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Pirbenicillin: comparison with carbenicillin and BL-P1654, alone and with gentamicin, against Pseudomonas aeruginosa
Abstract:
Minimum inhibitory concentrations (MIC) of pirbenicillin against 135 clinical isolates of Pseudomonas aeruginosa were one-fourth of those required for carbenicillin but two times higher than those for BL-P1654. Increasing the inoculum size produced an adverse effect on the bactericidal activity for all three antibiotics. This was more apparent for pirbenicillin than for carbenicillin, but less than the effect on BL-P1654. When concentrations of antibiotics likely to be achieved clinically were used, gentamicin increased the inhibitory and bactericidal effects of all three semisynthetic penicillins for the majority of isolates. Strains highly resistant to the aminoglycoside antibiotic, however, were inhibited no more by the penicillin-gentamicin combinations than by the most effective of the antibiotics alone.
Insights
Pirbenicillin shows promising activity against Pseudomonas aeruginosa, but its effectiveness is reduced by higher bacterial loads. Combining pirbenicillin with gentamicin enhances its antibacterial effects, except in highly resistant strains.
Area of Science:
- Microbiology
- Pharmacology
- Infectious Diseases
Background:
- Pseudomonas aeruginosa is a significant opportunistic pathogen.
- The emergence of antibiotic resistance necessitates the development of new therapeutic strategies.
- Semisynthetic penicillins and aminoglycosides are important classes of antibiotics used to treat bacterial infections.
Purpose of the Study:
- To evaluate the in vitro activity of pirbenicillin against clinical isolates of Pseudomonas aeruginosa.
- To compare pirbenicillin with carbenicillin and BL-P1654.
- To assess the impact of inoculum size on antibiotic activity.
- To investigate the synergistic effects of combining pirbenicillin with gentamicin.
Main Methods:
- Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assays were performed.
- 135 clinical isolates of Pseudomonas aeruginosa were tested.
- Antibiotic susceptibility testing was conducted with varying inoculum sizes.
- Checkerboard assays were used to evaluate drug combinations.
Main Results:
- Pirbenicillin exhibited lower MICs than carbenicillin but higher MICs than BL-P1654.
- Increased inoculum size adversely affected bactericidal activity, more so for pirbenicillin and BL-P1654 than carbenicillin.
- Gentamicin enhanced the inhibitory and bactericidal effects of pirbenicillin, carbenicillin, and BL-P1654 in most isolates.
- Combinations were less effective in strains highly resistant to gentamicin.
Conclusions:
- Pirbenicillin demonstrates significant in vitro activity against Pseudomonas aeruginosa.
- The efficacy of pirbenicillin is influenced by bacterial inoculum size.
- Combination therapy with gentamicin can potentiate the activity of pirbenicillin, offering a potential strategy for treating Pseudomonas aeruginosa infections.
- Treatment failure may occur in patients with strains exhibiting high-level gentamicin resistance.