Negligible systemic absorption of topical isotretinoin cream: implications for teratogenicity.

The objective of the study was to assess the extent of systemic exposure of retinoic acid metabolites after excessive application of 0.1% isotretinoin cream in patients with photodamaged skin. This was a single-center, open-label, noncomparative, multiple-dose study of isotretinoin cream. Eighteen female patients with photodamaged skin received a 10 g topical application of isotretinoin cream once daily to a surface area of approximately 2,300 cm2 for 42 days. The patients were not allowed to have high vitamin A-containing foods, vitamin A supplements, or concomitant medications during the entire study period. Plasma levels of four retinoic acids (isotretinoin, tretinoin, 4-oxo-isotretinoin, and 4-oxo-tretinoin) were evaluated after 42 days of isotretinoin application and compared with baseline (pretreatment) levels. The mean area under the curve (AUC) in plasma increased by 48% (+/-SE 9.2) and 77% (+/-13) from the 24-hour pretreatment baseline level for isotretinoin and 4-oxo-isotretinoin, respectively, after treatment with excessive amounts of isotretinoin cream, suggesting systemic absorption of isotretinoin cream. This increase in systemic exposure of retinoic acids was less than that reported earlier after the U.S. recommended daily allowance of 5,000 i.u. of vitamin A supplementation (isotretinoin 141 +/- 19% and 4-oxo-isotretinoin 171 +/- 27%). The minimal systemic availability of isotretinoin cream compared with the U.S. recommended daily allowance for vitamin A supplements provides reasonable evidence for lack of its potential teratogenic risk.