Adefovir Side Effects: What to Expect and When to Call Your Doctor

Adefovir dipivoxil (Hepsera) is generally well-tolerated at the approved 10 mg daily dose for chronic hepatitis B, but it does carry important side effects — some of which can be serious. Understanding what to watch for can help you take this medication safely.

The Four Boxed Warnings: What the FDA Considers Most Serious

The FDA requires adefovir to carry a black box warning — the most serious warning type — for four potential risks:

1. Severe acute exacerbation of hepatitis B after stopping treatment. Up to 25% of patients experienced serious hepatitis flares (ALT rising to 10x the upper limit of normal) after discontinuing adefovir in clinical trials. This can occur within weeks of stopping and may require immediate medical attention. Never stop adefovir without your doctor's guidance.

2. Nephrotoxicity (kidney damage). Adefovir can damage the kidneys with long-term use, especially in patients who already have kidney problems. By week 96 of treatment at the 10 mg dose, approximately 2-3% of patients had meaningful increases in serum creatinine. This risk is higher in patients with baseline renal impairment or those taking other nephrotoxic drugs.

3. HIV resistance. If you have undiagnosed or untreated HIV and take adefovir for hepatitis B, the medication may cause your HIV to develop resistance to key antiviral drugs. Your doctor should test you for HIV before and during treatment.

4. Lactic acidosis and severe hepatomegaly with steatosis. A rare but potentially fatal complication seen with nucleoside/nucleotide analogs. Risk factors include obesity and prolonged exposure. Symptoms include unexplained muscle pain, weakness, trouble breathing, stomach pain, or unusual fatigue.

Common Side Effects (Greater Than 5%)

At the approved 10 mg daily dose, these side effects occurred at rates similar to placebo in clinical trials — meaning they were uncommon and mild:

Asthenia (weakness or fatigue) — approximately 13%

Headache — approximately 9%

Abdominal pain — approximately 9%

Nausea — approximately 5%

Diarrhea, flatulence, upset stomach (less common)

Note: These rates were essentially the same as in placebo-treated patients in clinical trials, suggesting they may be related to the underlying hepatitis B illness rather than adefovir itself.

Serious Side Effects That Require Immediate Medical Attention

Kidney injury signs: Decreased urine output, swelling in the ankles or feet, unusual fatigue, or confusion

Liver flare signs (after stopping): Yellowing of the skin or eyes (jaundice), dark urine, pale stools, severe fatigue, right upper abdominal pain

Lactic acidosis signs: Severe muscle pain or cramps, trouble breathing, fast or irregular heartbeat, stomach pain, general discomfort

Allergic reaction: Skin rash, itching, hives, swelling of the face, lips, tongue, or throat — seek emergency care

Long-Term Side Effects to Monitor

With long-term adefovir use, two additional concerns have been identified in post-marketing reports:

Proximal renal tubulopathy (Fanconi syndrome): A kidney condition affecting the reabsorption of phosphate and other substances. Signs include bone pain, fractures, and low phosphate levels (hypophosphatemia).

Myopathy and osteomalacia: Muscle weakness and bone softening, both associated with the proximal renal tubulopathy described above.

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Routine Monitoring While on Adefovir

Your doctor should monitor the following regularly:

Serum creatinine and eGFR (kidney function) — at least every 3-6 months

Serum phosphorus — to detect early Fanconi syndrome

ALT/AST (liver enzymes) — to assess treatment response and detect flares

HBV DNA levels — to assess antiviral efficacy and detect resistance

If you are struggling to find adefovir for your next refill, medfinder can locate a pharmacy with it in stock near you. Also read: Adefovir Drug Interactions: What to Avoid