ADEFOVIR DIPIVOXIL Drug Interactions: What You Need to Know

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 )

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 )

AND PRECAUTIONS Severe acute exacerbations of hepatitis: Monitor hepatic function closely at repeated intervals for at least several months in patients who discontinue Adefovir Dipivoxil Tablets. ( 5.1 ) 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. ( 5.2 )

Hiv

Resistance: Offer HIV testing to all patients prior to initiating Adefovir Dipivoxil Tablets. Untreated HIV may result in HIV resistance. ( 5.3 ) Lactic acidosis and severe hepatomegaly with steatosis: If suspected, suspend treatment. ( 5.4 ) Coadministration with Other Products: Do not administer Adefovir Dipivoxil Tablets concurrently with VIREAD ® or other tenofovir-containing products. ( 5.5 )

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. ( 5.6 )

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 Tablets. 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 Tablets. If appropriate, resumption of anti-hepatitis B therapy may be warranted. In clinical trials of Adefovir Dipivoxil Tablets, 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 Tablets. 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.

5.2 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 Tablets (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 [See Adverse Reactions (6.2) and Clinical Pharmacology (12.3) ] . It is recommended that creatinine clearance is calculated in all patients prior to initiating therapy with Adefovir Dipivoxil Tablets. It is important to monitor renal function for all patients during treatment with Adefovir Dipivoxil Tablets, 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 [See Dosage and Administration (2.2) ] . The risks and benefits of Adefovir Dipivoxil Tablets treatment should be carefully evaluated prior to discontinuing Adefovir Dipivoxil Tablets in a patient with treatment-emergent nephrotoxicity.

Pediatric Patients

The efficacy and safety of Adefovir Dipivoxil Tablets 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 [See Dosage and Administration (2.2) ]. Caution should be exercised when prescribing Adefovir Dipivoxil Tablets to adolescents with underlying renal dysfunction, and renal function in these patients should be closely monitored.

5.3 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 Tablets, 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

Tablets has not been shown to suppress HIV RNA in patients; however, there are limited data on the use of Adefovir Dipivoxil Tablets to treat patients with chronic hepatitis B co-infected with HIV.

5.4 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 Tablets therapy 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).

5.5 Coadministration with Other Products Adefovir Dipivoxil Tablets should not be used concurrently with products containing tenofovir disoproxil fumarate or tenofovir alafenamide.

5.6 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.

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 Tablets. 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 Tablets. If appropriate, resumption of anti-hepatitis B therapy may be warranted. In clinical trials of Adefovir Dipivoxil Tablets, 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 Tablets. 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.

5.2 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 Tablets (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 [See Adverse Reactions (6.2) and Clinical Pharmacology (12.3) ] . It is recommended that creatinine clearance is calculated in all patients prior to initiating therapy with Adefovir Dipivoxil Tablets. It is important to monitor renal function for all patients during treatment with Adefovir Dipivoxil Tablets, 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 [See Dosage and Administration (2.2) ] . The risks and benefits of Adefovir Dipivoxil Tablets treatment should be carefully evaluated prior to discontinuing Adefovir Dipivoxil Tablets in a patient with treatment-emergent nephrotoxicity.

Pediatric Patients

The efficacy and safety of Adefovir Dipivoxil Tablets 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 [See Dosage and Administration (2.2) ]. Caution should be exercised when prescribing Adefovir Dipivoxil Tablets to adolescents with underlying renal dysfunction, and renal function in these patients should be closely monitored.

5.3 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 Tablets, 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

Tablets has not been shown to suppress HIV RNA in patients; however, there are limited data on the use of Adefovir Dipivoxil Tablets to treat patients with chronic hepatitis B co-infected with HIV.

5.4 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 Tablets therapy 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).

5.5 Coadministration with Other Products Adefovir Dipivoxil Tablets should not be used concurrently with products containing tenofovir disoproxil fumarate or tenofovir alafenamide.

5.6 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.