Antibacterial effect of meropenem and imipenem on Proteus mirabilis

Imipenem and meropenem: Comparison of in vitro activity, pharmacokinetics, clinical trials and adverse effects

OBJECTIVE

To compare and contrast imipenem and meropenem in terms of in vitro activity, pharmacokinetics, clinical efficacy and adverse effects.

DATA SELECTION

MEDLINE search from 1975 to 1997 and follow-up of references.

DATA EXTRACTION

Clinical trials comparing imipenem with meropenem, or either imipenem or meropenem with standard therapy in the treatment of serious infections were selected.

DATA SYNTHESIS

Imipenem, the first carbapenem, was first marketed in 1987; meropenem was introduced to the market in 1996. In general, imipenem is more active against Gram-positive cocci while meropenem is more active against Gram-negative bacilli. The agents display similar pharmacokinetics. Clinical studies in patients with serious infections (intra-abdominal infection, respiratory infection, septicemia, febrile neutropenia) report similar bacteriological and clinical cure rates with imipenem and meropenem. Meropenem is approved for the treatment of bacterial meningitis, whereas imipenem is not. Adverse effects are similar.

CONCLUSIONS

Current literature supports the use of imipenem at a dose of 500 mg every 6 h and meropenem at 1 g every 8 h for the treatment of severe infections. For the treatment of serious infections, imipenem (500 mg every 6 h or 2 g/day [$98/day]) is more economical than meropenem (1 g every 8 h or 3 g/day [$142/day]) based on acquisition cost.

Morphological changes induced by imipenem and meropenem at sub-inhibitory concentrations in Acinetobacter baumannii

Abstract Sub-inhibitory concentrations of imipenem and meropenem were evaluated for their ability to induce morphological changes with six strains of Acinetobacter baumannii isolated from patients with nosocomial pneumonia. Three strains were susceptible and three were resistant to carbapenems. The strains were grown in the presence of 0 (controls), 0.25x, 0.5x and 1x the MIC of both carbapenems for 4 h, and then examined after Gram's stain. Cells > or = 3 microm in size (spheroplasts) were considered to be altered. Both carbapenems induced significant numbers of spheroplasts compared to controls. Imipenem had more effect against susceptible strains, while meropenem had a greater effect against resistant strains.

In vitro activity of meropenem against ciprofloxacin-resistant enterobacteriaceae and Pseudomonas aeruginosa

The in-vitro susceptibilities of a total of 174 ciprofloxacin-resistant Enterobacteriaceae and Pseudomonas aeruginosa were determined. According to the BSAC and NCCLS breakpoints, meropenem, aztreonam, ceftibuten, ceftazidime, imipenem and cefotaxime were the most active (> 90%) antimicrobial agents tested against Enterobacteriaceae. Susceptibility of these strains to piperacillin/tazobactam, cefpodoxime and cefixime (84.96%) was higher than that to tobramycin, gentamicin and fosfomycin (50-75%). More than 90% of P. aeruginosa were susceptible to meropenem when both interpretative susceptibility breakpoint criteria were used. Piperacillin, piperacillin/tazobactam and ceftazidime were active against 50-75% of the same strains. Meropenem was the most active antimicrobial tested against all ciprofloxacin-resistant clinical isolates assayed.

Discrepancies in susceptibility test results for imipenem employing different in vitro test methods and DIN 58,940 breakpoints

During the first half of 1993, bacteria that were isolated from clinical materials and found to have intermediate susceptibility by an agar dilution breakpoint method were collected in a large service laboratory in Germany. All of these isolates were gram-negative bacteria. They were re-tested employing full-scale agar dilution, broth microdilution, E-test and agar diffusion procedures. The results obtained indicated that 76.9% of the isolates were actually susceptible upon re-testing with a reference agar dilution technique. The reason for the discrepant results remained largely unclear. There was a high correlation between agar dilution and E-test results while the agreement with broth microdilution and agar diffusion was less satisfactory. It is suggested that the breakpoint between susceptible and intermediate categories currently recommended by DIN 58,940 (standard set by Deutsches Institut für Normung e.V.) be raised to reduce erroneous interpretations of minimum inhibitory concentrations.