The effect of beta-adrenoceptor blockers on the absorption and excretion of chlorothiazide in man.

The effect of beta-adrenoceptor blockers on the absorption and elimination of the diuretic chlorothiazide was studied in healthy subjects. A week of pretreatment with either pindolol (10 mg twice daily) or propranolol (80 mg twice daily) resulted in significant reduction in 36 h mean cumulative urinary recovery of chlorothiazide in two groups of six subjects compared with a control (untreated) group. A week of pretreatment with atenolol (100 mg daily) did not significantly alter 36 h cumulative urinary excretion in another group of six subjects. None of the beta-blockers significantly changed chlorothiazide half-life. It is suggested that the non-selective (as opposed to the cardioselective) beta-blockers reduce chlorothiazide absorption by the mechanism(s) discussed.