- The effect of calcium channel blocking agents on the killing activity of human peritoneal polymorphonuclears (PMN) and monocytes was studied. The organisms used were Escherichia coli, Staphylococcus aureus and Candida albicans. The pharmacological concentration of verapamil (5 microM), nifedipine (10 microM) and diltiazem (10 microM) caused a similar inhibition of killing activity in both PMN and monocytes. The calcium channel blockers significantly reduced the in vitro killing of E. coli, S. aureus and C. albicans by PMN to about 47%, 30% and 20% respectively, compared with 81 +/- 6%, 65 +/- 5% and 40 +/- 4% in the controls. The killing of these organisms by monocytes was 60 +/- 6%, 42 +/- 7% and 35 +/- 5% respectively, as compared with 30%, 20% and 17% in the presence of these drugs. The bactericidal activity of the phagocytic cells from patients under treatment with calcium channel blockers was not affected and was found to be within the normal range, indicating that calcium channel blockers do not cause an irreversible impairment in PMN and monocyte killing activity. However, their potential inhibition of phagocytic cell activity should be taken into consideration during treatment.