Her medication history included calcium acetate (950 mg twice daily), long-term co-trimoxazole (480 mg daily for Pneumocystis carinii pneumonia (PCP) prophylaxis), and a weaning dose of prednisolone and cyclophosphamide, which was transitioned to azathioprine after thiopurine methyltransferase (TPMT) levels were found just below the normal range (64). Here, TPMT is linked to pneumocystosis.