Zidovudine (AZT)

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  • Zidovudine, also known as AZT, azidothymidine, or ZDV, is a drug used for the treatment of feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV).
  • Zidovudine is a synthetic analog of the nucleoside, thymidine. In AZT, the 3'-hydroxyl (-OH) group of thymidine is replaced with an azido(-N3) group.
  • It was originally thought that AZT may have potential as an anti-cancer agent but later the drug was found effective against a specific type of leukemia virus.
  • More recently, AZT has been demonstrated to have anti-retroviral activity and has emerged as an important treatment for HIV.
  • AZT, classed as a nucleoside reverse transcriptase inhibitor (NRTI), is converted in cells to the 5'-triphosphate analog, an active metabolite that selectively inhibits viral RNA-directed DNA polymerase with virustatic consequences. It can be given orally or by injection (IV or SC).
  • It is well absorbed after oral administration in cats and peak blood levels occur about 2 hour after ingestion.
  • Information about AZT's effects and side effects in cats and other species is somewhat sparse.
  • AZT is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.
  • This drug is not approved for use in animals by the Food and Drug Administration but it is prescribed legally by veterinarians as an extra-labeldrug.

    Brand Names and Other Names

  • This drug is registered for use in humans only.
  • Human formulations: Retrovir® (GlaxoSmithKline)
  • Veterinary formulations: None

    Uses of Zidovudine

  • Zidovudine is used in the treatment of FIV and FeLV. The drug effect is considered palliative. If given within 1 week of exposure to FeLV, no viremia occurs. If given within 3 weeks of exposure, the antigen load is decreased. The efficacy on full blown infections is uncertain.

    Precautions and Side Effects

  • Zidovudine should not be used in animals with known hypersensitivity or allergy to the drug.
  • AZT may cause blood dyscrasias including anemia and neutropenia.
  • When AZT is being administered on a regular basis it is prudent to monitor the CBC. Blood cell damage may be prevented or treated with vitamin E or erythropoietin.
  • AZT may cause disturbances in liver function and gastrointestinal disturbances.
  • It should be used with caution in patients with hepatic dysfunction, impaired renal function, and bone marrow depression.
  • Liver function and serum creatinine should be monitored during long-term treatment with AZT.

    Drug Interactions

    AZT may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with AZT. Interactions may include:

  • Drugs that inhibit glucuronyl transferase increase the risk of blood dyscrasias. Such drugs include acetominophen, aspirin, and indomethacin.
  • Cytotoxic drugs administered concurrently with AZT may also increase the risk of blood dyscrasias.
  • Fluconazole, interferon, probenecid, and trimethoprim may increase AZT blood levels and thus increase its toxicity.
  • Antibiotic drugs rifabutin (Mycobutin) and rifampin can lower AZT blood levels by increasing its rate of hepatic metabolism.
  • Lethargy has been reported to occur when AZT and acyclovir are used together.

    How Zidovudine is Supplied

  • Zidovudine is available in 300 mg oral tablets and 100 mg capsules.
  • Zidovudine is avaialbe as a 10mg/ml in 240mL bottles.
  • The injectable forms of Zidovudine is a 10mg/mL concentration in 20 mL single-use vial.

    Dosing Information

  • Medication should never be administered without first consulting your veterinarian.
  • Doses of zidovudine may vary depending on the reason for prescribing.
  • The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your pet feels better, the entire treatment plan should be completed to prevent relapse.
  • The usual dose for FIV or FeLV is 2.5 to 7.5 mg per pound (5 to 15 mg/kg) every 12 hours orally or 5 mg per pound (10 mg/kg) subcutaneously every 12 hours for 3 weeks.
  • Oral AZT is best administered on an empty stomach.
  • AZT may be given alone or in combination with interferon or interleukin.

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