Immunosuppresants: Corticosteroids act on cytosolic rather than cell membrane receptors. Both mycophenolate and azathioprine

Approximately 1 in 300 Caucasians have  thiopurine methyl transferase (TPMT) deficiency. TPMT is the enzyme that metabolises 6-mercaptopurine and its deficiency results in high risk of azathioprine toxicity.