Clinical pharmacology of 3 generations of retinoids.

The bioavailability, plasma transport and tissue distribution of various retinoids are largely determined by their physicochemical properties; some are extremely lipidsoluble whereas others are relatively hydrophilic. Isotretinoin, a 1st generation retinoid, lacks the problematic affinity for fat. Etretinate, a 2nd generation aromatic retinoid, has been shown to accumulate in both fat tissues and in the adrenals. Etretin, the main free-acid metabolite of etretinate, is less lipophilic and is presently being tested as an alternative drug. Arotinoid ethyl ester, a 3rd generation aromatic retinoid which has as yet only undergone limited trials, is extremely potent making pharmacological evaluation difficult. The search for more potent retinoids has not so far resulted in a complete resolution of the efficacy and toxicity of the drugs.