What it is
Cyclosporine is a ring of 11 amino acids made by a fungus. The labels describe it as "a cyclic polypeptide immunosuppressant agent consisting of 11 amino acids," produced as a metabolite by Beauveria nivea. It is also written ciclosporin (the international name) and cyclosporin A.
Read from the label's chemical name, the ring is: L-alanine, D-alanine, three N-methyl-leucines and an N-methyl-valine around the ring, an N-methyl-glycine (sarcosine), α-aminobutyric acid, valine, and one residue found nowhere in human proteins — MeBmt, a nine-carbon amino acid with a hydroxyl group and a double bond. Seven of the eleven residues carry an N-methyl group on the backbone nitrogen (our count). That, with the closed ring, is what makes it unusual among peptide drugs. The bond between residues is the ordinary peptide bond; the building blocks are what differ (see the amino acid chart).
How it works
The labels describe the effect rather than the molecular target: cyclosporine works by "specific and reversible inhibition of immunocompetent lymphocytes in the G0- or G1-phase of the cell cycle." T-lymphocytes are preferentially inhibited, the T-helper cell is "the main target", and the drug "inhibits lymphokine production and release, including interleukin-2" — the signal T-cells use to multiply. The labels also note that it does not suppress the bone marrow. The newer eye-drop labels (Cequa, Verkazia, Vevye) name the class directly: cyclosporine is "a calcineurin inhibitor immunosuppressant"; calcineurin is the enzyme T-cells need to switch on interleukin-2. The effect is broad, which is why every systemic label leads with infection and cancer risk.
Why it works by mouth
Most peptides are digested before they can be absorbed. Cyclosporine survives better: a closed ring leaves no free ends for enzymes, and the N-methyl groups strip out most of the backbone's hydrogen-bond donors, so the molecule behaves more like a fat-soluble drug. Absorption is still uneven. The Sandimmune label calls chronic absorption from its capsules "erratic", and Neoral, a microemulsion approved in 1995, gives more exposure — so much that the two "are not bioequivalent and cannot be used interchangeably without physician supervision" (Neoral boxed warning).
What it is approved for
| Product (application, first approval) | Form | Approved use (label) |
|---|---|---|
| Sandimmune (NDA 050573, 1983-11-14; capsules NDA 050625, 1990-03-02) | Injection, capsules, oral solution | Preventing rejection of kidney, liver and heart transplants, with corticosteroids; chronic rejection after other immunosuppressants |
| Neoral (NDA 050715/050716, 1995-07-14) | Microemulsion capsules and oral solution | Transplant rejection; severe active rheumatoid arthritis not adequately controlled by methotrexate; severe recalcitrant plaque psoriasis in adults |
| Gengraf and generic "modified" capsules | Capsules | As Neoral (generic applications from 2000) |
| Restasis (NDA 050790, 2002-12-23) · Cequa (NDA 210913, 2018-08-14) | Eye emulsion or solution | Increasing tear production in keratoconjunctivitis sicca (dry eye) |
| Vevye (NDA 217469, 2023-05-30) | Eye solution | Signs and symptoms of dry eye disease |
| Verkazia (NDA 214965, 2021-06-23) | Eye emulsion | Vernal keratoconjunctivitis in children and adults |
Dates and application numbers are from Drugs@FDA (openFDA, 2026-10-14). Twenty cyclosporine applications are listed there in all.
What the labels warn
The systemic labels carry boxed warnings, summarised here as the labels state them:
- Experienced prescribers only. Only physicians experienced in immunosuppressive therapy should prescribe it, with patients managed where laboratory support is available.
- Infection and cancer. Immunosuppression "may increase the susceptibility to infection and the development of neoplasia", including lymphoma.
- No mg-for-mg switching between Sandimmune and Neoral capsules; inappropriate switching can raise exposure and side effects or lower it and risk rejection (Sandimmune boxed warning).
- Blood-level monitoring in transplant and rheumatoid arthritis patients, because both high and low concentrations carry risk.
- Anaphylaxis with the injection, whose solvent is polyoxyethylated castor oil (Cremophor EL); the injection is reserved for patients who cannot take capsules.
The Neoral label adds that in psoriasis, "most patients will experience relapse" after treatment stops. Doses, set by body weight and blood levels, are on the labels and are decided by the treating team.
Where it stands
- Approved in the US since 1983-11-14, now in oral, intravenous and eye forms from Novartis, AbbVie, Sun Pharma, Harrow and several generic makers.
- Research record: PubMed indexes 65,340 records for cyclosporine or ciclosporin, 2,757 tagged as randomised trials (2026-10-14) — one of the most studied peptide drugs in the library.
Related reading
Two other ring-shaped peptide drugs made by microbes are the antibiotics daptomycin and bacitracin; desmopressin is a peptide drug that is also given as a tablet. For how a peptide's chain is built, see the peptide bond and peptide chain entries.