Tacrolimus
Tacrolimus (FK 506) is a potent macrolide immunosuppressant. In veterinary medicine, it is primarily used topically for immune-mediated dermatoses (such as perianal fistulas and atopic dermatitis) and ophthalmically for keratoconjunctivitis sicca (KCS). Systemic use is less common due to potential toxicity but may be utilized for severe immune-mediated diseases. **Clinical Pearl:** Tacrolimus is often effective in KCS cases that are refractory to cyclosporine.
Mecanismo: Binds to the intracellular protein **FKBP-12** (FK506 binding protein) → forms a complex that inhibits **calcineurin** (a calcium-dependent phosphatase) → prevents dephosphorylation of NF-AT (nuclear factor of activated T-cells) → inhibits transcription of **IL-2** and other cytokines → profound **T-lymphocyte inhibition**.
Vías de administración
Contraindicaciones
- Hypersensitivity to macrolides
- Active systemic infections
- Malignancy (for systemic use)
Efectos adversos
- Topical: local irritation, erythema, pruritus
- Ophthalmic: mild ocular irritation
- Systemic: GI upset (vomiting, diarrhea), nephrotoxicity, neurotoxicity, secondary infections
Interacciones farmacológicas
- Ketoconazole · Inhibits CYP3A metabolism, significantly increasing systemic tacrolimus levels · major
- Erythromycin · Inhibits metabolism, increasing tacrolimus levels · major
- Grapefruit juice · Increases systemic absorption and blood levels of tacrolimus · moderate
Monitorización
- Tear production (Schirmer Tear Test) for KCS
- Resolution of skin lesions
- Whole blood trough levels (if used orally)
- Renal and hepatic function (if used orally)
Sobredosis
Systemic overdose can lead to severe nephrotoxicity, neurotoxicity (tremors, seizures), and profound immunosuppression. Treatment is supportive and symptomatic. No specific antidote exists.
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