Tacrolimus

# Tacrolimus ## Overview - **Classification**: Calcineurin Inhibitor (CNI), Immunosuppressant - **Mechanism**: Inhibits calcineurin, which prevents T-lymphocyte activation and proliferation. Reduces cytokine production (e.g., IL-2). ## Primary Indications 1. **Prophylaxis of organ rejection** - In patients receiving allogeneic liver, kidney, or heart transplants. 2. **Rescue therapy for organ rejection** - When other immunosuppressants fail. 3. **Treatment of Atopic Dermatitis** - Topical formulation (not covered in this systemic dosing). ## Adult Dosing ### Standard Dosing **Prophylaxis of Organ Rejection (Initial Oral Dosing)** - **Liver Transplant**: - **Dose**: **0.1-0.15 mg/kg/day** - **Frequency**: Divided into **two daily doses** (every 12 hours) - **Route**: Oral - **Kidney Transplant**: - **Dose**: **0.2 mg/kg/day** - **Frequency**: Divided into **two daily doses** (every 12 hours) - **Route**: Oral - **Heart Transplant**: - **Dose**: **0.075 mg/kg/day** - **Frequency**: Divided into **two daily doses** (every 12 hours) - **Route**: Oral **Prophylaxis of Organ Rejection (Initial IV Dosing)** - **Liver Transplant**: - **Dose**: **0.03-0.05 mg/kg/day** - **Frequency**: Continuous intravenous infusion - **Route**: IV - **Kidney Transplant**: - **Dose**: **0.05-0.1 mg/kg/day** - **Frequency**: Continuous intravenous infusion - **Route**: IV - **Heart Transplant**: - **Dose**: **0.01-0.05 mg/kg/day** - **Frequency**: Continuous intravenous infusion - **Route**: IV - **Special Considerations**: Convert from IV to oral as soon as possible. Oral dose is typically 3-4 times the IV dose. Doses are titrated to target trough levels. ### Dose Adjustments - **Renal Impairment**: No specific dose adjustment generally needed. Monitor renal function and tacrolimus trough levels closely due to nephrotoxicity risk. - **Hepatic Impairment**: Initiate at the lower end of the dosing range. Monitor tacrolimus trough levels closely and adjust as needed. Patients with severe hepatic dysfunction may require significant dose reductions. - **Elderly Patients**: Start at the lower end of the dosing range. Monitor closely for adverse effects and trough levels. ## Pediatric Dosing *Note: Pediatric patients generally require higher mg/kg doses due to faster metabolism.* ### Neonates (0-28 days) - **Special Notes**: Limited data. Consult transplant center protocols. Often require higher mg/kg doses than older children due to rapid metabolism. - **Dose**: Typically **0.03-0.05 mg/kg/day** IV continuous infusion or **0.15-0.2 mg/kg/day** oral BID initially. - **Frequency**: Continuous IV or BID oral - **Maximum**: Titrate to target trough levels. ### Infants (1-12 months) - **Dose**: - **Liver Transplant**: Oral **0.15-0.2 mg/kg/day** BID. IV **0.03-0.05 mg/kg/day** continuous infusion. - **Kidney/Heart Transplant**: Oral **0.3 mg/kg/day** BID. IV **0.075-0.1 mg/kg/day** continuous infusion. - **Frequency**: BID oral or continuous IV infusion. - **Maximum**: Titrate to target trough levels; typically higher mg/kg than adults. ### Children (1-12 years) - **Dose**: - **Liver Transplant**: Oral **0.15-0.2 mg/kg/day** BID. IV **0.03-0.05 mg/kg/day** continuous infusion. - **Kidney/Heart Transplant**: Oral **0.3 mg/kg/day** BID. IV **0.075-0.1 mg/kg/day** continuous infusion. - **Frequency**: BID oral or continuous IV infusion. - **Maximum**: Titrate to target trough levels. Higher mg/kg doses are common. ### Adolescents (13-18 years) - **Dose**: May require higher mg/kg doses than adults due to faster metabolism. Transition towards adult dosing as metabolism matures. - **Maximum**: Titrate to target trough levels. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to tacrolimus or any component of the formulation. - **Absolute**: Hypersensitivity to HCO-60 (polyoxyl 60 hydrogenated castor oil) found in injectable formulation. ### Common Adverse Effects - **Very Common (>10%)**: Nephrotoxicity, Neurotoxicity (tremor, headache, insomnia, paresthesia), Hyperglycemia, Hypertension, Hyperkalemia, Nausea, Diarrhea, Constipation. - **Common (1-10%)**: Anemia, Leukopenia, Hyperlipidemia, Hypomagnesemia, Peripheral edema, Abdominal pain, Fever, Pruritus, Dyspnea. - **Serious but Rare**: Lymphoma, Post-transplant lymphoproliferative disorder (PTLD), Opportunistic infections, Seizures, Torsades de pointes, Anaphylaxis, Pure red cell aplasia (PRCA). ### Key Drug Interactions - **CYP3A4/5 Inhibitors (e.g., Azole antifungals like ketoconazole, voriconazole; Macrolide antibiotics like erythromycin, clarithromycin; Protease inhibitors; Diltiazem, Verapamil; Grapefruit juice)**: Significantly **increase** tacrolimus levels. - **Clinical Significance**: Risk of toxicity. - **Monitoring Requirement**: Close monitoring of tacrolimus trough levels and dose reduction (often by 50% or more) is required. - **CYP3A4/5 Inducers (e.g., Rifampin, Phenytoin, Carbamazepine, St. John's Wort)**: Significantly **decrease** tacrolimus levels. - **Clinical Significance**: Risk of organ rejection. - **Monitoring Requirement**: Close monitoring of tacrolimus trough levels and dose increase is required. - **Nephrotoxic Agents (e.g., NSAIDs, Aminoglycosides, Amphotericin B)**: Additive nephrotoxicity risk. - **Clinical Significance**: Increased kidney damage. - **Monitoring Requirement**: Avoid co-administration if possible, or monitor renal function very closely. - **Live Vaccines**: Avoid live vaccines (e.g., MMR, varicella, rotavirus) due to immunosuppression. ## Monitoring & Follow-up - **Before Treatment**: Baseline renal function (SCr, BUN), Liver function tests (ALT, AST, bilirubin), Blood pressure, Fasting glucose, Electrolytes (K+, Mg2+), CBC with differential. - **During Treatment**: - **Tacrolimus Trough Levels (C0)**: Initially 2-3 times/week, then 1-2 times/week, then monthly once stable. Target ranges vary by transplant type and time post-transplant. - **Renal Function**: SCr, BUN (weekly initially, then monthly). - **Electrolytes**: K+, Mg2+ (weekly initially, then monthly). - **Blood Pressure**: Regularly. - **Blood Glucose**: Regularly. - **Liver Function Tests**: Periodically. - **CBC with differential**: Periodically. - **Clinical Signs**: Monitor for signs of infection (fever, chills), neurotoxicity (tremor, headache, seizures), hyperglycemia (polyuria, polydipsia), and hypertension. ## Clinical Pearls - 💡 **Consistent Administration**: Administer consistently relative to food (e.g., always 1 hour before or 2-3 hours after a meal) to minimize variability in absorption. Most prefer taking on an empty stomach. - 💡 **Narrow Therapeutic Index**: Tacrolimus has a narrow therapeutic index; small changes in dose can lead to toxicity or rejection. Meticulous monitoring is crucial. - 💡 **Formulation Differences**: Extended-release (ER) and immediate-release (IR) formulations are **not interchangeable** on a milligram-to-milligram basis. Patients should remain on the same formulation. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.