Zidovudine Disease Interactions

Zidovudine (AZT) may cause bone marrow toxicity, most commonly manifested as granulocytopenia and anemia, particularly in patients with advanced, symptomatic HIV disease. Thrombocytopenia not related to HIV may also occasionally occur. Zidovudine should be given with extreme caution to patients with preexisting bone marrow depression (indicated by a granulocyte count below 1000 cells/mm3 or hemoglobin less than 9.5 g/dL) or blood dyscrasias. Routine blood counts are recommended, and generally should occur more frequently in patients with advanced HIV disease. Dosage reductions may be necessary.

Prolonged use of certain nucleoside reverse transcriptase inhibitors (NRTIs) such as zidovudine and telbivudine may commonly cause myopathy, including rare cases of rhabdomyolysis. The myopathy may be dose-related and is characterized by persistent, unexplained muscle aches and/or weakness in conjunction with increases in creatine phosphokinase (CPK) values. Therapy with these NRTIs should be administered cautiously in patients with preexisting myopathy or a myoneural disorder, since it may delay the recognition or confound the diagnosis of a drug-induced musculoskeletal effect. Patients should be advised to report promptly any unusual muscle pain, tenderness or weakness, particularly if accompanied by malaise or fever. NRTI therapy should be interrupted if drug-related myopathy is suspected, and discontinued if myopathy is diagnosed.

Hepatotoxicity including lactic acidosis, severe hepatomegaly with steatosis, fulminant hepatitis, and hepatic failure has been associated with the use of some nucleoside reverse transcriptase inhibitors (NRTIs) alone or in combination with other antiretroviral agents. Therapy with NRTIs should be administered cautiously in patients with preexisting liver disease, a history of alcohol abuse, or hepatitis. Therapy should be suspended if clinical or laboratory findings suggestive of lactic acidosis or pronounced hepatotoxicity occur. The use of abacavir is contraindicated in patients with moderate to severe liver dysfunction as its safety and efficacy have not been established in these patients.

The apparent oral clearance of nucleoside reverse transcriptase inhibitors is decreased in patients with renal dysfunction. Dosage adjustments are recommended for lamivudine and stavudine in patients with CrCl less than 50 mL/min; zidovudine dosage should be reduced in patients with CrCl less than 15 mL/min. Fixed-dose combination products containing lamivudine are not recommended for patients with CrCl less than 30 or 50 mL/min; the manufacturer product information should be consulted.