increased metabolism to dihydrodigoxin after intake of a microencapsulated formulation of digoxin a capsule preparation containing small entericcoated granules of digoxin was developed to prevent acid hydrolysis of the drug in the stomach and to diminish the variation in plasma glycoside concentration during the intervals between doses the absorption and metabolism of tritiated digoxin after a single oral loading dose of this formulation formulation c were compared to those after ingestion of a digoxin solution formulation s by 8 healthy men drug concentrations were measured by radioimmunoassay ria and liquid chromatography lc the percentage of the digoxin dose excreted in the urine during 72 h as measured by ria was significantly lower after the capsule 205 20 vs 362 30 after s mean sem but total urinary radioactivity after the two treatments was similar c 353 52 and s 412 26 p greater than 005 the discrepancy was mainly due to significantly greater excretion of dihydrodigoxin after the capsule m 128 range 0286 of the dose than after the digoxin solution m 54 range 0145 dihydrodigoxin was not measured by the ria the recovery of hydrolysis metabolites lc was greater during the first 24 h after s 23 06 vs 09 03 after c p less than 005 the peak plasma concentration of digoxin ria was significantly reduced and delayed after intake of c 25 04 nmoll at 38 03 h vs 83 08 nmoll at 09 01 h after s and so was the shortening of electromechanical systole at 15 h 25 h and 3 habstract truncated at 250 words