Azathioprine and Pyridostigmine: Side Effects and Monitoring

Azathioprine Side Effects and Monitoring

The British Society of Gastroenterology recommends monitoring for bone marrow suppression, particularly leukopenia followed by thrombocytopenia, as the most significant concern in patients with low thiopurine methyltransferase (TPMT) activity, especially in patients taking azathioprine 1, 2
Approximately 25% of patients develop side effects, requiring withdrawal in about 10% of cases, according to the British Society of Gastroenterology guidelines for azathioprine use 1
Common adverse reactions to azathioprine include gastrointestinal disturbances (nausea, vomiting, anorexia), as reported by the British Society of Gastroenterology and the British Association of Dermatologists 1, 2
The British Association of Dermatologists notes that hepatotoxicity and idiosyncratic hypersensitivity reactions (rare but can include fever, rash, malaise) are also potential side effects of azathioprine 3

The British Association of Dermatologists recommends checking TPMT activity in all patients prior to starting azathioprine, and baseline tests should include FBC with differential white cell count, renal function, and liver function tests 4
Regular monitoring of blood counts is essential, with weekly monitoring for the first 4 weeks and monthly for 1-3 months thereafter, depending on response, as suggested by the British Society of Gastroenterology 1

The British Association of Dermatologists warns that azathioprine with allopurinol or febuxostat can cause severe, life-threatening myelotoxicity, and azathioprine may interact with warfarin, causing warfarin resistance 5
The British Association of Dermatologists also notes that azathioprine combined with other immunosuppressants increases myelotoxicity risk, and the manufacturer's datasheet suggests azathioprine may alter neuromuscular blockade by succinylcholine and tubocurarine 5