Enhanced antibacterial effect of erythromycin in the presence of 3,5-dibenzoyl-1,4-dihydropyridines.

Fifteen 3,5-dibenzoyl-1,4-dihydropyridines (BzDHP, GB1-GB15) (nifedipine (NP) analogs) were tested on three different E. coli strains. The compounds had relatively high MIC values on these strains. In combination with erythromycin (Er), compounds (G1,3,4,6,7,10,12) reduced MIC values of Er. When the BzDHPs were tested on E. coli Gy-1/Apsen.Erres strain isolated from a clinical specimen, the reduction of MIC values were similar to the previous strains, but not identical. In the polyresistant clinically isolated E. coli Gy-2/Apres.Erres strain, the MIC values of Er were slightly reduced in the presence of GB1-GB7. Compound GB12 was the most effective in enhancing the activity of Er, and was selected for plasmid elimination studies. However, GB12 itself had no antiplasmid effect and did not alter the promethazine induced plasmid elimination.