Comparative in vitro evaluation of BL-P1654 and carbenicillin against Pseudomonas

Prior investigators have reported a broad gram-negative spectrum and a marked anti-Pseudomonas activity in vitro with BL-P1654, 6-[R-alpha-(guanylureido)phenylacetamido]-penicillanic acid. An in vitro comparison of BL-P1654 to carbenicillin was performed against 84 strains of Pseudomonas and 39 strains of Enterobacteriaceae. Mean minimal inhibitory concentrations in Mueller-Hinton broth of BL-P1654 and carbenicillin were 12.5 and 100 mug/ml, respectively. Bactericidal studies with representative strains of Pseudomonas showed a consistent lack of bactericidal activity with BL-P1654. Mean bactericidal concentrations of BL-P1654 and carbenicillin were >/=200 and 100 mug/ml, respectively. The lack of bactericidal activity of BL-P1654 was further substantiated with the "killing curve" technique. Based on these data, BL-P1654 can not be considered a substitute for carbenicillin as the penicillin analogue of choice for Pseudomonas infections.