Cyclophosphamide in dogs - Canine Cyclophosphamide

Cyclophosphamide in dogs

(Cytoxan, Mead Johnson, Evansville, Ind) is a very effective immunosuppressive agent for inducing remission in dogs and possibly cats with IMDs. This drug is an alkylator anticancer agent, which appears to suppress cell-mediated and humoral immunity, as well as mononuclear-phagocytic function. It is activated and metabolized by the microsomal fraction of the liver and is available as 25 and 50 mg tablets and injectable vials of 100, 200, 500, and 1000 mg.

Cyclophosphamide has been effective in inducing or consolidating remission in dogs with immune-mediated hemolytic anemia (IHA) or immune-mediated thrombocytopenia (IMT). It is also effective in dogs with immune-mediated polyarthritis, dermatitis, or systemic lupus erythematosus (SLE). It is commonly administered in one dose of 200 to 300 mg/m2 intravenously in dogs with steroid-nonresponsive or severe IHA or IMT. In cats, the same dose is administered orally, because gastrointestinal adverse effects (e.g., vomiting, anorexia) appear to be more common after intravenous injections of this agent.

The oral form of cyclophosphamide can be given on a continuous basis either every other day of for 4 consecutive days followed by 3 days off, at a dose of 50 mg/m2. However, one of the common adverse effects of long term cyclophosphamide treatment in dogs is sterile hemorrhagic cystitis, which frequently develops after 8 to 10 weeks of continuous treatment. Female dogs are at an increased risk for this toxicity and should therefore undergo periodic urinalisys and physical examination while receiving the drug. The concurrent administration of prednisone appears to decrese the risk of cystitis in dogs receiving ongoing cyclophosphamide treatment. Cystitis caused by long-term cyclophosphamide treatment is extremely rare in cats.

Two other common adverse effects of cyclophosphamide include anorexia (mainly in cats) and myelosuppression (in both dogs and cats). Because of this agent's potential to cause myelosuppression, a complete blood count should be performed every 2 to 4 weeks, and the dose adjusted accordingly.

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