No Clinically Significant Interaction Between Imuran and Camrese Lo
There is no documented adverse interaction between Imuran (azathioprine) and Camrese Lo (levonorgestrel/ethinyl estradiol) birth control, and these medications can be used together safely without dose adjustments.
Evidence Base
The available evidence demonstrates no pharmacokinetic or pharmacodynamic interaction between azathioprine and hormonal contraceptives:
Azathioprine does not induce hepatic enzymes that metabolize contraceptive hormones, unlike certain anticonvulsants (phenobarbital, phenytoin, carbamazepine) or rifampicin that increase clearance of oral contraceptive steroids 1, 2.
Hormonal contraceptives do not affect azathioprine metabolism, which occurs primarily through thiopurine methyltransferase (TPMT) and xanthine oxidase pathways—mechanisms unrelated to estrogen or progestin metabolism 3.
No reports exist in the literature of contraceptive failure or azathioprine toxicity when these medications are combined, despite extensive use of azathioprine in women of reproductive age with autoimmune conditions 3.
Clinical Monitoring Remains Essential
While no interaction exists between these specific medications, standard monitoring for azathioprine therapy must continue:
Complete blood count monitoring is mandatory: weekly for the first 4 weeks, then monthly for 1-3 months, then every 2 months thereafter to detect bone marrow suppression 3, 4.
Liver function tests should be checked monthly for the first 3 months, then every 2 months 3.
TPMT activity testing prior to azathioprine initiation helps identify patients at risk for severe myelosuppression 3, 4.
Important Contraceptive Considerations in Azathioprine Users
Pregnancy planning requires special attention in women taking azathioprine:
Azathioprine carries FDA pregnancy category D, indicating potential fetal risk, though human data show no consistent increase in birth defects 3.
Preconceptional counseling is advised, with attempts to discontinue immunosuppression if disease activity permits 3.
If pregnancy occurs on azathioprine, the medication is often continued when disease control is necessary, as outcomes are generally acceptable with careful monitoring 3.
Contraception should be reliable in women with advanced liver disease or cirrhosis, as pregnancy carries increased risks of variceal hemorrhage and hepatic decompensation 3.
Actual Drug Interactions to Avoid with Azathioprine
The clinically significant interactions with azathioprine involve entirely different medications:
Allopurinol or febuxostat cause severe, life-threatening myelotoxicity and require 75% azathioprine dose reduction if co-administration is unavoidable 3, 4.
Warfarin may require dose adjustment as azathioprine can cause warfarin resistance 3, 4.
Other immunosuppressants increase cumulative myelotoxicity risk 4.
Cotrimoxazole increases hematologic toxicity risk 3.