Open trial of imipenem/cilastatin therapy for serious bacterial infections

Microbiological and clinical aspects of infection associated with Stenotrophomonas maltophilia

The gram-negative bacterium Stenotrophomonas maltophilia is increasingly recognized as an important cause of nosocomial infection. Infection occurs principally, but not exclusively, in debilitated and immunosuppressed individuals. Management of S. maltophilia-associated infection is problematic because many strains of the bacterium manifest resistance to multiple antibiotics. These difficulties are compounded by methodological problems in in vitro susceptibility testing for which there are, as yet, no formal guidelines. Despite its acknowledged importance as a nosocomial pathogen, little is known of the epidemiology of S. maltophilia, and although it is considered an environmental bacterium, its sources and reservoirs are often not readily apparent. Molecular typing systems may contribute to our knowledge of the epidemiology of S. maltophilia infection, thus allowing the development of strategies to interrupt the transmission of the bacterium in the hospital setting. Even less is known of pathogenic mechanisms and putative virulence factors involved in the natural history of S. maltophilia infection and this, coupled with difficulties in distinguishing colonization from true infection, has fostered the view that the bacterium is essentially nonpathogenic. This article aims to review the current taxonomic status of S. maltophilia, and it discusses the laboratory identification of the bacterium. The epidemiology of the organism is considered with particular reference to nosocomial outbreaks, several of which have been investigated by molecular typing techniques. Risk factors for acquisition of the bacterium are also reviewed, and the ever-expanding spectrum of clinical syndromes associated with S. maltophilia is surveyed. Antimicrobial resistance mechanisms, pitfalls in in vitro susceptibility testing, and therapy of S. maltophilia infections are also discussed.

Randomized multicenter clinical trial with imipenem/cilastatin versus cefotaxime/gentamicin in the treatment of patients with non-life-threatening infections. German and Austrian Imipenem/Cilastatin Study Group

In an open, controlled, randomized study the safety and efficacy of imipenem/cilastatin was compared with that of the combination cefotaxime/gentamicin (plus metronidazole in patients with suspected anaerobe infection) in the treatment of 337 patients from 12 German and 5 Austrian centers who had non-life-threatening infections. The evaluation was done on an intention-to-treat basis (i.e. all patients including protocol violators) and according to the protocol (144 patients in the imipenem/cilastatin group and 124 in the cefotaxime/gentamicin group). No significant differences were seen between the two treatment groups in terms of the clinical and bacteriological outcome. The frequency of infusion intolerance and thrombophlebitis was low in both groups (< 2%). The overall rate of adverse events was comparable in the two groups, nausea, vomiting and diarrhea being the most frequent events. Nephrotoxicity, indicated by an increase in serum creatinine, was significantly higher in the cefotaxime/gentamicin group. Imipenem/cilastatin was shown to be as effective as cefotaxime/gentamicin (metronidazole) and appears to be well tolerated.

Review of imipenem

Imipenem, a new carbapenem beta-lactam broad-spectrum antibiotic, is highly active in vitro against most aerobic and anaerobic gram-positive and gram-negative bacteria isolated from infectious diseases of human beings. Except for enterococci and methicillin-resistant staphylococci most gram-positive cocci are inhibited by less than 2 micrograms/ml. Although the MIC-90 of methicillin-resistant staphylococci may be less than 4 micrograms/ml, these bacteria are usually resistant to imipenem by modified testing methods. The enterococcus, S. faecalis, has an MIC-90 of less than 8 micrograms/ml but bactericidal concentration may be much higher. Most Enterobacteriaceae are highly susceptible to imipenem with MIC-90 of 0.5 to 2.0 micrograms/ml. Proteus species are less susceptible with MICs of 4 to 8 micrograms/ml. Isolates of P. aeruginosa have variable susceptibility with MICs ranging from 0.25 to 16 micrograms/ml. Pseudomonas maltophilia and P. cepacia are usually resistant to imipenem. Except for Clostridium species, most strict anaerobes are susceptible to less than 1.0 micrograms/ml of imipenem. When combined with cilastatin (1:1 ratio), the renal elimination of the active form is increased. The serum halflife in normal renal function is about 1 hour and increases to 3.4 hours in anuria. Major adverse effects are similar to those of cephalosporins except for seizures in some patients. Colonization with fungi and drug-resistant bacteria occurs in about 5% of imipenem-treated patients. Clinical studies have demonstrated efficacy in 79% to 96% of patients treated.

[Effect and tolerance of daily 2 X 1 g imipenem/cilastatin in general surgery]

The clinical efficacy, tolerability and safety of imipenem/cilastatin were studied in a open, prospective trial with 63 general surgical patients suffering from bacterial infections. According to study criteria, 48 of the patients were evaluable. Clinical cure was achieved in 47 of these 48 patients (97.9%). The causative organisms were eliminated in 39 of the 47 patients cured. Clinical side-reactions were observed in 4.2% of the 63 patients treated. In 8.3% of these laboratory parameters were changed. 77 of the 78 microorganisms isolated before therapy were sensitive to imipenem (MICs 0.02-2.0 mg/l). In one patient a coagulase-negative staphylococcus with an MIC of 16 mg/l was isolated after five days of therapy.

[Clinical experience with imipenem/cilastatin in the treatment of severe infections in general surgery]

In a prospective study 43 patients (19 men, 24 women) suffering from severe bacterial infections such as peritonitis (n = 16), soft tissue infection (n = 12), pneumonia (n = 7), septicemia (n = 6), catheter sepsis (n = 2), cholangitis (n = 4), osteomyelitis (n = 3), complicated urinary tract infection (n = 2) or endocarditis (n = 1) were treated t. i. d. with short-time i. v. infusions of 0.5 g imipenem/cilastatin for five to 37 days (means = 9). All the patients were cured or significantly improved following therapy with imipenem/cilastatin alone or in combination with surgical intervention. The most frequent isolates were Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis, Staphylococcus aureus, Staphylococcus epidermidis and Streptococcus faecalis. 58 (83%) of the 70 pathogens isolated initially were eliminated. The 12 microorganisms (gram-negative aerobic bacteria) which persisted were non-contributory to the course of the infection and had MICs between 0.32 and 4 mg/l. The MICs for 60 isolates were less than or equal to 1 mg/l; the MICs for nine isolates were in the range of 2 to 8 mg/l. One S. epidermidis isolate presented primary resistance to imipenem (MIC 16 mg/l). The tolerability was good. Phlebitis was observed in one case only. Based on our experience we conclude that monotherapy with imipenem/cilastatin at a dosage of 0.5 g t. i. d. is appropriate for the treatment of severe bacterial infections.