cyclosporiinin

Cyclosporine is a cyclic peptide immunosuppressant that was first isolated in 1971 from the fungus Tolypocladium inflatum. The active form, cyclosporine A, is commercially available under several trade names, including Sandimmune, Neoral, and Restasis. Its structure, a 11‑residue peptide with unusual amino acids such as (R)-2-aminobutyric acid, gives it high affinity for a cytosolic receptor protein called cyclophilin.

Binding of cyclosporine to cyclophilin forms a complex that inhibits the phosphatase calcineurin. This blockade prevents dephosphorylation of the nuclear factor of activated T‑cells (NF‑AT), thereby reducing transcription of interleukin‑2 and other cytokines that drive T‑cell proliferation. Because of this mechanism, cyclosporine suppresses both innate and adaptive immune responses.

The drug is primarily used to prevent rejection after solid‑organ transplantation, particularly kidney, heart, and liver grafts. It is also prescribed for autoimmune disorders such as severe psoriasis, graft‑versus‑host disease, rheumatoid arthritis, and uveitis. In ophthalmic preparations, cyclosporin reduces ocular inflammation in dry eye disease.

Common adverse effects include nephrotoxicity, hypertension, neurotoxicity, hirsutism, and gastrointestinal upset. The drug is teratogenic and contraindicated during pregnancy; it can also interact with many other medications by inducing or inhibiting cytochrome P‑450 enzymes. Dose adjustments are necessary in patients with hepatic or renal impairment.

Screening for nephrotoxicity and monitoring blood concentrations are routine parts of therapeutic protocols. Despite its side‑effect profile, cyclosporine remains a cornerstone in transplantation medicine and in the management of several severe inflammatory conditions.