OBJECT DRUGS

Antimetabolites:

• Azathioprine (Imuran, etc.)
• Mercaptopurine (Purinethol, etc.)

PRECIPITANT DRUGS

• Ribavirin (Rebetol, etc.)

Comment:

Ribavirin appears to inhibit one of the steps in the metabolism of azathioprine and mercaptopurine, and may increase the risk of toxicity, usually bone marrow suppression. A number of patients have developed severe pancytopenia, usually after several weeks of combined therapy.

Class 2: Use Only if Benefit Felt to Outweigh Risk

• Circumvent/Minimize: If appropriate for the patient, it may be prudent to withdraw azathioprine or mercaptopurine therapy during ribavirin therapy. If the combination is used, it may be necessary to reduce the dose of azathioprine or mercaptopurine.
• Monitor: If the combination is used, monitor for evidence of bone marrow suppression, and instruct the patient to contact their prescriber immediately if they experience evidence of pancytopenia such as fever, sore throat, easy bruising, or bleeding.