Percutaneous absorption, excretion and metabolism of all-trans-retinoyl beta-glucuronide and of all-trans-retinoic acid in the rat.

The purpose of these studies was to compare directly the percutaneous absorption,excretion and metabolism of all-trans-retinoyl beta-glucuronide (RAG), a nontoxic retinoid, with all-trans-retinoic acid (RA) in the rat. Previously, it was demonstrated that topical treatment of human acne with either RAG or RA in cream resulted in a significant reduction of lesions. Whereas 0.1% RA showed adverse effects, concentrations of RAG up to 2.4% did not cause any adverse reactions. In the present studies, radiolabeled RAG or RA, dispersed in a water-based cream, was applied to the shaved dorsal skin of vitamin A-sufficient rats. Both RAG and RA were absorbed from the skin in a similar way. In both cases, radioactivity peaked in the plasma within 2-4 h and within the liver at 4-12 h. During a 7-day period, the overall excretion of radioactivity derived from RA and RAG in the feces and urine were similar, e.g. 17 and 12%, respectively. it is concluded that: (1) the transport, metabolism and excretion of topically applied radioactive RA and RAG are similar, although not identical, in the rat and (2) the toxic skin manifestations induced by RA but not by RAG cannot be attributed to major differences in their overall absorption, metabolism and excretion.