Cyclosporine A

Cyclosporine A is a cyclic undecapeptide from the fungus Tolypocladium inflatum, containing several N-methylated and non-proteinogenic residues that give it oral bioavailability and protease resistance no ordinary peptide would have. Inside the T-cell it binds the immunophilin cyclophilin A; the cyclosporine-cyclophilin complex then binds and inhibits the phosphatase calcineurin. Because calcineurin is what dephosphorylates NFAT to let it enter the nucleus, the result is blockade of IL-2, IL-4 and interferon-gamma transcription and a profound, selective shutdown of T-helper cell activation without myelosuppression. The same calcineurin inhibition in renal afferent arterioles and tubules is the direct cause of its dose-limiting nephrotoxicity - the toxicity and the therapeutic effect are two faces of the same mechanism, which is why blood-level monitoring is mandatory rather than optional.

Targets: Cyclophilin A, Calcineurin, NFAT, IL-2 transcription

• · Dosed by weight, typically 2-5 mg/kg/day divided twice daily and then adjusted to trough blood levels. The numbers here are the equivalent per-dose range for a typical adult; never dose this drug without level monitoring.
• · 2.5-5 mg/kg/day divided twice daily, limited to a maximum of one year of continuous treatment because of cumulative renal damage.
• · 0.05% (Restasis) or 0.09% (Cequa) emulsion. Systemic absorption is negligible; this route carries none of the oral drug's risks.

Work out your exact syringe units →

• very commonNephrotoxicity— Dose-dependent and can become permanent with prolonged exposure. This is the reason for level monitoring.
• very commonHypertension— Affects a large fraction of patients and often needs treating.
• very commonIncreased infection risk— This is a genuine immunosuppressant, not an immune modulator.
• commonGum hyperplasia— Characteristic and largely cosmetic; worse with poor oral hygiene.
• commonHirsutism— Increased body and facial hair growth.
• commonTremor and paraesthesia— Usually early and dose-related.
• commonHyperkalaemia and hypomagnesaemia— Direct tubular effects.
• uncommonIncreased malignancy risk, especially skin cancer and lymphoma— Cumulative with duration of exposure; sun protection is not optional on this drug.

• Uncontrolled hypertension, which the drug will worsen.
• Significant renal impairment outside a transplant indication.
• Active untreated infection.
• Prior or current malignancy other than in transplant contexts, given the lymphoma and skin-cancer risk.
• Concurrent PUVA or extensive UVB phototherapy in psoriasis - the skin cancer risk compounds sharply.
• Pregnancy requires specialist supervision; the drug crosses the placenta.

• cautionCYP3A4 inhibitors (ketoconazole, clarithromycin, diltiazem, grapefruit juice) — Raise cyclosporine levels sharply and can precipitate acute nephrotoxicity.
• cautionCYP3A4 inducers (rifampicin, carbamazepine, St John's wort) — Drop levels and can cause graft rejection.
• cautionStatins — Cyclosporine raises statin exposure substantially and increases rhabdomyolysis risk.
• conflictNSAIDs and aminoglycosides — Additive nephrotoxicity.
• conflictthymosin-alpha-1 — Directly opposing immune pharmacology.

• · Whole-blood cyclosporine trough levels - mandatory, not optional.
• · Serum creatinine and eGFR at every visit.
• · Blood pressure at every visit.
• · Potassium, magnesium, uric acid and lipids.
• · Regular dermatological skin cancer surveillance during long-term use.

FDA and EMA approved, prescription only. Not something to source or self-administer outside medical supervision.

• Neoral (cyclosporine capsules, USP) MODIFIED, US prescribing information (label)
• KDIGO clinical practice guideline for the care of kidney transplant recipients (guideline)
• Restasis (cyclosporine ophthalmic emulsion 0.05%) US prescribing information (label)

The therapeutic effect and the dose-limiting toxicity are the same molecular event, and understanding that is the difference between managing this drug and being surprised by it. Cyclosporine binds cyclophilin A; neither cyclosporine alone nor cyclophilin alone inhibits anything. The composite surface of the drug-immunophilin complex is what docks into calcineurin and blocks its phosphatase active site. Calcineurin's job is to dephosphorylate NFAT so it can enter the nucleus, and NFAT is what transcribes IL-2, IL-4 and interferon-gamma. So the block is upstream of T-cell clonal expansion and is remarkably selective - no myelosuppression, unlike cytotoxic immunosuppressants. The problem is that calcineurin is not a lymphocyte-specific enzyme. In the renal afferent arteriole, calcineurin inhibition shifts the vasoconstrictor-vasodilator balance toward endothelin and away from nitric oxide and prostacyclin, producing acute, dose-dependent, reversible vasoconstriction and a fall in GFR. That is the early nephrotoxicity, and it tracks blood level. Chronic nephrotoxicity is a different and more serious animal: arteriolar hyalinosis, striped interstitial fibrosis and tubular atrophy, driven partly by TGF-beta upregulation, and it is not reversible. Naesens' review is the definitive account. The clinical consequence is the one-year cap in dermatology and the permanent monitoring in transplantation. The same calcineurin block in the distal tubule explains the hyperkalaemia and hypomagnesaemia, and in vascular smooth muscle the hypertension. Gum hyperplasia and hirsutism come from a separate effect on fibroblast and follicle biology. Nothing here is idiosyncratic; it is all one mechanism reaching tissues you did not aim at.

Almost every serious cyclosporine problem is a level problem, and almost every level problem is an interaction. Someone starts fluconazole for a nail infection, or clarithromycin for a chest infection, or buys St John's wort for low mood, and within a week the level has doubled or halved. The first produces acute nephrotoxicity, hypertension and tremor; the second produces rejection. Nobody in that chain necessarily did anything obviously wrong, which is why level monitoring is mandatory rather than sensible. The second failure is chronic: creatinine drifts up by ten percent a year, nobody acts because each individual rise is small, and by the time it is obvious the histology shows irreversible interstitial fibrosis. The dermatology one-year cap exists precisely because that drift is silent. Third, malignancy: cumulative skin cancer risk is substantial and rises steeply with prior PUVA, and post-transplant lymphoproliferative disorder is a real if uncommon outcome. Fourth, the formulation trap: Neoral and Sandimmune are not interchangeable, generic substitution at the pharmacy counter has caused both toxicity and rejection, and this is what the boxed warning is about. Finally, the thing that separates this from everything else in this class - it is a genuine immunosuppressant, so infections present late and atypically, and an unexplained fever on cyclosporine is an emergency rather than an inconvenience.

• Cyclophilin A (peptidyl-prolyl cis-trans isomerase) — Low nanomolar binding; the drug-immunophilin complex, not the drug alone, is the active species

  Formation of the inhibitory composite surface. Cyclophilin binding by itself has no immunosuppressive consequence.

• Calcineurin (protein phosphatase 2B) — The cyclosporine-cyclophilin complex inhibits calcineurin phosphatase activity in the low nanomolar range

  Blocks NFAT dephosphorylation and therefore nuclear translocation. In T-cells this shuts down IL-2, IL-4 and IFN-gamma transcription. In renal afferent arterioles the same inhibition produces vasoconstriction and reduced GFR - the therapeutic effect and the nephrotoxicity are one mechanism.

• P-glycoprotein (MDR1) — Substrate and inhibitor

  Explains a second layer of drug interactions independent of CYP3A4, and contributes to limited but non-zero CNS penetration - which is why neurotoxicity, tremor and posterior reversible encephalopathy syndrome occur at all.

• Mitochondrial permeability transition pore (via cyclophilin D) — Not the therapeutic target

  An off-target consequence of cyclophilin binding, relevant to research on ischaemia-reperfusion but not to immunosuppressive dosing.

Hours 1.5-2: peak blood concentration after an oral dose. Day 1-3: steady state reached, which is why levels are checked three days after any dose change and not before. Days 3-7: immunosuppression is established; this is fast enough to matter clinically in transplantation. Weeks 2-6: psoriasis and atopic dermatitis responses appear - dermatology is the slowest of the common indications. Weeks 2-8: hypertension, gum hyperplasia, hirsutism and tremor emerge if they are going to. Months 3-12: the acute haemodynamic component of nephrotoxicity is well established and still largely reversible on dose reduction. Year 1 onward: chronic structural nephrotoxicity accumulates and stops being reversible. Years 2+: skin cancer and lymphoproliferative risk becomes the dominant long-term concern.

Cyclosporine's interaction profile is not a list of cautions, it is the main clinical problem. Anything that touches CYP3A4 or P-glycoprotein moves the level, and the level determines both efficacy and toxicity. Raising agents: azole antifungals, macrolides other than azithromycin, diltiazem, verapamil, HIV protease inhibitors, and grapefruit juice acting on intestinal CYP3A4. Lowering agents: rifampicin, carbamazepine, phenytoin, and St John's wort - the last of which is bought over the counter and has caused graft loss. Additive nephrotoxicity: NSAIDs, aminoglycosides, amphotericin, high-dose trimethoprim. Statins: cyclosporine raises statin exposure severalfold with real rhabdomyolysis risk, so low-dose pravastatin or fluvastatin rather than simvastatin. Potassium-sparing diuretics, ACE inhibitors and ARBs stack with the drug's own hyperkalaemia. Within this class, running cyclosporine alongside thymosin alpha-1, thymopentin, pidotimod or any thymic peptide is pharmacologically self-cancelling - one blocks IL-2 transcription and the other exists to raise it. The ophthalmic emulsion is a different story entirely: systemic absorption is negligible and none of the above applies to Restasis or Cequa.

Cyclosporine is in this dataset as the reference point for what a peptide drug looks like when it actually works and when its toxicity has been quantified over four decades. Compare it against anything else in the class and the contrast is instructive: it has an absolute contraindication list derived from observed harm rather than mechanism, a mandatory monitoring schedule, a boxed warning, and a nephrotoxicity profile characterised down to the histology. That is what forty years of real-world use produces. Against voclosporin, its own successor, the differences are concrete: voclosporin is roughly fourfold more potent per unit exposure, has a cleaner metabolite profile, and is dosed flat without therapeutic drug monitoring - which is the single biggest practical advance. Against tacrolimus, the other calcineurin inhibitor, cyclosporine causes more hirsutism, gum hyperplasia and hyperlipidaemia and less new-onset diabetes and neurotoxicity. Against anakinra, the comparison is instructive in the other direction: anakinra blocks one receptor and washes out in a day, cyclosporine blocks a node upstream of an entire transcriptional programme and accumulates. Nothing about cyclosporine belongs in a self-directed protocol.

Deliberately null. Generic cyclosporine has been available for decades and acquisition cost is low relative to almost everything in this class, but actual out-of-pocket cost is dominated by which formulation is dispensed, insurance status, and the recurring cost of whole-blood level monitoring and renal function testing - which is not optional and is not free. No verified pricing was resolved in this session, and a made-up number here would be worse than useless.

• ?Absolute bioavailability for the modified Neoral formulation has not been determined in adults, per the label itself. The 10-89 percent range quoted is for Sandimmune.
• ?The volume of distribution given as 280 L is calculated from the label's 3-5 L/kg for a 70 kg adult, not a directly reported figure. The label states the per-kilogram range.
• ?Target trough concentration ranges vary substantially by indication, transplanted organ, time post-transplant, assay method and local protocol, and are deliberately not quoted here. Whole-blood HPLC and immunoassay methods do not give interchangeable numbers.
• ?Blood-brain barrier penetration is marked partial: cyclosporine is a P-glycoprotein substrate and CNS penetration is limited, yet tremor, seizures and posterior reversible encephalopathy syndrome all occur, which implies meaningful exposure under some conditions. The determinants are not fully characterised.
• ?The three principal metabolites AM1, AM9 and AM4N have some immunosuppressive activity of their own, but the extent to which they contribute to either efficacy or nephrotoxicity is not settled.
• ?Half-life is quoted by the label as approximately 8.4 hours with a range of 5-18 for the modified formulation, while the Core record cites 8-27 hours across formulations and populations. Both are defensible; the spread reflects genuine population variability rather than a discrepancy.

• NEORAL (cyclosporine capsules, USP) MODIFIED - US prescribing information Novartis Pharmaceuticals, FDA approved product labeling (accessed via openFDA)

  Source of every pharmacokinetic number quoted here: tmax 1.5-2.0 h, volume of distribution 3-5 L/kg, blood clearance 5-7 mL/min/kg, protein binding approximately 90 percent, erythrocyte partitioning 41-58 percent, half-life about 8.4 hours (range 5-18), metabolites AM1/AM9/AM4N at 70/21/7.5 percent of parent AUC, biliary elimination with 6 percent urinary and 0.1 percent unchanged, and the food effect. Also the boxed warning and the non-interchangeability of Neoral and Sandimmune.

• Calcineurin inhibitor nephrotoxicity Naesens M, Kuypers DR, Sarwal M, Clinical Journal of the American Society of Nephrology, 2009 · PMID 19218475

  The definitive review separating acute reversible haemodynamic nephrotoxicity from chronic irreversible structural injury. If you take this drug or prescribe it, this is the paper that explains why the monitoring schedule looks the way it does.

• Calcineurin inhibitor-induced renal allograft nephrotoxicity Krejci K, Tichy T, Bachleda P, Zadrazil J, Biomedical Papers of the Medical Faculty of the University Palacky, Olomouc, 2010 · PMID 21293540

  Histological detail on arteriolar hyalinosis and striped fibrosis - what chronic calcineurin inhibitor damage actually looks like under a microscope.