Azathioprine
Azathioprine is a derivative of mercaptopurine
and is a cytotoxic immunosuppressant. It acts as an antimetabolite or structural
analogue, disrupting purine synthesis and therefore DNA replication. It produces
immunosuppression by inhibiting lymphocyte proliferation in response to antigenic stimuli.
It is often used to assist in reducing the requirement for steroids - a "steroid-sparing" agent.
Side effects
Bone marrow suppression. Blood counts should be checked every few months.
Hypersensitivity reactions, cholestatic jaundice, hepatic dysfunction, interstitial
nephritis.
Mycophenolate mofetil
This is a newer immunosuppressant which blocks
the de novo synthesis of purine nucleotides. Lymphocytes preferentially use
this pathway whereas other tissues such as brain use a salvage pathway. This
selectively interferes with proliferative responses of T and B lymphocytes, inhibiting
clonal expansion and thus antibody production, the generation of cytotoxic T cells and the
development of delayed type hypersensitivity.
Side effects
The major toxicity is gastrointestinal.
Risk of infection, although may be protective against Pneumocytis carinii
pneumonia.