Description: Tacrolimus is a potent immunosuppressive drug. It is a macrolide that is used to reduce the activity of the body’s immune system. It comes in various forms, including oral capsules, extended-release capsules, and a topical ointment.

Indications:

• Primary Indication: Prophylaxis (prevention) of organ rejection in patients who have received an allogeneic (from another person) organ transplant, such as a kidney, liver, heart, or lung. It is typically used in combination with other immunosuppressive agents.
• Other Uses: Tacrolimus is also used as a topical ointment for the treatment of moderate to severe atopic dermatitis (eczema) in patients who have not responded to or cannot use other therapies. It is also sometimes used off-label for other autoimmune conditions.

Mechanism of Action: Tacrolimus works by inhibiting the function of T-cells, which are a type of white blood cell that plays a key role in the immune system’s response to foreign invaders, including transplanted organs.

1. Tacrolimus binds to an intracellular protein called FKBP-12.
2. This new complex of Tacrolimus and FKBP-12 then inhibits a protein phosphatase called calcineurin.
3. By inhibiting calcineurin, the drug prevents the dephosphorylation of a nuclear factor known as NF-AT (nuclear factor of activated T-cells).
4. This action prevents NF-AT from entering the nucleus and activating the transcription of genes that are critical for T-cell activation and proliferation, such as those that produce interleukin-2 (IL-2).
5. Ultimately, this process suppresses the T-cell-mediated immune response, preventing the body from rejecting the transplanted organ.