High dose phenoxymethylpenicillin for preventing endocarditis.

Single oral doses of phenoxymethylpenicillin were administered to 12 healthy volunteers, and their serum, saliva, and urine phenoxymethylpenicillin concentrations were determined. At all dose levels (0.4, 1, 2 and 3 g) phenoxymethylpenicillin was rapidly absorbed usually giving peak serum concentrations after 0.75 h. The relationship between mean peak serum concentration and dose was nonlinear (p less than 0.001); between area under serum concentration vs. time curve (AUC) and dose, it did not deviate from linearity (NS). Very low penicillin concentrations were obtained in saliva and the changes in the normal microflora were minor. The urinary excretion during the 10 h period after drug administration was 37-43 % of the given doses. After the 3 g doses, 3 volunteers had loose stools.