[Drug interaction between digoxin and bisacodyl].

Digoxin is one of the inotropic agents commonly used to improve cardiac performance in patients with congestive heart failure and to control ventricular response in atrial fibrillation and other supraventricular tachycardias. Bisacodyl (dulcolax), a stimulant laxative, is also commonly prescribed to prevent straining at stool or constipation in these patients. Therapeutic monitoring of digoxin is helpful in the evaluation of clinical response and intoxication of digoxin. For the convenience of serum level measurement, digoxin is usually administered at night before sleep to allow ample time for tissue distribution and then blood sampling the next morning. Concomitant use of these drugs may increase the likelihood of drug interaction. Eleven healthy volunteers, aged 22-26, were studied within 35 days accordingly in four phases. The serum digoxin concentration (SDC) in phase 2 (digoxin and bisacodyl together) showed a significant decrease as compared with phase 1 (digoxin alone) (0.58 +/- 0.03 vs. 0.66 +/- 0.03 ng/ml, M +/- SE, p less than 0.05). The percentage of SDC changes was down to -11.7 +/- 5.4%. Phase 4 (digoxin taken 2 hours before bisacodyl) showed an increase in SDC in comparison with phase 3 (digoxin alone) but was not statistically significant (0.65 +/- 0.03 vs. 0.62 +/- 0.03 ng/ml, M +/- SE, p greater than 0.05). The average frequency of diarrhea was 3.5 times in the first day of phase 2 and 2.7 times in the first day of phase 4. We conclude that in volunteers bisacodyl interacts with digoxin resulting in reduction of the SDC. Interference of the absorption is the most likely mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)