Short answer: Tazarotene has a half-life of about 18 hours (tazarotenic acid, after use on the skin). People vary, so treat these as estimates.
Tazarotene is a prescription retinoid applied to the skin. The skin turns it into its active form, tazarotenic acid, which binds retinoic acid receptors. It is sold as Tazorac cream and gel for plaque psoriasis and acne, and as Arazlo lotion for acne.
Also known as: Tazorac, Arazlo, tazarotenic acid.
Tazorac cream and gel come in 0.05% and 0.1% (0.5 mg and 1 mg of tazarotene per gram); the gel comes in 30 g and 100 g tubes. Arazlo lotion is 0.045%.
The Tazorac labels approve the 0.05% and 0.1% cream for plaque psoriasis and the 0.1% cream for acne; the gel is approved for plaque psoriasis covering up to 20% of the body and, at 0.1%, for mild to moderate acne on the face. Arazlo 0.045% lotion is approved for acne from age 9. The label directions are a thin film (2 mg per square centimeter) once a day in the evening, only on the affected skin. For psoriasis the labels recommend starting at 0.05% and moving to 0.1% if tolerated, with any moisturizer applied at least an hour before.
Pregnancy: tazarotene can harm a fetus and is contraindicated in pregnancy. The labels call for a negative pregnancy test within 2 weeks before starting, starting during a menstrual period, and effective birth control during treatment; it is stopped as soon as pregnancy is recognized. The labels also warn about sun sensitivity, including with other drugs that increase it (such as thiazides, tetracyclines, fluoroquinolones, phenothiazines and sulfonamides).
In the cream trials, itching, redness and burning were the most common side effects in psoriasis (10% to 23% of people), and peeling, dry skin, redness and burning in acne (10% to 30%). The 0.1% cream was more irritating than the 0.05% cream.
The Tazorac cream label says little tazarotene itself reaches the blood; it is turned into tazarotenic acid, which has a half-life of about 18 hours after use on normal, acne or psoriatic skin. In 5 psoriasis patients using the 0.1% cream once a day for 2 weeks, blood levels peaked about 8 hours after the last dose. How much reaches the blood depends on how much skin is treated.
Numbers shown are taken from the source above. Half-life varies from person to person.
How Dose Track handles peptides · Reconstitution calculator · Half-life calculator