Tacrolimus is a potent immunosuppressant medicine that helps prevent the body's immune system from rejecting a transplanted organ. It belongs to a class of medicines called calcineurin inhibitors, and is also used topically for certain skin conditions. It is a prescription-only medicine with a narrow therapeutic window, meaning blood levels must be carefully monitored.

• Therapeutic Class: Immunosuppressant (systemic); topical calcineurin inhibitor (dermatology).

• Pharmacological Class: Calcineurin inhibitor.

• Drug Family: Macrolide immunosuppressants (also known as FK506).

• ATC Classification: L04AD02 (Tacrolimus).

Approved: Prevention of organ rejection in patients receiving kidney, liver, or heart transplants (oral/injectable forms), and moderate to severe atopic dermatitis not adequately responsive to other treatments (topical ointment form).

Commonly used for: Transplant recipients as part of a combination immunosuppressive regimen, and patients with eczema/atopic dermatitis where topical steroids are unsuitable or insufficient.

Off-label use (only under medical guidance): Sometimes used for other autoimmune conditions (e.g., certain kidney diseases, graft-versus-host disease prevention) under specialist care.

●       Oral capsules (immediate-release): commonly 0.5 mg, 1 mg, and 5 mg.

●       Oral capsules/tablets (extended-release, once-daily formulations): various strengths available.

●       Injection (intravenous): used short-term when oral dosing isn't possible.

●       Topical ointment: 0.03% and 0.1%, for atopic dermatitis.

Tacrolimus binds to a protein inside immune cells (an immunophilin called FKBP-12), and this complex then blocks an enzyme called calcineurin. Calcineurin is needed to activate T-cells, the immune cells primarily responsible for rejecting a transplanted organ. By blocking this pathway, tacrolimus suppresses the immune response that would otherwise attack the new organ.

• Standard starting dose (oral, adults): Typically 0.10-0.15 mg/kg/day, divided into two doses, adjusted based on organ transplanted and combination immunosuppressive regimen used.

• Condition-wise dose: Trough blood levels are generally targeted around 6-10 ng/mL during the first month post-transplant, then 4-8 ng/mL thereafter, though exact targets vary by transplant type, combination therapy, and institutional protocol.

• Route: Oral (capsule/tablet), or intravenous infusion short-term when oral dosing isn't tolerated; topical ointment applied to affected skin for dermatitis.

• Missed dose: Take as soon as remembered unless close to the next dose; contact the transplant team rather than doubling up, given the narrow therapeutic window.

• Overdose: Can cause significant kidney toxicity, tremor, or other exaggerated side effects; requires urgent medical attention and blood level monitoring.

• Common: Tremor, headache, diarrhoea, high blood pressure, elevated blood sugar, and difficulty sleeping.

• Serious: Kidney toxicity, increased risk of infections (including opportunistic infections) and certain cancers (including lymphoma and skin cancers) due to immune suppression, and neurotoxicity (confusion, seizures in severe cases).

• Emergency symptoms: Signs of serious infection (fever, chills), severe tremor or seizures, significant swelling or reduced urine output, or new vision changes.

• Recovery advice: Regular blood level monitoring is central to managing tacrolimus safely — levels that are too low risk organ rejection, while levels that are too high increase toxicity, so dose adjustments are made based on these results rather than symptoms alone.

• Pregnancy: Used when clearly needed in transplant patients, under close specialist supervision, weighing risks of stopping immunosuppression against medicine-related risks.

• Breastfeeding: Generally not recommended without specific medical guidance.

• Liver disease: Dose adjustment may be needed; liver function is monitored, and tacrolimus is itself sometimes used in liver transplant patients.

• Kidney disease: Used with caution, given tacrolimus's own potential to affect kidney function; closely monitored.

• Elderly: Used with caution; often requires closer monitoring given age-related changes in drug clearance.

• Children: Used in pediatric transplant patients under specialist care, with weight-based dosing (commonly 0.15-0.2 mg/kg/day, divided into two doses).

●       Strong CYP3A4 inhibitors (e.g., ketoconazole, clarithromycin, certain antivirals): significantly increase tacrolimus levels, raising toxicity risk; dose reduction and closer monitoring are needed.

●       Strong CYP3A4 inducers (e.g., rifampin, phenytoin, St. John's Wort): can significantly reduce tacrolimus levels, risking organ rejection.

●       Other nephrotoxic drugs (e.g., NSAIDs, aminoglycosides, amphotericin B): increase the risk of kidney toxicity when combined.

●       Live vaccines: should generally be avoided during treatment due to the immunosuppressive effect.

●       Tacrolimus trough blood levels, monitored frequently, especially early post-transplant or after any dose/medication change.

●       Kidney function tests regularly.

●       Blood pressure and blood glucose monitoring.

●       Monitoring for signs of infection and, over the longer term, skin and other cancer screening given cumulative immunosuppression.

Cyclosporine (an older calcineurin inhibitor), Sirolimus, Everolimus (mTOR inhibitors, different mechanism, sometimes used instead of or alongside tacrolimus).

Typically combined with other immunosuppressants — such as mycophenolate mofetil, azathioprine, or an mTOR inhibitor, plus corticosteroids — as part of a multi-drug regimen to prevent organ rejection, allowing lower individual doses and trough targets than with tacrolimus alone.

●       Organ Transplant / Anti-Rejection Medicines

●       Calcineurin Inhibitors

●       Atopic Dermatitis Treatments (topical form)

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1. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm

2. https://stanfordlab.com/content/stanfordlab/en/test-details/f/FK506L.html

The information on this page is for educational purposes only and is not a substitute for medical advice. Please consult your doctor to know if this treatment is appropriate for your condition.