Valacyclovir Hydrochloride

1 INDICATIONS AND USAGE Valacyclovir hydrochloride is a deoxynucleoside analogue DNA polymerase inhibitor indicated for: Adult Patients ( 1.1 ) Cold Sores (Herpes Labialis) Genital Herpes Treatment in immunocompetent patients (initial or recurrent episode) Suppression in immunocompetent or HIV-1-infected patients Reduction of transmission Herpes Zoster Pediatric Patients (1.2) Cold Sores (Herpes Labialis) Chickenpox Limitations of Use (1.3) The efficacy and safety of valacyclovir tablets have not been established in immunocompromised patients other than for the suppression of genital herpes in HIV-1-infected patients. 1.1 Adult Patients Cold Sores (Herpes Labialis) Valacyclovir tablets are indicated for treatment of cold sores (herpes labialis). The efficacy of valacyclovir tablets initiated after the development of clinical signs of a cold sore (e.g., papule, vesicle, or ulcer) has not been established. Genital Herpes Initial Episode: Valacyclovir tablets are indicated for treatment of the initial episode of genital herpes in immunocompetent adults. The efficacy of treatment with valacyclovir tablets when initiated more than 72 hours after the onset of signs and symptoms has not been established. Recurrent Episodes: Valacyclovir tablets are indicated for treatment of recurrent episodes of genital herpes in immunocompetent adults. The efficacy of treatment with valacyclovir tablets when initiated more than 24 hours after the onset of signs and symptoms has not been established. Suppressive Therapy: Valacyclovir tablets are indicated for chronic suppressive therapy of recurrent episodes of genital herpes in immunocompetent and in HIV-1-infected adults. The efficacy and safety of valacyclovir tablets for the suppression of genital herpes beyond 1 year in immunocompetent patients and beyond 6 months in HIV-1-infected patients have not been established. Reduction of Transmission: Valacyclovir tablets are indicated for the reduction of transmission of genital herpes in immunocompetent adults. The efficacy of valacyclovir tablets for the reduction of transmission of genital herpes beyond 8 months in discordant couples has not been established. The efficacy of valacyclovir tablets for the reduction of transmission of genital herpes in individuals with multiple partners and non-heterosexual couples has not been established. Safer sex practices should be used with suppressive therapy (see current Centers for Disease Control and Prevention [CDC] Sexually Transmitted Diseases Treatment Guidelines ). Herpes Zoster Valacyclovir tablets are indicated for the treatment of herpes zoster (shingles) in immunocompetent adults. The efficacy of valacyclovir tablets when initiated more than 72 hours after the onset of rash and the efficacy and safety of valacyclovir tablets for treatment of disseminated herpes zoster have not been established. 1.2 Pediatric Patients Cold Sores (Herpes Labialis) Valacyclovir tablets are indicated for the treatment of cold sores (herpes labialis) in pediatric patients aged greater than or equal to 12 years. The efficacy of valacyclovir tablets initiated after the development of clinical signs of a cold sore (e.g., papule, vesicle, or ulcer) has not been established. Chickenpox Valacyclovir tablets are indicated for the treatment of chickenpox in immunocompetent pediatric patients aged 2 to less than 18 years. Based on efficacy data from clinical trials with oral acyclovir, treatment with valacyclovir tablets should be initiated within 24 hours after the onset of rash [see Clinical Studies (14.4) ] . 1.3 Limitations of Use The efficacy and safety of valacyclovir tablets have not been established in: Immunocompromised patients other than for the suppression of genital herpes in HIV-1-infected patients with a CD4+ cell count greater than or equal to 100 cells/mm 3 . Patients aged less than 12 years with cold sores (herpes labialis). Patients aged less than 2 years or greater than or equal to 18 years with chickenpox. Patients aged less than 18 years with genital herpes. Patients aged less than 18 years with herpes zoster. Neonates and infants as suppressive therapy following neonatal herpes simplex virus (HSV) infection.

2 DOSAGE AND ADMINISTRATION Valacyclovir tablets may be given without regard to meals. Valacyclovir oral suspension (25 mg/mL or 50 mg/mL) may be prepared extemporaneously from 500 mg valacyclovir tablets for use in pediatric patients for whom a solid dosage form is not appropriate [see Dosage and Administration (2.3) ] . Adult Dosage (2.1) Cold Sores 2 grams every 12 hours for 1 day Genital Herpes Initial episode 1 gram twice daily for 10 days Recurrent episodes 500 mg twice daily for 3 days Suppressive therapy Immunocompetent patients Alternate dose in patients with less than or equal to 9 recurrences/year HIV-1-infected patients 1 gram once daily 500 mg once daily 500 mg twice daily Reduction of transmission 500 mg once daily Herpes Zoster 1 gram 3 times daily for 7 days Pediatric Dosage (2.2) Cold Sores (aged greater than or equal to 12 years) 2 grams every 12 hours for 1 day Chickenpox (aged 2 to less than 18 years) 20 mg/kg 3 times daily for 5 days; not to exceed 1 gram 3 times daily Valacyclovir oral suspension (25 mg/mL or 50 mg/mL) can be prepared from the 500 mg valacyclovir tablets. ( 2.3 ) 2.1 Adult Dosing Recommendations Cold Sores (Herpes Labialis) The recommended dosage of valacyclovir tablets for treatment of cold sores is 2 grams twice daily for 1 day taken 12 hours apart. Therapy should be initiated at the earliest symptom of a cold sore (e.g., tingling, itching, or burning). Genital Herpes Initial Episode: The recommended dosage of valacyclovir tablets for treatment of initial genital herpes is 1 gram twice daily for 10 days. Therapy was most effective when administered within 48 hours of the onset of signs and symptoms. Recurrent Episodes: The recommended dosage of valacyclovir tablets for treatment of recurrent genital herpes is 500 mg twice daily for 3 days. Initiate treatment at the first sign or symptom of an episode. Suppressive Therapy: The recommended dosage of valacyclovir tablets for chronic suppressive therapy of recurrent genital herpes is 1 gram once daily in patients with normal immune function. In patients with a history of 9 or fewer recurrences per year, an alternative dose is 500 mg once daily. In HIV-1-infected patients with a CD4+ cell count greater than or equal to 100 cells/mm 3 , the recommended dosage of valacyclovir tablets for chronic suppressive therapy of recurrent genital herpes is 500 mg twice daily. Reduction of Transmission: The recommended dosage of valacyclovir tablets for reduction of transmission of genital herpes in patients with a history of 9 or fewer recurrences per year is 500 mg once daily for the source partner. Herpes Zoster The recommended dosage of valacyclovir tablets for treatment of herpes zoster is 1 gram 3 times daily for 7 days. Therapy should be initiated at the earliest sign or symptom of herpes zoster and is most effective when started within 48 hours of the onset of rash. 2.2 Pediatric Dosing Recommendations Cold Sores (Herpes Labialis) The recommended dosage of valacyclovir tablets for the treatment of cold sores in pediatric patients aged greater than or equal to 12 years is 2 grams twice daily for 1 day taken 12 hours apart. Therapy should be initiated at the earliest symptom of a cold sore (e.g., tingling, itching, or burning). Chickenpox The recommended dosage of valacyclovir tablets for treatment of chickenpox in immunocompetent pediatric patients aged 2 to less than 18 years is 20 mg/kg administered 3 times daily for 5 days. The total dose should not exceed 1 gram 3 times daily. Therapy should be initiated at the earliest sign or symptom [see Use in Specific Populations (8.4) , Clinical Pharmacology (12.3) , Clinical Studies (14.4) ] . 2.3 Extemporaneous Preparation of Oral Suspension Ingredients and Preparation per USP-NF Valacyclovir tablets 500 mg, cherry flavor, and Suspension Structured Vehicle USP-NF (SSV). Valacyclovir oral suspension (25 mg/mL or 50 mg/mL) should be prepared in lots of 100 mL. Instructions for Preparing Suspension at Time of Dispensing Prepare SSV according to the USP-NF. Using a pestle and mortar, grind the required number of valacyclovir 500 mg tablets until a fine powder is produced (5 valacyclovir tablets for 25 mg/mL suspension; 10 valacyclovir tablets for 50 mg/mL suspension). Gradually add approximately 5 mL aliquots of SSV to the mortar and triturate the powder until a paste has been produced. Ensure that the powder has been adequately wetted. Continue to add approximately 5 mL aliquots of SSV to the mortar, mixing thoroughly between additions, until a concentrated suspension is produced, to a minimum total quantity of 20 mL SSV and a maximum total quantity of 40 mL SSV for both the 25 mg/mL and 50 mg/mL suspensions. Transfer the mixture to a suitable 100 mL measuring flask. Transfer the cherry flavor* to the mortar and dissolve in approximately 5 mL of SSV. Once dissolved, add to the measuring flask. Rinse the mortar at least 3 times with approximately 5 mL aliquots of SSV, transferring the rinsing to the measuring flask between additions. Make the suspension to volume (100 mL) with SSV and shake thoroughly to mix. Transfer the suspension to an amber glass medicine bottle with a child-resistant closure. The prepared suspension should be labeled with the following information “Shake well before using. Store suspension between 2° to 8°C (36° to 46°F) in a refrigerator. Discard after 28 days.” *The amount of cherry flavor added is as instructed by the suppliers of the cherry flavor. 2.4 Patients with Renal Impairment Dosage recommendations for adult patients with reduced renal function are provided in Table 1 [see Use in Specific Populations (8.5 , 8.6) , Clinical Pharmacology (12.3) ] . Data are not available for the use of valacyclovir tablets in pediatric patients with a creatinine clearance less than 50 mL/min/1.73 m 2 . Table 1. Valacyclovir Tablets Dosage Recommendations for Adults with Renal Impairment Indications Normal Dosage Regimen (Creatinine Clearance ≥50 mL/min) Creatinine Clearance (mL/min) 30 to 49 10 to 29 <10 Cold sores (Herpes Labialis) Do not exceed 1 day of treatment. Two 2 gram doses taken 12 hours apart Two 1 gram doses taken 12 hours apart Two 500 mg doses taken 12 hours apart 500 mg single dose Genital herpes: Initial episode 1 gram every 12 hours no reduction 1 gram every 24 hours 500 mg every 24 hours Genital herpes: Recurrent episode 500 mg every 12 hours no reduction 500 mg every 24 hours 500 mg every 24 hours Genital herpes: Suppressive therapy Immunocompetent patients Alternate dose for immunocompetent patients with less than or equal to 9 recurrences/year HIV-1-infected patients 1 gram every 24 hours 500 mg every 24 hours 500 mg every 12 hours no reduction no reduction no reduction 500 mg every 24 hours 500 mg every 48 hours 500 mg every 24 hours 500 mg every 24 hours 500 mg every 48 hours 500 mg every 24 hours Herpes zoster 1 gram every 8 hours 1 gram every 12 hours 1 gram every 24 hours 500 mg every 24 hours Hemodialysis Patients requiring hemodialysis should receive the recommended dose of valacyclovir tablets after hemodialysis. During hemodialysis, the half-life of acyclovir after administration of valacyclovir tablets is approximately 4 hours. About one-third of acyclovir in the body is removed by dialysis during a 4-hour hemodialysis session. Peritoneal Dialysis There is no information specific to administration of valacyclovir tablets in patients receiving peritoneal dialysis. The effect of chronic ambulatory peritoneal dialysis (CAPD) and continuous arteriovenous hemofiltration/dialysis (CAVHD) on acyclovir pharmacokinetics has been studied. The removal of acyclovir after CAPD and CAVHD is less pronounced than with hemodialysis, and the pharmacokinetic parameters closely resemble those observed in patients with end-stage renal disease (ESRD) not receiving hemodialysis. Therefore, supplemental doses of valacyclovir tablets should not be required following CAPD or CAVHD.

6 ADVERSE REACTIONS The following serious adverse reactions are discussed in greater detail in other sections of the labeling: Thrombotic Thrombocytopenic Purpura/Hemolytic Uremic Syndrome [see Warnings and Precautions (5.1) ] . Acute Renal Failure [see Warnings and Precautions (5.2) ] . Central Nervous System Effects [see Warnings and Precautions (5.3) ] . The most common adverse reactions reported in at least 1 indication by greater than 10% of adult subjects treated with valacyclovir hydrochloride and observed more frequently with valacyclovir hydrochloride compared with placebo are headache, nausea, and abdominal pain. The only adverse reaction reported in greater than 10% of pediatric subjects aged less than 18 years was headache. The most common adverse reactions reported in at least one indication by greater than 10% of adult subjects treated with valacyclovir hydrochloride and more commonly than in subjects treated with placebo are headache, nausea, and abdominal pain. (6.1) The only adverse reaction occurring in greater than 10% of pediatric subjects aged less than 18 years was headache. (6.2) To report SUSPECTED ADVERSE REACTIONS, contact Aurobindo Pharma USA, Inc. at 1-866-850-2876 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 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 practice. Cold Sores (Herpes Labialis) In clinical trials for the treatment of cold sores, the adverse reactions reported by subjects receiving valacyclovir hydrochloride 2 grams twice daily (n = 609) or placebo (n = 609) for 1 day, respectively, included headache (14%, 10%) and dizziness (2%, 1%). The frequencies of abnormal ALT (greater than 2 x ULN) were 1.8% for subjects receiving valacyclovir hydrochloride compared with 0.8% for placebo. Other laboratory abnormalities (hemoglobin, white blood cells, alkaline phosphatase, and serum creatinine) occurred with similar frequencies in the 2 groups. Genital Herpes Initial Episode: In a clinical trial for the treatment of initial episodes of genital herpes, the adverse reactions reported by greater than or equal to 5% of subjects receiving valacyclovir hydrochloride 1 gram twice daily for 10 days (n = 318) or oral acyclovir 200 mg 5 times daily for 10 days (n = 318), respectively, included headache (13%, 10%) and nausea (6%, 6%). For the incidence of laboratory abnormalities see Table 2. Recurrent Episodes: In 3 clinical trials for the episodic treatment of recurrent genital herpes, the adverse reactions reported by greater than or equal to 5% of subjects receiving valacyclovir hydrochloride 500 mg twice daily for 3 days (n = 402), valacyclovir hydrochloride 500 mg twice daily for 5 days (n = 1,136), or placebo (n = 259), respectively, included headache (16%, 11%, 14%) and nausea (5%, 4%, 5%). For the incidence of laboratory abnormalities see Table 2. Suppressive Therapy: Suppression of Recurrent Genital Herpes in Immunocompetent Adults: In a clinical trial for the suppression of recurrent genital herpes infections, the adverse reactions reported by subjects receiving valacyclovir hydrochloride 1 gram once daily (n = 269), valacyclovir hydrochloride 500 mg once daily (n = 266), or placebo (n = 134), respectively, included headache (35%, 38%, 34%), nausea (11%, 11%, 8%), abdominal pain (11%, 9%, 6%), dysmenorrhea (8%, 5%, 4%), depression (7%, 5%, 5%), arthralgia (6%, 5%, 4%), vomiting (3%, 3%, 2%), and dizziness (4%, 2%, 1%). For the incidence of laboratory abnormalities see Table 2. Suppression of Recurrent Genital Herpes in HIV-1-Infected Subjects: In HIV-1-infected subjects, frequently reported adverse reactions for valacyclovir hydrochloride (500 mg twice daily; n = 194, median days on therapy = 172) and placebo (n = 99, median days on therapy = 59), respectively, included headache (13%, 8%), fatigue (8%, 5%), and rash (8%, 1%). Post-randomization laboratory abnormalities that were reported more frequently in valacyclovir subjects versus placebo included elevated alkaline phosphatase (4%, 2%), elevated ALT (14%, 10%), elevated AST (16%, 11%), decreased neutrophil counts (18%, 10%), and decreased platelet counts (3%, 0%), respectively. Reduction of Transmission: In a clinical trial for the reduction of transmission of genital herpes, the adverse reactions reported by subjects receiving valacyclovir hydrochloride 500 mg once daily (n = 743) or placebo once daily (n = 741), respectively, included headache (29%, 26%), nasopharyngitis (16%, 15%), and upper respiratory tract infection (9%, 10%). Herpes Zoster In 2 clinical trials for the treatment of herpes zoster, the adverse reactions reported by subjects receiving valacyclovir hydrochloride 1 gram 3 times daily for 7 to 14 days (n = 967) or placebo (n = 195), respectively, included nausea (15%, 8%), headache (14%, 12%), vomiting (6%, 3%), dizziness (3%, 2%), and abdominal pain (3%, 2%). For the incidence of laboratory abnormalities see Table 2. Table 2. Incidence (%) of Laboratory Abnormalities in Herpes Zoster and Genital Herpes Trial Populations a Data were not collected prospectively. LLN = Lower limit of normal. ULN = Upper limit of normal. Laboratory Abnormality Herpes Zoster Genital Herpes Treatment Genital Herpes Suppression Valacyclovir Hydrochloride 1 gram 3 Times Daily (n = 967) Placebo (n = 195) Valacyclovir Hydrochloride 1 gram Twice Daily (n = 1,194) Valacyclovir Hydrochloride 500 mg Twice Daily (n = 1,159) Placebo (n = 439) Valacyclovir Hydrochloride 1 gram Once Daily (n = 269) Valacyclovir Hydrochloride 500 mg Once Daily (n = 266) Placebo (n = 134) Hemoglobin (<0.8 x LLN) White blood cells (<0.75 x LLN) Platelet count (<100,000/mm 3 ) AST (SGOT) (>2 x ULN) Serum creatinine (>1.5 x ULN) 0.8% 1.3% 1% 1% 0.2% 0% 0.6% 1.2% 0% 0% 0.3% 0.7% 0.3% 1% 0.7% 0.2% 0.6% 0.1% a 0% 0% 0.2% 0.7% 0.5% 0% 0% 0.7% 0.4% 4.1% 0% 0.8% 0.8% 1.1% 3.8% 0% 0.8% 1.5% 1.5% 3% 0% 6.2 Clinical Trials Experience in Pediatric Subjects The safety profile of valacyclovir hydrochloride has been studied in 177 pediatric subjects aged 1 month to less than 18 years. Sixty-five of these pediatric subjects, aged 12 to less than 18 years, received oral tablets for 1 to 2 days for treatment of cold sores. The remaining 112 pediatric subjects, aged 1 month to less than 12 years, participated in 3 pharmacokinetic and safety trials and received valacyclovir oral suspension. Fifty-one of these 112 pediatric subjects received oral suspension for 3 to 6 days. The frequency, intensity, and nature of clinical adverse reactions and laboratory abnormalities were similar to those seen in adults. Pediatric Subjects Aged 12 to Less than 18 Years (Cold Sores) In clinical trials for the treatment of cold sores, the adverse reactions reported by adolescent subjects receiving valacyclovir hydrochloride 2 grams twice daily for 1 day, or valacyclovir hydrochloride 2 grams twice daily for 1 day followed by 1 gram twice daily for 1 day (n = 65, across both dosing groups), or placebo (n = 30), respectively, included headache (17%, 3%) and nausea (8%, 0%). Pediatric Subjects Aged 1 Month to Less than 12 Years Adverse events reported in more than 1 subject across the 3 pharmacokinetic and safety trials in children aged 1 month to less than 12 years were diarrhea (5%), pyrexia (4%), dehydration (2%), herpes simplex (2%), and rhinorrhea (2%). No clinically meaningful changes in laboratory values were observed. 6.3 Postmarketing Experience In addition to adverse events reported from clinical trials, the following events have been identified during postmarketing use of valacyclovir hydrochloride. Because they are reported voluntarily from a population of unknown size, estimates of frequency cannot be made. These events have been chosen for inclusion due to a combination of their seriousness, frequency of reporting, or potential causal connection to valacyclovir hydrochloride. General Facial edema, hypertension, tachycardia. Allergic Acute hypersensitivity reactions including anaphylaxis, angioedema, dyspnea, pruritus, rash, and urticaria [see Contraindications (4) ] . Central Nervous System (CNS) Symptoms Aggressive behavior; agitation; ataxia; coma; confusion; decreased consciousness; dysarthria; encephalopathy; mania; and psychosis, including auditory and visual hallucinations, seizures, tremors [see Warnings and Precautions (5.3) , Use in Specific Populations (8.5 , 8.6) ] . Eye Visual abnormalities. Gastrointestinal Diarrhea. Hepatobiliary Tract and Pancreas Liver enzyme abnormalities, hepatitis. Renal Renal failure, renal pain (may be associated with renal failure) [see Warnings and Precautions (5.2) , Use in Specific Populations (8.5 , 8.6) ] . Hematologic Thrombocytopenia, aplastic anemia, leukocytoclastic vasculitis, TTP/HUS [see Warnings and Precautions (5.1) ] . Skin Erythema multiforme, rashes including photosensitivity, alopecia.

12.3 Pharmacokinetics The pharmacokinetics of valacyclovir and acyclovir after oral administration of valacyclovir hydrochloride have been investigated in 14 volunteer trials involving 283 adults and in 3 trials involving 112 pediatric subjects aged 1 month to less than 12 years. Pharmacokinetics in Adults Absorption and Bioavailability: After oral administration, valacyclovir hydrochloride is rapidly absorbed from the gastrointestinal tract and nearly completely converted to acyclovir and L- valine by first-pass intestinal and/or hepatic metabolism. The absolute bioavailability of acyclovir after administration of valacyclovir hydrochloride is 54.5% ± 9.1% as determined following a 1 gram oral dose of valacyclovir hydrochloride and a 350 mg intravenous acyclovir dose to 12 healthy volunteers. Acyclovir bioavailability from the administration of valacyclovir hydrochloride is not altered by administration with food (30 minutes after an 873 Kcal breakfast, which included 51 grams of fat). Acyclovir pharmacokinetic parameter estimates following administration of valacyclovir hydrochloride to healthy adult volunteers are presented in Table 3. There was a less than dose-proportional increase in acyclovir maximum concentration (C max ) and area under the acyclovir concentration-time curve (AUC) after single-dose and multiple-dose administration (4 times daily) of valacyclovir hydrochloride from doses between 250 mg to 1 gram. There is no accumulation of acyclovir after the administration of valacyclovir at the recommended dosage regimens in adults with normal renal function. Table 3. Mean (±SD) Plasma Acyclovir Pharmacokinetic Parameters Following Administration of Valacyclovir Hydrochloride to Healthy Adult Volunteers a Administered 4 times daily for 11 days. ND = not done. Dose Single-Dose Administration (N = 8) Multiple-Dose Administration a (N = 24, 8 per treatment arm) C max (±SD) (mcg/mL) AUC (±SD) (h•mcg/mL) C max (±SD) (mcg/mL) AUC (±SD) (h•mcg/mL) 100 mg 0.83 (±0.14) 2.28 (±0.4) ND ND 250 mg 2.15 (±0.5) 5.76 (±0.6) 2.11 (±0.33) 5.66 (±1.09) 500 mg 3.28 (±0.83) 11.59 (±1.79) 3.69 (±0.87) 9.88 (±2.01) 750 mg 4.17 (±1.14) 14.11 (±3.54) ND ND 1,000 mg 5.65 (±2.37) 19.52 (±6.04) 4.96 (±0.64) 15.7 (±2.27) Distribution: The binding of valacyclovir to human plasma proteins ranges from 13.5% to 17.9%. The binding of acyclovir to human plasma proteins ranges from 9% to 33%. Metabolism: Valacyclovir is converted to acyclovir and L -valine by first-pass intestinal and/or hepatic metabolism. Acyclovir is converted to a small extent to inactive metabolites by aldehyde oxidase and by alcohol and aldehyde dehydrogenase. Neither valacyclovir nor acyclovir is metabolized by cytochrome P450 enzymes. Plasma concentrations of unconverted valacyclovir are low and transient, generally becoming non-quantifiable by 3 hours after administration. Peak plasma valacyclovir concentrations are generally less than 0.5 mcg/mL at all doses. After single-dose administration of 1 gram of valacyclovir hydrochloride, average plasma valacyclovir concentrations observed were 0.5, 0.4, and 0.8 mcg/mL in subjects with hepatic dysfunction, renal insufficiency, and in healthy subjects who received concomitant cimetidine and probenecid, respectively. Elimination: The pharmacokinetic disposition of acyclovir delivered by valacyclovir is consistent with previous experience from intravenous and oral acyclovir. Following the oral administration of a single 1 gram dose of radiolabeled valacyclovir to 4 healthy subjects, 46% and 47% of administered radioactivity was recovered in urine and feces, respectively, over 96 hours. Acyclovir accounted for 89% of the radioactivity excreted in the urine. Renal clearance of acyclovir following the administration of a single 1 gram dose of valacyclovir hydrochloride to 12 healthy subjects was approximately 255 ± 86 mL/min which represents 42% of total acyclovir apparent plasma clearance. The plasma elimination half-life of acyclovir typically averaged 2.5 to 3.3 hours in all trials of valacyclovir hydrochloride in subjects with normal renal function. Specific Populations Patients with Renal Impairment: Reduction in dosage is recommended in patients with renal impairment [see Dosage and Administration (2.4) , Use in Specific Populations (8.5 , 8.6) ] . Following administration of valacyclovir hydrochloride to subjects with ESRD, the average acyclovir half-life is approximately 14 hours. During hemodialysis, the acyclovir half-life is approximately 4 hours. Approximately one-third of acyclovir in the body is removed by dialysis during a 4-hour hemodialysis session. Apparent plasma clearance of acyclovir in subjects on dialysis was 86.3 ± 21.3 mL/min/1.73 m 2 compared with 679.16 ± 162.76 mL/min/1.73 m 2 in healthy subjects. Patients with Hepatic Impairment: Administration of valacyclovir hydrochloride to subjects with moderate (biopsy-proven cirrhosis) or severe (with and without ascites and biopsy-proven cirrhosis) liver disease indicated that the rate but not the extent of conversion of valacyclovir to acyclovir is reduced, and the acyclovir half-life is not affected. Dosage modification is not recommended for patients with cirrhosis. Patients with HIV-1 Disease: In 9 subjects with HIV-1 disease and CD4+ cell counts less than 150 cells/mm 3 who received valacyclovir hydrochloride at a dosage of 1 gram 4 times daily for 30 days, the pharmacokinetics of valacyclovir and acyclovir were not different from that observed in healthy subjects. Geriatric Patients: After single-dose administration of 1 gram of valacyclovir hydrochloride in healthy geriatric subjects, the half-life of acyclovir was 3.11 ± 0.51 hours compared with 2.91 ± 0.63 hours in healthy younger adult subjects. The pharmacokinetics of acyclovir following single- and multiple-dose oral administration of valacyclovir hydrochloride in geriatric subjects varied with renal function. Dose reduction may be required in geriatric patients, depending on the underlying renal status of the patient [see Dosage and Administration (2.4) , Use in Specific Populations (8.5, 8.6) ] . Pediatric Patients: Acyclovir pharmacokinetics have been evaluated in a total of 98 pediatric subjects (aged 1 month to less than 12 years) following administration of the first dose of an extemporaneous oral suspension of valacyclovir [see Adverse Reactions (6.2) , Use in Specific Populations (8.4) ] . Acyclovir pharmacokinetic parameter estimates following a 20 mg/kg dose are provided in Table 4. Table 4. Mean (±SD) Plasma Acyclovir Pharmacokinetic Parameter Estimates Following First-Dose Administration of 20 mg/kg Valacyclovir Oral Suspension to Pediatric Subjects vs. 1 Gram Single Dose of Valacyclovir Hydrochloride to Adults a Historical estimates using pediatric pharmacokinetic sampling schedule. Parameter Pediatric Subjects (20 mg/kg Oral Suspension) Adults 1 gram Solid Dose of Valacyclovir Hydrochloride a (n = 15) 1 to <2 year (n = 6) 2 to <6 year (n = 12) 6 to <12 year (n = 8) AUC (mcg•h/mL) C max (mcg/mL) 14.4 (±6.26) 4.03 (±1.37) 10.1 (±3.35) 3.75 (±1.14) 13.1 (±3.43) 4.71 (±1.2) 17.2 (±3.1) 4.72 (±1.37) Drug Interaction Studies When valacyclovir hydrochloride is coadministered with antacids, cimetidine and/or probenecid, digoxin, or thiazide diuretics in patients with normal renal function, the effects are not considered to be of clinical significance (see below). Therefore, when valacyclovir hydrochloride is coadministered with these drugs in patients with normal renal function, no dosage adjustment is recommended. Antacids: The pharmacokinetics of acyclovir after a single dose of valacyclovir hydrochloride (1 gram) were unchanged by coadministration of a single dose of antacids (Al 3+ or Mg ++ ). Cimetidine: Acyclovir C max and AUC following a single dose of valacyclovir hydrochloride (1 gram) increased by 8% and 32%, respectively, after a single dose of cimetidine (800 mg). Cimetidine plus Probenecid: Acyclovir C max and AUC following a single dose of valacyclovir hydrochloride (1 gram) increased by 30% and 78%, respectively, after a combination of cimetidine and probenecid, primarily due to a reduction in renal clearance of acyclovir. Digoxin: The pharmacokinetics of digoxin were not affected by coadministration of valacyclovir hydrochloride 1 gram 3 times daily, and the pharmacokinetics of acyclovir after a single dose of valacyclovir hydrochloride (1 gram) was unchanged by coadministration of digoxin (2 doses of 0.75 mg). Probenecid: Acyclovir C max and AUC following a single dose of valacyclovir hydrochloride (1 gram) increased by 22% and 49%, respectively, after probenecid (1 gram). Thiazide Diuretics: The pharmacokinetics of acyclovir after a single dose of valacyclovir hydrochloride (1 gram) were unchanged by coadministration of multiple doses of thiazide diuretics.