Effect of clavulanic acid on the activity of ticarcillin against Pseudomonas aeruginosa

Mechanisms of multidrug resistance in Acinetobacter species and Pseudomonas aeruginosa

Acinetobacter species and Pseudomonas aeruginosa are noted for their intrinsic resistance to antibiotics and for their ability to acquire genes encoding resistance determinants. Foremost among the mechanisms of resistance in both of these pathogens is the production of beta -lactamases and aminoglycoside-modifying enzymes. Additionally, diminished expression of outer membrane proteins, mutations in topoisomerases, and up-regulation of efflux pumps play an important part in antibiotic resistance. Unfortunately, the accumulation of multiple mechanisms of resistance leads to the development of multiply resistant or even "panresistant" strains.

An update on community-acquired pneumonia in adults

Community-acquired pneumonia (CAP) is a leading cause of morbidity and mortality, despite effective therapies. Guidelines for CAP management vary widely in their approach. Resistance of S pneumoniae to penicillins and other antibiotics has prompted evaluation of the new fluoroquinolones.

Influence of beta-lactamase inhibitors on the potency of their companion drug with organisms possessing class I enzymes

The ability of beta-lactamase inhibitors to induce class I beta-lactamases in certain organisms in vitro suggests a potential for antagonism in vivo. Therefore, a study was designed to assess the ability of sulbactam and clavulanate to induce beta-lactamases in two strains each of Enterobacter cloacae, Citrobacter freundii, Serratia marcescens, and Pseudomonas aeruginosa both in vitro and in vivo. Induction in vitro was observed only with S. marcescens and P. aeruginosa and generally only when inhibitor concentrations greater than 2 micrograms/ml were examined. A mouse model of lethal infection, designed to detect in vivo antagonism arising from beta-lactamase induction, was used to determine what effect sulbactam and clavulanate would have on the 50% protective doses (PD50s) of cefoperazone and ticarcillin. Antagonism (a significant increase in the PD50) was observed in only 4 of 32 tests. Three of these involved antagonism of cefoperazone by clavulanate, and one involved antagonism of cefoperazone by sulbactam. In 6 of 32 tests, enhancement of efficacy (a significant decrease in PD50) was observed. In four of these, sulbactam enhanced cefoperazone; in one, sulbactam enhanced ticarcillin; and in one, clavulanate enhanced ticarcillin. Four of the six cases of enhancement occurred when the beta-lactamase inhibitor was given at the time of challenge. None of these positive or negative in vivo effects were predicted by in vitro tests. These data suggest that beta-lactamase inhibitors can influence the in vivo potency of their companion drug in both a beneficial and detrimental fashion against organisms with class I beta-lactamases and that these effects cannot be predicted from in vitro assays.

Antibacterial therapy in cystic fibrosis

Bacterial lung infections determine the prognosis for most cystic fibrosis patients. The antibacterial therapy is difficult because of the host-bacterium interaction and altered pharmacokinetics. The new insights in the working mechanisms of antibiotics that may lead to better treatment results have been discussed, and guidelines for treatment of lung infections in cystic fibrosis patients were given.

In vitro activity of combinations of beta-lactam antibiotics with beta-lactamase inhibitors against cephalosporinase-producing bacteria

Combinations of different beta-lactam antibiotics, including cefotaxime, with three beta-lactamase inhibitors were tested against cephalosporinase producing bacterial strains. The most significant antagonism was obtained with a combination of clavulanic acid and cefotaxime, while almost no antagonism was observed with sulbactam and tazobactam. In strains belonging to five different species there was a correlation between the levels of cephalosporinase produced after exposure to different concentrations of inhibitors and the MICs of cefotaxime combined with the same concentrations of inhibitors. It is concluded that there is little likelihood of antagonism between beta-lactam antibiotics and sulbactam or tazobactam.

Antibiotic pharmacokinetics in cystic fibrosis. Differences and clinical significance

Antibiotics are administered to cystic fibrosis patients for chronic endobronchial infection complicated by frequent exacerbations. Agents active against Staphylococcus aureus, Pseudomonas aeruginosa or both are administered. Serum antibiotic concentrations were measured in cystic fibrosis patients in an effort to optimise antibiotic dose and frequency. This led to the observation that cystic fibrosis subjects had (in general) a larger Vd and increased total body clearance of beta-lactams and aminoglycosides than non-cystic fibrosis subjects. The larger Vd is mainly due to the increased amount of lean body mass per kg bodyweight, although increased tissue binding may also account for part of this. The increased total body clearance of beta-lactams appears to be due to increased renal elimination, particularly tubular secretion. Decreased tubular reabsorption and increased non-renal clearance contribute to the increased total body clearance of metabolised beta-lactams and aminoglycosides. However, the lack of concomitant controls in many studies make these generalisations tentative. The result of the apparent cystic fibrosis-specific differences is lower peak serum antibiotic concentrations, a smaller AUC, and a shorter elimination half-life than non-cystic fibrosis subjects. Since sputum (and bronchial mucosal) concentration is dependent on the peak serum concentration (and AUC), cystic fibrosis subjects require larger doses of most antibiotics more frequently. Newer quinolones may be an exception. Studies comparing the efficacy and safety of larger and more frequent antibiotic doses to conventional therapy are not available. Although it appears logical to mimic serum antibiotic concentrations found in non-cystic fibrosis subjects, the lack of information on the ideal sputum concentration versus time curve should temper our enthusiasm for cystic fibrosis-specific dosage regimens.

Clinical significance of beta-lactamase induction and stable derepression in gram-negative rods

Most strains of enterobacteria and Pseudomonas aeruginosa produce chromosomally-determined Class I beta-lactamases. When synthesized copiously these enzymes cause resistance to almost all beta-lactams, except imipenem and, sometimes, carbenicillin and tenocillin. Elevated beta-lactamase production arises transiently, via induction, in Pseudomonas aeruginosa and Enterobacter, Citrobacter, Morganella, indole-positive Proteus and Serratia spp. when these organisms are exposed to beta-lactams. Permanent high-level enzyme production arises via mutation, in the stably-derepressed mutants of these species. These mutants arise spontaneously at high frequency (10(-5) -10(-8). Most early penicillins and first-generation cephalosporins are strong inducers of Class I enzymes at sub-inhibitory concentrations, as are cefoxitin and imipenem. Consequently their MICs reflect what lability these antibiotics have to inducibly-expressed beta-lactamase. Except with imipenem this lability usually is so great that the inducible enzyme causes clinical resistance. Although most other newer cephalosporins and ureidopenicillins are labile to the Class I enzymes they induce poorly below the MIC, and their lability is not reflected in resistance unless secondary inducers (e.g. cefoxitin or imipenem) are present. Although the weak inducer activity of these agents helps to maintain their activity against the inducible cells it renders the drugs highly selective for the pre-existing stably-derepressed mutants. Many cases have been reported where stably-derepressed mutants have overrun inducible populations of bacteria in patients undergoing therapy with beta-lactamase-labile weak inducers such as ureidopenicillin and third-generation cephalosporins.