Immunosuppressant Monitoring

Immunosuppressant monitoring means scheduled laboratory, clinical and infection-prevention checks that detect organ toxicity, marrow suppression and infection early while ensuring the drug dose remains effective. Poor monitoring is a leading cause of avoidable harm with azathioprine, methotrexate, mycophenolate and leflunomide.

Core elements. Baseline testing, a fixed monitoring schedule, a named responsible clinician, written withhold thresholds, patient education on infection symptoms, and shared-care agreements with the primary care team.

Infection risk. Prednisolone 20 mg or more daily for over 4 weeks, or any combination of a steroid and another immunosuppressant, carries a risk of Pneumocystis jirovecii pneumonia.

Monitoring schedule by drug (after baseline).

Azathioprine. Check thiopurine methyltransferase and NUDT15 activity before starting. Start at 25 to 50 mg daily and titrate by 25 mg every 1 to 2 weeks to 1 to 2.5 mg/kg daily (lower with reduced enzyme activity). Reduce to a quarter or a third of the dose if taking allopurinol or febuxostat.

Prophylaxis.

• Pneumocystis: co-trimoxazole 480 mg daily or 960 mg 3 times weekly when prednisolone 20 mg or more daily is expected for over 4 weeks together with another agent, with cyclophosphamide or rituximab, or with CD4 count under 200 cells/microlitre. Alternative if sulphonamide allergic: atovaquone 1500 mg daily.
• Bone: calcium 1000 mg and vitamin D 800 to 1000 units daily; alendronate 70 mg weekly when prednisolone 7.5 mg or more daily is expected over 3 months.
• Gastric protection with a proton pump inhibitor if combined with an NSAID or anticoagulant.

Infection. Hold the immunosuppressant (except steroids) during significant infection; give stress-dose steroid cover if steroid dependent.

Kidney and liver impairment. Reduce methotrexate in eGFR 30 to 59 mL/min and avoid under 30; mycophenolate maximum 1 g twice daily if eGFR under 25 mL/min; azathioprine reduce by one third to half with severe kidney or liver impairment.

Pregnancy planning. Switch methotrexate, mycophenolate, leflunomide and cyclophosphamide to compatible agents (azathioprine, hydroxychloroquine, sulfasalazine, ciclosporin, tacrolimus) before conception.

Vaccination. Give inactivated vaccines (influenza yearly, pneumococcal, recombinant zoster, hepatitis B, COVID-19) ideally before intensifying immunosuppression; avoid live vaccines.

Skin cancer. Sun protection and annual skin checks, especially with azathioprine, ciclosporin and tacrolimus.

Regional. Screen for tuberculosis, hepatitis B and HIV before treatment; offer isoniazid preventive therapy for latent tuberculosis. Infection symptoms should prompt same-day review in malaria-endemic areas, since malaria can present as fever on immunosuppression.

Patient safety counselling. Report fever, sore throat, mouth ulcers, bruising, new cough, jaundice or rash at once. Carry a drug card. Do not stop steroids suddenly.

Escalation. Fever with neutropenia (neutrophils under 1.0 x 10⁹/L) is an emergency: stop the drug, take cultures and give broad-spectrum IV antibiotics within 1 hour.

Stopping. Stop drugs that cause severe marrow suppression, hepatotoxicity over 3 times the upper limit with symptoms, pneumonitis, severe skin reactions or malignancy; refer urgently.