adefovir dipivoxil
Pharmacologic class: Nucleotide reverse transcriptase inhibitor
Therapeutic class: Antiviral
Pregnancy risk category C
FDA Box Warning
• Severe acute hepatitis exacerbations have occurred after drug withdrawal. Monitor hepatic function closely for at least several months in patients who discontinue drug or other anti-hepatitis B therapy; if appropriate, resume such therapy.
• Long-term therapy may cause nephrotoxicity in patients with or at risk for underlying renal dysfunction. Monitor renal function closely and adjust dosage as needed.
• Human immunodeficiency virus (HIV) resistance may occur during therapy in patients with chronic hepatitis B infection who have unrecognized or untreated HIV infection.
• Lactic acidosis and severe hepatomegaly with steatosis (including fatal cases) may occur with use of drug alone or combined with other antiretrovirals.
Action
Inhibits hepatitis B virus (HBV) DNA polymerase and suppresses HBV replication
Availability
Tablets: 10 mg
Indications and dosages
➣ Chronic HBV with active viral replication plus persistent elevations in alanine aminotransferase (ALT) or aspartate aminotransferase (AST) or histologically active disease
Adults: 10 mg P.O. daily
Dosage adjustment
• Renal impairment
Contraindications
• Hypersensitivity to drug
Precautions
Use cautiously in:
• lactic acidosis, renal or hepatic impairment
• elderly patients
• pregnant or breastfeeding patients
• children.
Administration
• Offer HIV testing before starting therapy. (Drug may increase resistance to antiretrovirals in HIV patients.)
• Give with or without food.
Adverse reactions
CNS: headache
GI: nausea, vomiting, diarrhea, abdominal pain, flatulence, dyspepsia, anorexia, pancreatitis
GU: renal dysfunction
Hepatic: severe hepatomegaly with steatosis, hepatitis exacerbation (if therapy is withdrawn)
Metabolic: lactic acidosis
Respiratory: pneumonia
Other: fever, infection, pain, antiretroviral resistance in patients with unrecognized HIV
Interactions
Drug-drug. Acetaminophen, aspirin, indomethacin: granulocytopenia
Acyclovir, adriamycin, amphotericin B, benzodiazepines, cimetidine, dapsone, doxorubicin, experimental nucleotide analogue, fluconazole, flucytosine, ganciclovir, indomethacin, interferon, morphine, phenytoin, probenecid, sulfonamide, trimethoprim, vinblastine, vincristine: increased risk of nephrotoxicity
Drug-diagnostic tests. Amylase, blood glucose, blood urea nitrogen, creatine kinase, hepatic enzymes, lipase: elevated levels
Patient monitoring
• Monitor fluid intake and output.
• Watch for hematuria.
• Assess for signs and symptoms of lactic acidosis, especially in women and overweight patients.
• Check for liver enlargement.
• Monitor liver and kidney function test results.
• After therapy ends, monitor patient for evidence of serious hepatitis exacerbation.
Patient teaching
• Advise patient to take drug with or without food.
• Instruct patient to drink plenty of fluids to ensure adequate urine output.
• Advise patient to monitor urine output and color and to report significant changes.
• Tell patient that drug may cause weakness. Discuss appropriate lifestyle adjustments.
• Caution patient not to take over-the-counter analgesics without prescriber's approval.
• Inform patient that he'll undergo regular blood testing during therapy.
• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above.
Adefovir Dipivoxil
A nucleoside analogue antiviral which is effective against viral polymerases (hepadnaviruses, retroviruses—e.g., HIV—herpesviruses—e.g., CMV), and used to treat hepatitis B in adults who have evidence of active viral replication, increased LFTs, histologically active liver disease, and evidence of HBV resistant to other antivirals—e.g., lamivudine.Benefits 48 weeks of adefovir dipivoxil results in histologic liver improvement, reduces serum HBV DNA and alanine aminotransferase (LFTs), and slows progression of chronic hepatitis B.
Adverse effects Renal toxicity requiring monitoring, asthenia, diarrhoea, dyspepsia, nausea, severe acute exacerbation of hepatitis B after discontinuing.
Mechanism of action Slows progression of chronic hepatitis B by interfering with viral replication and causing DNA chain termination after its incorporation into viral DNA.