Two multipore-type sustained-release preparations (VC-SR-A and VC-SR-B) containing 500 mg of vitamin C were prepared, which were coated with mixtures of water-soluble polyethylene glycol and insoluble ethylcellulose. The preparations differed in the dissolution profile of vitamin C; the in vitro release rates being 7.3 %/h for VC-SR-A and 14.2 %/h for VC-SR-B. The bioavailability of vitamin C after the administration of a single dose was examined in six subjests (25-32 years) who had been saturated with vitamin C, and compared with an osmorelease-type sustained-release preparation (AcuSystem C) and a conventional immediate-release preparation (VC-IR) in a crossover trial. The mean T_<max> was 3 h for VC-IR, 6 h for VC-SR-B, 7 h for VC-SR-A and 8.5 h for AcuSystem C. Mean C_<max> (mg/100ml) were 0.28 for VC-SR-A, 0.40 for AcuSystem C, 0.48 for VC-SR-B and 0.74 for VC-IR. The mean AUC (mg.h/100 ml, 0-24 h) was 3.43 for VC-SR-A, 5.73 for AcuSystem C, 6.68 for VC-SR-B and 6.80 for VC-IR. The mean percentages of the dose excreted in the 24-h urine were 7.7 for VC-SR-A, 17.6 for AcuSystem, 23.4 for VC-SR-B and 39.1 for VC-IR. The results indicate that for VC-SR-B the rate of bioavailability is slower but prolonged and thus the extent of bioavailability is almost equal to that of VC-IR. Also, concerning retention of vitamin C in the body, VC-SR-B seems to be preferable to VC-IR.
