Digitoxin elimination in healthy subjects taking ampicillin.

The present study was carried out to evaluate the changes in digitoxin kinetics during ampicillin administration. Subjects were informed of the nature of the study and the treatment was applied to those who gave their written consent. Six healthy volunteers received a single oral dose of 1.0 mg of digitoxin. Three days later, they were given orally ampicillin trihydrate, 500 mg four times daily, for five consecutive days. Blood samples were taken at 24, 36, 48, 60, 72, 96, 120, 144, 168 and 192 hours after digitoxin. Compliance with ampicillin regimen was verified by fluorimetric measurement of serum ampicillin. Concentrations of serum digitoxin were determined by radioimmunoassay. The mean digitoxin elimination half-life changed from 162.8 +/- 12.9 h before to 181.3 +/- 10.1 h (mean +/- s.e. mean) after ampicillin. These differences were not significant. No consistent evidence of a kinetic interaction between digitoxin and the broad-spectrum antibiotic ampicillin was found.