Pharmacokinetic modelling of the plasma concentration-time profile of the vitamin retinyl palmitate following intramuscular administration

Seven healthy male volunteers (21–24 y) received by the ventro-gluteal route a single dose of 100 000 I.U. of the vitamin retinyl palmitate (RP) in a water-miscible preparation (W) and 5 weeks later the same dose in an oily solution (S). After administration of W median (range) peak plasma concentrations of 5.6(4.4–8.7). 103 μg 1-−1 were reached after 12 h and high levels persisted for another 50 h. At 144 h levels were still, by a factor 3, higher than baseline. Plasma levels of RP after S remained close to baseline (20–50 μg.1−1) suggesting negligibly low bioavailability. The plasma level profile of RP after W could well be described by use of a one-compartment model with Weibull-type absorption and Michaelis-Menten elimination. The median (range) absolute bioavailability (estimates of lower limits) was 42 (32–52) per cent.