adefovir

General

Pronunciation:
a-def-oh-veer


Trade Name(s)

  • Hepsera

Ther. Class.
antivirals

Pharm. Class.
nucleotides

Indications

Treatment of chronic hepatitis B in patients with evidence of active viral replication and either evidence of persistently elevated liver function tests or active disease (should be used with lamivudine to ↓ risk of resistance).

Action

Converted to adefovir diphosphate which inhibits viral DNA polymerase (reverse transcriptase). Incorporation into viral DNA causes termination of the DNA chain.

Therapeutic Effect(s):

Decreased progression/sequelae of chronic hepatitis B infection.

Pharmacokinetics

Absorption: Rapidly converted from prodrug form (adefovir dipivoxil) to adefovir following oral administration; 59% bioavailable.

Distribution: 0.35–0.39 L/kg.

Metabolism and Excretion: Elimination is primarily renal as unchanged drug.

Half-life: 7.5 hr.

TIME/ACTION PROFILE (blood levels)

ROUTEONSETPEAKDURATION
POunknown1–4 hrunknown

Contraindication/Precautions

Contraindicated in:

  • Hypersensitivity
  • Concurrent use with products containing tenofovir disoproxil fumarate or tenofovir alafenamide.

Use Cautiously in:

  • Unrecognized HIV infection (may foster resistance)
  • Patients with renal impairment or at risk of renal impairment (↑ risk of nephrotoxicity; dose adjustment recommended if CCr <50 mL/min)
  • Liver disease or risk factors for liver disease (↑ risk of hepatotoxicity)
  • Women, obese patients, patients with previous nucleoside exposure (↑ risk of lactic acidosis and hepatotoxicity)
  • Geri:   Greater risk of side effects due to greater risk of renal or cardiac disorders
  • OB:  Use in pregnancy only if maternal benefit outweighs potential risk to fetus;
  • Lactation: Use while breastfeeding only if maternal benefit outweighs potential risk to infant;
  • Pedi:  Children <12 yr (safety not established).

Adverse Reactions/Side Effects

CNS: headache

Derm: pruritus, rash

F and E: LACTIC ACIDOSIS

GI: dyspepsia, HEPATOMEGALY WITH STEATOSIS, abdominal pain, diarrhea, flatulence, ↑ liver enzymes, nausea, vomiting

GU: hematuria, nephrotoxicity

MS: weakness

Resp: cough, pharyngitis, sinusitis

Misc: fever, HIV resistance

* CAPITALS indicate life-threatening.
Underline indicate most frequent.

Interactions

Drug-Drug

  •  Drugs that are renally excreted or alter renal function  should be used cautiously as they may affect levels.
  •  Ibuprofen  may ↑levels.
  • Should not be used with  tenofovir -containing products.

Route/Dosage

PO (Adults and Children ≥12 yr): 10 mg once daily.

Renal Impairment 
PO (Adults  ):  CCr 30–49 mL/min– 10 mg every 48 hr;  CCr 10–29 mL/min– 10 mg every 72 hr;  Hemodialysis patients– 10 mg every 7 days following dialysis.

Availability (generic available)

Tablets: 10 mg

Assessment

  • May cause lactic acidosis and severe hepatomegaly with steatosis. Monitor patient for signs (increased serum lactate levels, elevated liver enzymes, liver enlargement on palpation). Therapy should be discontinued if clinical or laboratory signs occur.

Lab Test Considerations:

Monitor viral load and CD4 cell count regularly during therapy in patients with HIV infection.

Monitor liver function tests and hepatitis B virus levels throughout and following therapy. If therapy is discontinued, may cause severe exacerbation of hepatitis B.
  • Calculate creatinine clearance to determine dose prior to starting therapy.
  • Monitor renal function closely. May cause nephrotoxicity.

Potential Diagnoses

Implementation

  • PO Administer once daily with or without food.

Patient/Family Teaching

  • Instruct patient to take adefovir as directed and not to discontinue medication without consulting health care professional. Take missed dose as soon as it is remembered that day. Do not take more than 1 dose in a day. Consult health care professional if unsure of what to do. Discontinuation may result in exacerbation of hepatitis, usually within 12 wks of stopping. Regular liver function tests and hepatitis B virus levels are required if adefovir is discontinued. Advise the patient that adefovir does not cure hepatitis B, but may lower amount of hepatitis B in the body and decrease the ability of the virus to multiply and infect new liver cells. Instruct patient to read the  Patient Information  sheet prior to starting therapy.
  • Inform patient that an HIV test should be taken before starting adefovir and anytime when there is a chance patient was exposed to HIV.
  • Inform patient that adefovir does not reduce the risk of transmission of hepatitis B to others through sexual contact or blood contamination. Caution patient to use a condom and to avoid sharing needles, toothbrushes or razor blades, or donating blood to prevent spreading the hepatitis B virus to others.
  • Instruct patient to notify health care professional immediately if signs of lactic acidosis (weakness or tiredness, unusual muscle pain, dyspnea, stomach pain with nausea and vomiting, feelings of coldness especially in arms or legs, dizziness, lightheadedness, fast or irregular heartbeat) occur. Risk is increased in patients with serious liver problems, are female, are obese, or have been taking nucleoside analog medicines for a long time.
  • Caution patient to notify health care professional if signs of hepatotoxicity (jaundice, dark urine, light colored bowel movement, anorexia, nausea, bruising, lower stomach pain) occur.
  • Instruct patient to notify health care professional of all Rx or OTC medications, vitamins, or herbal products being taken and consult health care professional before taking any new medications.
  • Advise female patient to avoid breastfeeding and to notify health care professional if pregnancy is planned or suspected. Encourage patients to enroll in pregnancy registry to monitor outcomes in women exposed to adefovir during pregnancy by calling the Antiretroviral Pregnancy Registry (APR) at 1-800-258- 4263.
  • Emphasize the importance of regular blood tests to check hepatitis B virus levels, as well as renal and hepatic function.

Evaluation/Desired Outcomes

Decrease in progression of chronic hepatitis B. Patients with serum HBV levels >1000 copies/mL at wk 48 of treatment are at greater risk for developing resistance and modification of therapy should be considered.

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