Imipenem therapy of Pseudomonas aeruginosa and other serious bacterial infections

rpoS-mutation variants are selected in Pseudomonas aeruginosa biofilms under imipenem pressure

Background

Pseudomonas aeruginosa is a notorious opportunistic pathogen causing various types of biofilm-related infections. Biofilm formation is a unique microbial strategy that allows P. aeruginosa to survive adverse conditions such as antibiotic treatment and human immune clearance.

Results

In this study, we experimentally evolved P. aeruginosa PAO1 biofilms for cyclic treatment in the presence of high dose of imipenem, and enriched hyperbiofilm mutants within six cycles in two independent lineages. The competition assay showed that the evolved hyperbiofilm mutants can outcompete the ancestral strain within biofilms but not in planktonic cultures. Whole-genome sequencing analysis revealed the hyperbiofilm phenotype is caused by point mutations in rpoS gene in all independently evolved mutants and the same mutation was found in P. aeruginosa clinical isolates. We further showed that mutation in rpoS gene increased the intracellular c-di-GMP level by turning on the expression of the diguanylate cyclases. Mutation in rpoS increased pyocyanin production and virulence in hyperbiofilm variants.

Conclusion

Here, our study revealed that antibiotic treatment of biofilm-related P. aeruginosa infections might induce a hyperbiofilm phenotype via rpoS mutation, which might partially explain antimicrobial treatment failure of many P. aeruginosa biofilm-related infections.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00655-9.

Resurgence of Pseudomonas endocarditis in Detroit, 2006-2008

A resurgence of endocarditis due to Pseudomonas aeruginosa was seen in 10 injection drug users (IDUs) in Detroit between 2006 and 2008 (6 men, 4 women; mean age, 48.1 yr). All patients tested negative for the human immunodeficiency virus (HIV). Five patients had left-sided endocarditis of the mitral valve and/or the aortic valve; 3 of 5 patients had prosthetic valve endocarditis. Four of 10 patients had right-sided endocarditis of the tricuspid valve alone. One patient had bilateral involvement of the aortic and tricuspid valves. Nine patients had Pseudomonas endocarditis (PsE); 1 patient had mixed endocarditis with P. aeruginosa and Candida parapsilosis. Seven of 10 patients were treated with a combination of intravenous cefepime, 4-6 g/d, plus high-dose tobramycin (HDT) for at least 6 weeks. Tobramycin, 8 mg/kg per day, was given as a single daily dose intravenously, aiming for peak serum levels of 18-22 microg/mL and trough levels of <1 microg/mL. The patient with mixed endocarditis was also treated with fluconazole. Two patients initially treated with other antipseudomonal regimens, including cefepime alone and piperacillin/tazobactam plus tobramycin, failed treatment and were switched to cefepime and HDT. A third patient was switched to cefepime and ciprofloxacin because of nephrotoxicity. Two patients developed nephrotoxicity to tobramycin; 1 patient developed ototoxicity. The overall medical cure rate for both left-sided and right-sided disease was 80% (4/5). All 5 patients who required surgery survived (5/5; 100%). Overall outcome was 90% (9/10). Indications for valve replacement were recurrent Pseudomonas bacteremia (n = 3), recurrent bacteremia and congestive heart failure (n = 1), and persistent bacteremia and fungemia (n = 1). Tricuspid valvulectomy with valve replacement was successful in 2 patients and in a third patient who had successful replacement of both the tricuspid and the aortic valve for recurrent bacteremia and congestive heart failure. Two patients with pure left-sided prosthetic valve endocarditis underwent successful repeat valve replacements. Although this is a small series, the overall mortality rate (1/10; 10%) was low. The patient who did not survive had left-sided involvement of the aortic valve and could not undergo surgery because of a large embolic cerebral infarct. The mortality rate of left-sided disease in the current series was 16.7% (1/6 including the patient with tricuspid and aortic valve PsE) compared to 60% in a series of 15 patients reported in 1990.Our current antimicrobial regimen for PsE consists of a combination of cefepime, 6 g/d, in 3 divided doses, plus HDT, 8 mg/kg per day, given as a single daily dose for 6 weeks. For cefepime-resistant Pseudomonas, imipenem, 4-6 g/d, or meropenem, 6 g/d, plus HDT has been successful. For right-sided disease refractory to medical therapy, surgical intervention is recommended if Pseudomonas bacteremia persists for 2 weeks on appropriate antimicrobial therapy or if bacteremia recurs after a 6-week course of treatment. Tricuspid repair/reconstruction or valvulectomy with valve replacement plus combined antipseudomonal regimen may be the optimal therapy for refractory right-sided endocarditis. This approach not only may prevent the development of severe and permanent impairment of right ventricular function, which is a complication of valvulectomy alone without valve replacement, but also may cure the infection. For left-sided disease, surgery is recommended if blood cultures remain positive for 7 days on appropriate antimicrobial therapy or if Pseudomonas bacteremia recurs after completion of a 6-week course of the combined regimen.

Clinical review: balancing the therapeutic, safety, and economic issues underlying effective antipseudomonal carbapenem use

Antipseudomonal carbapenems have played a useful role in our antimicrobial armamentarium for 20 years. However, a review of their use during that period creates concern that their clinical effectiveness is critically dependent on attainment of an appropriate dosing range. Unfortunately, adequate carbapenem dosing is missed for many reasons, including benefit/risk misconceptions, a narrow therapeutic window for imipenem and meropenem (due to an increased rate of seizures at higher doses), increasingly resistant pathogens requiring higher doses than are typically given, and cost containment issues that may limit their use. To improve the use of carbapenems, several initiatives should be considered: increase awareness about appropriate treatment with carbapenems across hospital departments; determine optimal dosing regimens for settings where multidrug resistant organisms are more likely encountered; use of, or combination with, an alternative antimicrobial agent having more favorable pharmacokinetic, pharmacodynamic, or adverse event profile; and administer a newer carbapenem with lower propensity for resistance development (for example, reduced expression of efflux pumps or greater stability against carbapenemases).

An overview of harms associated with beta-lactam antimicrobials: where do the carbapenems fit in?

The US Institute of Medicine's focus on patient safety has motivated hospital administrators to facilitate a culture of safety. As a result, subcommittees of the pharmacy and therapeutics committee have emerged in many hospitals to focus on adverse events and patient safety. Antimicrobial harms have gained the attention of practicing clinicians and hospital formulary committees, because they top the list of drugs that are associated with adverse events and because of certain serious harms that have ultimately led to the withdrawal of some antimicrobial agents. In the near future, several antimicrobials in the late phase of development will become available for clinical use (ceftobiprole, ceftaroline, and telavancin), and others (doripenem and dalbavancin) have recently joined the armamentarium. Because new antimicrobials will become part of the treatment armamentarium, it is important to discuss our current understanding of antimicrobial harms in general. Although not thought of as traditional adverse events, Clostridium difficile infection and development of resistance during therapy are adverse events that occur as a result of antimicrobial exposure and therefore are discussed. In addition, a distillation of our current understanding of β-lactam specific adverse events will be provided. Finally, new methods of administration are being evaluated that may influence peak concentration-related antimicrobial adverse events.

Pseudomonas infections in the thermally injured patient

Pseudomonas aeruginosa, remains a serious cause of infection and septic mortality in burn patients, particularly when nosocomially acquired. A prototypic burn patient who developed serious nosocomially acquired Pseudomonas infection is described as an index case which initiated investigations and measures taken to identify the source of the infection. The effect of changes in wound care to avoid further nosocomial infections was measured to provide data on outcome and cost of care. The bacteriology of Pseudomonas is reviewed to increase the burn care providers understanding of the behaviour of this very common and serious pathogen in the burn care setting, before reviewing the approach to detection of the organism and treatment both medically and surgically. After controlling the nosocomial spread of Pseudomonas in our burn unit, we investigated the morbidity and mortality associated with nosocomial infection with an aminoglycoside resistant Pseudomonas and the associated costs compared to a group of case-matched control patients with similar severity of burn injury, that did not acquire resistant Pseudomonas during hospitalization at our institution. We found a significant increase in the mortality rate in the Pseudomonas group compared to controls. The morbidity in terms of length of stay, ventilator days, number of surgical procedures, and the amount of blood products used were all significantly higher in the Pseudomonas group compared to controls. Costs associated with antibiotic requirements were also significantly higher in the Pseudomonas group. Despite this increased resource consumption necessary to treat Pseudomonas infections, these efforts did not prevent significantly higher mortality rates when compared to control patients who avoided infection with the resistant organism. Thus, in addition to the specific measures required to identify and treat nosocomial Pseudomonas infections in burn patients, prevention of infection through modification of treatment protocols together with continuous infection control measures to afford early identification and eradication of nosocomial Pseudomonas infection are critical for cost-effective, successful burn care.

Nosocomial pneumonia in pediatric patients: practical problems and rational solutions

Nosocomial pneumonia is a common hospital-acquired infection in children, and is often fatal. Risk factors for nosocomial pneumonia include admission to an intensive care unit, intubation, burns, surgery, and underlying chronic illness. Viruses, predominantly respiratory syncytial virus (RSV), are the most common cause of pediatric nosocomial respiratory tract infections. Gram-negative bacteria (Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa) are the predominant bacterial pathogens, and are associated with a high mortality rate. Staphylococcus aureus and Staphylococcus epidermidis are the most common Gram-positive bacteria causing nosocomial pneumonia; infections with these organisms have a better outcome than those with Gram-negative organisms. An increasing problem is the emergence of multiresistant Gram-positive and Gram-negative nosocomial pathogens. Distinguishing nosocomial pneumonia from other pulmonary processes may be difficult; diagnosis is based on clinical signs, radiological findings, and microbiological results. Recommended empiric therapy should consider factors such as the time of onset of illness, severity of disease, and specific risk factors for nosocomial pneumonia, including use of mechanical ventilation, underlying disease, or recent use of antibacterials. The resident local hospital flora should be considered when selecting therapy for nosocomial pneumonia. Early initiation of appropriate empiric therapy reduces morbidity and mortality. For empiric treatment of bacterial nosocomial pneumonia, an intravenous antibacterial regimen that includes coverage of Gram-negative bacilli and Gram-positive organisms should be used. A carbapenem or ureidopenicillin derivative (piperacillin) plus a beta-lactamase inhibitor should be used where extended spectrum beta-lactamase-producing Enterobacteriaceae are endemic. Therapy should be modified when a specific pathogen and its antimicrobial susceptibility are identified. Effective prevention of nosocomial pneumonia requires infection control measures that affect the environment, personnel, and patients. Of these, hand hygiene, appropriate infection control policies, and judicious use of antibacterials are essential.

Empiric therapy of sepsis in the surgical intensive care unit with broad-spectrum antibiotics for 72 hours does not lead to the emergence of resistant bacteria

BACKGROUND

It is our practice to treat suspected sepsis with imipenem/cilastatin and gentamicin (IMP/GENT) for 72 hours while awaiting culture results. We wanted to determine if this practice engenders antimicrobial resistance.

METHODS

Review of prospectively collected data regarding use of IMP/GENT and microbial sensitivity to imipenem/cilastatin during the first and last 7 months of a 19-month study period (October 1, 1995, to April 30, 1997).

RESULTS

The susceptibility of appropriate organisms to imipenem/cilastatin was 76% in the early period and 80% in the late period (p = 0.42). Pseudomonas aeruginosa was more susceptible in the late period (88 vs. 62%; p = 0.007). Resistance to gentamicin (30% early vs. 21% late; p = 0.02) and representative cephalosporins (cefoxitin, 52% early vs. 61% late; p = 0.35; ceftazidime, 26% early vs. 23% late; p = 0.76) did not develop during the study period. The incidence of fungemia was the same in both periods (4 of 467 admissions vs. 3 of 599 admissions; p = 0.48).

CONCLUSION

This protocol did not lead to the emergence of resistant bacteria.

Imipenem versus targeted therapy in cancer patients

In many instances, broad-spectrum antibiotics are initiated empirically in febrile cancer patients and continued for the whole duration of therapy. An alternative is to narrow the spectrum whenever the offending pathogen is identified. This study is aimed at comparing these two options. Non-neutropenic cancer patients with severe infections received empiric imipenem. After 72 h, those with microbiologically documented infection were randomized either to continue imipenem or to receive a targeted therapy. After 72 h of imipenem 76.1% were improved. After randomization, a higher efficacy was observed with imipenem (88.5 vs. 72.1%: P = 0.025). Bacterial and fungal superinfections were comparable. Costs were lower for targeted therapy in gram-positive infection and higher in gram-negative infection.

Bacterial pneumonia associated with HIV-1 infection

Bacterial pneumonia remains an important cause of treatable morbidity among HIV-1-infected persons. These pneumonias occur at all CD4 counts but are especially common as the HIV-1 infection progresses. Bronchopneumonia should be considered particularly in the setting of segmental or lobar consolidation associated with productive cough and fever. S. pneumoniae remains the most common pathogen causing bronchopneumonia. Because of the high rate of bacteremia, diagnosis may be facilitated by blood cultures. Treatment is similar to management of HIV-1-seronegative persons, although drug resistance against some bacteria may be an emerging problem. Several opportunities exist for prevention, and these should be pursued vigorously.

Activity of the carbapenem panipenem and role of the OprD (D2) protein in its diffusion through the Pseudomonas aeruginosa outer membrane

Evidence of permeation of panipenem through the OprD (D2) channel of Pseudomonas aeruginosa outer membrane was shown by using OprD protein-producing and -nonproducing strains which contained plasmid pHN4, which codes for L-1 beta-lactamase of Xanthomonas maltophilia. Permeation by panipenem was determined by measuring hydrolysis of the carbapenem by beta-lactamase in the periplasmic space. Permeation by panipenem was also determined by counting uptake of [14C]panipenem into P. aeruginosa PAO1 and its OprD protein-deficient mutant, and this permeation of PAO1 was inhibited by L-lysine. These results indicate that panipenem, as well as imipenem, uses the OprD channel, which functions as a specific channel for diffusion of basic amino acids. Panipenem and imipenem showed stronger activities against PAO1 and clinical isolates in human serum than in Mueller-Hinton broth, which contains more amino acids than human serum does. The activities of the carbapenems were reduced by addition of L-lysine to human serum. Similar results were obtained with mouse serum and ascitic fluid. In contrast, such a change in the activities of carbapenems was not observed with an OprD protein-deficient mutant, suggesting that the main reason for the strong activities of carbapenems in biological fluids is a decrease in competition between the antibiotics and basic amino acids for permeation through the OprD channel. Panipenem and imipenem showed much stronger therapeutic efficacies against experimental infections with P. aeruginosa in mice than did the reference antibiotics. Their in vivo activities were more consistent with their MICs in biological fluids than with those in Mueller-Hinton broth.

Pseudoresistance of Pseudomonas aeruginosa resulting from degradation of imipenem in an automated susceptibility testing system with predried panels

During the use of a single lot of custom breakpoint panels (Sensititre; Radiometer America Inc., Westlake, Ohio), imipenem susceptibility declined from 70 to 44% for clinical isolates of Pseudomonas aeruginosa. With a new lot, susceptibility increased to 73%. Subsequent evaluations with P. aeruginosa ATCC 27853 revealed a similar susceptibility pattern and an increase in the MIC of imipenem when determined in panels with increasing ages. Imipenem concentrations were determined by high-performance liquid chromatography by using 11 different lots of MIC and breakpoint panels (139 to 893 days of age). The amount of imipenem remaining declined from 94.4 to 13.8% (r = 0.9225) over the age range of the panels. These data suggest that imipenem in Sensititre MIC and breakpoint panels degrades over time and that the decrease in imipenem may be largely responsible for the decline in P. aeruginosa susceptibility.

In vitro activity of Ro 23-9424, ceftazidime, and eight other newer beta-lactams against 100 gram-positive blood culture isolates

One hundred Gram-positive bacteremia organisms from five important genus groups were tested against 10 newer beta-lactams. Ceftazidime was significantly less active (50% of strains at less than or equal to 8 micrograms/ml) compared to other cephalosporins. The penems (FCE-22101 and HRE-664) and imipenem were each superior to the cephalosporins with 92-93% inhibition of strains. A novel fused co-drug of fleroxacin and desacetyl-cefotaxime, Ro 23-9424, was 100% effective against these Gram-positive pathogens at less than or equal to 8 micrograms/ml. Several of these compounds should receive consideration for clinical trials for empiric therapy among neutropenic patient infections where Gram-positive pathogens may be more prevalent.

Emergence of imipenem-resistant Pseudomonas aeruginosa during treatment of intra-abdominal infection in a patient with ovarian carcinoma

A 59-year-old woman was admitted to the hospital with ovarian carcinoma. After cytoreductive surgery, the patient developed intra-abdominal sepsis. After 17 days of intravenous imipenem, the patient's sputum culture grew imipenem-resistant Pseudomonas aeruginosa. On the 21st day of treatment with imipenem, her peritoneal culture also grew imipenem-resistant Pseudomonas aeruginosa.

Selective imipenem resistance in Pseudomonas aeruginosa associated with diminished outer membrane permeability

The permeability of the outer membranes of imipenem-susceptible and imipenem-resistant clinical isolates of Pseudomonas aeruginosa was investigated by the liposome swelling assay. Sugars and cephaloridine penetrated rapidly, whereas imipenem penetrated poorly into liposomes constructed from porin-rich outer membrane fractions of the resistant isolates.

Controlled trials of double beta-lactam therapy with cefoperazone plus piperacillin in febrile granulocytopenic patients

The efficacy and safety of double beta-lactam therapy with cefoperazone plus piperacillin in febrile granulocytopenic patients were compared with moxalactam plus piperacillin, ceftazidime plus piperacillin, and imipenem alone in two separate clinical trials. All patients also received prophylactic vitamin K. When National Committee for Clinical Laboratory Standards breakpoints for susceptibility were used, a greater proportion of pretherapy isolates of gram-negative aerobic bacilli and gram-positive organisms were found to be susceptible to cefoperazone (94 percent) and imipenem (91 percent) than to moxalactam (84 percent), ceftazidime (85 percent), or piperacillin (85 percent). In trial I, the overall response rates for documented or possible infections were 78 percent (76 of 97 patients) for cefoperazone/piperacillin and 80 percent (72 of 90 patients) for moxalactam/piperacillin. In trial II, the overall response rates were 86 percent (25 of 29 patients) for cefoperazone/piperacillin, 74 percent (20 of 27 patients) for ceftazidime/piperacillin, and 72 percent (21 of 29 patients) for imipenem alone. There was no nephrotoxicity or hemorrhage related to the study drugs. Diarrhea was more frequent with each of the double beta-lactam regimens, whereas nausea and seizures were more common with imipenem given at a dosage of 1.0 g intravenously every six hours. Seizures occurred in three of 29 imipenem-treated patients but in none of 243 patients treated with the double beta-lactam regimens (p less than 0.001). These results suggest that cefoperazone plus piperacillin provides adequate coverage for most common bacterial pathogens and is safe and effective therapy for febrile granulocytopenic patients.

Recent advances in the treatment of pneumonia in the intensive care unit

The treatment of pneumonia acquired in the intensive care unit (ICU) includes intravenous antibiotics and supportive care. In many cases, the aetiologic agent of infection is not clear and empirical broad-spectrum antibiotic regimens are commonly used. Combinations of beta-lactam and aminoglycoside agents are particularly popular due to the high incidence of Gram-negative bacillary and Staphylococcus aureus pneumonias in the hospital setting. Several new approaches to treatment of pneumonia in the ICU are currently being evaluated including single-agent empirical treatment with broad-spectrum beta-lactam agents; intrabronchial aminoglycoside instillation therapy; oral quinolone agents for treatment of Gram-negative bacillary pneumonia; and passive immune therapy. Conventional and experimental therapy are discussed in this report.

Agents for the treatment of Pseudomonas aeruginosa infections

Pseudomonas aeruginosa is the most common pathogen of Pseudomonas species. One of the most virulent organisms pathogenic to man, P aeruginosa can cause a variety of infections in humans. Despite the introduction of many new antimicrobial agents with enhanced activity against P aeruginosa, the high mortality rate associated with the organism over the past two decades continues.

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.

Nosocomial and nursing home-acquired pneumonia. Recent therapeutic advances

In recent years, new broad-spectrum antibiotics have become available for the treatment of complex pneumonia. Used with care, these agents may allow effective monotherapy of difficult-to-treat pulmonary infections, with the added benefit of decreased toxicity in comparison with the more traditional multiple-drug combinations. The newer antibiotics are relatively expensive, but cost of their use can be justified by their reduced toxicity (in comparison with some antibiotic combinations) and by the avoidance of additional laboratory fees for routine drug monitoring. It is hoped that the major benefits that can accrue with proper use of the newer agents will not be outweighed by problems resulting from their indiscriminate use, such as increased bacterial resistance and exorbitant healthcare costs.

Serum bactericidal activity and killing rate for volunteers receiving imipenem, imipenem plus amikacin, and ceftazidime plus amikacin against Pseudomonas aeruginosa

Serum bactericidal activity against 20 strains of Pseudomonas aeruginosa was studied in 10 volunteers after administration of imipenem (25 mg/kg), imipenem (25 mg/kg) plus amikacin (7.5 mg/kg), and ceftazidime (25 mg/kg) plus amikacin (7.5 mg/kg). Eight strains were susceptible and 12 were resistant to ticarcillin. Serum levels were measured microbiologically after 30 and 60 min and were, respectively, 97 and 46 micrograms/ml for imipenem given alone and 79 and 45 micrograms/ml for imipenem given with amikacin. Despite the very large dose of imipenem used, imipenem and imipenem plus amikacin appeared slightly less active than ceftazidime plus amikacin (P less than or equal to 0.1; Wilcoxon matched-pairs test), with respective median titers at 30 min of 1:128, 1:128, and 1:256 against ticarcillin-susceptible strains and 1:32, 1:32, and 1:64 against ticarcillin-resistant strains; however, more than 90% of the serum determinations, regardless of the regimen, had a serum bactericidal activity greater than or equal to 1:8. Amikacin significantly increased the rate of killing in serum of P. aeruginosa by imipenem. Imipenem plus amikacin appeared as effective as ceftazidime plus amikacin in reducing the viable counts of P. aeruginosa after 24 h of incubation.

Aminoglycoside resistance: a worldwide perspective

Two concerns, neither of which is particularly new, underlie the current reluctance to use aminoglycosides more broadly. First, an undeniable fact is that these compounds can be toxic, particularly in patients with impaired renal function or those receiving other nephrotoxic medications. Second, a more emotional concern is that widespread use of aminoglycosides, particularly the newer compounds that are more resistant to enzymatic inactivation, may engender widespread resistance. In fact, several sources lead one to doubt whether widespread use of potent and highly effective agents like amikacin will by itself increase a clinical reservoir of more resistant microbes. First, the surveillance studies undertaken in many hospitals show some modest reduction in overall aminoglycoside resistance even when a drug like amikacin is used to supplant antecedent compounds of the same class. Second, in institutions where no official surveillance programs have been undertaken but where ongoing surveillance has been maintained, susceptibility to amikacin has remained constant when recent blood isolates are compared with blood isolates from more than 10 years ago. Third, in controlled clinical trials, particularly in immunocompromised patients, the overall emergence of resistance has been remarkably low and contrasts rather strikingly with what has been observed in some monotherapeutic studies of beta-lactam agents. The presence of aminoglycoside-resistant strains cannot be denied, but the circumstances leading to the emergence of such resistance must be carefully assessed, particularly outside of the setting in which these drugs are used as first-line therapy for critically ill patients. For instance, there is substantial evidence to suggest that the topical use of aminoglycosides or the use of these agents when there may be environmental contamination could lead to the emergence of resistance. Before one incriminates the use of any one drug as predisposing to the emergence of resistance, one needs to have more information about the total exposure of a given bacterial population to aminoglycoside therapy. The emergence of resistance to aminoglycosides has been associated with exposure to the more commonly used agents such as gentamicin or tobramycin. With some of the newer beta-lactam agents, the rate of emergence of resistance, unlike that of the aminoglycosides, has appeared to be remarkably high. If the concern about emergence of resistance is genuine, and to maintain consistency of approaches, the infectious disease community should focus more attention on limiting or restricting the use of the more widely used beta-lactam compounds.(ABSTRACT TRUNCATED AT 400 WORDS)

[Treatment of respiratory tract infections with imipenem/cilastatin in critical patients with respiratory insufficiency]

In an open prospective study the efficacy and tolerance of imipenem/cilastatin was investigated in 24 critically ill patients on mechanical ventilation with nosocomial respiratory tract infection. Nine patients had previously received antibiotic therapy, eight of them with various other beta-lactam antibiotics which had failed. Imipenem was given in a dose of 1-3 g/24 h over 5-37 (mean 11) days. Seven patients were additionally treated with aminoglycosides, one patient with erythromycin. Pseudomonas aeruginosa (n = 14), Staphylococcus aureus (n = 4), Haemophilus influenzae (n = 4) and Escherichia coli (n = 3) were the potential pathogens most frequently isolated from tracheo-bronchial secretions. All of the isolates were susceptible to imipenem. 91% of the infections without and 77% with involvement of P. aeruginosa were successfully treated. Two patients who had not responded to previous treatment succumbed to the consequences of progressive respiratory distress syndrome. All of the gram-positive and 85% of the gram-negative pathogens (Pseudomonas not included) were eliminated in the course of therapy. By contrast, 64% of the isolates of P. aeruginosa persisted; half of these became imipenem-resistant. Nine patients showed adverse reactions including one case of pseudomembranous colitis or laboratory abnormalities which were all reversible. Imipenem/cilastatin proved highly effective and was relatively well tolerated; it is suitable as a single agent for the initial treatment of nosocomial respiratory tract infections in ventilated patients, although only with limitations in cases of infection due to P. aeruginosa.

Cilastatin does not alter superoxide dismutase activity

Cilastatin inhibits dehydropeptidase-I, a zinc metaloenzyme that metabolizes imipenem. Because zinc stabilizes the mammalian superoxide dismutase, we postulated that cilastatin would also inhibit the dismutase. Cilastatin concentrations at levels threefold higher than those expected in urine, however, did not inhibit the superoxide dismutase activity.

Potential of imipenem as single-agent empiric antibiotic therapy of febrile neutropenic patients with cancer

Infection remains a major cause of morbidity and mortality for the patient with cancer who experiences episodes of severe granulocytopenia. The search continues for new antimicrobial agents with improved efficacy and lower incidence of toxicity. Imipenem is a new carbapenem antibiotic which possesses a broad antibacterial spectrum with excellent activity against Pseudomonas aeruginosa and the other commonly recovered enteric gram-negative bacilli that infect the granulocytopenic patient with cancer. The combination of imipenem plus an aminoglycoside has shown in vitro synergy against P. aeruginosa and Staphylococcus aureus whereas the combination of imipenem plus piperacillin or the extended spectrum cephalosporins have frequently shown antagonism when tested against P. aeruginosa and Serratia marcescens. The use of a P. aeruginosa-infected neutropenic rat model has provided an in vivo system to evaluate the activity of new antibiotics or antibiotic combinations. Monotherapy with imipenem is as effective in this model as any of the currently available synergistic antibiotic combinations. This degree of activity has not been found with other broad-spectrum antibiotics when used alone. Imipenem provides serum bactericidal activity well above a 1:8 dilution for the four most commonly isolated pathogens: P. aeruginosa, Escherichia coli, Klebsiella species, and S. aureus. In addition, imipenem's post-antibiotic effect against P. aeruginosa may be pertinent. Imipenem is a unique antibiotic, with properties that make it well suited for study as monotherapy for fever and suspected infection in granulocytopenic patients with cancer. A prospective randomized, double-blind study comparing imipenem with a control regimen of piperacillin plus amikacin as empiric antibiotic therapy of febrile granulocytopenic patients with cancer is currently underway at the University of Maryland Cancer Center.

Antimicrobial therapy of bacterial sepsis in the newborn infant

Septicemia continues to be an important cause of neonatal morbidity and mortality. The bacteria most commonly responsible are group B beta-hemolytic streptococci and Escherichia coli, but regional differences exist. Recently sepsis caused by Staphylococcus epidermidis has occurred with increasing frequency in several neonatal intensive care units. Other organisms are less commonly responsible. The choice of antibiotics for suspected sepsis is based on the possible organisms involved and their antibiotic susceptibility patterns, which vary from hospital to hospital and at different times in the same hospital. Currently recommended initial therapy consists of a penicillin and an aminoglycoside, usually ampicillin and gentamicin. The addition of vancomycin is indicated when staphylococcal septicemia is suspected. During outbreaks of neonatal sepsis caused by aminoglycoside-resistant gram-negative bacteria, the use of third-generation cephalosporins or acylaminopenicillins may be appropriate, depending on the results of susceptibility tests. Continuing efforts to develop antibiotics for the treatment of neonatal sepsis are warranted.

Safety and efficacy of high-dose treatment with imipenem-cilastatin in seriously ill patients

Imipenem-cilastatin was given in doses of 1 g intravenously every 6 h to 31 patients. Twenty-five patients, with 27 infections, were clinically evaluable and received 20 to 210 g of imipenem for a duration of 5 to 56 days (average 16.3 days). Infections included seven cases of osteomyelitis, seven of bacteremia, five of cellulitis, two of pneumonia, three of pelvic cellulitis, two of intraabdominal abscess, and one each of empyema, mediastinitis, and endometritis. Fifty-five percent of the infections were caused by gram-negative bacilli, 33% were due to gram-positive organisms, and 10% were caused by anaerobes. Twenty-two patients (81%) were cured, three improved, one relapsed, and one became superinfected with a resistant organism. In 5 of 11 cases with Pseudomonas aeruginosa, the imipenem MIC for organisms isolated by the end of treatment was higher than it was initially, raising concern that imipenem should not be used alone to treat Pseudomonas aeruginosa infections. Twenty-one patients had no adverse reaction; of the remaining 10 patients, 4 had nausea, 1 had urticaria, and 6 had mild abnormalities in hepatic function; three episodes of diarrhea included two with Clostridium difficile toxin in stool and one with pseudomembranous colitis, as determined by sigmoidoscopy. Levels of creatinine, hemoglobin, leukocytes, platelets, prothrombin, and urine components were unchanged. Imipenem-cilastatin is a clinically effective antibiotic with freedom from nephrotoxicity and hematological abnormalities in the large doses used in this study.