In vivo and in vitro availability of commercial vitamin C tablets.

In vitro release of vitamin C from commercial tablets of three different manufacturers was measured by the Levy beaker, a modified USP basket and Magnetic Basket techniques and this was correlated with urinary excretion of the drug from normal, healthy, human males of 23 to 25 years of age weighing 50-72 Kg. Results showed that there was dissolution variability between the different brands of vitamin C tablets as well as between the in vitro dissolution methods used. There was also an inverse correlation between the time of in vitro release and the percent vitamin C excreted at the end of 2 hours. However, at the end of 24 hours the most rapidly dissolving tablets in vitro indicated only 66 percent excretion of the vitamin C as compared with nearly 83 percent for the slow dissolving types. It is concluded that to determine the total drug from a particular formulation, only disintegration and/or dissolution is not a good measure for an unstable and relatively rapid dissolving substance such as vitamin C. It is further suggested that perhaps if unstable rapid-dissolving substances were made more slowly released by formulation, a greater quantity of the drug would be physiologically avaiable.