Imuran Drug Interactions

Vaccines: The immunosuppressive activity of Imuran could result in an atypical and potentially deleterious response to live vaccines, the administration of live vaccines to patients receiving Imuran therapy is not recommended (see Precautions).
A diminished response to killed vaccines is likely and such a response to hepatitis B vaccine has been observed among patients treated with a combination of azathioprine and corticosteroids.
A small clinical study has indicated that standard therapeutic doses of Imuran do not deleteriously affect the response to polyvalent pneumococcal vaccine, as assessed on the basis of mean anti-capsular specific antibody concentration.
Cytostatic/myelosuppressive agents (see Precautions): Where possible, concomitant administration of cytostatic drugs, or drugs which may have a myelosuppressive effect, such as penicillamine, should be avoided. There are conflicting clinical reports of interactions, resulting in serious haematological abnormalities, between Imuran and co-trimoxazole.
There have been case reports suggesting that haematological abnormalities may develop due to the concomitant administration of Imuran and captopril.
It has been suggested that cimetidine and indomethacin may have myelosuppressive effects which may be enhanced by concomitant administration of Imuran.
Allopurinol/oxipurinol/thiopurinol: Xanthine oxidase activity is inhibited by allopurinol, oxipurinol and thiopurinol, which results in reduced conversion of biologically active 6-thioinosinic acid to biologically inactive 6-thiouric acid. When allopurinol, oxipurinol and/or thiopurinol are given concomitantly with 6-MP or azathioprine, the dose of 6-MP and azathioprine should be reduced to ¼ of the original dose (see Drug Interactions under Dosage & Administration).
Aminosalicylates: There is in vitro and in vivo evidence that aminosalicylate derivatives (e.g. olsalazine, mesalazine or sulphasalazine) inhibit the TPMT enzyme. Therefore, lower doses of Imuran may need to be considered when administered concomitantly with aminosalicylate derivatives (see Precautions).
Methotrexate: Methotrexate (20 mg/m² orally) increased 6-MP AUC by approximately 31% and methotrexate (2 or 5 g/m² intravenously) increased 6-MP AUC by 69% and 93%, respectively. Therefore, when Imuran is administered concomitantly with high dose methotrexate, the dose should be adjusted to maintain a suitable white blood cell count.
Effect of azathioprine on other drugs: Anticoagulants: Inhibition of the anticoagulant effect of warfarin and acenocoumarol has been reported when co-administered with Imuran; therefore higher doses of the anticoagulant may be needed. It is recommended that coagulation tests are closely monitored when anticoagulants are concurrently administered with Azathioprine (Imuran).
Ribavirin: Ribavirin inhibits the enzyme, inosine monophosphate dehydrogenase (IMPDH), leading to a lower production of the active 6-thioguanine nucleotides. Severe myelosuppression has been reported following concomitant administration of Imuran and ribavirin; therefore, co-administration is not advised (see Pharmacokinetics: Metabolism under Pharmacology under Actions and Precautions).