Lamivudine

1 INDICATIONS & USAGE Lamivudine is nucleoside analogue indicated in combination with other antiretroviral agents for the treatment of human immunodeficiency virus type 1 (HIV-1) infection. Limitations of Use: • The dosage of this product is for HIV-1 and not for HBV. Lamivudine is a nucleoside analogue reverse transcriptase inhibitor indicated in combination with other antiretroviral agents for the treatment of HIV-1 infection. Limitations of Use: The dosage of this product is for HIV-1 and not for HBV.( 1 )

2 DOSAGE & ADMINISTRATION • Adults: 300 mg daily, administered as either 150 mg twice daily or 300 mg once daily. ( 2.1 ) • Pediatric Patients Aged 3 Months and Older: Administered either once or twice daily. Dose should be calculated on body weight (kg) and should not exceed 300 mg daily. ( 2.2 ) • Patients with Renal Impairment: Doses of lamivudine must be adjusted in accordance with renal function. ( 2.3 ) 2.1 Recommended Dosage for Adult Patients The recommended dosage of lamivudine in HIV-1-infected adults is 300 mg daily, administered as either 150 mg taken orally twice daily or 300 mg taken orally once daily with or without food. If lamivudine is administered to a patient infected with HIV-1 and HBV, the dosage indicated for HIV-1 therapy should be used as part of an appropriate combination regimen [see Warnings and Precautions ( 5.1 )]. 2.2 Recommended Dosage for Pediatric Patients Lamivudine scored tablet is the preferred formulation for HIV-1-infected pediatric patients who weigh at least 14 kg and for whom a solid dosage form is appropriate. Before prescribing lamivudine scored tablets, pediatric patients should be assessed for the ability to swallow tablets.For patients unable to safely and reliably swallow lamivudine tablets, the oral solution formulation may be prescribed [see Warnings and Precautions (5.5)]. The recommended oral dosage of lamivudine for HIV-1-infected pediatric patients is presented in Table 1. Table 1. Dosing Recommendations for Lamivudine Scored (150-mg) Tablets in Pediatric Patients Weight (kg) Once-Daily Dosing Regimen a Twice-Daily Dosing Regimen Using Scored 150-mg Tablet AM Dose PM Dose Total Daily Dose 14 to <20 1 tablet (150 mg) ½ tablet (75 mg) ½ tablet (75 mg) 150 mg ≥20 to <25 1½ tablets (225 mg) ½ tablet (75 mg) 1 tablet (150 mg) 225 mg ≥25 2 tablets (300mg) b 1 tablet (150 mg) 1 tablet (150 mg) 300 mg a Data regarding the efficacy of once-daily dosing is limited to subjects who transitioned from twice-daily dosing to once-daily dosing after 36 weeks of treatment [see Clinical Studies ( 14.2 )]. b Patients may alternatively take one 300-mg tablet, which is not scored. 2.3 Patients with Renal Impairment Dosing of lamivudine are adjusted in accordance with renal function. Dosage adjustments are listed in Table 2 [see Clinical Pharmacology ( 12.3 )]. Table 2. Adjustment of Dosage of Lamivudine in Adults and Adolescents (Greater than or Equal to 25 kg) in Accordance with Creatinine Clearance Creatinine Clearance (mL/min) Recommended Dosage of Lamivudine ≥50 150 mg twice daily or 300 mg once daily 30-49 150 mg once daily 15-29 150 mg first dose, then 100 mg once daily 5-14 150 mg first dose, then 50 mg once daily <5 50 mg first dose, then 25 mg once daily No additional dosing of lamivudine is required after routine (4-hour) hemodialysis or peritoneal dialysis. Although there are insufficient data to recommend a specific dose adjustment of lamivudine in pediatric patients with renal impairment, a reduction in the dose and/or an increase in the dosing interval should be considered.

6 ADVERSE REACTIONS The following adverse reactions are discussed in other sections of the labeling: • Exacerbations of hepatitis B [see Boxed Warning, Warnings and Precautions ( 5.1 )]. • Lactic acidosis and severe hepatomegaly with steatosis [see Warnings and Precautions ( 5.2 )]. • Pancreatitis [see Warnings and Precautions ( 5.3 )]. • Immune reconstitution syndrome [see Warnings and Precautions ( 5.4 )]. • The most common reported adverse reactions (incidence greater than or equal to 15%) in adults were headache, nausea, malaise and fatigue, nasal signs and symptoms, diarrhea, and cough. ( 6.1 ) • The most common reported adverse reactions (incidence greater than or equal to 15%) in pediatric subjects were fever and cough. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Macleods Pharma USA, Inc. at 1-888-943-3210 or 1-855-926-3384 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch . 6.1 Clinical Trials Experience Clinical Trials Experience in Adult Subjects 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 clinical practice. The safety profile of lamivudine in adults is primarily based on 3,568 HIV-1-infected subjects in 7 clinical trials. The most common adverse reactions are headache, nausea, malaise, fatigue, nasal signs and symptoms, diarrhea, and cough. Selected clinical adverse reactions in greater than or equal to 5% of subjects during therapy with lamivudine 150 mg twice daily plus RETROVIR 200 mg 3 times daily for up to 24 weeks are listed in Table 3. Table 3. Selected Clinical Adverse Reactions (Greater than or Equal to 5% Frequency) in Four Controlled Clinical Trials (NUCA3001, NUCA3002, NUCB3001, NUCB3002) Adverse Reaction LAMIVUDINE 150 mg Twice Daily plus RETROVIR (n = 251) RETROVIR a (n = 230) Body as a Whole Headache 35% 27% Malaise & fatigue 27% 23% Fever or chills 10% 12% Digestive Nausea 33% 29% Diarrhea 18% 22% Nausea & vomiting 13% 12% Anorexia and/or decreased appetite 10% 7% Abdominal pain 9% 11% Abdominal cramps 6% 3% Dyspepsia 5% 5% Nervous System Neuropathy 12% 10% Insomnia & other sleep disorders 11% 7% Dizziness 10% 4% Depressive disorders 9% 4% Respiratory Nasal signs & symptoms 20% 11% Cough 18% 13% Skin Skin rashes 9% 6% Musculoskeletal Musculoskeletal pain 12% 10% Myalgia 8% 6% Arthralgia 5% 5% a Either zidovudine monotherapy or zidovudine in combination with zalcitabine. Pancreatitis: Pancreatitis was observed in 9 out of 2,613 adult subjects (0.3%) who received lamivudine in controlled clinical trials EPV20001, NUCA3001, NUCB3001, NUCA3002, NUCB3002, and NUCB3007 [see Warnings and Precautions ( 5.4 )]. Lamivudine 300 mg Once Daily: The types and frequencies of clinical adverse reactions reported in subjects receiving lamivudine 300 mg once daily or lamivudine 150 mg twice daily (in 3-drug combination regimens in EPV20001 and EPV40001) for 48 weeks were similar. Selected laboratory abnormalities observed during therapy are summarized in Table 4. Table 4. Frequencies of Selected Grade 3-4 Laboratory Abnormalities in Adults in Four 24-Week Surrogate Endpoint Trials (NUCA3001, NUCA3002, NUCB3001, NUCB3002) and a Clinical Endpoint Trial (NUCB3007) Test (Threshold Level) 24-Week Surrogate Endpoint Trials a Clinical Endpoint Trial a LAMIVUDINE plus RETROVIR RETROVIR b LAMIVUDINE plus Current Therapy c Placebo plus Current Therapy c Absolute neutrophil count (<750/mm 3 ) 7.2% 5.4% 15% 13% Hemoglobin (<8.0 g/dL) 2.9% 1.8% 2.2% 3.4% Platelets (<50,000/mm 3 ) 0.4% 1.3% 2.8% 3.8% ALT (>5.0 x ULN) 3.7% 3.6% 3.8% 1.9% AST (>5.0 x ULN) 1.7% 1.8% 4.0% 2.1% Bilirubin (>2.5 x ULN) 0.8% 0.4% ND ND Amylase (>2.0 x ULN) 4.2% 1.5% 2.2% 1.1% a The median duration on study was 12 months. b Either zidovudine monotherapy or zidovudine in combination with zalcitabine. c Current therapy was either zidovudine, zidovudine plus didanosine, or zidovudine plus zalcitabine. ULN = Upper limit of normal. ND = Not done. The frequencies of selected laboratory abnormalities reported in subjects receiving lamivudine 300 mg once daily or lamivudine 150 mg twice daily (in 3-drug combination regimens in EPV20001 and EPV40001) were similar. Clinical Trials Experience in Pediatric Subjects Lamivudine oral solution has been studied in 638 pediatric subjects aged 3 months to 18 years in 3 clinical trials. Selected clinical adverse reactions and physical findings with a greater than or equal to 5% frequency during therapy with lamivudine 4 mg per kg twice daily plus RETROVIR 160 mg per m 2 3 times daily in therapy-naive (less than or equal to 56 days of antiretroviral therapy) pediatric subjects are listed in Table 5. Table 5. Selected Clinical Adverse Reactions and Physical Findings (Greater than or Equal to 5% Frequency) in Pediatric Subjects in Trial ACTG300 Adverse Reaction LAMIVUDINE plus RETROVIR (n = 236) Didanosine (n = 235) Body as a Whole Fever 25% 32% Digestive Hepatomegaly 11% 11% Nausea & vomiting 8% 7% Diarrhea 8% 6% Stomatitis 6% 12% Splenomegaly 5% 8% Respiratory Cough 15% 18% Abnormal breath sounds/wheezing 7% 9% Ear, Nose, and Throat Signs or symptoms of ears a 7% 6% Nasal discharge or congestion 8% 11% Other Skin rashes 12% 14% Lymphadenopathy 9% 11% a Includes pain, discharge, erythema, or swelling of an ear. Pancreatitis: Pancreatitis, which has been fatal in some cases, has been observed in antiretroviral nucleoside-experienced pediatric subjects receiving lamivudine alone or in combination with other antiretroviral agents. In an open-label dose-escalation trial (NUCA2002), 14 subjects (14%) developed pancreatitis while receiving monotherapy with lamivudine. Three of these subjects died of complications of pancreatitis. In a second open-label trial (NUCA2005), 12 subjects (18%) developed pancreatitis. In Trial ACTG300, pancreatitis was not observed in 236 subjects randomized to lamivudine plus RETROVIR. Pancreatitis was observed in 1 subject in this trial who received open-label lamivudine in combination with RETROVIR and ritonavir following discontinuation of didanosine monotherapy [see Warnings and Precautions ( 5.4 )]. Paresthesias and Peripheral Neuropathies: Paresthesias and peripheral neuropathies were reported in 15 subjects (15%) in Trial NUCA2002, 6 subjects (9%) in Trial NUCA2005, and 2 subjects (less than 1%) in Trial ACTG300. Selected laboratory abnormalities experienced by therapy-naive (less than or equal to 56 days of antiretroviral therapy) pediatric subjects are listed in Table 6. Table 6. Frequencies of Selected Grade 3-4 Laboratory Abnormalities in Pediatric Subjects in Trial ACTG300 Test (Threshold Level) LAMIVUDINE plus RETROVIR Didanosine Absolute neutrophil count (<400/mm 3 ) Hemoglobin (<7.0 g/dL) Platelets (<50,000/mm 3 ) ALT (>10 x ULN) AST (>10 x ULN) Lipase (>2.5 x ULN) Total Amylase (>2.5 x ULN) 8% 4% 1% 1% 2% 3% 3% 3% 2% 3% 3% 4% 3% 3% ULN = Upper limit of normal. Pediatric Subjects Once-Daily versus Twice-Daily Dosing (COL105677): The safety of once-daily compared with twice-daily dosing of lamivudine was assessed in the ARROW trial. Primary safety assessment in the ARROW trial was based on Grade 3 and Grade 4 adverse events. The frequency of Grade 3 and 4 adverse events was similar among subjects randomized to once-daily dosing compared with subjects randomized to twice-daily dosing. One event of Grade 4 hepatitis in the once-daily cohort was considered as uncertain causality by the investigator and all other Grade 3 or 4 adverse events were considered not related by the investigator. Neonates: Limited short-term safety information is available from 2 small, uncontrolled trials in South Africa in neonates receiving lamivudine with or without zidovudine for the first week of life following maternal treatment starting at Week 38 or 36 of gestation [see Clinical Pharmacology ( 12.3 )] . Selected adverse reactions reported in these neonates included increased liver function tests, anemia, diarrhea, electrolyte disturbances, hypoglycemia, jaundice and hepatomegaly, rash, respiratory infections, and sepsis; 3 neonates died (1 from gastroenteritis with acidosis and convulsions, 1 from traumatic injury, and 1 from unknown causes). Two other nonfatal gastroenteritis or diarrhea cases were reported, including 1 with convulsions; 1 infant had transient renal insufficiency associated with dehydration. The absence of control groups limits assessments of causality, but it should be assumed that perinatally exposed infants may be at risk for adverse reactions comparable to those reported in pediatric and adult HIV-1-infected patients treated with lamivudine-containing combination regimens. Long-term effects of in utero and infant lamivudine exposure are not known. 6.2 Postmarketing Experience The following adverse reactions have been identified during post-approval use of lamivudine. Because these reactions are reported voluntarily from a population of unknown size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. These reactions have been chosen for inclusion due to a combination of their seriousness, frequency of reporting, or potential causal connection to lamivudine. Body as a Whole Redistribution/accumulation of body fat. Endocrine and Metabolic Hyperglycemia. General Weakness. Hemic and Lymphatic Anemia (including pure red cell aplasia and severe anemias progressing on therapy). Hepatic and Pancreatic Lactic acidosis and hepatic steatosis [see Warnings and Precautions ( 5.2 )], posttreatment exacerbations of hepatitis B [see Warnings and Precautions ( 5.1 )]. Hypersensitivity Anaphylaxis,urticaria. Musculoskeletal Muscle weakness, CPK elevation, rhabdomyolysis. Skin Alopecia, pruritus.

12.3 Pharmacokinetics Pharmacokinetics in Adults The pharmacokinetic properties of lamivudine have been studied in asymptomatic, HIV-1-infected adult subjects after administration of single intravenous (IV) doses ranging from 0.25 to 8 mg per kg, as well as single and multiple (twice-daily regimen) oral doses ranging from 0.25 to 10 mg per kg. The pharmacokinetic properties of lamivudine have also been studied as single and multiple oral doses ranging from 5 mg to 600 mg per day administered to HBV-infected subjects. The steady-state pharmacokinetic properties of the lamivudine 300-mg tablet once daily for 7 days compared with the lamivudine 150-mg tablet twice daily for 7 days were assessed in a crossover trial in 60 healthy subjects. Lamivudine 300 mg once daily resulted in lamivudine exposures that were similar to lamivudine 150 mg twice daily with respect to plasma AUC 24,ss ; however, C max,ss was 66% higher and the trough value was 53% lower compared with the 150-mg twice-daily regimen. Intracellular lamivudine triphosphate exposures in peripheral blood mononuclear cells were also similar with respect to AUC 24,ss and C max24,ss ; however, trough values were lower compared with the 150-mg twice-daily regimen. Inter-subject variability was greater for intracellular lamivudine triphosphate concentrations versus lamivudine plasma trough concentrations. The pharmacokinetics of lamivudine was evaluated in 12 adult HIV-1-infected subjects dosed with lamivudine 150 mg twice daily in combination with other antiretroviral agents. The geometric mean (95% CI) for AUC (0-12) was 5.53 (4.58, 6.67) mcg.h per mL and for C max was 1.40 (1.17, 1.69) mcg per mL. Absorption and Bioavailability: Absolute bioavailability in 12 adult subjects was 86% ± 16% (mean ± SD) for the 150-mg tablet and 87% ± 13% for the oral solution. After oral administration of 2 mg per kg twice a day to 9 adults with HIV-1, the peak serum lamivudine concentration (C max ) was 1.5 ± 0.5 mcg per mL (mean ± SD). The area under the plasma concentration versus time curve (AUC) and C max increased in proportion to oral dose over the range from 0.25 to 10 mg per kg. The accumulation ratio of lamivudine in HIV-1-positive asymptomatic adults with normal renal function was 1.50 following 15 days of oral administration of 2 mg per kg twice daily. Effects of Food on Oral Absorption: Lamivudine tablets and oral solution may be administered with or without food. An investigational 25-mg dosage form of lamivudine was administered orally to 12 asymptomatic, HIV-1-infected subjects on 2 occasions, once in the fasted state and once with food (1,099 kcal; 75 grams fat, 34 grams protein, 72 grams carbohydrate). Absorption of lamivudine was slower in the fed state (T max : 3.2 ± 1.3 hours) compared with the fasted state (T max : 0.9 ± 0.3 hours); C max in the fed state was 40% ± 23% (mean ± SD) lower than in the fasted state. There was no significant difference in systemic exposure (AUC∞) in the fed and fasted states. Distribution: The apparent volume of distribution after IV administration of lamivudine to 20 subjects was 1.3 ± 0.4 L per kg, suggesting that lamivudine distributes into extravascular spaces. Volume of distribution was independent of dose and did not correlate with body weight. Binding of lamivudine to human plasma proteins is less than 36%. In vitro studies showed that over the concentration range of 0.1 to 100 mcg per mL, the amount of lamivudine associated with erythrocytes ranged from 53% to 57% and was independent of concentration. Metabolism: Metabolism of lamivudine is a minor route of elimination. In humans, the only known metabolite of lamivudine is the trans-sulfoxide metabolite (approximately 5% of an oral dose after 12 hours). Serum concentrations of this metabolite have not been determined. Lamivudine is not significantly metabolized by cytochrome P450 enzymes. Elimination: The majority of lamivudine is eliminated unchanged in urine by active organic cationic secretion. In 9 healthy subjects given a single 300-mg oral dose of lamivudine, renal clearance was 199.7 ± 56.9 mL per min (mean ± SD). In 20 HIV-1-infected subjects given a single IV dose, renal clearance was 280.4 ± 75.2 mL per min (mean ± SD), representing 71% ± 16% (mean ± SD) of total clearance of lamivudine. In most single-dose trials in HIV-1-infected subjects, HBV-infected subjects, or healthy subjects with serum sampling for 24 hours after dosing, the observed mean elimination half-life (t ½ ) ranged from 5 to 7 hours. In HIV-1-infected subjects, total clearance was 398.5 ± 69.1 mL per min (mean ± SD). Oral clearance and elimination half-life were independent of dose and body weight over an oral dosing range of 0.25 to 10 mg per kg. Specific Populations Patients with Renal Impairment: The pharmacokinetic properties of lamivudine have been determined in a small group of HIV-1-infected adults with impaired renal function (Table 7). Table 7. Pharmacokinetic Parameters (Mean ± SD) after a Single 300-mg Oral Dose of Lamivudine in 3 Groups of Adults with Varying Degrees of Renal Function Parameter Creatinine Clearance Criterion (Number of Subjects) >60 mL/min (n = 6) 10-30 mL/min (n = 4) <10 mL/min (n = 6) Creatinine clearance (mL/min) C max (mcg/mL) AUC∞ (mcg•h/mL) Cl/F (mL/min) 111 ± 14 2.6 ± 0.5 11.0 ± 1.7 464 ± 76 28 ± 8 3.6 ± 0.8 48.0 ± 19 114 ± 34 6 ± 2 5.8 ± 1.2 157 ± 74 36 ± 11 T max was not significantly affected by renal function. Based on these observations, it is recommended that the dosage of lamivudine be modified in patients with renal impairment [see Dosage and Administration ( 2.3 )]. Based on a trial in otherwise healthy subjects with impaired renal function, hemodialysis increased lamivudine clearance from a mean of 64 to 88 mL per min; however, the length of time of hemodialysis (4 hours) was insufficient to significantly alter mean lamivudine exposure after a single-dose administration. Continuous ambulatory peritoneal dialysis and automated peritoneal dialysis have negligible effects on lamivudine clearance. Therefore, it is recommended, following correction of dose for creatinine clearance, that no additional dose modification be made after routine hemodialysis or peritoneal dialysis. The effects of renal impairment on lamivudine pharmacokinetics in pediatric patients are not known. Patients with Hepatic Impairment: The pharmacokinetic properties of lamivudine have been determined in adults with impaired hepatic function. Pharmacokinetic parameters were not altered by diminishing hepatic function. Safety and efficacy of lamivudine have not been established in the presence of decompensated liver disease. Pregnant Women: Lamivudine pharmacokinetics were studied in 36 pregnant women during 2 clinical trials conducted in South Africa. Lamivudine pharmacokinetics in pregnant women were similar to those seen in non-pregnant adults and in postpartum women. Lamivudine concentrations were generally similar in maternal, neonatal, and umbilical cord serum samples. Pediatric Patients: The pharmacokinetics of lamivudine have been studied after either single or repeat doses of lamivudine in 210 pediatric subjects. Pediatric subjects receiving lamivudine oral solution (dosed at approximately 8 mg per kg per day) achieved approximately 25% lower plasma concentrations of lamivudine compared with HIV-1-infected adults. Pediatric subjects receiving lamivudine oral tablets achieved plasma concentrations comparable to or slightly higher than those observed in adults. The absolute bioavailability of both lamivudine tablets and oral solution are lower in children than adults. The relative bioavailability of lamivudine oral solution is approximately 40% lower than tablets containing lamivudine in pediatric subjects despite no difference in adults. Lower lamivudine exposures in pediatric patients receiving lamivudine oral solution is likely due to the interaction between lamivudine and concomitant solutions containing sorbitol (such as ZIAGEN). Modeling of pharmacokinetic data suggests increasing the dosage of lamivudine oral solution to 5 mg per kg taken orally twice daily or 10 mg per kg taken orally once daily (up to a maximum of 300 mg daily) is needed to achieve sufficient concentrations of lamivudine [see Dosage and Administration ( 2.2 )]. There are no clinical data in HIV-1 infected pediatric patients coadministered with sorbitol-containing medicines at this dose. The pharmacokinetics of lamivudine dosed once daily in HIV-1-infected pediatric subjects aged 3 months through 12 years was evaluated in 3 trials (PENTA-15 [n = 17], PENTA 13 [n = 19], and ARROW PK [n = 35]). All 3 trials were 2-period, crossover, open-label pharmacokinetic trials of twice-versus once-daily dosing of abacavir and lamivudine. These 3 trials demonstrated that once-daily dosing provides similar AUC 0-24 to twice-daily dosing of lamivudine at the same total daily dose when comparing the dosing regimens within the same formulation (i.e., either the oral solution or the tablet formulation). The mean C max was approximately 80% to 90% higher with lamivudine once-daily dosing compared with twice-daily dosing. Table 8. Pharmacokinetic Parameters (Geometric Mean [95% CI]) after Repeat Dosing of Lamivudine in 3 Pediatric Trials Trial (Number of Subjects) ARROW PK (n = 35) PENTA-13 (n = 19) PENTA-15 (n = 17) a Age Range 3-12 years 2-12 years 3-36 months Formulation Tablet Solution b and Tablet c Solution b Parameter Once Daily Twice Daily Once Daily Twice Daily Once Daily Twice Daily C max (mcg/mL) 3.17 (2.76, 3.64) 1.80 (1.59, 2.04) 2.09 (1.80, 2.42) 1.11 (0.96, 1.29) 1.87 (1.65, 2.13) 1.05 (0.88, 1.26) AUC (0-24) (mcg•h/mL) 13.0 (11.4, 14.9) 12.0 (10.7, 13.4) 9.80 (8.64, 11.1) 8.88 (7.67, 10.3) 8.66 (7.46, 10.1) 9.48 (7.89, 11.4) a n = 16 for PENTA-15 Cmax. b Solution was dosed at 8 mg per kg per day. c Five subjects in PENTA-13 received lamivudine tablets. Distribution of lamivudine into cerebrospinal fluid (CSF) was assessed in 38 pediatric subjects after multiple oral dosing with lamivudine. CSF samples were collected between 2 and 4 hours postdose. At the dose of 8 mg per kg per day, CSF lamivudine concentrations in 8 subjects ranged from 5.6% to 30.9% (mean ± SD of 14.2% ± 7.9%) of the concentration in a simultaneous serum sample, with CSF lamivudine concentrations ranging from 0.04 to 0.3 mcg per mL. Limited, uncontrolled pharmacokinetic and safety data are available from administration of lamivudine (and zidovudine) to 36 infants aged up to 1 week in 2 trials in South Africa. In these trials, lamivudine clearance was substantially reduced in 1-week-old neonates relative to pediatric subjects (aged over 3 months) studied previously. There is insufficient information to establish the time course of changes in clearance between the immediate neonatal period and the age-ranges over 3 months old [see Adverse Reactions ( 6.1 )]. Geriatric Patients: The pharmacokinetics of lamivudine after administration of lamivudine to subjects over 65 years have not been studied [see Use in Specific Populations ( 8.5 )]. Male and Female Patients: There are no significant or clinically relevant gender differences in lamivudine pharmacokinetics. Racial Groups: There are no significant or clinically relevant racial differences in lamivudine pharmacokinetics. Drug Interaction Studies Effect of Lamivudine on the Pharmacokinetics of Other Agents: Based on in vitro study results, lamivudine at therapeutic drug exposures is not expected to affect the pharmacokinetics of drugs that are substrates of the following transporters: organic anion transporter polypeptide 1B1/3 (OATP1B1/3), breast cancer resistance protein (BCRP), P-glycoprotein (P-gp), multidrug and toxin extrusion protein 1 (MATE)1, MATE2-K, organic cation transporter 1 (OCT)1, OCT2, or OCT3. Effect of Other Agents on the Pharmacokinetics of Lamivudine: Lamivudine is a substrate of MATE1, MATE2-K, and OCT2 in vitro . Trimethoprim (an inhibitor of these drug transporters) has been shown to increase lamivudine plasma concentrations. This interaction is not considered clinically significant as no dose adjustment of lamivudine is needed. Lamivudine is a substrate of P-gp and BCRP; however, considering its absolute bioavailability (87%), it is unlikely that these transporters play a significant role in the absorption of lamivudine. Therefore, coadministration of drugs that are inhibitors of these efflux transporters is unlikely to affect the disposition and elimination of lamivudine. Interferon Alfa: There was no significant pharmacokinetic interaction between lamivudine and interferon alfa in a trial of 19 healthy male subjects. Ribavirin: In vitro data indicate ribavirin reduces phosphorylation of lamivudine, stavudine, and zidovudine. However, no pharmacokinetic (e.g., plasma concentrations or intracellular triphosphorylated active metabolite concentrations) or pharmacodynamic (e.g., loss of HIV-1/HCV virologic suppression) interaction was observed when ribavirin and lamivudine (n = 18), stavudine (n = 10), or zidovudine (n = 6) were coadministered as part of a multi-drug regimen to HIV-1/HCV co-infected subjects . Sorbitol (Excipient): Lamivudine and sorbitol solutions were coadministered to 16 healthy adult subjects in an open-label, randomized-sequence, 4-period, crossover trial. Each subject received a single 300-mg dose of lamivudine oral solution alone or coadministered with a single dose of 3.2 grams, 10.2 grams, or 13.4 grams of sorbitol in solution. Coadministration of lamivudine with sorbitol resulted in dose-dependent decreases of 20%, 39%, and 44% in the AUC (0-24) , 14%, 32%, and 36% in the AUC (∞) , and 28%, 52%, and 55% in the C max ; of lamivudine, respectively. Trimethoprim/Sulfamethoxazole: Lamivudine and TMP/SMX were coadministered to 14 HIV-1-positive subjects in a single-center, open-label, randomized, crossover trial. Each subject received treatment with a single 300-mg dose of lamivudine and TMP 160 mg/SMX 800 mg once a day for 5 days with concomitant administration of lamivudine 300 mg with the fifth dose in a crossover design. Coadministration of TMP/SMX with lamivudine resulted in an increase of 43% ± 23% (mean ± SD) in lamivudine AUC∞, a decrease of 29% ± 13% in lamivudine oral clearance, and a decrease of 30% ± 36% in lamivudine renal clearance. The pharmacokinetic properties of TMP and SMX were not altered by coadministration with lamivudine. There is no information regarding the effect on lamivudine pharmacokinetics of higher doses of TMP/SMX such as those used in treat PCP. Zidovudine: No clinically significant alterations in lamivudine or zidovudine pharmacokinetics were observed in 12 asymptomatic HIV-1-infected adult subjects given a single dose of zidovudine (200 mg) in combination with multiple doses of lamivudine (300 mg every 12 hours).