Adefovir

Pronunciation

(a DEF o veer)

U.S. Brand Names

Hepsera™

Synonyms

Adefovir Dipivoxil

Generic Available

Use

Treatment of chronic hepatitis B with evidence of active viral replication (based on persistent elevation of ALT/AST or histologic evidence), including patients with lamivudine-resistant hepatitis B

Pregnancy Risk Factor

Pregnancy Implications

There are no adequate and well-controlled studies in pregnant women. Use in pregnancy only when clearly needed.

Lactation

Excretion in breast milk unknown/not recommended

Contraindications

Hypersensitivity to adefovir or any component of the formulation

Warnings/Precautions

Use with caution in patients with renal dysfunction or in patients at risk of renal toxicity (including concurrent nephrotoxic agents or NSAIDs). Chronic administration may result in nephrotoxicity. Dosage adjustment is required in patients with renal dysfunction or in patients who develop renal dysfunction during therapy. May cause the development of resistance in patients with unrecognized or untreated HIV infection. Lactic acidosis and severe hepatomegaly with steatosis (sometimes fatal) have occurred with antiretroviral nucleoside analogues; female gender, obesity, and prolonged treatment may increase the risk of hepatotoxicity. Treatment should be discontinued in patients with lactic acidosis or signs/symptoms of hepatotoxicity (which may occur without marked transaminase elevations). Acute exacerbations of hepatitis may occur (in up to 25% of patients) when antihepatitis therapy is discontinued. Exacerbations typically occur within 12 weeks; monitor patients following discontinuation of therapy. Safety and efficacy in pediatric patients have not been established.

Adverse Reactions

>10%: Renal: Hematuria (11% vs. 10% in placebo-treated)

1% to 10%:

Central nervous system: Fever, headache,

Dermatologic: Rash, pruritus

Gastrointestinal: Dyspepsia (3%), nausea, vomiting, flatulence, diarrhea, abdominal pain

Hepatic: AST/ALT increased, abnormal liver function, hepatic failure

Neuromuscular & skeletal: Weakness

Renal: Serum creatinine increased (4%), renal failure, renal insufficiency

Note: In patients with baseline renal dysfunction, frequency of increased serum creatinine has been observed to be as high as 26% to 37%; the role of adefovir in these changes could not be established.

Respiratory: Cough increased, sinusitis, pharyngitis

Overdosage/Toxicology

Limited experience in acute overdose. Chronic overdose may be associated with renal toxicity and gastrointestinal adverse effects. Hemodialysis may be effective in the removal of adefovir (35% of a 10 mg dose removed in 4 hours).

Drug Interactions

Aminoglycosides: May increase the risk of renal toxicity with adefovir.

Ibuprofen: Increases the bioavailability of adefovir.

Immunosuppressants (cyclosporine, tacrolimus): May increase the risk of renal toxicity with adefovir.

Nephrotoxic agents: May increase the risk of renal toxicity with adefovir.

NSAIDs: May increase the risk of renal toxicity with adefovir (also see Ibuprofen above).

Vancomycin: May increase the risk of renal toxicity with adefovir.

Ethanol/Nutrition/Herb Interactions

Ethanol: Should be avoided in hepatitis B infection due to potential hepatic toxicity.

Food: Does not have a significant effect on adefovir absorption.

Stability

Store at 25°C (77 °F); excursions permitted to 15°C to 30°C (59°F to 86°F).

Mechanism of Action

Acyclic nucleotide reverse transcriptase inhibitor (adenosine analog) which interferes with HBV viral RNA dependent DNA polymerase resulting in inhibition of viral replication.

Pharmacodynamics/Kinetics

Distribution: 0.35-0.39 L/kg

Protein binding: 4%

Metabolism: Prodrug; rapidly converted to adefovir (active metabolite) in intestine

Bioavailability: 59%

Half-life elimination: 7.5 hours; prolonged in renal impairment

Time to peak: 1.75 hours

Excretion: Urine (45% as active metabolite within 24 hours)

Dosage

Oral: Adults: 10 mg once daily

Dosage adjustment in renal impairment:

Clcr 20-49 mL/minute: 10 mg every 48 hours

Clcr 10-19 mL/minute: 10 mg every 72 hours

Hemodialysis: 10 mg every 7 days (following dialysis)

Administration

May be administered without regard to food.

Monitoring Parameters

HIV status (prior to initiation of therapy); serum creatinine (prior to initiation and during therapy)

Dietary Considerations

May be taken without regard to food.

Patient Education

Inform prescriber of all prescriptions, OTC medications, or herbal products you are taking, and any allergies you have. Do not take any new medication during therapy without consulting prescriber. Use appropriate precautions to prevent spread to other persons. Take as directed. Do not discontinue without consulting prescriber. You will require frequent blood tests; follow recommended schedule. Maintain adequate hydration (2-3 L/day of fluids) unless instructed to restrict fluid intake. You may be more susceptible to infection (avoid crowds and exposure to infection and do not have any vaccinations without consulting prescriber). May cause headache or abdominal pain (consult prescriber for approved analgesia); or nausea or vomiting (small, frequent meals, frequent mouth care, sucking lozenges, or chewing gum may help). Report unusual bleeding (blood in urine, tarry stools, or easy bruising); unresolved nausea or vomiting; signs of infection (eg, fever, chills, sore throat, burning urination, flu-like symptoms); persistent fatigue; muscle weakness; changes in urinary pattern; or other persistent adverse effects. Pregnancy/breast-feeding precautions: Inform prescriber if you are or intend to become pregnant. Breast-feeding is not recommended.

Additional Information

Adefovir dipivoxil is a prodrug, rapidly converted to the active component (adefovir). It was previously investigated as a treatment for HIV infections (at dosages substantially higher than the approved dose for hepatitis B). The NDA was withdrawn, and no further studies in the treatment of HIV are anticipated (per manufacturer).

Dental Health: Effects on Dental Treatment

No significant effects or complications reported

Dental Health: Vasoconstrictor/Local Anesthetic Precautions

No information available to require special precautions

Mental Health: Effects on Mental Status

None reported

Mental Health: Effects on Psychiatric Treatment

Chronic administration may cause nephrotoxicity. In patients receiving lithium, gabapentin, or levetiracetam, a dosage adjustment may be needed; monitor.

Dosage Forms

Tablet, as dipivoxil: 10 mg

International Brand Names

Hepsera® (AT, AU, BE, CH, CY, CZ, DE, DK, ES, FI, FR, GB, GR, HU, IE, IS, IT, LT, LV, MT, NL, NO, PL, PT, SE, SI, SK)

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