Pharmacokinetics and metabolism of retinol administered at a chemopreventive level to normal subjects.

Thirteen subjects between the ages of 50 years and 70 years were administered a daily 25,000 IU dose of retinol for 9 months. Two subjects experienced mild skin dryness, headaches, and/or alopecia. There were no significant changes in serum chemistries. High performance liquid chromatography assays for plasma retinol revealed no evidence of drug accumulation; however, there was a significant increase in the plasma concentration-versus-time curve for retinyl palmitate concentrations between the first and subsequent sampling days (P = 0.009). The mean skin retinol and retinyl palmitate concentrations in 7 retinol-treated subjects (131.7 and 15.9 ng/g, respectively) were not significantly different from those observed in 13 age-matched controls (118.9 and 25.5 ng/gm, respectively).