Tacrolimus

Day 1: In the same class as ciclosporin A (superior to), #tacrolimus was found in Japan ©1984 from soil bacterium strep. tsukubaensis; the name is a combination of tsuku, macrolide and immunosuppressant. The first use was as an anti-rejection drug post-transplant, then later was formulated as a topical application for dermatological use.

Day 2: #tacrolimus is taken orally once daily for prevention of graft rejection or iv infusion for up to 1-week post-transplant pre-oral therapy; dose varies per organ/licensed neonatal, child, adult. Topical is licensed for atopic eczema; also an alternative to topical steroids eg use on the face. 0.03 or 0.1% ointment (short-term or intermittent long-term). Licensed from age 2 for atopic eczema only, but 0.03% if <16; Off-license adult-use includes 2nd line psoriasis face/flexures/genitals. Can use with emollients, but leave 2 hr window.

Day 3: #tacrolimus has moderate oral bioavailability, best fasted. Despite high RBC and protein binding, distribution is high. Liver CYP3A4 breakdown and bile/faecal elimination. T½ ~43 hr, but half-life is reduced post-transplant. Narrow therapeutic index with high variation in kinetics; systemic use needs therapeutic monitoring.