Abstract
In vitro dissolution tests by the U.S.P. rotating basket method were carried out on double layer tablets of pyridoxine hydrochloride (PDH) or sodium riboflavin phosphate (SRP) held in a simple powder mixture (PM) and a spray-dried mixture (SDM) of hydroxy-propyl cellulose and lactose according to four different formulae. The dissolution properties of these tablets could be controlled by adjusting the amounts of drug combined into the PM layer and SDM layer and the volumes of the layers. In order to confirm the practical utility of the present dosage form, an absorption study was carried out in healthy male volunteers, using tablets containing PDH or SRP. The drug powder, mixed powder of the components of the tablet, or the same tablets used in the dissolution tests were administered orally and the urinary excretion of total VB6 or VB2 was determined. The maximum excretion time was delayed quite markedly in the slowest releasing PDH and SRP tablets. The long half-life observed after the administration of the slowest releasing tablet of SRP appeared to be due to the low value of maximum excretion and the contirruance of slow nonspecific drug absorption from the tablet, which retained about 60% of the initial drug content after passing the major absorption site. Plots of cumulative excretion amount against the amount dissolved in vitro at various periods indicated approximately constant absorption of VB6 over a wide region of the intestine and were consistent with specific transport of VB2 at the proximal region of the small intestine, as reported by Levy et al.
