considered if a change in seizure control or an appearance or worsening of adverse reactions is observed. If a decision is made to discontinue therapy with Lamotrigine Extended-Release Tablets, a step-wise reduction of dose over at least 2 weeks (approximately 50% per week) is recommended unless safety concerns require a more rapid withdrawal [see Warnings and Precautions (5.10)] . Discontinuing carbamazepine, phenytoin, phenobarbital, primidone, or other drugs such as rifampin and the protease inhibitors lopinavir/ritonavir and atazanavir/ritonavir that induce lamotrigine glucuronidation should prolong the half-life of lamotrigine; discontinuing valproate should shorten the half-life of lamotrigine. 2.2 Adjunctive Therapy for Primary Generalized Tonic-Clonic and Partial-Onset Seizures This section provides specific dosing recommendations for patients aged 13 years and older. Specific dosing recommendations are provided depending upon concomitant AEDs or other concomitant medications. Table 1. Escalation Regimen for Lamotrigine Extended-Release Tablets in Patients Aged 13 Years and Older In Patients TAKING Valproate a In Patients NOT TAKING Carbamazepine, Phenytoin, Phenobarbital, Primidone, b or Valproate a In Patients TAKING Carbamazepine, Phenytoin, Phenobarbital, or Primidone b and NOT TAKING Valproate a Weeks 1 and 2 25 mg every other day 25 mg every day 50 mg every day Weeks 3 and 4 25 mg every day 50 mg every day 100 mg every day Week 5 50 mg every day 100 mg every day 200 mg every day Week 6 100 mg every day 150 mg every day 300 mg every day Week 7 150 mg every day 200 mg every day 400 mg every day Maintenance range(week 8 and onward) 200 to 250 mg every day c 300 to 400 mg every day c 400 to 600 mg every day c a Valproate has been shown to inhibit glucuronidation and decrease the apparent clearance of lamotrigine [see Drug Interactions (7), Clinical Pharmacology (12.3)] . b Drugs that induce lamotrigine glucuronidation and increase clearance, other than the specified antiepileptic drugs, include estrogen-containing oral contraceptives, rifampin, and the protease inhibitors lopinavir/ritonavir and atazanavir/ritonavir. Dosing recommendations for oral contraceptives and the protease inhibitor atazanavir/ritonavir can be found in General Dosing Considerations [see Dosage and Administration (2.1)] . Patients on rifampin and the protease inhibitor lopinavir/ritonavir should follow the same dosing titration/maintenance regimen used with antiepileptic drugs that induce glucuronidation and increase clearance [see Dosage and Administration (2.1), Drug Interactions (7), Clinical Pharmacology (12.3)] . c Dose increases at week 8 or later should not exceed 100 mg daily at weekly intervals. 2.3 Conversion from Adjunctive Therapy to Monotherapy The goal of the transition regimen is to attempt to maintain seizure control while mitigating the risk of serious rash associated with the rapid titration of Lamotrigine Extended-Release Tablets. To avoid an increased risk of rash, the recommended maintenance dosage range of Lamotrigine Extended-Release Tablets as monotherapy is 250 to 300 mg given once daily. The recommended initial dose and subsequent dose escalations for Lamotrigine Extended-Release Tablets should not be exceeded [see Boxed Warning] . Conversion from Adjunctive Therapy with Carbamazepine, Phenytoin, Phenobarbital, or Primidone to Monotherapy with Lamotrigine Extended-Release Tablets After achieving a dose of 500 mg/day of Lamotrigine Extended-Release Tablets using the guidelines in Table 1, the concomitant enzyme-inducing AED should be withdrawn by 20% decrements each week over a 4-week period. Two weeks after completion of withdrawal of the enzyme-inducing AED, the dosage of Lamotrigine Extended-Release Tablets may be decreased no faster than 100 mg/day each week to achieve the monotherapy maintenance dosage range of 250 to 300 mg/day. The regimen for the withdrawal of the concomitant AED is based on experience gained in the controlled monotherapy clinical trial using immediate-release lamotrigine. Conversion from Adjunctive Therapy with Valproate to Monotherapy with Lamotrigine Extended-Release Tablets The conversion regimen involves the 4 steps outlined in Table 2. Table 2. Conversion from Adjunctive Therapy with Valproate to Monotherapy with Lamotrigine Extended-Release Tablets in Patients Aged 13 Years and Older with Epilepsy Lamotrigine Extended-Release Tablets Valproate Step 1 Achieve a dose of 150 mg/day according to guidelines in Table 1. Maintain established stable dose. Step 2 Maintain at 150 mg/day. Decrease dose by decrements no greater than 500 mg/day/week to 500 mg/day and then maintain for 1 week. Step 3 Increase to 200 mg/day. Simultaneously decrease to 250 mg/day and maintain for 1 week. Step 4 Increase to 250 or 300 mg/day. Discontinue. Conversion from Adjunctive Therapy with Antiepileptic Drugs other than Carbamazepine, Phenytoin, Phenobarbital, Primidone, or Valproate to Monotherapy with Lamotrigine Extended-Release Tablets After achieving a dosage of 250 to 300 mg/day of Lamotrigine Extended-Release Tablets using the guidelines in Table 1, the concomitant AED should be withdrawn by 20% decrements each week over a 4-week period. No adjustment to the monotherapy dose of Lamotrigine Extended-Release Tablets is needed. 2.4 Conversion from Immediate-Release Lamotrigine Tablets to Lamorigine Extended-Release Tablets Patients may be converted directly from immediate-release lamotrigine to Lamotrigine Extended-Release Tablets. The initial dose of Lamotrigine Extended-Release Tablets should match the total daily dose of immediate-release lamotrigine. However, some subjects on concomitant enzyme-inducing agents may have lower plasma levels of lamotrigine on conversion and should be monitored [see Clinical Pharmacology (12.3)]. Following conversion to Lamotrigine Extended-Release Tablets, all patients (but especially those on drugs that induce lamotrigine glucuronidation) should be closely monitored for seizure control [see Drug Interactions (7)]. Depending on the therapeutic response after conversion, the total daily dose may need to be adjusted within the recommended dosing instructions (see Table 1).

6 ADVERSE REACTIONS The following serious adverse reactions are described in more detail in the Warnings and Precautions section of the labeling: • Serious Skin Rashes [see Warnings and Precautions (5.1)] • Hemophagocytic Lymphohistiocytosis [see Warnings and Precautions (5.2)] • Multiorgan Hypersensitivity Reactions and Organ Failure [see Warnings and Precautions (5.3)] • Cardiac Rhythm and Conduction Abnormalities [see Warnings and Precautions (5.4)] • Blood Dyscrasias [see Warnings and Precautions (5.5)] • Suicidal Behavior and Ideation [see Warnings and Precautions (5.6)] • Aseptic Meningitis [see Warnings and Precautions (5.7)] • Withdrawal Seizures [see Warnings and Precautions (5.10)] • Status Epilepticus [see Warnings and Precautions (5.11)] • Sudden Unexplained Death in Epilepsy [see Warnings and Precautions (5.12)] • Most common adverse reactions with use as adjunctive therapy (treatment difference between Lamotrigine Extended-Release Tablets and placebo≥4%) were dizziness, tremor/intention tremor, vomiting, and diplopia. ( 6.1 ) • Most common adverse reactions with use as monotherapy were similar to those seen with previous trials conducted with immediate-release lamotrigine and Lamotrigine Extended-Release Tablets. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Camber Pharmaceuticals Inc at 1-866-495-1995 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch . 6.1 Clinical Trial Experience with Lamotrigine Extended-Release Tablets for Treatment of Primary Generalized Tonic-Clonic and Partial-Onset Seizures Most Common Adverse Reactions in Clinical Trials Adjunctive Therapy in Patients with Epilepsy: Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared with rates in the clinical trials of another drug and may not reflect the rates observed in practice. In these 2 trials, adverse reactions led to withdrawal of 4 (2%) patients in the group receiving placebo and 10 (5%) patients in the group receiving Lamotrigine Extended-Release Tablets. Dizziness was the most common reason for withdrawal in the group receiving Lamotrigine Extended-Release Tablets (5 patients [3%]). The next most common adverse reactions leading to withdrawal in 2 patients each (1%) were rash, headache, nausea, and nystagmus. Table 4 displays the incidence of adverse reactions in these two 19-week, double-blind, placebo-controlled trials of patients with PGTC and partial onset seizures. Table 4. Adverse Reactions in Pooled, Placebo-Controlled, Adjunctive Trials in Patients with Epilepsy a Body System/ Adverse Reaction Percent of Patients Receiving Adjunctive Lamotrigine Extended-Release Tablets (n = 190) Percent of Patients Receiving Adjunctive Placebo (n = 195) Ear and labyrinth disorders Vertigo 3 <1 Eye disorders Diplopia Vision blurred 5 3 <1 2 Gastrointestinal disorders Nausea Vomiting Diarrhea Constipation Dry mouth 7 6 5 2 2 4 3 3 <1 1 General disorders and administration site conditions Asthenia and fatigue 6 4 Infections and infestations Sinusitis 2 1 Metabolic and nutritional disorders Anorexia 3 2 Musculoskeletal and connective tissue disorder Myalgia 2 0 Nervous system Dizziness Tremor and intention tremor Somnolence Cerebellar coordination and balance disorder Nystagmus 14 6 5 3 2 6 1 3 0 <1 Psychiatric disorders Depression Anxiety 3 3 <1 0 Respiratory, thoracic, and mediastinal disorders Pharyngolaryngeal pain 3 2 Vascular disorder Hot flush 2 0 a Adverse reactions that occurred in at least 2% of patients treated with Lamotrigine Extended-Release Tablets and at a greater incidence than placebo. Note: In these trials the incidence of nonserious rash was 2% for Lamotrigine Extended-Release Tablets and 3% for placebo. In clinical trials evaluating immediate-release lamotrigine, the rate of serious rash was 0.3% in adults on adjunctive therapy for epilepsy [see Boxed Warning] . Adverse reactions were also analyzed to assess the incidence of the onset of an event in the titration period, and in the maintenance period, and if adverse reactions occurring in the titration phase persisted in the maintenance phase. The incidence for many adverse reactions caused by treatment with Lamotrigine Extended-Release Tablets was increased relative to placebo (i.e., treatment difference between Lamotrigine Extended-Release Tablets and placebo≥2%) in either the titration or maintenance phases of the trial. During the titration phase, an increased incidence (shown in descending order of percent treatment difference) was observed for diarrhea, nausea, vomiting, somnolence, vertigo, myalgia, hot flush, and anxiety. During the maintenance phase, an increased incidence was observed for dizziness, tremor, and diplopia.Some adverse reactions developing in the titration phase were notable for persisting (>7 days) into the maintenance phase. These persistent adverse reactions included somnolence and dizziness. There were inadequate data to evaluate the effect of dose and/or concentration on the incidence of adverse reactions because, although patients were randomized to different target doses based upon concomitant AEDs, the plasma exposure was expected to be generally similar among all patients receiving different doses. However, in a randomized, parallel trial comparing placebo with 300 and 500 mg/day of immediate-release lamotrigine, the incidence of the most common adverse reactions (≥5%) such as ataxia, blurred vision, diplopia, and dizziness were dose related. Less common adverse reactions (<5%) were not assessed for dose-response relationships. Monotherapy in Patients with Epilepsy: Adverse reactions observed in this trial were generally similar to those observed and attributed to drug in adjunctive and monotherapy immediate-release lamotrigine and adjunctive Lamotrigine Extended-Release Tablets placebo-controlled trials. Only 2 adverse events, nasopharyngitis and upper respiratory tract infection, were observed at a rate of ≥3% and not reported at a similar rate in previous trials. Because this trial did not include a placebo control group, causality could not be established [see Clinical Studies (14.3)] . 6.2 Other Adverse Reactions Observed during the Clinical Development of Immediate-Release Lamotrigine All reported reactions are included except those already listed in the previous tables or elsewhere in the labeling, those too general to be informative, and those not reasonably associated with the use of the drug. Adjunctive Therapy in Adults with Epilepsy In addition to the adverse reactions reported above from the development of Lamotrigine Extended-Release Tablets, the following adverse reactions with an uncertain relationship to lamotrigine were reported during the clinical development of immediate-release lamotrigine for treatment of epilepsy in adults. These reactions occurred in ≥2% of patients receiving immediate-release lamotrigine and more frequently than in the placebo group. Body as a Whole: Headache, flu syndrome, fever, neck pain. Musculoskeletal: Arthralgia. Nervous: Insomnia, convulsion, irritability, speech disorder, concentration disturbance. Respiratory: Pharyngitis, cough increased. Skin and Appendages: Rash, pruritus. Urogenital (female patients only): Vaginitis, amenorrhea, dysmenorrhea. Monotherapy in Adults with Epilepsy In addition to the adverse reactions reported above from the development of Lamotrigine Extended-Release Tablets, the following adverse reactions with an uncertain relationship to lamotrigine were reported during the clinical development of immediate-release lamotrigine for treatment of epilepsy in adults. These reactions occurred in >2% of patients receiving immediate-release lamotrigine and more frequently than in the placebo group. Body as a Whole: Chest pain. Digestive: Rectal hemorrhage, peptic ulcer. Metabolic and Nutritional: Weight decrease, peripheral edema. Nervous: Hypesthesia, libido increase, decreased reflexes. Respiratory: Epistaxis, dyspnea. Skin and Appendages: Contact dermatitis, dry skin, sweating. Special Senses: Vision abnormality. Urogenital (female patients only): Dysmenorrhea. Other Clinical Trial Experience Immediate-release lamotrigine has been administered to 6,694 individuals for whom complete adverse reaction data was captured during all clinical trials, only some of which were placebo controlled. Adverse reactions are further classified within body system categories and enumerated in order of decreasing frequency using the following definitions: frequent adverse reactions are defined as those occurring in at least 1/100 patients; infrequent adverse reactions are those occurring in 1/100 to 1/1,000 patients; rare adverse reactions are those occurring in fewer than 1/1,000 patients. Cardiovascular System: Infrequent: Hypertension, palpitations, postural hypotension, syncope, tachycardia, vasodilation. Dermatological: Infrequent: Acne, alopecia, hirsutism, maculopapular rash, urticaria. Rare: Leukoderma, multiforme erythema, petechial rash, pustular rash. Digestive System: Infrequent: Dysphagia, liver function tests abnormal, mouth ulceration. Rare: Gastrointestinal hemorrhage, hemorrhagic colitis, hepatitis, melena, stomach ulcer. Endocrine System: Rare: Goiter, hypothyroidism. Hematologic and Lymphatic System: Infrequent: Ecchymosis, leukopenia. Rare: Anemia, eosinophilia, fibrin decrease, fibrinogen decrease, iron deficiency anemia, leukocytosis, lymphocytosis, macrocytic anemia, petechia, thrombocytopenia. Metabolic and Nutritional Disorders: Infrequent: Aspartate transaminase increased. Rare: Alcohol intolerance, alkaline phosphatase increase, alanine transaminase increase, bilirubinemia, gamma glutamyl transpeptidase increase, hyperglycemia. Musculoskeletal System: Rare: Muscle atrophy, pathological fracture, tendinous contracture. Nervous System: Frequent: Confusion. Infrequent: Akathisia, apathy, aphasia, depersonalization, dysarthria, dyskinesia, euphoria, hallucinations, hostility, hyperkinesia, hypertonia, libido decreased, memory decrease, mind racing, movement disorder, myoclonus, panic attack, paranoid reaction, personality disorder, psychosis, stupor. Rare: Choreoathetosis, delirium, delusions, dysphoria, dystonia, extrapyramidal syndrome, hemiplegia, hyperalgesia, hyperesthesia, hypokinesia, hypotonia, manic depression reaction, neuralgia, paralysis, peripheral neuritis. Respiratory System: Rare: Hiccup, hyperventilation. Special Senses: Frequent: Amblyopia. Infrequent: Abnormality of accommodation, conjunctivitis, dry eyes, ear pain, photophobia, taste perversion, tinnitus. Rare: Deafness, lacrimation disorder, oscillopsia, parosmia, ptosis, strabismus, taste loss, uveitis, visual field defect. Urogenital System: Infrequent: Abnormal ejaculation, hematuria, impotence, menorrhagia, polyuria, urinary incontinence. Rare: Acute kidney failure, breast neoplasm, creatinine increase, female lactation, kidney failure, kidney pain, nocturia, urinary retention, urinary urgency. 6.3 Postmarketing Experience with Immediate-Release Lamotrigine The following adverse reactions have been identified during postapproval use of immediate-release lamotrigine. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. Blood and Lymphatic Agranulocytosis, hemolytic anemia, lymphadenopathy not associated with hypersensitivity disorder. Gastrointestinal Esophagitis. Hepatobiliary Tract and Pancreas Pancreatitis. Immunologic Hypogammaglobulinemia, lupus-like reaction, vasculitis. Lower Respiratory Apnea. Musculoskeletal Rhabdomyolysis has been observed in patients experiencing hypersensitivity reactions. Nervous System Aggression, exacerbation of Parkinsonian symptoms in patients with pre-existing Parkinson’s disease, tics. Non-site Specific Progressive immunosuppression. Renal and Urinary Disorders Tubulointerstitial nephritis (has been reported alone and in association with uveitis).

12.3 Pharmacokinetics In comparison with immediate-release lamotrigine, the plasma lamotrigine levels following administration of Lamotrigine Extended-Release Tablets are not associated with any significant changes in trough plasma concentrations, and are characterized by lower peaks, longer time to peaks, and lower peak-to-trough fluctuation, as described in detail below. Absorption Lamotrigine is absorbed after oral administration with negligible first-pass metabolism. The bioavailability of lamotrigine is not affected by food. In an open-label, crossover study of 44 subjects with epilepsy receiving concomitant AEDs, the steady-state pharmacokinetics of lamotrigine were compared following administration of equivalent total doses of Lamotrigine Extended-Release Tablets given once daily with those of lamotrigine immediate‑release given twice daily. In this study, the median time to peak concentration (T max ) following administration of Lamotrigine Extended-Release Tablets was 4 to 6 hours in subjects taking carbamazepine, phenytoin, phenobarbital, or primidone; 9 to 11 hours in subjects taking valproate; and 6 to 10 hours in subjects taking AEDs other than carbamazepine, phenytoin, phenobarbital, primidone, or valproate. In comparison, the median T max following administration of immediate-release lamotrigine was between 1 and 1.5 hours. The steady-state trough concentrations for extended-release lamotrigine were similar to or higher than those of immediate-release lamotrigine depending on concomitant AED (see Table 6). A mean reduction in the lamotrigine C max by 11% to 29% was observed for Lamotrigine Extended-Release Tablets compared with immediate-release lamotrigine, resulting in a decrease in the peak-to-trough fluctuation in serum lamotrigine concentrations. However, in some subjects receiving enzyme-inducing AEDs, a reduction in C max of 44% to 77% was observed. The degree of fluctuation was reduced by 17% in subjects taking enzyme-inducing AEDs; 34% in subjects taking valproate; and 37% in subjects taking AEDs other than carbamazepine, phenytoin, phenobarbital, primidone, or valproate. Lamotrigine Extended-Release Tablets and immediate-release lamotrigine regimens were similar with respect to area under the curve (AUC, a measure of the extent of bioavailability) for subjects receiving AEDs other than those known to induce the metabolism of lamotrigine. The relative bioavailability of extended-release lamotrigine was approximately 21% lower than immediate-release lamotrigine in subjects receiving enzyme-inducing AEDs. However, a reduction in exposure of up to 70% was observed in some subjects in this group when they switched to Lamotrigine Extended-Release Tablets. Therefore, doses may need to be adjusted in some patients based on therapeutic response. Table 6. Steady-State Bioavailability of Lamotrigine Extended-Release Tablets Relative to Immediate-Release Lamotrigine at Equivalent Daily Doses (Ratio of Extended-Release to Immediate-Release 90% CI) Concomitant Antiepileptic Drug AUC (0-24ss) C max C min Enzyme-inducing antiepileptic drugs a 0.79 (0.69, 0.90) 0.71 (0.61, 0.82) 0.99 (0.89, 1.09) Valproate 0.94 (0.81, 1.08) 0.88 (0.75, 1.03) 0.99 (0.88, 1.10) Antiepileptic drugs other than enzyme-inducing antiepileptic drugs a or valproate 1.00 (0.88, 1.14) 0.89 (0.78, 1.03) 1.14 (1.03, 1.25) a Enzyme-inducing antiepileptic drugs include carbamazepine, phenytoin, phenobarbital, and primidone. Dose Proportionality In healthy volunteers not receiving any other medications and given Lamotrigine Extended-Release Tablets once daily, the systemic exposure to lamotrigine increased in direct proportion to the dose administered over the range of 50 to 200 mg. At doses between 25 and 50 mg, the increase was less than dose proportional, with a 2-fold increase in dose resulting in an approximately 1.6-fold increase in systemic exposure. Distribution Estimates of the mean apparent volume of distribution (Vd/F) of lamotrigine following oral administration ranged from 0.9 to 1.3 L/kg. Vd/F is independent of dose and is similar following single and multiple doses in both patients with epilepsy and in healthy volunteers. Protein Binding Data from in vitro studies indicate that lamotrigine is approximately 55% bound to human plasma proteins at plasma lamotrigine concentrations from 1 to 10 mcg/mL (10 mcg/mL is 4 to 6 times the trough plasma concentration observed in the controlled efficacy trials). Because lamotrigine is not highly bound to plasma proteins, clinically significant interactions with other drugs through competition for protein binding sites are unlikely. The binding of lamotrigine to plasma proteins did not change in the presence of therapeutic concentrations of phenytoin, phenobarbital, or valproate. Lamotrigine did not displace other AEDs (carbamazepine, phenytoin, phenobarbital) from protein-binding sites. Metabolism Lamotrigine is metabolized predominantly by glucuronic acid conjugation; the major metabolite is an inactive 2-N-glucuronide conjugate. After oral administration of 240 mg of 14 C-lamotrigine (15 μCi) to 6 healthy volunteers, 94% was recovered in the urine and 2% was recovered in the feces. The radioactivity in the urine consisted of unchanged lamotrigine (10%), the 2-N-glucuronide (76%), a 5-N-glucuronide (10%), a 2-N-methyl metabolite (0.14%), and other unidentified minor metabolites (4%). Enzyme Induction The effects of lamotrigine on the induction of specific families of mixed-function oxidase isozymes have not been systematically evaluated. Following multiple administrations (150 mg twice daily) to normal volunteers taking no other medications, lamotrigine induced its own metabolism, resulting in a 25% decrease in t ½ and a 37% increase in CL/F at steady state compared with values obtained in the same volunteers following a single dose. Evidence gathered from other sources suggests that self-induction by lamotrigine may not occur when lamotrigine is given as adjunctive therapy in patients receiving enzyme-inducing drugs such as carbamazepine, phenytoin, phenobarbital, primidone, or other drugs such as rifampin and the protease inhibitors lopinavir/ritonavir and atazanavir/ritonavir that induce lamotrigine glucuronidation [see Drug Interactions (7)] . Elimination The elimination half-life and apparent clearance of lamotrigine following oral administration of immediate-release lamotrigine to adult subjects with epilepsy and healthy volunteers is summarized in Table 7. Half-life and apparent oral clearance vary depending on concomitant AEDs. Since the half-life of lamotrigine following administration of single doses of immediate-release lamotrigine is comparable with that observed following administration of Lamotrigine Extended-Release Tablets, similar changes in the half-life of lamotrigine would be expected for Lamotrigine Extended-Release Tablets. Table 7. Mean Pharmacokinetic Parameters a of Immediate-Release Lamotrigine in Healthy Volunteers and Adult Subjects with Epilepsy Adult Study Population Number of Subjects t ½ : Elimination Half-life (h) CL/F:Apparent Plasma Clearance (mL/min/kg) Healthy volunteers taking no other medications: Single-dose lamotrigine 179 32.8(14.0-103.0) 0.44(0.12-1.10) Multiple-dose lamotrigine 36 25.4(11.6-61.6) 0.58(0.24-1.15) Healthy volunteers taking valproate: Single-dose lamotrigine 6 48.3(31.5-88.6) 0.30(0.14-0.42) Multiple-dose lamotrigine 18 70.3(41.9-113.5) 0.18(0.12-0.33) Subjects with epilepsy taking valproate only: Single-dose lamotrigine 4 58.8(30.5-88.8) 0.28(0.16-0.40) Subjects with epilepsy taking carbamazepine, phenytoin, phenobarbital, or primidone b plus valproate: Single-dose lamotrigine 25 27.2(11.2-51.6) 0.53(0.27-1.04) Subjects with epilepsy taking carbamazepine, phenytoin, phenobarbital, or primidone: b Single-dose lamotrigine 24 14.4(6.4-30.4) 1.10(0.51-2.22) Multiple-dose lamotrigine 17 12.6(7.5-23.1) 1.21(0.66-1.82) a The majority of parameter means determined in each study had coefficients of variation between 20% and 40% for half-life and CL/F and between 30% and 70% for T max . The overall mean values were calculated from individual study means that were weighted based on the number of volunteers/subjects in each study. The numbers in parentheses below each parameter mean represent the range of individual volunteer/subject values across studies. b Carbamazepine, phenytoin, phenobarbital, and primidone have been shown to increase the apparent clearance of lamotrigine. Estrogen-containing oral contraceptives and other drugs, such as rifampin and protease inhibitors lopinavir/ritonavir and atazanavir/ritonavir, that induce lamotrigine glucuronidation have also been shown to increase the apparent clearance of lamotrigine [see Drug Interactions (7)] . Drug Interactions The apparent clearance of lamotrigine is affected by the coadministration of certain medications [see Warnings and Precautions (5.9, 5.13), Drug Interactions (7)] . The net effects of drug interactions with lamotrigine, based on drug interaction studies using immediate-release lamotrigine, are summarized in Tables 5 and 8, followed by details of the drug interaction studies below. Table 8. Summary of Drug Interactions with Lamotrigine Drug Drug Plasma Concentration with Adjunctive Lamotrigine a Lamotrigine Plasma Concentration with Adjunctive Drugs b Oral contraceptives (e.g., ethinylestradiol/levonorgestrel) c ↔ d ↓ Aripiprazole Not assessed ↔ e Atazanavir/ritonavir ↔ f ↓ Bupropion Not assessed ↔ Carbamazepine ↔ ↓ Carbamazepine epoxide g ? Felbamate Not assessed ↔ Gabapentin Not assessed ↔ Lacosamide Not assessed ↔ Levetiracetam ↔ ↔ Lithium ↔ Not assessed Lopinavir/ritonavir ↔ e ↓ Olanzapine ↔ ↔ e Oxcarbazepine ↔ ↔ 10-Monohydroxy oxcarbazepine metabolite h ↔ Perampanel Not assessed ↔ e Phenobarbital/primidone ↔ ↓ Phenytoin ↔ ↓ Pregabalin ↔ ↔ Rifampin Not assessed ↓ Risperidone ↔ Not assessed 9-Hydroxyrisperidone i ↔ Topiramate ↔ j ↔ Valproate ↓ ↑ Valproate + phenytoin and/or Not assessed ↔ carbamazepine Zonisamide Not assessed ↔ a From adjunctive clinical trials and volunteer trials. b Net effects were estimated by comparing the mean clearance values obtained in adjunctive clinical trials and volunteer trials. c The effect of other hormonal contraceptive preparations or hormone replacement therapy on the pharmacokinetics of lamotrigine has not been systematically evaluated in clinical trials, although the effect may be similar to that seen with the ethinylestradiol/levonorgestrel combinations. d Modest decrease in levonorgestrel. e Slight decrease, not expected to be clinically meaningful. f Compared with historical controls. g Not administered, but an active metabolite of carbamazepine. h Not administered, but an active metabolite of oxcarbazepine. i Not administered, but an active metabolite of risperidone. j Slight increase, not expected to be clinically meaningful. ↔ = No significant effect. ? = Conflicting data. Estrogen-Containing Oral Contraceptives In 16 female volunteers, an oral contraceptive preparation containing 30 mcg ethinylestradiol and 150 mcg levonorgestrel increased the apparent clearance of lamotrigine (300 mg/day) by approximately 2-fold with mean decreases in AUC of 52% and in C max of 39%. In this study, trough serum lamotrigine concentrations gradually increased and were approximately 2-fold higher on average at the end of the week of the inactive hormone preparation compared with trough lamotrigine concentrations at the end of the active hormone cycle. Gradual transient increases in lamotrigine plasma levels (approximate 2-fold increase) occurred during the week of inactive hormone preparation (pill-free week) for women not also taking a drug that increased the clearance of lamotrigine (carbamazepine, phenytoin, phenobarbital, primidone, or other drugs such as rifampin and the protease inhibitors lopinavir/ritonavir and atazanavir/ritonavir that induce lamotrigine glucuronidation) [see Drug Interactions (7)] . The increase in lamotrigine plasma levels will be greater if the dose of Lamotrigine Extended-Release Tablets is increased in the few days before or during the pill-free week. Increases in lamotrigine plasma levels could result in dose-dependent adverse reactions. In the same study, coadministration of lamotrigine (300 mg/day) in 16 female volunteers did not affect the pharmacokinetics of the ethinylestradiol component of the oral contraceptive preparation. There were mean decreases in the AUC and C max of the levonorgestrel component of 19% and 12%, respectively. Measurement of serum progesterone indicated that there was no hormonal evidence of ovulation in any of the 16 volunteers, although measurement of serum FSH, LH, and estradiol indicated that there was some loss of suppression of the hypothalamic-pituitary-ovarian axis. The effects of doses of lamotrigine other than 300 mg/day have not been systematically evaluated in controlled clinical trials. The clinical significance of the observed hormonal changes on ovulatory activity is unknown. However, the possibility of decreased contraceptive efficacy in some patients cannot be excluded. Therefore, patients should be instructed to promptly report changes in their menstrual pattern (e.g., break-through bleeding). Dosage adjustments may be necessary for women receiving estrogen-containing oral contraceptive preparations [see Dosage and Administration (2.1)] . Other Hormonal Contraceptives or Hormone Replacement Therapy The effect of other hormonal contraceptive preparations or hormone replacement therapy on the pharmacokinetics of lamotrigine has not been systematically evaluated. It has been reported that ethinylestradiol, not progestogens, increased the clearance of lamotrigine up to 2-fold, and the progestin-only pills had no effect on lamotrigine plasma levels. Therefore, adjustments to the dosage of Lamotrigine Extended-Release Tablets in the presence of progestogens alone will likely not be needed. Aripiprazole In 18 patients with bipolar disorder on a stable regimen of 100 to 400 mg/day of lamotrigine, the lamotrigine AUC and C max were reduced by approximately 10% in patients who received aripiprazole 10 to 30 mg/day for 7 days, followed by 30 mg/day for an additional 7 days. This reduction in lamotrigine exposure is not considered clinically meaningful. Atazanavir/Ritonavir In a study in healthy volunteers, daily doses of atazanavir/ritonavir (300 mg/100 mg) reduced the plasma AUC and C max of lamotrigine (single 100-mg dose) by an average of 32% and 6%, respectively, and shortened the elimination half-lives by 27%. In the presence of atazanavir/ritonavir (300 mg/100 mg), the metabolite-to-lamotrigine ratio was increased from 0.45 to 0.71 consistent with induction of glucuronidation. The pharmacokinetics of atazanavir/ritonavir were similar in the presence of concomitant lamotrigine to the historical data of the pharmacokinetics in the absence of lamotrigine. Bupropion The pharmacokinetics of a 100-mg single dose of lamotrigine in healthy volunteers (n = 12) were not changed by coadministration of bupropion sustained-release formulation (150 mg twice daily) starting 11 days before lamotrigine. Carbamazepine Lamotrigine has no appreciable effect on steady-state carbamazepine plasma concentration. Limited clinical data suggest there is a higher incidence of dizziness, diplopia, ataxia, and blurred vision in patients receiving carbamazepine with lamotrigine than in patients receiving other AEDs with lamotrigine [see Adverse Reactions (6.1)] . The mechanism of this interaction is unclear. The effect of lamotrigine on plasma concentrations of carbamazepine-epoxide is unclear. In a small subset of patients (n = 7) studied in a placebo-controlled trial, lamotrigine had no effect on carbamazepine-epoxide plasma concentrations, but in a small, uncontrolled study (n = 9), carbamazepine-epoxide levels increased. The addition of carbamazepine decreases lamotrigine steady-state concentrations by approximately 40%. Esomeprazole In a study of 30 subjects, coadministration of Lamotrigine Extended-Release Tablets with esomeprazole resulted in no significant change in lamotrigine levels and a small decrease in T max . The levels of gastric pH were not altered compared with pre-lamotrigine dosing. Felbamate In a trial in 21 healthy volunteers, coadministration of felbamate (1,200 mg twice daily) with lamotrigine (100 mg twice daily for 10 days) appeared to have no clinically relevant effects on the pharmacokinetics of lamotrigine. Folate Inhibitors Lamotrigine is a weak inhibitor of dihydrofolate reductase. Prescribers should be aware of this action when prescribing other medications that inhibit folate metabolism. Gabapentin Based on a retrospective analysis of plasma levels in 34 subjects who received lamotrigine both with and without gabapentin, gabapentin does not appear to change the apparent clearance of lamotrigine. Lacosamide Plasma concentrations of lamotrigine were not affected by concomitant lacosamide (200, 400, or 600 mg/day) in placebo-controlled clinical trials in patients with partial-onset seizures. Levetiracetam Potential drug interactions between levetiracetam and lamotrigine were assessed by evaluating serum concentrations of both agents during placebo-controlled clinical trials. These data indicate that lamotrigine does not influence the pharmacokinetics of levetiracetam and that levetiracetam does not influence the pharmacokinetics of lamotrigine. Lithium The pharmacokinetics of lithium were not altered in healthy subjects (n = 20) by coadministration of lamotrigine (100 mg/day) for 6 days. Lopinavir/Ritonavir The addition of lopinavir (400 mg twice daily)/ritonavir (100 mg twice daily) decreased the AUC, C max , and elimination half-life of lamotrigine by approximately 50% to 55.4% in 18 healthy subjects. The pharmacokinetics of lopinavir/ritonavir were similar with concomitant lamotrigine, compared with that in historical controls. Olanzapine The AUC and Cmax of olanzapine were similar following the addition of olanzapine (15 mg once daily) to lamotrigine (200 mg once daily) in healthy male volunteers (n = 16) compared with the AUC and Cmax in healthy male volunteers receiving olanzapine alone (n = 16). In the same trial, the AUC and Cmax of lamotrigine were reduced on average by 24% and 20%, respectively, following the addition of olanzapine to lamotrigine in healthy male volunteers compared with those receiving lamotrigine alone. This reduction in lamotrigine plasma concentrations is not expected to be clinically meaningful. Oxcarbazepine The AUC and Cmax of oxcarbazepine and its active 10-monohydroxy oxcarbazepine metabolite were not significantly different following the addition of oxcarbazepine (600 mg twice daily) to lamotrigine (200 mg once daily) in healthy male volunteers (n = 13) compared with healthy male volunteers receiving oxcarbazepine alone (n = 13). In the same trial, the AUC and C max of lamotrigine were similar following the addition of oxcarbazepine (600 mg twice daily) to lamotrigine in healthy male volunteers compared with those receiving lamotrigine alone. Limited clinical data suggest a higher incidence of headache, dizziness, nausea, and somnolence with coadministration of lamotrigine and oxcarbazepine compared with lamotrigine alone or oxcarbazepine alone. Perampanel In a pooled analysis of data from 3 placebo-controlled clinical trials investigating adjunctive perampanel in patients with partial-onset and primary generalized tonic-clonic seizures, the highest perampanel dose evaluated (12 mg/day) increased lamotrigine clearance by <10%. An effect of this magnitude is not considered to be clinically relevant. Phenobarbital, Primidone The addition of phenobarbital or primidone decreases lamotrigine steady-state concentrations by approximately 40%. Phenytoin Lamotrigine has no appreciable effect on steady-state phenytoin plasma concentrations in patients with epilepsy. The addition of phenytoin decreases lamotrigine steady-state concentrations by approximately 40%. Pregabalin Steady-state trough plasma concentrations of lamotrigine were not affected by concomitant pregabalin (200 mg 3 times daily) administration. There are no pharmacokinetic interactions between lamotrigine and pregabalin. Rifampin In 10 male volunteers, rifampin (600 mg/day for 5 days) significantly increased the apparent clearance of a single 25-mg dose of lamotrigine by approximately 2-fold (AUC decreased by approximately 40%). Risperidone In a 14 healthy volunteers study, multiple oral doses of lamotrigine 400 mg daily had no clinically significant effect on the single-dose pharmacokinetics of risperidone 2 mg and its active metabolite 9-OH risperidone. Following the coadministration of risperidone 2 mg with lamotrigine, 12 of the 14 volunteers reported somnolence compared with 1 out of 20 when risperidone was given alone, and none when lamotrigine was administered alone. Topiramate Topiramate resulted in no change in plasma concentrations of lamotrigine. Administration of lamotrigine resulted in a 15% increase in topiramate concentrations. Valproate When lamotrigine was administered to healthy volunteers (n = 18) receiving valproate, the trough steady-state valproate plasma concentrations decreased by an average of 25% over a 3-week period, and then stabilized. However, adding lamotrigine to the existing therapy did not cause a change in valproate plasma concentrations in either adult or pediatric patients in controlled clinical trials. The addition of valproate increased lamotrigine steady-state concentrations in normal volunteers by slightly more than 2-fold. In 1 trial, maximal inhibition of lamotrigine clearance was reached at valproate doses between 250 and 500 mg/day and did not increase as the valproate dose was further increased. Zonisamide In a study in 18 patients with epilepsy, coadministration of zonisamide (200 to 400 mg/day) with lamotrigine (150 to 500 mg/day for 35 days) had no significant effect on the pharmacokinetics of lamotrigine. Known Inducers or Inhibitors of Glucuronidation Drugs other than those listed above have not been systematically evaluated in combination with lamotrigine. Since lamotrigine is metabolized predominately by glucuronic acid conjugation, drugs that are known to induce or inhibit glucuronidation may affect the apparent clearance of lamotrigine, and doses of Lamotrigine Extended-Release Tablets may require adjustment based on clinical response. Other In vitro assessment of the inhibitory effect of lamotrigine at OCT2 demonstrate that lamotrigine, but not the N(2)-glucuronide metabolite, is an inhibitor of OCT2 at potentially clinically relevant concentrations, with IC 50 value of 53.8 µM [see Drug Interactions (7)] . Results of in vitro experiments suggest that clearance of lamotrigine is unlikely to be reduced by concomitant administration of amitriptyline, clonazepam, clozapine, fluoxetine, haloperidol, lorazepam, phenelzine, sertraline, or trazodone. Results of in vitro experiments suggest that lamotrigine does not reduce the clearance of drugs eliminated predominantly by CYP2D6. Specific Populations Patients with Renal Impairment: Twelve volunteers with chronic renal failure (mean creatinine clearance: 13 mL/min, range: 6 to 23) and another 6 individuals undergoing hemodialysis were each given a single 100-mg dose of immediate-release lamotrigine. The mean plasma half-lives determined in the study were 42.9 hours (chronic renal failure), 13.0 hours (during hemodialysis), and 57.4 hours (between hemodialysis) compared with 26.2 hours in healthy volunteers. On average, approximately 20% (range: 5.6 to 35.1) of the amount of lamotrigine present in the body was eliminated by hemodialysis during a 4-hour session [see Dosage and Administration (2.1)] . Patients with Hepatic Impairment: The pharmacokinetics of lamotrigine following a single 100‑ mg dose of immediate-release lamotrigine were evaluated in 24 subjects with mild, moderate, and severe hepatic impairment (Child-Pugh classification system) and compared with 12 subjects without hepatic impairment. The subjects with severe hepatic impairment were without ascites (n = 2) or with ascites (n = 5). The mean apparent clearances of lamotrigine in subjects with mild (n = 12), moderate (n = 5), severe without ascites (n = 2), and severe with ascites (n = 5) liver impairment were 0.30 ± 0.09, 0.24 ± 0.1, 0.21 ± 0.04, and 0.15 ± 0.09 mL/min/kg, respectively, as compared with 0.37 ± 0.1 mL/min/kg in the healthy controls. Mean half-lives of lamotrigine in subjects with mild, moderate, severe without ascites, and severe with ascites hepatic impairment were 46 ± 20, 72 ± 44, 67 ± 11, and 100 ± 48 hours, respectively, as compared with 33 ± 7 hours in healthy controls [see Dosage and Administration (2.1)] . Geriatric Patients: The pharmacokinetics of lamotrigine following a single 150-mg dose of immediate-release lamotrigine were evaluated in 12 elderly volunteers between the ages of 65 and 76 years (mean creatinine clearance: 61 mL/min, range: 33 to 108 mL/min). The mean half-life of lamotrigine in these subjects was 31.2 hours (range: 24.5 to 43.4 hours), and the mean clearance was 0.40 mL/min/kg (range: 0.26 to 0.48 mL/min/kg). Male and Female Patients: The clearance of lamotrigine is not affected by gender. However, during dose escalation of immediate-release lamotrigine in 1 clinical trial in patients with epilepsy on a stable dose of valproate (n = 77), mean trough lamotrigine concentrations unadjusted for weight were 24% to 45% higher (0.3 to 1.7 mcg/mL) in females than in males. Racial or Ethnic Groups: The apparent oral clearance of lamotrigine was 25% lower in non- Caucasians than Caucasians. Pediatric Patients: Safety and effectiveness of Lamotrigine Extended-Release Tablets for use in patients younger than 13 years have not been established.