For clinicians
Azathioprine
AZA, 6-mercaptopurine (related)
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Bottom lineBottom line: compatible across pregnancy, lactation, and paternal exposure at usual doses (commonly up to ~2 mg/kg/day). A useful pregnancy-compatible immunosuppressant. Broad guideline agreement.
By reproductive phase
| Phase | Position | Detail | Evidence |
|---|---|---|---|
| Pre-conception | Continue | Continue at usual doses.[1, 2, 3] | ●●●○moderate evidencestrong |
| 1st trimester | Continue | Continue.[1, 2] | ●●●○moderate evidencestrong |
| 2nd/3rd trimester | Continue | Continue.[1, 2] | ●●●○moderate evidencestrong |
| Breastfeeding | Continue | Compatible with lactation; low infant exposure.[2, 3] | ●●●○moderate evidenceconditional |
| Paternal | Continue | Compatible with paternal exposure.[2] | ●●○○low evidenceconditional |
Guideline comparison
| Guideline | Position | Strength |
|---|---|---|
| ACR 2020 | Strongly recommend continuing before and during pregnancy (Table 3: ++/++); conditionally recommend during breastfeeding (+, low transfer). Paternal: strongly recommend continuing.[1] | Strong (pregnancy); conditional (lactation) |
| EULAR 2024 | Compatible with pregnancy (2a/B) and lactation (2a/B); continuable in men (2b/B).[2] | Oxford LoE/GoR as shown |
| BSR 2022/23 | Compatible across peri-conception, both trimesters, breastfeeding, and paternal exposure.[3] | Verified against BSR Table 1 |
=Guideline agreement. VERIFIED AGREEMENT. EULAR 2024 (pregnancy 2a/B, lactation 2a/B, male 2b/B) and BSR 2023 (compatible across all five phases) agree.
Key points
| Point | Evidence |
|---|---|
| A common pregnancy-compatible step-up immunosuppressant (for example when transitioning off mycophenolate).[1] | ●●○○low evidenceconditional |
Monitoring
- Usual azathioprine monitoring continues (blood counts, liver function).
References
- Sammaritano LR, et al. 2020 ACR Guideline for the Management of Reproductive Health in RMD. Arthritis Rheumatol. 2020;72(3):529-556. https://acrjournals.onlinelibrary.wiley.com/doi/10.1002/art.41191
- Ruegg L, et al. EULAR recommendations for antirheumatic drugs in reproduction, pregnancy, and lactation: 2024 update. Ann Rheum Dis. 2025;84(6):910-926. https://ard.eular.org/article/S0003-4967(25)00818-0/fulltext
- Russell MD, et al. BSR guideline on prescribing drugs in pregnancy and breastfeeding: immunomodulatory drugs and corticosteroids. Rheumatology (Oxford). 2023;62(4):e48-e88. https://academic.oup.com/rheumatology/article/62/4/e48/6783012