Molecule

Drug Groups

withdrawn

Description

Etretinate is a medication used to treat severe psoriasis. It is a synthetic aromatic retinoid. The mechanism of action of etretinate is still incompletely understood although, like retinoic acid, it is thought to interfere with the terminal differentiation of keratinocytes. It is thought to bind to the retinoic acid receptors. Etretinate is also believed to enhance the binding of cAMP to the regulatory RI subunit of cAMP dependent protein kinases. It was removed from the United States market in 1998 and the Canadian market in 1996 as a psoriasis medication, due to the high risk of birth defects. Etretinate is now used to treat T-cell lymphomas. It also appears to inhibit NADH oxidase activity.

Indication

For the treatment of severe psoriasis in adults.

Pharmacology

The active metabolite responsible for etretinate's effects, acitretin, is a retinoid. Retinoids have a structure similar to vitamin A and are involved in the normal growth of skin cells. Acitretin works by inhibiting the excessive cell growth and keratinisation (process by which skin cells become thickened due to the deposition of a protein within them) seen in psoriasis. It therefore reduces the thickening of the skin, plaque formation and scaling.

Toxicity

Symptoms of overdose include headache and vertigo.

Affected Organisms

Biotransformation

Extensively metabolized, with significant first-pass metabolism to the pharmacologically active acid form. Subsequent metabolism results in the inactive 13-cis acid form, chain-shortened breakdown products, and conjugates that are ultimately excreted.

Absorption

Absorbed in the small intestine. Studies in normal volunteers indicate that the absorption of etretinate is greater in patients consuming whole milk or a high-fat diet than in patients in a fasting state.

Half Life

In one study, the apparent terminal half-life of etretinate after 6 months of therapy was approximately 120 days. In another study of 47 patients who had undergone chronic therapy with etretinate, 5 patients had detectable serum drug concentrations (0.5 to 12 ng/mL) 2.1 to 2.9 years after therapy was completed.

Protein Binding

More than 99% bound to plasma proteins, predominantly lipoproteins, whereas its active metabolite, acetretin (etretin), is predominantly bound to albumin.

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