BLP-1654

The minimal inhibitory concentrations (MIC) of carbenicillin, ticarcillin and BL-P 1654 for gram-negative udder pathogens were determined using the agar plate dilution method. The MIC of the drugs for 50% and 90% of the isolates examined ranged for Escherichia coli and Aerobacter spp. from 1.56 to 25 micrograms/ml, and for Klebsiella spp. and Pseudomonas spp. from 3.12 to 50 micrograms/ml. The Serratia spp. were relatively non-susceptible for the drugs studied (MIC greater than 50 micrograms/ml). Each drug was administered intravenously at 5 g and 15 g per cow to different groups of cows with normal and inflamed quarters of the udder. Distribution and elimination kinetic parameters calculated from serum drug level data were very similar to those of other beta-lactam antibiotics. Although drug concentrations in milk from inflamed quarters were higher than in milk from normal quarters, they were considerably below the MIC for the majority of gram-negative udder pathogens. The data suggest that parenteral treatment of gram-negative udder infections with carbenicillin, carfecillin, ticarcillin and BL-P 1654 at the dose levels used in the present study is unlikely to result in a bacteriological cure and would probably be clinically ineffective.

BL-P1654 is a new semisynthetic penicillin that possesses broad spectrum antimicrobial activity against many gram-positive and gram-negative bacteria, including Pseudomonas aeruginosa. An in vitro profile of BL-P1654 was established against strains of Staphylococcus aureus, Streptococcus pneumoniae, and Pseudomonas aeruginosa, three bacteria frequently associated with infections of the eye. The effectiveness of BL-P1654 in preventing the development of experimentally-induced keratitis by each of these bacteria was determined. The results of these experiments show BL-P1654 to be more effective than gentamicin and support further evaluation of the semisynthetic penicillin for ophthalmic indications.

The activity of azlocillin, a new semisynthetic penicillin, was determined against 582 clinical isolates of gram-negative bacilli and gram-positive cocci. Over 75% of the isolates of Pseudomonas aeruginosa were inhibited at a concentration of 12.5 mug or less per ml. Azlocillin is also active against indole-negative and -positive Proteus spp., inhibiting 98 and 71%, respectively, at a concentration of 12.5 mug or less per ml. Isolates of Klebsiella spp. and Enterobacter spp. showed less susceptibility than isolates of Escherichia coli and Serratia spp. Gram-positive cocci except penicillin G-resistant Staphylococcus aureus were susceptible to azlocillin. Azlocillin failed to inhibit the growth of gram-negative bacilli when large inocula were used. It was more active in alkaline pH, but the type of medium used had little effect on its activity. Azlocillin was more active than mezlocillin, ticarcillin, and carbenicillin and as active as BLP-1654 against isolates of P. aeruginosa. It was not as active as mezlocillin against the majority of the other gram-negative bacilli.