Comparative in vitro activities of N-formimidoyl thienamycin and moxalactam against nonfermentative aerobic gram-negative rods

In vitro activities of quinolones, beta-lactams, tobramycin, and trimethoprim-sulfamethoxazole against nonfermentative gram-negative bacilli

From 1991 to 1995, 8,975 nonfermentative gram-negative bacilli were isolated from patients at The Ohio State University Medical Center: 71% Pseudomonas aeruginosa, 14% Stenotrophomonas maltophilia, 7.6% Acinetobacter baumannii, and < 2% each of 25 other species. The MICs of trovafloxacin (CP-99,219), ciprofloxacin, ofloxacin, ampicillin-sulbactam, piperacillin, piperacillin-tazobactam, ceftazidime, cefoperazone, ceftriaxone, imipenem, tobramycin, and trimethoprim-sulfamethoxazole (TMP-SMZ) were determined for 308 isolates, representing 13 species, by a standardized broth microdilution method. The activities of all drugs were species dependent. The fluoroquinolones had inconsistent activity against most species, although several relatively uncommon nonfermenters were consistently susceptible or resistant. Trovafloxacin was considerably more active than ciprofloxacin and ofloxacin against S. maltophilia, A. baumannii, and several less common species. Among the beta-lactams, relative activities varied considerably; overall, imipenem had the broadest spectrum of activity but was inactive against S. maltophilia and Burkholderia cepacia isolates. Tobramycin and TMP-SMZ had stereotypic spectra of activity. Tobramycin was active against most species except S. maltophilia, Alcaligenes xylosoxidans subsp. xylosoxidans, Burkholderia spp., and Weeksella virosa. TMP-SMZ was active against most species except P. aeruginosa and Pseudomonas fluorescens-putida. A review of laboratory records indicated few changes in susceptibility patterns from 1991 to 1995; the only clear trend was toward increasing P. aeruginosa resistance to all classes of drugs.

Penetration of imipenem into human aqueous and vitreous humor

Twenty-five patients about to undergo cataract surgery and ten patients about to undergo vitrectomy received a 1-g intravenous dose of imipenem before surgery. Specimens of aqueous or vitreous humor were then obtained and assayed for antibiotic content with a microbiologic disk agar technique. A mean peak aqueous humor level of 2.99 micrograms/ml was found at approximately two hours after administration, and a mean vitreous level of 2.53 micrograms/ml was found from two hours to three hours 15 minutes after administration. These concentrations were well above the minimum inhibitory concentration of imipenem for 90% (MIC90) of Staphylococcus epidermidis, S. aureus, and the Enterobacteriaceae commonly involved in bacterial endophthalmitis.

Imipenem/cilastatin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic efficacy

Imipenem is the first available semisynthetic thienamycin and is administered intravenously in combination with cilastatin, a renal dipeptidase inhibitor that increases urinary excretion of active drug. In vitro studies have demonstrated that imipenem has an extremely wide spectrum of antibacterial activity against Gram-negative and Gram-positive aerobic and anaerobic bacteria, even against many multiresistant strains of bacteria. It is very potent against species which elaborate beta-lactamases. Imipenem in combination with equal doses of cilastatin has been shown to be generally well tolerated and an effective antimicrobial for the treatment of infections of various body systems. It is likely to be most valuable as empirical treatment of mixed aerobic and anaerobic infections, bacteraemia in non-neutropenic patients and serious hospital-acquired infections.

[Calculated initial chemotherapy in mechanically-ventilated postoperative patients with peritonitis, sepsis and pneumonia]

Calculated chemotherapy is based on the knowledge of the typical bacterial agents of a particular infection. From January 1983 to August 1985 bacteriological findings from surgical patients with peritonitis, septicemia or pneumonia treated in an intensive care unit were analysed. The study concentrated on those findings only which differed from previous bacteriological investigations. During the first three days 53 patients on assisted ventilation suffering from peritonitis exhibited mainly enterobacteria in their peritoneal secretions. At day 10 or later we also found bacteria from the pseudomonas group. At that time the bacterial spectrum of bronchial secretions was comparable to that of the peritoneal secretions of the same patient. After day 10, the bacterial spectrum was similar in 36 ventilated patients without peritonitis, in 56 patients suffering from post-operative pneumonia and in peritonitis patients. According to our findings, calculated chemotherapy may be based on the fact that patients with peritonitis who cannot be cured within a few days have a bacterial flora comparable to that of patients with septicemia or pneumonia. Patients with severe infections following surgery, such as potentially fatal pneumonia, generalised peritonitis or septicemia were treated with imipenem/cilastatin, according to the above definitions of calculated chemotherapy. 37 of 46 patients treated between May and December 1985, were clinically cured. Microorganisms persisted in five clinically cured patients. Development of resistance to imipenem was observed in one case. In one case treatment had to be stopped because of an allergic skin reaction. Monotherapy of peritonitis by imipenem/cilastatin appeared more satisfactory than treatment with combinations of other antibiotics.

In vitro activities of enoxacin, ticarcillin plus clavulanic acid, aztreonam, piperacillin, and imipenem and comparison with commonly used antimicrobial agents

A total of 745 gram-negative and 313 gram-positive clinical isolates were tested against enoxacin, ticarcillin plus clavulanic acid, aztreonam, imipenem, and piperacillin and compared with commonly used antimicrobial agents. Ticarcillin plus clavulanic acid, imipenem, and piperacillin were active against Pseudomonas aeruginosa and Acinetobacter spp. and most Pseudomonas spp. Aztreonam was active against members of the family Enterobacteriaceae but was less effective against the nonfermenters. Enoxacin was active against the Enterobacteriaceae, P. aeruginosa, the staphylococci, and most Acinetobacter spp. but was less active against Pseudomonas spp. and streptococci. Imipenem was very active against all gram-positive and -negative organisms tested except for Pseudomonas maltophilia.

Pathogenesis and treatment of endocarditis

The rabbit model has been invaluable for in vivo studies in the pathogenesis and treatment of bacterial endocarditis. Both of the features of the mature bacterial vegetations in this rabbit model, i.e., absence of phagocytosis and decreased metabolic activity, provide evidence to support the concept that a rapidly bactericidal antimicrobial agent provides the optimal approach to the successful treatment of endocarditis. Imipenem, a carbapenem with a very broad spectrum of in vitro activity, has been shown to be rapidly bactericidal in animals and highly effective in the treatment of experimental bacterial endocarditis. In addition, twenty-six patients with endocarditis, caused largely by Staphylococcus aureus, have been successfully treated with imipenem/cilastatin.

Review of the in vitro spectrum of activity of imipenem

Imipenem (N-formimidoyl thienamycin, MK0787), a new carbapenem was found to have the widest antimicrobial activity of currently available beta-lactam drugs. Enterobacteriaceae had minimal inhibitory concentrations of imipenem of 8.0 micrograms/ml or less for 99.8 percent of clinical isolates. Only rare strains of Enterobacter species and Proteus mirabilis have higher imipenem minimal inhibitory concentration results. Hemophilus and Neisseria species were inhibited, but minimal inhibitory concentrations of imipenem were higher than those reported for third-generation cephalosporins. Only Pseudomonas maltophilia and Pseudomonas cepacia strains were imipenem resistant (MIC50 greater than 32 micrograms/ml) among the commonly isolated non-enteric gram-negative bacilli. All anaerobes were found susceptible to imipenem with the exception of some strains of Clostridium difficile. Staphylococcus species and non-enterococcal streptococci were very susceptible to imipenem. Streptococcus faecalis had higher minimal inhibitory concentrations of imipenem (MIC90 3.1 micrograms/ml) and S. faecium strains were frankly resistant. Methicillin-resistant S. aureus isolates had a MIC90 of 27.2 micrograms imipenem/ml. Imipenem was generally bactericidal except for marked minimal inhibitory and minimal bactericidal concentration differences with enterococci, Listeria, methicillin-resistant staphylococci, and some P. aeruginosa strains. The minimal inhibitory and minimal bactericidal concentrations of imipenem were not significantly influenced by organism inoculum size, probably because of its beta-lactamase stability to nearly all commonly encountered bacterial enzymes. Imipenem was found to be an excellent inhibitor of beta-lactamases and a potent enzyme inducer. The induction characteristic seems responsible for the antagonistic interactions of imipenem with some enzyme-labile beta-lactams in combination. Imipenem had limited stability in some in vitro susceptibility test systems. The 10 micrograms disk test or dry-form broth micro-dilution systems were preferred, applying the interpretive criteria from the National Committee for Clinical Laboratory Standards (M2-A3). Imipenem-resistant strains were rarely found in clinical practice and bacteria resistant to newer beta-lactams and aminoglycosides were generally very susceptible to this new carbapenem.

In vitro activity of imipenem--a review

A review is given of the microbiological properties of imipenem, a new carbapenem antibiotic with an exceptionally broad spectrum of antibacterial activity. An evaluation of results of numerous in vitro studies reveals that imipenem effectively inhibited growth of 53 of 55 bacterial species, the mean MIC90 being less than 8 mg/l. The MIC90 for cocci, with the exception of Staphylococcus epidermidis, is in the range of 0.01-3.1 mg/l. The MIC90 for all Enterobacteriaceae is equal to or less than 8 mg/l. Pseudomonas aeruginosa and other non-fermentative gram-negative bacteria are generally susceptible to imipenem, only Pseudomonas maltophilia and Pseudomonas cepacia showing intrinsic resistance. Imipenem is currently the most active drug available against anaerobic bacteria, the MIC usually being below 1 mg/l even for Bacteroides fragilis. Rare bacteria such as Nocardia asteroides, Listeria monocytogenes or fast growing Mycobacterium spp. which cause difficult-to-treat infections are also susceptible to imipenem. Increases in inoculum size have only a minimal effect on activity of the drug. In most species the MBC only slightly exceeded the MIC; however in the case of Streptococcus faecalis the MBC value was many times the MIC value. Synergism has been observed in combinations of imipenem with aminoglycosides, and antagonism in combinations with other beta-lactam antibiotics against Pseudomonas aeruginosa and Serratia marcescens. Imipenem is stable in the presence of the common chromosomal and plasmid-mediated enzymes. Induction of inactivating enzymes was observed in staphylococci, Pseudomonas aeruginosa and Serratia marcescens.

Activities of aztreonam and new cephalosporins against infrequently isolated gram-negative bacilli

The susceptibilities of 159 clinical isolates of glucose nonfermentative gram-negative bacilli were determined for eight new monobactam or beta-lactam antibiotics. Imipemide (N-formimidoyl thienamycin) was effective against the largest number of species, although not against Pseudomonas maltophilia. Cefoperazone and ceftazidime, but not cefsulodin, were active against infrequently isolated Pseudomonas species. Aztreonam, moxalactam, cefotaxime, and ceftizoxime demonstrated selective activity against several species, including certain amino-glycoside-resistant isolates.

N-formimidoyl thienamycin: in vitro comparison with cefoxitin and tobramycin against clinical, bacterial isolates

The in vitro activity of the novel beta-lactam antibiotic, N-formimidoyl thienamycin (N-f thienamycin) has been compared with those of cefoxitin and tobramycin. An agar dilution method was employed. N-f thienamycin was active against all Enterobacteriaceae isolates (MIC less than or equal to 4 mg/l). All Pseudomonas aeruginosa isolates were inhibited by 2 mg/l. N-f thienamycin was also active against Acinetobacter calcoaceticus (96 per cent inhibited by 0.5 mg/l) and Gram-positive cocci. All enterococci were inhibited by 2 mg/l. The drug was active against Haemophilus influenzae (MIC less than or equal to 1 mg/l) and the Bacteroides fragilis group (MIC less than or equal to 0.5 mg/l). Cefoxitin was inactive against most Enterobacter and A. calcoaceticus isolates and all P. aeruginosa and enterococcal isolates. Tobramycin was virtually inactive against Gram-positive cocci other than Staphylococcus aureus. N-f thienamycin thus has a broad spectrum of in vitro activity, greater than that of cefoxitin and tobramycin, and may therefore be useful in the treatment of serious infection, particularly when the aetiology is unknown.