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 501.47 g/mol and the following structural formula: Adefovir dipivoxil is a white to off-white 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: croscarmellose sodium, lactose monohydrate, magnesium stearate, starch and talc. adefovir-dipivoxil

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.

Adefovir Dipivoxil Tablets are white to off-white, round, flat-faced bevelled edge tablets, engraved “APO” on one side, “A10” on the other side. Tablets: 10 mg

One tablet containing 10 mg adefovir dipivoxil once daily orally with or without food. Dose adjustment in renal impairment for adults Creatinine Clearance (mL/min) Creatinine clearance calculated by Cockcroft-Gault method using lean or ideal body weight. Greater than or equal to 50 30 to 49 10 to 29 Hemodialysis Patients 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 No dose recommendations for: Non-hemodialysis patients with creatinine clearance less than 10 mL per minute. Adolescent patients with renal impairment

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 are not recommended for use in children less than 12 years of age

Dose Adjustment in Renal Impairment Significantly increased drug exposures were seen when adefovir dipivoxil tablets were administered to adult patients with renal impairment . 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 . 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) Creatinine clearance calculated by Cockcroft-Gault method using lean or ideal body weight. Greater than or equal to 50 30 to 49 10 to 29 Hemodialysis Patients 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 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 .

Severe acute exacerbations of hepatitis: Monitor hepatic function closely at repeated intervals for at least several months in patients who discontinue adefovir dipivoxil. Nephrotoxicity: Monitor renal function during therapy for all patients, particularly those with pre-existing or other risks for renal impairment. Dose adjustment may be required. HIV Resistance: Offer HIV testing to all patients prior to initiating adefovir dipivoxil. Untreated HIV may result in HIV resistance. Lactic acidosis and severe hepatomegaly with steatosis: If suspected, suspend treatment. Coadministration with Other Products: Do not administer adefovir dipivoxil concurrently with VIREAD ® or other tenofovir-containing products. Clinical Resistance: For patients with lamivudine-resistant HBV use adefovir dipivoxil in combination with lamivudine. For all patients, consider modifying treatment in case serum HBV DNA remains above 1000 copies/mL with continued treatment. 5.1 Exacerbation of Hepatitis after Discontinuation of Treatment Severe acute exacerbation of hepatitis has been reported in patients who have discontinued anti-hepatitis B therapy, including therapy with adefovir dipivoxil. Hepatic function should be monitored at repeated intervals with both clinical and laboratory follow-up for at least several months in patients who discontinue adefovir dipivoxil. If appropriate, resumption of anti-hepatitis B therapy may be warranted. In clinical trials of adefovir dipivoxil, exacerbations of hepatitis (ALT elevations 10 times the upper limit of normal or greater) occurred in up to 25% of patients after discontinuation of adefovir dipivoxil. These events were identified in studies GS-98-437 and GS-98-438 (N=492). Most of these events occurred within 12 weeks of drug discontinuation. These exacerbations generally occurred in the absence of HBeAg seroconversion, and presented as serum ALT elevations in addition to re-emergence of viral replication. In the HBeAg-positive and HBeAg-negative studies in patients with compensated liver function, the exacerbations were not generally accompanied by hepatic decompensation. However, patients with advanced liver disease or cirrhosis may be at higher risk for hepatic decompensation. Although most events appear to have been self-limited or resolved with re-initiation of treatment, severe hepatitis exacerbations, including fatalities, have been reported. Therefore, patients should be closely monitored after stopping treatment

Nephrotoxicity Nephrotoxicity characterized by a delayed onset of gradual increases in serum creatinine and decreases in serum phosphorus was historically shown to be the treatment-limiting toxicity of adefovir dipivoxil therapy at substantially higher doses in HIV-infected patients (60 and 120 mg daily) and in chronic hepatitis B patients (30 mg daily). Chronic administration of adefovir dipivoxil (10 mg once daily) may result in delayed nephrotoxicity. The overall risk of nephrotoxicity in patients with adequate renal function is low. However, this is of special importance in patients at risk of or having underlying renal dysfunction and patients taking concomitant nephrotoxic agents such as cyclosporine, tacrolimus, aminoglycosides, vancomycin and non-steroidal anti-inflammatory drugs . It is recommended that creatinine clearance is calculated in all patients prior to initiating therapy with adefovir dipivoxil. It is important to monitor renal function for all patients during treatment with adefovir dipivoxil, particularly for those with pre-existing or other risks for renal impairment. Patients with renal insufficiency at baseline or during treatment may require dose adjustment . The risks and benefits of adefovir dipivoxil treatment should be carefully evaluated prior to discontinuing adefovir dipivoxil in a patient with treatment-emergent nephrotoxicity. Pediatric Patients The efficacy and safety of adefovir dipivoxil have not been studied in patients less than 18 years of age with different degrees of renal impairment and no data are available to make dosage recommendations in these patients . Caution should be exercised when prescribing adefovir dipivoxil to adolescents with underlying renal dysfunction, and renal function in these patients should be closely monitored

HIV Resistance Prior to initiating adefovir dipivoxil therapy, HIV antibody testing should be offered to all patients. Treatment with anti-hepatitis B therapies, such as adefovir dipivoxil, that have activity against HIV in a chronic hepatitis B patient with unrecognized or untreated HIV infection may result in emergence of HIV resistance. Adefovir dipivoxil has not been shown to suppress HIV RNA in patients; however, there are limited data on the use of adefovir dipivoxil to treat patients with chronic hepatitis B co-infected with HIV

Lactic Acidosis/Severe Hepatomegaly with Steatosis Lactic acidosis and severe hepatomegaly with steatosis, including fatal cases, have been reported with the use of nucleoside analogs alone or in combination with antiretrovirals. A majority of these cases have been in women. Obesity and prolonged nucleoside exposure may be risk factors. Particular caution should be exercised when administering nucleoside analogs to any patient with known risk factors for liver disease; however, cases have also been reported in patients with no known risk factors. Treatment with adefovir dipivoxil should be suspended in any patient who develops clinical or laboratory findings suggestive of lactic acidosis or pronounced hepatotoxicity (which may include hepatomegaly and steatosis even in the absence of marked transaminase elevations)

Coadministration with Other Products Adefovir dipivoxil should not be used concurrently with products containing tenofovir disoproxil fumarate or tenofovir alafenamide

Clinical Resistance Resistance to adefovir dipivoxil can result in viral load rebound which may result in exacerbation of hepatitis B and, in the setting of diminished hepatic function, lead to liver decompensation and possible fatal outcome. In order to reduce the risk of resistance in patients with lamivudine resistant HBV, adefovir dipivoxil should be used in combination with lamivudine and not as adefovir dipivoxil monotherapy. In order to reduce the risk of resistance in all patients receiving adefovir dipivoxil monotherapy, a modification of treatment should be considered if serum HBV DNA remains above 1000 copies/mL with continued treatment. Long-term (144 week) data from Study 438 (N=124) show that patients with HBV DNA levels greater than 1000 copies/mL at Week 48 of treatment with adefovir dipivoxil were at greater risk of developing resistance than patients with serum HBV DNA levels below 1000 copies/mL at Week 48 of therapy.

Since adefovir is eliminated by the kidney, coadministration of adefovir dipivoxil with drugs that reduce renal function or compete for active tubular secretion may increase serum concentrations of either adefovir and/or these coadministered drugs . Patients should be monitored closely for adverse events when adefovir dipivoxil is coadministered with drugs that are excreted renally or with other drugs known to affect renal function [ See Warnings and Precautions ] . Adefovir dipivoxil should not be administered in combination with VIREAD [ See Warnings and Precautions] . 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 associated adverse events.