Tacrolimus inhibits T-lymphocyte activation, although the exact mechanism of action is not known. Experimental evidence suggests that Tacrolimus binds to an intracellular protein, FKBP-12. A complex of Tacrolimus-FKBP-12, calcium, calmodulin, and calcineurin is then formed and the phosphatase activity of calcineurin inhibited. This effect may prevent the dephosphorylation and translocation of nuclear factor of activated T-cells (NF-AT), a nuclear component thought to initiate gene transcription for the formation of lymphokines (such as interleukin-2, gamma interferon). The net result is the inhibition of T-lymphocyte activation (i.e., immunosuppression).

Tacrolimus prolongs the survival of the host and transplanted graft in animal transplant models of liver, kidney, heart, bone marrow, small bowel and pancreas, lung and trachea, skin, cornea, and limb.

In animals, Tacrolimus has been demonstrated to suppress some humoral immunity and, to a greater extent, cell-mediated reactions such as allograft rejection, delayed type hypersensitivity, collagen-induced arthritis, experimental allergic encephalomyelitis, and graft versus host disease.

Tacrolimus is a calcineurin-inhibitor immunosuppressant indicated for the prophylaxis of organ rejection in kidney transplant patients in combination with other immunosuppressants

Usual Adult Dose for Organ Transplant- Rejection Prophylaxis

KIDNEY TRANSPLANT:

• In combination with azathioprine: Initial dose: 0.1 mg/kg orally every 12 hours. Initiate within 24 hours of surgery, but delay until renal function has recovered.
• In combination with mycophenolate mofetil (MMF)/interleukin-2 (IL-2) receptor antagonist: Initial dose: 0.05 mg/kg orally every 12 hours. Initiate within 24 hours of surgery, but delay until renal function has recovered.

LIVER TRANSPLANT:

• Initial dose: 0.05 to 0.075 mg/kg orally every 12 hours. Initiate no sooner than 6 hours after surgery.

HEART TRANSPLANT:

• Initial dose: 0.0375 mg/kg orally every 12 hours. Initiate no sooner than 6 hours after surgery

Usual Pediatric Dose for Organ Transplant- Rejection Reversal

LIVER TRANSPLANT:

• Initial dose: 0.075 to 0.1 mg/kg orally every 12 hours

Tacrolimus capsules are contraindicated in patients with a hypersensitivity to Tacrolimus. Tacrolimus injection is contraindicated in patients with a hypersensitivity to HCO-60 (polyoxyl 60 hydrogenated castor oil). Hypersensitivity symptoms reported include dyspnea, rash, pruritus, and acute respiratory distress syndrome

Overdose Effects

Limited overdosage experience is available. Acute overdosages of up to 30 times the intended dose have been reported. Almost all cases have been asymptomatic and all patients recovered with no sequelae. Acute overdosage was sometimes followed by adverse reactions (including tremors, abnormal renal function, hypertension, and peripheral edema); in one case of acute overdosage, transient urticaria and lethargy were observed. Based on the poor aqueous solubility and extensive erythrocyte and plasma protein binding, it is anticipated that Tacrolimus is not dialyzable to any significant extent; there is no experience with charcoal hemoperfusion. The oral use of activated charcoal has been reported in treating acute overdoses, but experience has not been sufficient to warrant recommending its use. General supportive measures and treatment of specific symptoms should be followed in all cases of overdosage.

In acute oral and IV toxicity studies, mortalities were seen at or above the following doses: in adult rats, 52 times the recommended human oral dose; in immature rats, 16 times the recommended oral dose; and in adult rats, 16 times the recommended human IV dose (all based on body surface area corrections).

Use in Special Populations

Pediatric Use: The safety and efficacy of Tacrolimus in pediatric kidney and heart transplant patients have not been established. Successful liver transplants have been performed in pediatric patients (ages up to 16 years) using Tacrolimus. Two randomized active-controlled trials of Tacrolimus in primary liver transplantation included 56 pediatric patients. Thirty-one patients were randomized to Tacrolimus-based and 25 to cyclosporine-based therapies. Additionally, a minimum of 122 pediatric patients were studied in an uncontrolled trial of Tacrolimus in living related donor liver transplantation. Pediatric patients generally required higher doses of Tacrolimus to maintain blood trough concentrations of Tacrolimus similar to adult patients.

Geriatric Use: Clinical trials of Tacrolimus did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

Use in Renal Impairment: The pharmacokinetics of Tacrolimus in patients with renal impairment was similar to that in healthy volunteers with normal renal function. However, consideration should be given to dosing Tacrolimus at the lower end of the therapeutic dosing range in patients who have received a liver or heart transplant and have pre-existing renal impairment. Further reductions in dose below the targeted range may be required

Use in Hepatic Impairment: The mean clearance of Tacrolimus was substantially lower in patients with severe hepatic impairment (mean Child-Pugh score: >10) compared to healthy volunteers with normal hepatic function. Close monitoring of Tacrolimus trough concentrations is warranted in patients with hepatic impairment.

The use of Tacrolimus in liver transplant recipients experiencing post-transplant hepatic impairment may be associated with increased risk of developing renal insufficiency related to high whole-blood trough concentrations of Tacrolimus. These patients should be monitored closely and dosage adjustments should be considered. Some evidence suggests that lower doses should be used in these patients

Pregnancy & Lactation

Pregnancy Category C. There are no adequate and well-controlled studies in pregnant women. Tacrolimus is transferred across the placenta. The use of Tacrolimus during pregnancy in humans has been associated with neonatal hyperkalemia and renal dysfunction. Tacrolimus given orally to pregnant rabbits at 0.5 to 4.3 times the clinical dose and pregnant rats at 0.8 to 6.9 times the clinical dose was associated with an increased incidence of fetal death in utero, fetal malformations (cardiovascular, skeletal, omphalocele, and gallbladder agenesis) and maternal toxicity. Tacrolimus should be used during pregnancy only if the potential benefit to the mother justifies the potential risk to the fetus.

Nursing Mothers: Tacrolimus is excreted in human milk. As the effect of chronic exposure to Tacrolimus in healthy infants is not established, patients maintained on Tacrolimus should discontinue nursing taking into consideration importance of drug to the mother.