Toxicology – Cyclosporine

Core Concept

Cyclosporine is a calcineurin-inhibitor immunosuppressant with a narrow therapeutic index and extensive drug-interaction potential. Acute oral overdose is often surprisingly well tolerated, whereas clinically important toxicity more commonly develops from chronic excessive exposure, formulation errors, CYP3A4/P-glycoprotein interactions, renal dysfunction, or accidental intravenous overdose.

The characteristic toxicity pattern is:

Excess cyclosporine exposure → renal vasoconstriction + endothelial/neural toxicity → AKI + hypertension + hyperkalemia/hypomagnesemia + tremor/encephalopathy/PRES ± hepatotoxicity

The most important management principles are:

Stop or reduce cyclosporine, identify the cause of excessive exposure, monitor whole-blood concentrations and renal function, correct electrolyte/BP abnormalities, and provide supportive care.

There is no specific antidote, and cyclosporine is not effectively removed by hemodialysis or charcoal hemoperfusion.

Current Uses

Systemic cyclosporine remains an important immunosuppressant in kidney, liver, and heart transplantation. Modified oral formulations are also FDA-labeled for severe active rheumatoid arthritis inadequately responsive to methotrexate and for severe recalcitrant plaque psoriasis in selected adults.

Cyclosporine is also widely used in specialist practice for other immune-mediated diseases.

Modern ophthalmic cyclosporine preparations—including formulations such as Restasis and Cequa—are used for ocular surface inflammatory disease/dry eye. These topical ophthalmic preparations have very different systemic exposure and should not be confused toxicologically with oral or IV cyclosporine.

The older description of routine rectal or pulmonary-aerosol cyclosporine formulations does not reflect standard current U.S. systemic formulations.

Sandimmune Versus Modified Cyclosporine – Critical Formulation Issue

One of the most important practical safety points is that Sandimmune and modified/microemulsion cyclosporine formulations such as Neoral are not bioequivalent and are not freely interchangeable milligram-for-milligram.

Modified cyclosporine has more predictable and generally greater bioavailability. Switching between formulations without appropriate supervision can lead either to excessive exposure and toxicity or to insufficient immunosuppression and graft rejection. Current Sandimmune labeling specifically warns that conversion between Sandimmune and Neoral requires increased concentration monitoring and possible dosage adjustment.

Therefore:

A formulation substitution can itself be the cause of cyclosporine toxicity.

Medication reconciliation should identify the exact formulation, concentration, dose, timing, and whether a recent product switch occurred.

Mechanism of Immunosuppression

Cyclosporine enters lymphocytes and binds the intracellular immunophilin cyclophilin. The cyclosporine–cyclophilin complex then inhibits calcineurin, preventing dephosphorylation and nuclear translocation of NFAT.

This reduces transcription of interleukin-2 and other T-cell activation genes, thereby suppressing activation and proliferation of T lymphocytes.

A useful sequence is:

Cyclosporine + cyclophilin → calcineurin inhibition → ↓ NFAT activation → ↓ IL-2 → ↓ T-cell activation

This is why cyclosporine is classified as a calcineurin inhibitor, along with tacrolimus.

Mechanisms of Toxicity

Cyclosporine toxicity is not simply “too much immunosuppression.” Calcineurin inhibition and related vascular/endothelial effects occur in nonimmune tissues, particularly the kidney, vasculature, and nervous system.

Important toxic mechanisms include:

Renal arteriolar vasoconstriction → ↓ renal blood flow/GFR → acute nephrotoxicity

Endothelial dysfunction + sodium retention + altered vasoactive mediators → hypertension

Tubular dysfunction → hyperkalemia + hypomagnesemia

Cerebral endothelial dysfunction + hypertension → encephalopathy/PRES

Chronic vascular/interstitial injury → arteriolopathy + striped tubulointerstitial fibrosis

Acute nephrotoxicity is often functional and reversible when exposure is reduced, while long-term high exposure can produce structural renal damage.

Acute Versus Chronic Toxicity

Acute and chronic cyclosporine toxicity behave differently.

A single oral overdose frequently causes only transient gastrointestinal or neurologic symptoms and modest renal dysfunction, even when the reported dose is very large.

By contrast, repeated excessive dosing or sustained high concentrations can cause progressive nephrotoxicity, hypertension, electrolyte abnormalities, neurotoxicity, and hepatotoxicity.

Accidental intravenous overdose is substantially more dangerous, because it bypasses variable GI absorption and can produce very high systemic exposure rapidly.

Toxic Dose

There is no reliable universal toxic dose.

Current Sandimmune prescribing information reports that oral doses as large as 10 g, approximately 150 mg/kg, have been associated mainly with vomiting, drowsiness, headache, tachycardia, and in some patients moderately severe but reversible renal impairment.

This means the old statement that “several grams have not produced toxicity” is partly true but potentially misleading:

Large acute oral ingestions may be relatively benign, but serious toxicity is still possible.

Severe neurotoxicity, nephrotoxicity, and hepatotoxicity have been reported after dosing errors, and fatal neurologic toxicity has occurred after massive IV overdose.

Dose alone should therefore never replace clinical assessment and therapeutic drug monitoring.

Intravenous Overdose

Parenteral overdose is more concerning than oral overdose.

Current labeling notes serious intoxication after accidental parenteral overdose, particularly in premature neonates.

A published adult case involving an IV infusion approximately ten times the intended rate developed massive cerebral edema and fatal brainstem compression; the estimated cyclosporine concentration may have approached approximately 1700 ng/mL.

Thus:

IV cyclosporine dosing errors should be treated as potentially severe even before symptoms develop.

Blood Concentrations – Important Unit Correction

The older chapter gives therapeutic cyclosporine concentrations in mg/mL. This is incorrect by roughly six orders of magnitude.

Modern cyclosporine concentrations are typically reported in:

ng/mL

not mg/mL.

For example, a trough might be reported as 100–300 ng/mL, not 100–300 mg/mL.

This is an important medication-safety correction.

Therapeutic Drug Monitoring

Cyclosporine has substantial interpatient and intrapatient pharmacokinetic variability, making therapeutic drug monitoring (TDM) essential during systemic therapy.

Monitoring usually uses whole blood, not plasma, because cyclosporine distributes substantially into erythrocytes and plasma measurements are temperature- and processing-dependent.

Two monitoring strategies are commonly used:

C0 = predose trough concentration

C2 = concentration approximately 2 hours after oral dosing

C2 may better reflect early drug exposure/AUC with modified formulations, although many centers continue to use C0 monitoring.

There Is No Universal Therapeutic or Toxic Level

The historical claim that the “therapeutic trough is 50–300” and toxicity develops “above 500” is too simplistic.

Cyclosporine target concentrations vary substantially according to:

• Transplanted organ
• Time since transplantation
• Immunologic risk
• Concomitant immunosuppression
• Assay technique
• Whether C0 or C2 is measured
• Nontransplant indication

There is no universally valid blood concentration above which toxicity always occurs.

Some patients develop toxicity at concentrations considered acceptable, while others tolerate substantially higher concentrations. In psoriasis trials, blood concentrations did not correlate reliably with either efficacy or renal dysfunction.

Therefore:

A cyclosporine concentration must be interpreted in clinical context—not as a stand-alone toxicity threshold.

Acute Overdose Concentrations

Markedly elevated levels can support the diagnosis after overdose.

A 2021 kidney-transplant medication error produced gastrointestinal and neurologic symptoms with a whole-blood concentration of 693 ng/mL.

A published prolonged overdose produced a trough concentration of 5877 ng/mL, accompanied by abdominal symptoms and renal dysfunction; recovery occurred after cyclosporine was discontinued.

A 2026 pediatric report described a child with a concentration around 1003 ng/mL after acute overdose who remained clinically stable apart from transient gastrointestinal effects, again illustrating that the number alone does not determine severity.

Pharmacokinetic Interactions

Cyclosporine is extensively metabolized by CYP3A4 and is a substrate of P-glycoprotein.

Consequently, inhibition of CYP3A4/P-gp can markedly increase cyclosporine exposure, while induction can markedly decrease exposure and risk graft rejection.

This makes drug interactions one of the most common modern pathways to toxicity.

Drugs That Increase Cyclosporine Concentrations

Clinically important inhibitors or interacting drugs include:

Clarithromycin, erythromycin, azole antifungals such as fluconazole/itraconazole/ketoconazole/voriconazole, diltiazem, verapamil, nicardipine, amiodarone, protease inhibitors, danazol, imatinib, metoclopramide, and others.

The medication list should therefore be reviewed carefully whenever a patient develops otherwise unexplained nephrotoxicity or neurotoxicity.

Grapefruit

Grapefruit and grapefruit juice should be avoided.

They can inhibit intestinal CYP3A activity and increase cyclosporine exposure. Current labeling specifically advises avoidance.

Drugs That Lower Cyclosporine Concentrations

Important enzyme-inducing drugs include:

Rifampin, carbamazepine, phenytoin, phenobarbital, oxcarbazepine, nafcillin, and St. John’s wort.

These can reduce cyclosporine concentrations and potentially precipitate transplant rejection. Current labeling specifically warns that St. John’s wort has caused subtherapeutic concentrations, rejection, and graft loss.

Thus, reducing cyclosporine concentrations is not automatically beneficial even in a toxicity situation, particularly in a transplant recipient.

Cyclosporine as an Interaction Perpetrator

Cyclosporine does not merely have its own concentration altered by other drugs. It also inhibits CYP3A4, P-glycoprotein, and other transport systems, thereby increasing concentrations of many coadministered medications.

Examples include:

• Digoxin
• Colchicine
• Statins
• Dabigatran
• Repaglinide
• Sirolimus
• Some other narrow-therapeutic-index drugs

Colchicine Interaction

Cyclosporine can markedly increase colchicine exposure and the risk of myopathy, neuropathy, rhabdomyolysis, and multiorgan colchicine toxicity, particularly in renal dysfunction.

This interaction is clinically important because gout is common among transplant and CKD patients.

Statin Interaction

Cyclosporine increases exposure to several statins and markedly increases the risk of myopathy and rhabdomyolysis.

Current labeling reports myotoxicity with combinations involving lovastatin, simvastatin, atorvastatin, pravastatin, and, less commonly, fluvastatin. Statin selection and dosing therefore require careful attention to the individual statin’s labeling.

Muscle weakness or elevated CK in a patient receiving cyclosporine plus a statin should not automatically be attributed to the transplant illness itself.

Additive Nephrotoxicity

Cyclosporine nephrotoxicity can be amplified by other nephrotoxic agents, including aminoglycosides, vancomycin, amphotericin B, trimethoprim-sulfamethoxazole, NSAIDs, tacrolimus, methotrexate, and others.

Volume depletion further increases risk.

Thus, rising creatinine in a patient taking cyclosporine may represent:

high cyclosporine exposure + dehydration + another nephrotoxin

rather than a single cause.

Clinical Features of Acute Oral Overdose

Acute oral overdose commonly causes nausea, vomiting, abdominal discomfort, drowsiness, headache, tremor, flushing, tachycardia, and occasionally hypertension.

Moderate transient creatinine elevation may occur.

Serious toxicity is uncommon after a single isolated oral ingestion but cannot be excluded, especially after massive exposure or in patients with impaired metabolism.

Nephrotoxicity

The kidney is the principal target organ of cyclosporine toxicity.

Acute cyclosporine nephrotoxicity is largely related to renal vasoconstriction and decreased renal blood flow/GFR. It may manifest as an otherwise unexplained increase in serum creatinine and BUN, sometimes accompanied by hypertension and electrolyte abnormalities.

Early acute nephrotoxicity is often reversible after dose reduction or discontinuation.

Chronic Nephrotoxicity

Prolonged cyclosporine exposure can produce progressive structural renal damage characterized by arteriolopathy, tubular atrophy, and striped interstitial fibrosis.

Unlike acute functional vasoconstriction, advanced chronic nephrotoxicity may not fully reverse when the drug is stopped.

In a transplant recipient, distinguishing cyclosporine nephrotoxicity from graft rejection can be difficult, and both can occur simultaneously.

Hyperkalemia

Cyclosporine may produce clinically important hyperkalemia, sometimes accompanied by a hyperchloremic metabolic acidosis.

Potassium should therefore be monitored closely during suspected toxicity.

Current labeling discourages use of potassium-sparing diuretics with cyclosporine and urges caution with ACE inhibitors, ARBs, potassium-containing medications, and potassium-rich diets because of additive hyperkalemia risk.

Hypomagnesemia

Cyclosporine can promote renal magnesium loss and hypomagnesemia.

This is particularly relevant in neurotoxicity because hypomagnesemia has been identified as one of several risk factors associated with cyclosporine-related seizures and encephalopathy.

Correct clinically significant magnesium deficiency.

Hyperuricemia

Hyperuricemia can develop during calcineurin-inhibitor therapy and contributes to the high frequency of gout in transplant recipients.

It is generally a chronic therapeutic adverse effect rather than a major acute-overdose manifestation.

Hypertension

Hypertension is one of the most common cyclosporine adverse effects.

Mechanisms include systemic and renal vasoconstriction, sodium retention, sympathetic effects, and altered endothelial mediators.

Significant hypertension can contribute to neurologic toxicity, including PRES.

In toxicity, management begins by reducing or withholding cyclosporine when clinically appropriate and treating blood pressure according to contemporary hypertension/emergency principles.

Treatment of Cyclosporine-Associated Hypertension

The older recommendation that nifedipine is uniquely preferred because it is renoprotective is too narrow.

Dihydropyridine calcium-channel blockers can be useful, but antihypertensive therapy should be individualized. Some calcium-channel blockers—particularly diltiazem and verapamil—can raise cyclosporine concentrations through metabolic inhibition.

Nifedipine can also exacerbate cyclosporine-associated gingival hyperplasia.

For severe hypertensive emergency, use standard titratable IV antihypertensives according to the clinical situation rather than relying on one specific oral agent.

Neurologic Toxicity

Cyclosporine neurotoxicity ranges from mild to severe.

Mild manifestations include:

• Tremor
• Headache
• Paresthesias
• Dizziness
• Confusion

Severe manifestations include:

• Altered consciousness
• Seizures
• Visual disturbances
• Cortical blindness
• Motor abnormalities
• Psychiatric symptoms
• Encephalopathy
• PRES

Current labeling specifically recognizes posterior reversible encephalopathy syndrome (PRES) as a cyclosporine complication.

Posterior Reversible Encephalopathy Syndrome

PRES should be suspected when a patient receiving cyclosporine develops:

Hypertension + headache + seizures + confusion/encephalopathy + visual disturbance

MRI typically demonstrates posterior-predominant vasogenic edema, although distribution can be more widespread.

Risk factors described with cyclosporine include hypertension, hypomagnesemia, high drug concentrations, high-dose corticosteroid therapy, and graft-versus-host disease.

Treatment consists of:

• Reducing or stopping cyclosporine
• Controlling blood pressure
• Correcting magnesium and other metabolic abnormalities
• Treating seizures
• MRI/neurocritical-care assessment when severe

Most cases improve after appropriate management, although severe complications can occur.

Seizures

Seizures may occur with cyclosporine neurotoxicity and have particularly been reported when cyclosporine is combined with high-dose methylprednisolone.

Treat seizures with standard benzodiazepine-based therapy while correcting hypertension, hypomagnesemia, and excessive cyclosporine exposure.

Routine use of phenytoin solely because the patient has cyclosporine toxicity is undesirable because phenytoin strongly induces CYP3A metabolism and can complicate subsequent immunosuppressant dosing.

Hepatic Toxicity

Cyclosporine can cause hyperbilirubinemia, cholestatic or hepatocellular injury, hepatitis, and rarely liver failure.

Current labeling notes that hepatotoxicity usually improves after dose reduction.

Serial bilirubin and liver enzymes should therefore be monitored after significant overdose or sustained supratherapeutic exposure.

Thrombotic Microangiopathy

Cyclosporine can rarely contribute to thrombotic microangiopathy, producing thrombocytopenia and microangiopathic hemolytic anemia with organ dysfunction.

Current labeling recognizes a syndrome of thrombocytopenia and microangiopathic hemolytic anemia associated with cyclosporine.

If anemia and thrombocytopenia develop, obtain a smear, LDH, bilirubin, haptoglobin, renal studies, and other appropriate TMA testing rather than assuming the abnormalities are simple marrow suppression.

Hematologic Effects

The old description suggesting that cyclosporine routinely causes a decreased WBC count, decreased platelets, and elevated hematocrit as a typical toxicity syndrome is misleading.

Cyclosporine does not characteristically produce the predictable bone-marrow suppression seen with cytotoxic chemotherapy. Cytopenias should prompt evaluation for:

• Infection
• Other immunosuppressants
• TMA
• Bone-marrow disease
• Graft-related complications

Gingival Hyperplasia

Gingival overgrowth is a classic chronic adverse effect, particularly when cyclosporine is combined with nifedipine.

This is not a sign of acute poisoning.

Hypertrichosis

Hypertrichosis is another classic chronic cyclosporine adverse effect and can help identify long-term therapy, but it does not indicate acute toxicity severity.

Infection Risk

Cyclosporine’s therapeutic immunosuppression increases susceptibility to opportunistic and serious infections.

Current labeling describes potentially serious viral complications such as JC-virus-associated progressive multifocal leukoencephalopathy and BK/polyomavirus-associated nephropathy in immunosuppressed patients.

In a chronically treated transplant patient presenting with confusion or renal deterioration, drug toxicity should therefore be considered alongside opportunistic infection and graft-related disease.

Malignancy Risk

Long-term immunosuppression increases the risk of lymphoma and other malignancies, particularly skin malignancies. The risk is related to the degree and duration of immunosuppression.

This is a chronic therapeutic complication rather than an acute-overdose problem.

Diagnosis

Acute cyclosporine toxicity is diagnosed from the combination of:

Exposure history + symptoms + blood concentration + renal/electrolyte abnormalities

In chronic therapy, diagnosis is more difficult because the same findings can result from infection, rejection, other nephrotoxins, hypertensive disease, or underlying transplant complications.

The exact medication formulation and recent interacting drugs are essential parts of the diagnostic history.

Laboratory Evaluation

For significant overdose or suspected chronic toxicity, obtain:

• Serum creatinine and BUN
• Sodium and potassium
• Magnesium
• Bicarbonate
• Glucose
• Liver enzymes and bilirubin
• CBC
• Cyclosporine whole-blood concentration
• Urinalysis

Additional tests should be guided by severity.

CK is appropriate when rhabdomyolysis is possible, particularly in a patient taking an interacting statin or colchicine.

Cyclosporine Concentration Timing

The timing of a cyclosporine concentration must be documented.

A “level” drawn:

• immediately after a dose,
• at random,
• at C0,
• or at C2

cannot be interpreted using the same target.

Therefore:

Never interpret a cyclosporine concentration without knowing when the last dose was given.

Neurologic Testing

MRI brain is preferred when PRES is suspected.

CT may be useful initially in an unstable patient or when hemorrhage must be excluded, but a normal CT does not exclude PRES.

Lumbar puncture should not be routine in cyclosporine toxicity; it is performed only when infection or another CNS diagnosis remains a concern after considering procedural safety.

Initial Treatment

There is no specific antidote.

For acute toxicity:

1. Stop cyclosporine temporarily
2. Assess airway, breathing, and circulation
3. Obtain ECG and vital signs
4. Check renal function, potassium, magnesium, liver function, and cyclosporine concentration
5. Identify formulation and interacting medications
6. Correct dehydration and metabolic abnormalities
7. Treat hypertension and neurologic complications

In transplant recipients, decisions about holding and restarting cyclosporine should involve the transplant team because excessive reduction in immunosuppression creates a competing risk of graft rejection.

Gastrointestinal Decontamination

Induced Emesis

Do not induce vomiting.

Although current product labeling still contains historical language stating that forced emesis may be useful after overdose, modern toxicology no longer recommends induced emesis as routine poisoning management.

The risks of aspiration and uncertain benefit outweigh its usefulness.

Gastric Lavage

Current Sandimmune labeling also retains historical language suggesting gastric lavage may be valuable within two hours because absorption is relatively slow.

This recommendation conflicts with modern general toxicology practice.

AACT/EAPCCT guidance states that gastric lavage should not be performed routinely, if at all, because outcome benefit has not been demonstrated and serious complications can occur.

Therefore:

Routine gastric lavage is obsolete for cyclosporine overdose.

Only an extraordinary, immediately life-threatening, very recent ingestion could justify consideration after expert toxicology consultation and airway protection.

Activated Charcoal

Single-dose activated charcoal may be considered after a recent substantial oral cyclosporine ingestion if the patient is alert with an intact airway or has a protected airway.

Activated charcoal has been reported in cyclosporine overdose, but there is no high-quality evidence that it improves clinical outcomes. General toxicology guidance states that charcoal is most likely to reduce absorption when given within approximately the first hour and should not be administered routinely.

Thus:

Activated charcoal is selective, not mandatory.

Multiple-dose charcoal is not an established cyclosporine elimination strategy.

IV Fluids

Patients with vomiting or volume depletion should receive appropriate isotonic crystalloid.

Avoid excessive fluid administration in transplant patients with impaired cardiac or renal function.

Correcting hypovolemia is important because dehydration can intensify calcineurin-inhibitor nephrotoxicity.

Treatment of AKI

Hold or reduce cyclosporine and discontinue avoidable nephrotoxins.

Correct volume depletion, electrolyte abnormalities, and hemodynamic disturbances.

Serially monitor:

• Creatinine
• Potassium
• Magnesium
• Urine output
• Acid-base status

Nephrology consultation is appropriate for severe or progressive AKI.

Hemodialysis

Cyclosporine is not effectively removed by hemodialysis.

Current prescribing information explicitly states that cyclosporine is not dialyzable to any significant extent and is also poorly cleared by charcoal hemoperfusion.

Hemodialysis should therefore not be initiated merely to eliminate cyclosporine.

It remains appropriate for standard indications such as:

• Refractory hyperkalemia
• Severe metabolic acidosis
• Pulmonary edema/volume overload
• Uremic complications
• Severe AKI requiring renal replacement

A published overdose case underwent hemodialysis because of acute renal failure, not because dialysis was expected to substantially clear cyclosporine.

Charcoal Hemoperfusion

Charcoal hemoperfusion does not reliably clear cyclosporine and is not recommended as routine enhanced elimination.

Plasma Exchange and Whole-Blood Exchange

There are case reports of whole-blood exchange and plasma exchange after exceptionally severe cyclosporine intoxication. One cardiac-transplant patient with severe nephrotoxicity, hepatotoxicity, and neurotoxicity recovered after erythrocytapheresis followed by plasma exchange.

However:

These procedures remain experimental rescue therapies, not standard care.

Evidence is limited to isolated cases.

CYP3A Enzyme Induction as Rescue Therapy

Because cyclosporine is metabolized by CYP3A, drugs such as phenobarbital, phenytoin, and rifampin have occasionally been deliberately used to accelerate elimination after severe supratherapeutic exposure.

A 2017 review found only a small number of case reports and concluded that routine use cannot be recommended.

A 2026 pediatric overdose report used rifampin and phenobarbital with rapid decline in cyclosporine concentration, but this remains case-level evidence.

The major danger is obvious:

CYP induction → cyclosporine concentration falls → prolonged under-immunosuppression → possible graft rejection

Rifampin induction can persist after the drug is stopped and has caused prolonged subtherapeutic cyclosporine concentrations.

Therefore:

Metabolic induction should be reserved for exceptional severe toxicity under transplant/toxicology/pharmacy guidance.

Hypertension Treatment

For mild-to-moderate cyclosporine-associated hypertension, reducing cyclosporine exposure may itself improve blood pressure.

When pharmacologic treatment is needed, choose antihypertensive agents based on the clinical situation while accounting for cyclosporine interactions.

Avoid automatically using:

• Potassium-sparing diuretics in hyperkalemia-prone patients
• Diltiazem or verapamil without recognizing that they may increase cyclosporine concentrations

Severe hypertension with neurologic symptoms should be treated as a hypertensive emergency.

Treatment of PRES

For suspected cyclosporine-associated PRES:

Hold/reduce cyclosporine → control severe hypertension → correct magnesium → treat seizures → obtain MRI → involve neurology/transplant specialists

PRES is often reversible when the cause is recognized early.

Hyperkalemia Treatment

Treat severe hyperkalemia using standard emergency measures:

• IV calcium for membrane stabilization when indicated
• Insulin plus glucose
• β₂-agonist therapy
• Bicarbonate when appropriate for significant metabolic acidosis
• Renal replacement for refractory cases

Simultaneously stop contributory potassium-retaining drugs when possible.

Hypomagnesemia Treatment

Replace magnesium when clinically significant, especially with:

• Seizures
• Ventricular dysrhythmias
• PRES/neurotoxicity
• Marked laboratory deficiency

Rhabdomyolysis

If rhabdomyolysis occurs, search for interacting drugs—especially statins or colchicine.

Stop implicated agents, provide appropriate crystalloid, and monitor CK, potassium, creatinine, calcium, and urine output.

Pregnancy

The old FDA Pregnancy Category C classification is obsolete.

Current Sandimmune labeling states that decades of human experience—including transplant registries, cohort studies, and case reports—have not identified a cyclosporine-associated increase in major congenital malformations or miscarriage. However, hypertension, preeclampsia, prematurity, and low birth weight are increased among cyclosporine-treated pregnant populations, although underlying disease and concomitant therapy make causality difficult to determine.

Therefore therapeutic cyclosporine may be continued during pregnancy when clinically necessary, particularly for transplant maintenance.

Acute maternal toxicity should be treated aggressively because maternal renal failure, severe hypertension, seizures, and hypoxia pose major fetal risks.

Breastfeeding

The historical implication that lactation should generally be avoided is outdated.

Current LactMed data indicate that a fully breastfed infant typically receives less than about 2% of the maternal weight-adjusted cyclosporine dose, often less than 1%. Most reported breastfed infants have undetectable blood cyclosporine concentrations, and published follow-up has not demonstrated adverse effects on growth, development, or renal function. Many professional guidelines consider cyclosporine compatible with breastfeeding with appropriate infant monitoring.

Current Sandimmune labeling likewise states that cyclosporine is present in human milk but that adverse effects in breastfed infants have not been reported.

Therapeutic breastfeeding data should not automatically be extrapolated to a mother with an acute massive overdose.

Ophthalmic Cyclosporine in Pregnancy/Lactation

Systemic absorption after ophthalmic cyclosporine is minimal. LactMed considers significant infant exposure unlikely, and punctal occlusion after eye-drop administration can further reduce systemic absorption.

Monitoring After Acute Overdose

Patients with a substantial ingestion should have serial assessment of:

• Mental status
• Blood pressure
• Heart rate
• Serum creatinine/BUN
• Potassium
• Magnesium
• Liver enzymes/bilirubin
• Cyclosporine concentration

The appropriate monitoring duration depends on formulation, amount, symptoms, concentration trend, renal function, and comorbidities.

The old rule simply to recheck “within a day or two” is inadequate for a symptomatic patient with marked overdose.

Monitoring During Chronic Therapy

Current systemic labeling emphasizes repeated monitoring of:

renal function, liver function, potassium, magnesium, lipids, and cyclosporine blood concentrations, especially in transplant patients.

Drug concentrations should also be reassessed whenever:

• An interacting medication is started or stopped
• Formulation is changed
• Graft dysfunction occurs
• Renal function deteriorates unexpectedly
• Neurotoxicity appears

Observation

A small isolated oral dosing error in an asymptomatic patient may require only clinical observation and follow-up testing after poison-center/transplant consultation.

Patients with:

• Significant intentional overdose
• Markedly elevated concentration
• AKI
• Hypertension
• Neurologic symptoms
• Significant electrolyte abnormalities
• IV overdose

require prolonged monitored evaluation.

There is no universally validated fixed “6-hour” discharge rule for cyclosporine overdose.

Admission

Hospital admission is appropriate for:

• Significant acute overdose with symptoms
• AKI
• Sustained hypertension
• Important hyperkalemia or hypomagnesemia
• Altered consciousness
• Tremor or progressive neurotoxicity
• Significant hepatotoxicity
• Substantial IV dosing error
• Inability to obtain reliable transplant follow-up

ICU admission is appropriate for:

• Seizures
• PRES
• Severe hypertensive emergency
• Coma
• Severe AKI with metabolic complications
• Hemodynamic instability
• Massive IV overdose

Discharge

Discharge requires:

• Stable mental status and vital signs
• Stable or improving renal function
• No significant electrolyte abnormality
• No progressive neurotoxicity
• A clearly declining/acceptable cyclosporine exposure pattern
• A safe plan for restarting or adjusting immunosuppression

For transplant recipients, discharge planning should include the transplant team because prolonged withholding of cyclosporine can create serious rejection risk.

Prognosis

Most isolated oral cyclosporine overdoses recover completely with drug withdrawal and supportive care.

Even doses approaching 10 g have produced relatively modest toxicity in many patients.

However, prognosis is worse when poisoning involves:

• Massive IV exposure
• Severe neurotoxicity/PRES
• Refractory hypertension
• Advanced AKI
• Significant hepatic dysfunction
• Prolonged repeated overdose
• Serious drug interactions

Chronic nephrotoxicity may leave persistent renal impairment even after cyclosporine is reduced or discontinued.

Important Pitfalls

A major pitfall is the historical concentration unit.

Cyclosporine levels are measured in ng/mL—not mg/mL.

A stated “500 mg/mL cyclosporine trough” would be physiologically implausible.

Another pitfall is assuming that a blood concentration above one arbitrary threshold proves toxicity. There is no universal toxic level, and therapeutic targets differ widely according to indication and timing.

Another major error is ignoring the exact formulation. Sandimmune and modified cyclosporine formulations such as Neoral are not bioequivalent or automatically interchangeable.

The most important modern source of toxicity is often drug interaction, particularly CYP3A4/P-gp inhibition.

Always ask about:

clarithromycin, erythromycin, azoles, diltiazem, verapamil, amiodarone, HIV antivirals, grapefruit, colchicine, statins, and additional nephrotoxins.

Another pitfall is interpreting rising creatinine in a transplant recipient as automatically due to rejection. Cyclosporine nephrotoxicity and rejection can look similar and may coexist.

Do not miss PRES in a cyclosporine-treated patient with hypertension, seizures, confusion, or visual symptoms.

The historical recommendation for gastric lavage and forced emesis should not be followed routinely. Modern toxicology discourages both; activated charcoal is selective rather than mandatory.

Another pitfall is ordering hemodialysis simply to clear cyclosporine.

Dialysis treats AKI complications—it does not effectively clear cyclosporine.

Finally, using rifampin, phenytoin, or phenobarbital to intentionally accelerate metabolism is not routine therapy. Evidence consists mainly of case reports, and prolonged enzyme induction may drive concentrations too low and endanger a transplanted organ.

High-Yield Toxicology Pearls

Cyclosporine toxicity is primarily a renal–vascular–neurologic syndrome.

Think:

AKI + hypertension + hyperkalemia/hypomagnesemia + tremor/encephalopathy

The mechanism is cyclophilin binding → calcineurin inhibition → reduced NFAT/IL-2 signaling, while toxicity reflects renal vasoconstriction, endothelial dysfunction, tubular effects, and CNS vascular injury.

A single oral overdose is often less toxic than expected. Current labeling reports oral doses up to 10 g (~150 mg/kg) producing mainly vomiting, drowsiness, headache, tachycardia, and reversible renal dysfunction in many patients.

However, IV overdose can be catastrophic and repeated excessive exposure can produce severe renal, hepatic, and neurologic toxicity.

Whole-blood concentrations are usually reported in ng/mL. Do not use the old mg/mL units.

There is no universal “toxic cyclosporine level.” Target concentrations vary by transplant type, time since transplantation, assay, and whether C0 or C2 monitoring is used.

Always establish the exact formulation:

Sandimmune and Neoral/modified cyclosporine are not automatically interchangeable.

Cyclosporine is a CYP3A4 and P-glycoprotein substrate. Clarithromycin, erythromycin, azole antifungals, diltiazem, verapamil, amiodarone, protease inhibitors, and grapefruit can raise concentrations.

Cyclosporine also raises concentrations of other drugs, notably colchicine and statins, increasing the risk of myopathy/rhabdomyolysis.

Acute nephrotoxicity is usually caused by renal vasoconstriction and reduced GFR and may improve after dose reduction. Chronic exposure can produce arteriolopathy and irreversible interstitial fibrosis.

Hypertension is common. Monitor potassium because hyperkalemia can occur, and monitor magnesium because hypomagnesemia may contribute to neurologic toxicity.

A patient receiving cyclosporine who develops:

Headache + hypertension + seizures + visual disturbance/confusion

should be evaluated urgently for PRES.

There is no antidote.

Activated charcoal can be considered after a recent substantial ingestion when the airway is safe, but routine lavage and induced emesis are obsolete.

Cyclosporine is not effectively removed by hemodialysis or charcoal hemoperfusion. Dialysis is reserved for conventional AKI/metabolic indications.

CYP enzyme induction with phenytoin, phenobarbital, or rifampin has been used in exceptional severe cases, but evidence is limited and routine use is not recommended because excessive reduction in immunosuppression can precipitate graft rejection.

Pregnancy Category C terminology is obsolete. Available human data have not demonstrated an increased rate of major congenital malformations or miscarriage, although prematurity, hypertension, preeclampsia, and low birth weight are more frequent in cyclosporine-treated transplant populations.

Therapeutic cyclosporine is increasingly regarded as compatible with breastfeeding with appropriate infant monitoring, with typical infant exposure well below the maternal weight-adjusted dose.

The most important clinical warning is:

In a patient taking cyclosporine, an unexplained rise in creatinine plus hypertension or tremor should trigger an immediate search for excessive drug exposure and a CYP3A4/P-gp interaction.