adefovir dipivoxil

1 INDICATIONS AND USAGE Adefovir dipivoxil tablets are indicated for the treatment of chronic hepatitis B in patients 12 years of age and older with evidence of active viral replication and either evidence of persistent elevations in serum aminotransferases (ALT or AST) or histologically active disease. This indication is based on histological, virological, biochemical, and serological responses in adult patients with HBeAg+ and HBeAg- chronic hepatitis B with compensated liver function, and with clinical evidence of lamivudine-resistant hepatitis B virus with either compensated or decompensated liver function. For patients 12 to less than 18 years of age, the indication is based on virological and biochemical responses in patients with HBeAg+ chronic hepatitis B virus infection with compensated liver function. Adefovir dipivoxil tablets are a nucleotide analogue indicated for the treatment of chronic hepatitis B in patients 12 years of age and older. ( 1 )

2 DOSAGE AND ADMINISTRATION One tablet containing 10 mg adefovir dipivoxil once daily orally with or without food. ( 2.1 ) Dose adjustment in renal impairment for adults ( 2.2 ) Creatinine Clearance (mL/min) a Hemodialysis Patients Greater than or equal to 50 30 - 49 10 - 29 Recommended dose and dosing interval 10 mg every 24 hours 10 mg every 48 hours 10 mg every 72 hours 10 mg every 7 days following dialysis a Creatinine clearance calculated by Cockcroft-Gault method using lean or ideal body weight. No dose recommendations for ( 2.1 ): Non-hemodialysis patients with creatinine clearance less than 10 mL per minute. Adolescent patients with renal impairment. 2.1 Chronic Hepatitis B The recommended dose of Adefovir Dipivoxil Tablets in chronic hepatitis B patients for patients 12 years of age and older with adequate renal function is 10 mg, once daily, taken orally, without regard to food. The optimal duration of treatment is unknown. Adefovir Dipivoxil Tablets is not recommended for use in children less than 12 years of age. 2.2 Dose Adjustment in Renal Impairment Significantly increased drug exposures were seen when Adefovir Dipivoxil Tablets was administered to adult patients with renal impairment [See Warnings and Precautions (5.2) and Clinical Pharmacology (12.3) ]. Therefore, the dosing interval of Adefovir Dipivoxil Tablets should be adjusted in adult patients with baseline creatinine clearance less than 50 mL per minute using the following suggested guidelines (See Table 1 ). The safety and effectiveness of these dosing interval adjustment guidelines have not been clinically evaluated. Additionally, it is important to note that these guidelines were derived from data in patients with pre-existing renal impairment at baseline. They may not be appropriate for patients in whom renal insufficiency evolves during treatment with Adefovir Dipivoxil Tablets. Therefore, clinical response to treatment and renal function should be closely monitored in these patients. Table 1 Dosing Interval Adjustment of Adefovir Dipivoxil Tablets in Adult Patients with Renal Impairment Creatinine Clearance (mL/min) a Hemodialysis Patients Greater than or equal to 50 30 - 49 10 - 29 Recommended dose and dosing interval 10 mg every 24 hours 10 mg every 48 hours 10 mg every 72 hours 10 mg every 7 days following dialysis a Creatinine clearance calculated by Cockcroft-Gault method using lean or ideal body weight. The pharmacokinetics of adefovir have not been evaluated in non-hemodialysis patients with creatinine clearance less than 10 mL per minute; therefore, no dosing recommendation is available for these patients. No clinical data are available to make dosing recommendations in adolescent patients with renal insufficiency [See Warnings and Precautions (5.2) ]

2.1 Chronic Hepatitis B The recommended dose of Adefovir Dipivoxil Tablets in chronic hepatitis B patients for patients 12 years of age and older with adequate renal function is 10 mg, once daily, taken orally, without regard to food. The optimal duration of treatment is unknown. Adefovir Dipivoxil Tablets is not recommended for use in children less than 12 years of age.

2.2 Dose Adjustment in Renal Impairment Significantly increased drug exposures were seen when Adefovir Dipivoxil Tablets was administered to adult patients with renal impairment [See Warnings and Precautions (5.2) and Clinical Pharmacology (12.3) ]. Therefore, the dosing interval of Adefovir Dipivoxil Tablets should be adjusted in adult patients with baseline creatinine clearance less than 50 mL per minute using the following suggested guidelines (See Table 1 ). The safety and effectiveness of these dosing interval adjustment guidelines have not been clinically evaluated. Additionally, it is important to note that these guidelines were derived from data in patients with pre-existing renal impairment at baseline. They may not be appropriate for patients in whom renal insufficiency evolves during treatment with Adefovir Dipiv …

3 DOSAGE FORMS AND STRENGTHS Adefovir Dipivoxil is available as tablets. Each tablet contains 10 mg of adefovir dipivoxil. The tablets are white, round, flat faced beveled edged tablets, debossed Σ 3 on one side and plain on the other side. Tablets: 10 mg ( 3 )

4 CONTRAINDICATIONS Adefovir dipivoxil tablets are contraindicated in patients with previously demonstrated hypersensitivity to any of the components of the product. Adefovir dipivoxil tablets are contraindicated in patients with previously demonstrated hypersensitivity to any of the components of the product. ( 4 )

6 ADVERSE REACTIONS The following adverse reactions are discussed in other sections of the labeling: Severe acute exacerbations of Hepatitis [See Boxed Warning , Warnings and Precautions (5.1) ] Nephrotoxicity [See Boxed Warning , Warnings and Precautions (5.2) ] Most common adverse reaction (incidence greater than 5%) in compensated liver disease patients were asthenia, headache, abdominal pain and nausea. ( 6.1 ) The most common adverse reacion in pre- and post-transplantation lamivudine-resistant liver disease patients was increased creatinine. ( 6.2 ) To report SUSPECTED ADVERSE REACTIONS, contact Sigmapharm Laboratories at (1-215-352-6655 ) or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. Clinical and laboratory evidence of exacerbations of hepatitis have occurred after discontinuation of treatment with Adefovir Dipivoxil Tablets. Adverse reactions to Adefovir Dipivoxil Tablets identified from placebo-controlled and open label studies include the following: asthenia, headache, abdominal pain, diarrhea, nausea, dyspepsia, flatulence, increased creatinine, and hypophosphatemia. The incidence of these adverse reactions in studies 437 and 438, where 522 patients with chronic hepatitis B and compensated liver disease received double-blind treatment with Adefovir Dipivoxil Tablets (N=294) or placebo (N=228) for 48 weeks is presented in Table 2. Patients who received open-label Adefovir Dipivoxil Tablets for up to 240 weeks in Study 438 reported adverse reactions similar in nature and severity to those reported in the first 48 weeks. Table 2 Adverse Reactions (Grades 1–4) Reported in ≥3% of All Adefovir Dipivoxil Tablets-Treated Patients in Pooled Studies 437–438 Studies (0–48 Weeks) a Adverse Reaction Adefovir Dipivoxil Tablets 10 mg (N=294) Placebo (N=228) Asthenia 13% 14% Headache 9% 10% Abdominal Pain 9% 11% Nausea 5% 8% Flatulence 4% 4% Diarrhea 3% 4% Dyspepsia 3% 2% a In these studies, the overall incidence of adverse reactions with Adefovir Dipivoxil Tablets was similar to that reported with placebo. The incidence of adverse reactions is derived from treatment-related events as identified by the study investigators. No patients treated with Adefovir Dipivoxil Tablets developed a confirmed serum creatinine increase greater than or equal to 0.5 mg/dL from baseline or confirmed phosphorus decrease to 2 mg/dL or less by Week 48. By Week 96, 2% of Adefovir Dipivoxil Tablets-treated patients, by Kaplan-Meier estimate, had increases in serum creatinine greater than or equal to 0.5 mg/dL from baseline (no placebo-controlled results were available for comparison beyond Week 48). For patients who chose to continue Adefovir Dipivoxil Tablets for up to 240 weeks in Study 438, 4 of 125 patients (3%) had a confirmed increase of 0.5 mg/dL from baseline. The creatinine elevation resolved in 1 patient who permanently discontinued treatment and remained stable in 3 patients who continued treatment. For 65 patients who chose to continue Adefovir Dipivoxil Tablets for up to 240 weeks in Study 437, 6 had a confirmed increase in serum creatinine of greater than or equal to 0.5 mg/dL from baseline with 2 patients discontinuing from the study due to the elevated serum creatinine concentration. See Adverse Reactions (6.2) for changes in serum creatinine in patients with underlying renal insufficiency at baseline. 6.2 Special Risk Patients Pre- and Post-Liver Transplantation Patients Additional adverse reactions observed from an open-label study (Study 435) in pre- and post- liver transplantation patients with chronic hepatitis B and lamivudine-resistant hepatitis B administered Adefovir Dipivoxil Tablets once daily for up to 203 weeks include: abnormal ren …

7 DRUG INTERACTIONS Since adefovir is eliminated by the kidney, coadministration of Adefovir Dipivoxil Tablets with drugs that reduce renal function or compete for active tubular secretion may increase serum concentrations of either adefovir and/or these coadministered drugs [See Clinical Pharmacology (12.3) ] . Patients should be monitored closely for adverse events when Adefovir Dipivoxil Tablets are coadministered with drugs that are excreted renally or with other drugs known to affect renal function [See Warnings and Precautions (5.2) ]. Adefovir Dipivoxil Tablets should not be administered in combination with VIREAD [See Warnings and Precautions (5.5) ]. Coadministration with drugs that reduce renal function or compete for active tubular secretion may increase serum concentrations of adefovir or the coadministered drug. Monitor for Adefovir Dipivoxil Tablets associated adverse events. ( 7 )

8 USE IN SPECIFIC POPULATION Pediatrics: Not recommended in children less than 12 years of age. ( 2.1 , 8.4 , 14.4 ) Renal Impairment: Dose adjustment may be required. ( 2.2 ) 8.1 Pregnancy Pregnancy Exposure Registry There is a pregnancy exposure registry that monitors pregnancy outcomes in women exposed to Adefovir Dipivoxil Tablets during pregnancy. Healthcare providers are encouraged to register patients by calling the Antiretroviral Pregnancy Registry (APR) at 1-800-258-4263. Risk Summary Prospective pregnancy data from the APR are not sufficient to adequately assess the risk of birth defects, miscarriage or adverse maternal or fetal outcomes. Adefovir disoproxil (ADV) use during pregnancy has been evaluated in a limited number of individuals reported to the APR and the number of exposures to adefovir is insufficient to make a risk assessment compared to a reference population. The estimated background rate for major birth defects is 2.7% in the U.S. reference population of the Metropolitan Atlanta Congenital Defects Program (MACDP). The estimated rate of miscarriage is not reported in the APR. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. The estimated background rate of miscarriage in the U.S. general population is 15–20%. In animal reproduction studies with oral ADV, no adverse developmental effects were observed at exposures (C max ) 23 times higher in rats and 40 times higher in rabbits than those at the recommended human dose (RHD) of Adefovir Dipivoxil Tablets ( see Data ). Data Animal Data In an embryo-fetal development study, ADV was administered orally to pregnant rabbits (at 1, 5, or 20 mg/kg/day) during organogenesis (on gestation day 6 through 18). No adverse developmental effects were observed at up to the highest dose tested, at systemic exposure (C max ) 40 times that in humans at the RHD of Adefovir Dipivoxil Tablets. In a pre/post-natal development study, ADV was administered orally to pregnant rats (at 2.5, 10, or 40 mg/kg/day) from organogenesis, through late gestation, delivery, and lactation (gestation day 7 to lactation/postpartum day 20). Reduced body weight of the offspring due to maternal toxicity was observed at systemic exposure 23 times that in humans at the RHD of Adefovir Dipivoxil Tablets. In an embryo-fetal development study, ADV was administered intravenously to pregnant rats (at 2.5, 10, and 20 mg/kg/day) during organogenesis (gestation day 6 through 15). Embryo-fetal toxicity including malformations (anasarca, depressed eye bulge, umbilical hernia and kinked tail) and skeletal variations (reduction of ossified metacarpal bones, increases in thoracic vertebrae and decreases in lumbar vertebrae) occurred at systemic exposure (C max ) 38 times that in humans at the RHD of Adefovir Dipivoxil Tablets. No adverse developmental effects were observed at an exposure (C max ) 12 times that in humans at the RHD of Adefovir Dipivoxil Tablets. 8.2 Lactation Risk Summary It is not known whether adefovir is present in human breast milk, affects human milk production, or has effects on the breastfed infant. The developmental and health benefits of breastfeeding should be considered along with the mother's clinical need for Adefovir Dipivoxil Tablets and any potential adverse effects on the breastfed infant from Adefovir Dipivoxil Tablets or from the underlying maternal condition. 8.4 Pediatric Use Pediatric patients 12 to less than 18 years: The safety, efficacy, and pharmacokinetics of Adefovir Dipivoxil Tablets in pediatric patients (aged 12 to less than 18 years) were evaluated in a double-blind, randomized, placebo-controlled study (GS-US-103-518, Study 518) in 83 pediatric patients with chronic hepatitis B and compensated liver disease. The proportion of patients treated with Adefovir Dipivoxil Tablets who achieved the primary efficacy endpoint of serum HBV DNA less than 1,000 copies/mL and normal ALT levels at the end of 48 weeks blinded treatment was si …

12.1 Mechanism of Action Adefovir is an antiviral drug [See Microbiology ( 12.4 )].

11 DESCRIPTION Adefovir dipivoxil is a diester prodrug of adefovir. Adefovir is an acyclic nucleotide analog with activity against human hepatitis B virus (HBV). The chemical name of adefovir dipivoxil is 9-[2-[[bis[(pivaloyloxy)methoxy]-phosphinyl]-methoxy]ethyl]adenine. It has a molecular formula of C 20 H 32 N 5 O 8 P, a molecular weight of 501.48 and the following structural formula: Adefovir dipivoxil is a white to off-white crystalline powder with an aqueous solubility of 19 mg/mL at pH 2.0 and 0.4 mg/mL at pH 7.2. It has an octanol/aqueous phosphate buffer (pH 7) partition coefficient (log p) of 1.91. Adefovir Dipivoxil Tablets are for oral administration. Each tablet contains 10 mg of adefovir dipivoxil and the following inactive ingredients: copovidone, anhydrous lactose, microcrystalline cellulose, silicon dioxide, crospovidone and magnesium stearate. chemical structure

10 OVERDOSAGE Doses of adefovir dipivoxil 500 mg daily for 2 weeks and 250 mg daily for 12 weeks have been associated with gastrointestinal side effects. If overdose occurs the patient must be monitored for evidence of toxicity, and standard supportive treatment applied as necessary. Following a 10 mg single dose of Adefovir Dipivoxil Tablets, a four-hour hemodialysis session removed approximately 35% of the adefovir dose.

16 HOW SUPPLIED / STORAGE AND HANDLING Adefovir Dipivoxil is available as tablets. Each tablet contains 10 mg of adefovir dipivoxil. The tablets are white, round, flat faced beveled edged tablets, debossed ∑3 on one side and plain on the other side. They are packaged as follows: Bottles of 30 tablets (NDC 42794-003-08) containing polyester and desiccant and closed with a child-resistant closure. Store in original container at 25 °C (77 °F), excursions permitted to 15° - 30 °C (59° - 86 °F) (See USP Controlled Room Temperature). Do not use if seal over bottle opening is broken or missing.