Effect of calcium content of diet on absorption of diphenylhydantoin

The effect produced by changes in the calcium content of the diet on the plasma concentration of diphenylhydantoin was studied. In subjects on a high calcium intake, plasma diphenylhydantoin levels were significantly lowered, probalby resulting from both the formation of an insoluble calcium-drug complex and the direct effect of calcium on the intestinal membrane. A similar but less pronounced effect was observed when calcium-rich foods were excluded from the diet. These observations indicate the need for a balanced calcium diet during diphenylhydantoin treatment.