フエニトイン散剤の剤形変更による吸収性および実服薬量の変化の有無

抄録

In our hospital, the dosage form of phenytoin (DPH) was switched from hospital pharmacy-made 50% fine granules to commercial 10% powder. We surveyed the change in the serum DPH concentration in epileptic patients administered both DPH formulations, and examined the pharmaceutical differences associated with the disposition of DPH. About a 25% elevation in the steady-state serum DPH concentration was found after changing from 50% fine gfanules to 10% powder, thus indicating the increase in the amount of DPH absorbed from the gastrointestinal tract. In a dissolution test, the rate of DPH release of 10% powder was similar to that of 50% fine granules irrespective of the medium conditions. These results were strongly suggestive of a bioequivalence between 50% fine granule and 10% powder in clinical practice. In dispensing 50% fine granules, there was not only a significant weight reduction at the dividing and packing steps but also considerable adsorption by the package, although this phenomenon tended to be attenuated by mixing the drug with lactose as vehicle. On the other hand, the 10% powder was highly recovered probably owing to the enhanced fluidity. There was no change in the DPH content per weight before and after dispensing process in each formulation, thus showing that the degree of weight reduction was consistent with that of the DPH loss. Based on the relative weight recovery of the preparations during the dispensing process, it is presumed that the ingestible dose of DPH was increased by about 6% due to the formulation change. The significant increase in serum DPH concentration after formulation change is likely to be attributed to an improvement in the dispensation loss prior to administration, because DPH shows non-linear pharmacokinetics within the therapeutic range. We consider that monitoring the serum DPH concentration is required especially when the other dosage forms are prescribed.