Correlation of in vitro activities of cephalothin and ceftazidime with their efficacies in the treatment of Staphylococcus aureus endocarditis in rabbits

A systematic review of optimal pharmacokinetic/pharmacodynamic parameters for beta-lactam therapy in infective endocarditis

BACKGROUND

Beta-lactam antibiotics are the mainstay of therapy for most bacterial causes of infective endocarditis (IE). Traditionally considered as agents with a broad therapeutic index, there is increasing recognition that standard doses may be subtherapeutic or toxic in critically ill patients. Optimizing therapy for efficacy requires a defined pharmacokinetic (PK)/pharmacodynamic (PD) target associated with clinical and microbiological cure.

OBJECTIVES

To elucidate the factors that influence beta-lactam PK and PD variability in IE and to examine optimal PK/PD target parameters for therapy.

METHODS

The review was conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Clinical and laboratory in vivo animal or human studies examining PK and/or PD of beta-lactam antibiotics in IE were eligible. Ovid MEDLINE, Embase and Cochrane Central Registry were searched using defined terms. The Office of Health Assessment and Translation (OHAT) tool was used for assessing risk of bias.

RESULTS

From 2677 abstracts, 62 articles were selected for review and synthesis, comprising: 45 animal studies investigating the broad categories of beta-lactam diffusion into vegetations, PK/PD determinants of outcome, mode of antibiotic delivery and synergistic impact of agents; and 17 human studies totalling 347 participants. Findings supported the importance of time-dependent killing for beta-lactams but heterogeneous data limited the determination of an optimal PK/PD target for IE treatment.

CONCLUSION

Beta-lactam PK and PD in endocarditis are variable and specific to the particular antibiotic-organism combination. Time-dependent killing is important, consistent with non-endocarditis studies, but there is little agreement on optimal drug exposure. Clinical studies examining PK/PD targets in endocarditis are required to further inform drug selection and dosing.

Relative efficacies of broad-spectrum cephalosporins for treatment of methicillin-susceptible Staphylococcus aureus experimental infective endocarditis

The effects of treatment with broad-spectrum parenterally administered cephalosporins and cefuroxime, cefazolin, or nafcillin were compared in an experimental model of Staphylococcus aureus infective endocarditis, and the results in vivo were compared with the activities of the study drugs in vitro. After 3 days of treatment, all antimicrobial agents tested were more effective than no treatment in reducing the number of surviving bacteria in cardiac valve vegetations. Nafcillin was the most effective agent studied and was significantly more active than was ceftizoxime, ceftriaxone, cefotaxime, cefoperazone, cefuroxime, or cefazolin (P < or = 0.05). Cefpirome and ceftazidime were the most effective broad-spectrum cephalosporins. The outcome of treatment with cefpirome or ceftazidime was similar to that of treatment with nafcillin and significantly better than that of treatment with ceftizoxime or cefotaxime (P < or = 0.05). Treatment outcome correlated closely with the MICs of the antimicrobial agents for the study strain with the exception of ceftazidime, which was significantly more active in vivo in comparison with other agents than predicted by its MIC (P < or = 0.0003). When ceftazidime was excluded as an outlier, treatment outcome correlated with the MICs of the remaining study drugs (Spearman's correlation coefficient, 0.95; P < or = 0.0004), as well as with the estimated percentage of time during which the concentration of total drug (correlation coefficient, -0.85; P < or = 0.007) or free drug (correlation coefficient, -0.90; P < or = 0.003) exceeded the MIC. A consideration of total or free drug concentrations in relation to MICs did not significantly improve the correlation with outcome observed with the MICs alone.

A morphological study of the effect of treatment with the antibiotic ceftazidime on experimental staphylococcal endocarditis and aortitis

The morphological effects of antibiotic therapy with either single or repeated (8 hourly) injections of ceftazidime were examined in rabbits with experimentally induced staphylococcal endocarditis and aortitis. At 3 h after initiating treatment, many of the bacteria, irrespective of the location of the colony, showed evidence of abnormal ultrastructural changes of the cytoplasm and/or cell wall. By 8 h many degenerate lysed bacteria were present. By 24 h, in rabbits which received a single injection, bacterial colonies contained many normal and dividing bacteria. In comparison, bacterial colonies at 24 h in rabbits receiving repeated injections consisted of large masses of lysed bacteria with only a few viable appearing thick-walled 'persistent' cells. At 48 and 72 h, no viable appearing bacteria were observed although they could be isolated by culture methods. Treatment was associated with an increased inflammatory cell response at the surface of the vegetation and within the vasculature. In the later stages there was evidence of healing with endothelialization of the lesions. It would appear, therefore, that ceftazidime penetrates efficiently into the vegetations with only a short transitory phase at sub-bactericidal concentrations. The few 'persistent' bacteria appear to be protected from the host defences by the surrounding thrombus which prevents their eradication.

Cephalosporins in cutaneous infections. A prospective comparison of two dosage regimens of ceftazidime for therapy of skin and skin structure infections

The safety and efficacy of ceftazidime administered as 0.5 g every 8 hours (q8h) or 1.0 g q8h for at least 5 days were compared in 197 patients and found to be effective in the treatment of cellulitis, abscesses, skin ulcers, and wound infections. Staphylococcus aureus was the predominant pathogen in both treatment groups with approximately half of the isolates from each treatment group being gram-positive. Pseudomonas aeruginosa was the most common gram-negative isolate. P. aeruginosa, Proteus mirabilis, and Escherichia coli each comprised 5-12% of the isolates from each treatment group. Clinical cure or improvement was achieved in 98.7% of the patients in each treatment group. Concurrently with clinically successful treatment, a high rate of bacteriologic eradication without superinfection was achieved with the 0.5-g regimen (84% of all isolates) and the 1.0-g regimen (92%).

Ceftazidime versus tobramycin-ticarcillin in the treatment of pneumonia and bacteremia

A prospective, randomized study was undertaken to compare the efficacy and safety of ceftazidime with those of a combination of ticarcillin and tobramycin in the treatment of 40 nonneutropenic patients with pneumonia or bacteremia. Altogether, 93% of the patients receiving ceftazidime for pneumonia were cured, and 87% of those with bacteremia responded favorably. Of the subjects who were treated with ticarcillin and tobramycin ceftazidime developed significant superinfection, and one individual treated with the aminoglycoside and carboxypenicillin developed reversible azotemia. Ceftazidime appears to be as efficacious as the ticarcillin-tobramycin combination and is probably safer with regard to oto-and nephrotoxicity; however, superinfections did occur more frequently in the group treated with ceftazidime.

Ceftazidime. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Ceftazidime is a new 'third generation' cephalosporin administered intravenously or intramuscularly. Similarly to other third generation cephalosporins it has a broad spectrum of in vitro activity against Gram-positive and Gram-negative aerobic bacteria, is particularly active against Enterobacteriaceae (including beta-lactamase-positive strains) and is resistant to hydrolysis by most beta-lactamases. Importantly, in vitro ceftazidime is presently the most active cephalosporin available against Pseudomonas aeruginosa, but it is less active against Staphylococcus aureus than first and second generation cephalosporins. Only larger comparative trials are likely to discern any statistically significant differences in clinical efficacy which may exist between ceftazidime and other antibiotics, but ceftazidime appears to be similar in efficacy to 'standard' comparative drugs in lower respiratory tract infections and complicated and/or chronic urinary tract infections among debilitated or hospitalised patients. Thus, in patients having Gram-negative infections at these sites and in whom the potential toxicity of the aminoglycosides is a concern, ceftazidime may be a valuable alternative in that it apparently lacks serious side effects and does not require routine drug plasma concentration monitoring. In fibrocystic patients having acute respiratory tract infections, ceftazidime is highly effective at both reducing symptoms of infection and temporarily reducing the sputum counts of Pseudomonas species. However, in these patients resistance to ceftazidime may develop, as seen with other beta-lactam antibiotics. In the treatment of fever of unknown origin or documented infections in immunocompromised adults and children, ceftazidime appears to be similar in efficacy to various 2- or 3-drug combinations. Nevertheless, the coadministration of an antibiotic having greater efficacy against Gram-positive bacteria should be considered in immunocompromised patients. Results from a small number of comparative trials suggest that ceftazidime may be as effective as the aminoglycosides in intra-abdominal, obstetric and gynaecological, and skin and soft tissue infections. However, further clinical experience, particularly a few well designed comparative studies, is needed to clarify the comparative efficacy in these conditions as well as in septicaemia/bacteraemia, meningitis, and bone and joint infections.