Oral isotretinoin (13-cis-retinoic acid) therapy in severe acne: drug and vitamin A concentrations in serum and skin.

The disposition of oral isotretinoin to the skin and the effects of the drug on the vitamin A levels in serum and skin were studied in 17 patients with nodulocystic acne. All patients received 0.5 mg/kg/day for 3 months and 8 patients continued treatment with 0.75 mg/kg/day for another 3 months. The parent drug, the major metabolite (4-oxo-isotretinoin), and 2 natural retinoids (retinol and dehydroretinol) were monitored in serum and biopsies of uninvolved skin, using adsorption high-pressure liquid chromatography. During the initial 3 months of treatment the mean isotretinoin level in the serum was 145 ng/ml and in the epidermis 73 ng/g. The corresponding values for 4-oxo-isotretinoin were 615 and 113 ng/g, respectively. Even at the highest dosage there was no progressive accumulation of isotretinoin in serum, epidermis, or subcutis. After discontinuation of therapy the drug disappeared from both serum and skin within 2-4 weeks. The serum transport of vitamin A, monitored by the concentrations of retinol, retinol-binding protein, and prealbumin (transthyretin), was not affected by the treatment. By contrast, the retinol level in the epidermis increased by an average of 53% (p less than 0.01) and the dehydroretinol level decreased by 79% (p less than 0.001) as a result of 3 months of treatment. Both changes were reversible. The results suggest that isotretinoin therapy interferes with the endogenous vitamin A metabolism in the skin.