Singapore Drugs Database

Indication

For use after allogenic organ transplant to reduce the activity of the patient's immune system and so the risk of organ rejection. It was first approved by the FDA in 1994 for use in liver transplantation, this has been extended to include kidney, heart, small bowel, pancreas, lung, trachea, skin, cornea, and limb transplants. It has also been used in a topical preparation in the treatment of severe atopic dermatitis.

Mechanism of Action

The mechanism of action of tacrolimus in atopic dermatitis is not known. While the following have been observed, the clinical significance of these observations in atopic dermatitis is not known. It has been demonstrated that tacrolimus inhibits T-lymphocyte activation by first binding 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 is inhibited. This prevents 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. Tacrolimus also inhibits the transcription for genes which encode IL-3, IL-4, IL-5, GM-CSF, and TNF-, all of which are involved in the early stages of T-cell activation. Additionally, tacrolimus has been shown to inhibit the release of pre-formed mediators from skin mast cells and basophils, and to downregulate the expression of FceRI on Langerhans cells.

Pharmacokinetics

Absorption

Absorption of tacrolimus from the gastrointestinal tract after oral administration is incomplete and variable. The absolute bioavailability in adult kidney transplant patients is 17±10%; in adults liver transplant patients is 22±6%; in healthy subjects is 18±5%. The absolute bioavailability in pediatric liver transplant patients was 31±24%. Tacrolimus maximum blood concentrations (Cmax) and area under the curve (AUC) appeared to increase in a dose-proportional fashion in 18 fasted healthy volunteers receiving a single oral dose of 3, 7, and 10 mg. When given without food, the rate and extent of absorption were the greatest. The time of the meal also affected bioavailability. When given immediately after a meal, mean Cmax was reduced 71%, and mean AUC was reduced 39%, relative to the fasted condition. When administered 1.5 hours following the meal, mean Cmax was reduced 63%, and mean AUC was reduced 39%, relative to the fasted condition.

Distribution

* 2.6 ± 2.1 L/kg [pediatric liver transplant patients] * 1.07 ± 0.20 L/kg [patients with renal impairment, 0.02 mg/kg/4 hr dose, IV] * 3.1 ± 1.6 L/kg [Mild Hepatic Impairment, 0.02 mg/kg/4 hr dose, IV] * 3.7 ± 4.7 L/kg [Mild Hepatic Impairment, 7.7 mg dose, PO] * 3.9 ± 1.0 L/kg [Severe hepatic impairment, 0.02 mg/kg/4 hr dose, IV] * 3.1 ± 3.4 L/kg [Severe hepatic impairment, 8 mg dose, PO]

Metabolism

Hepatic, extensive, primarily by CYP3A4. The major metabolite identified in incubations with human liver microsomes is 13-demethyl tacrolimus. In in vitro studies, a 31-demethyl metabolite has been reported to have the same activity as tacrolimus.

Elimination

Clearance

* 0.040 L/hr/kg [healthy subjects, IV] * 0.172 ± 0.088 L/hr/kg [healthy subjects, oral] * 0.083 L/hr/kg [adult kidney transplant patients, IV] * 0.053 L/hr/kg [adult liver transplant patients, IV] * 0.051 L/hr/kg [adult heart transplant patients, IV] * 0.138 ± 0.071 L/hr/kg [pediatric liver transplant patients] * 0.12 ± 0.04 (range 0.06-0.17) L/hr/kg [pediatric kidney transplant patients] * 0.038 ± 0.014 L/hr/kg [patients with renal impairment, 0.02 mg/kg/4 hr dose, IV] * 0.042 ± 0.02 L/hr/kg [Mild Hepatic Impairment, 0.02 mg/kg/4 hr dose, IV] * 0.034 ± 0.019 L/hr/kg [Mild Hepatic Impairment, 7.7 mg dose, PO] * 0.017 ± 0.013 L/hr/kg [Severe hepatic impairment, 0.02 mg/kg/4 hr dose, IV] * 0.016 ± 0.011 L/hr/kg [Severe hepatic impairment, 8 mg dose, PO]

Toxicity

Side effects can be severe and include blurred vision, liver and kidney problems (it is nephrotoxic), seizures, tremors, hypertension, hypomagnesemia, diabetes mellitus, hyperkalemia, itching, insomnia, confusion. LD₅₀=134-194 mg/kg (rat).

Active Ingredient/Synonyms

Anhydrous tacrolimus | Tacrolimus anhydrous | Tacrolimus, anhydrous | Tacrolimus |