Tacrolimus is a potent macrolide immunosuppressant derived from *Streptomyces tsukubaensis*. It is a calcineurin inhibitor that suppresses T-lymphocyte activation, primarily used to prevent organ rejection in transplant recipients. In the Indian context, it is a cornerstone of post-transplant immunosuppressive regimens and is also used topically for atopic dermatitis.
Adult: INITIAL: Individualized based on transplant type, concomitant immunosuppression, and patient status. Typical oral starting doses: Liver transplant: 0.10-0.15 mg/kg/day in two divided doses. Kidney transplant: 0.2 mg/kg/day in two divided doses. Heart transplant: 0.075 mg/kg/day in two divided doses. MAINTENANCE: Adjusted based on therapeutic drug monitoring (TDM) of trough whole blood levels. Target ranges vary by transplant type, time post-transplant, and institution protocol (e.g., early post-op: 10-15 ng/mL; maintenance: 5-10 ng/mL).
Note: Administer orally twice daily, approximately 12 hours apart, on an empty stomach. Take at least 1 hour before or 2-3 hours after a meal to ensure consistent absorption. Capsules should be swallowed whole with water; do not crush, chew, or break. If a dose is missed, take as soon as remembered unless it is close to the next dose. Do not double the dose.
Tacrolimus binds intracellularly to the immunophilin FKBP-12 (FK506 binding protein-12). This drug-immunophilin complex specifically and potently inhibits the calcium-dependent serine-threonine phosphatase, calcineurin. Inhibition of calcineurin prevents the dephosphorylation and nuclear translocation of the cytosolic component of the nuclear factor of activated T-cells (NF-AT). This blocks the transcription of early T-cell activation genes, particularly those for interleukin-2 (IL-2), a critical cytokine for T-cell proliferation.
Pregnancy: Pregnancy Category C (US FDA). Animal studies show fetotoxicity and embryotoxicity. There are no adequate, well-controlled studies in pregnant women. Use only if the potential benefit justifies the potential risk to the fetus. Increased risk of premature birth, low birth weight, and hyperkalemia in the newborn. Pregnancy should be planned, and management requires a high-risk obstetrician and transplant team.
Driving: May cause visual disturbances, dizziness, confusion, or somnolence. Patients should be cautioned about operating machinery or driving until they are certain tacrolimus does not affect them adversely.
| Cyclosporine | Increased risk of severe nephrotoxicity. Tacrolimus should be started at least 24 hours after discontinuing cyclosporine. | Contraindicated |
| Strong CYP3A4 Inhibitors (e.g., Ketoconazole, Itraconazole, Voriconazole, Clarithromycin, Erythromycin, Ritonavir, Boceprevir) | Dramatically increase tacrolimus blood levels, leading to toxicity. Dose reduction of tacrolimus by 50-90% is often required with close TDM. | Major |
| Strong CYP3A4 Inducers (e.g., Rifampicin, Rifabutin, Phenytoin, Carbamazepine, Phenobarbital, St. John's Wort) | Significantly decrease tacrolimus blood levels, risking graft rejection. Dose increase with close TDM is required. | Major |
| Nephrotoxic drugs (e.g., Aminoglycosides, Amphotericin B, NSAIDs like Ibuprofen/Diclofenac) | Additive risk of renal impairment. | Major |
| Potassium-sparing diuretics (e.g., Spironolactone, Amiloride), ACE Inhibitors (e.g., Ramipril), ARBs (e.g., Telmisartan) | Increased risk of hyperkalemia. | Moderate |
| Vaccines (Live Attenuated) e.g., MMR, Varicella, Yellow Fever | Risk of disseminated infection due to immunosuppression. Generally contraindicated. | Major |