In vitro activity of imipenem--a review

Human Vitreous Penetration of Imipenem

The purpose of this study was to determine imipenem concentrations in vitreous humor of non-infected human eyes. Ten patients undergoing vitrectomy were infused with a single dose of either 0.5g (5 patients) or 1g (5 patients) of imipenem. Vitreous humor was withdrawn 2 or 4 hours after the end of the infusion. Results differed in relation to the dose. After 0.5g, vitreous levels were stable (approximately 0.20 mg/l), but after 1g they were significantly higher (approximately 2 mg/l). These levels were above the minimum inhibitory concentration of imipenem for 90% (MIC 90) of the main species responsible for endophthalmitis.

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.

Oral management of the patient with end-stage liver disease and the liver transplant patient

The patient with end-stage liver disease who is in need of a liver transplant should have a pretransplant dental evaluation. Such a patient faces lifelong immunosuppression with an increased risk of infection. This article discusses both the need for control of oral diseases before liver transplantation and guidelines for oral care in the immediately postoperative and long-term transplant patient. Specific indications for antibiotic prophylaxis and antibiotic regimens are presented; in addition, adverse reactions and side effects of immunosuppressant drugs are discussed. Pertinent drug interactions salient to the dental management of patients with end-stage liver disease are reviewed, and specific management recommendations for these patients are presented.

Comparative activities of clinafloxacin against gram-positive and -negative bacteria

Activities of clinafloxacin, ciprofloxacin, levofloxacin, sparfloxacin, trovafloxacin, piperacillin, piperacillin-tazobactam, trimethoprim-sulfamethoxazole, ceftazidime, and imipenem against 354 ciprofloxacin-susceptible and -intermediate-resistant organisms were tested by agar dilution. Clinafloxacin yielded the lowest quinolone MICs (< or = 0.5 microg/ml against ciprofloxacin-susceptible organisms and < or = 16.0 microg/ml against ciprofloxacin-intermediate-resistant organisms) compared to those of levofloxacin, trovafloxacin, and sparfloxacin. Ceftazidime, piperacillin alone or combined with tazobactam, trimethoprim-sulfamethoxazole, and imipenem usually yielded higher MICs against ciprofloxacin-resistant strains.

Pharmacokinetics of imipenem-cilastatin in critically ill patients undergoing continuous venovenous hemofiltration

The pharmacokinetics of imipenem-cilastatin were investigated in 12 critically ill patients with acute renal failure (ARF) managed by continuous veno-venous hemofiltration (CVVH) while receiving a fixed combination of 500 mg of imipenem-cilastatin intravenously three or four times daily. No adverse drug reactions were observed. Plasma and hemofiltrate samples were taken at specified times during one dosing interval, and the concentrations of imipenem and cilastatin were determined by high-performance liquid chromatography. Pharmacokinetic variables were calculated by a first-order, two-compartment pharmacokinetic model for both substances. Total clearances of imipenem and cilastatin (mean +/- standard deviations) were 122.2 +/- 28.6 and 29.2 +/- 13.7 ml/min, respectively, with hemofiltration clearances of 22.9 +/- 2.5 and 16.1 +/- 3.1 ml/min, respectively, and nonrenal, nonhemofiltration clearances of 90.8 +/- 26.3 and 13.2 +/- 13.9 ml/min, respectively. Mean imipenem dosage requirements were approximately 2,000 mg/24 h (2,111.8 +/- 493.4 mg/24 h). They were calculated in order to achieve an average steady-state concentration of 12 mg/liter to ensure that concentrations in plasma exceeded the MICs at which 90% of intermediately resistent bacteria are inhibited (8 mg/liter) during the majority of the dosing interval. By contrast, the recommended dosage for patients with end-stage renal failure (ESRF) and infections caused by intermediately resistant bacteria is 1,000 mg/24 h. This remarkable difference may be due (i) to differences in the nonrenal clearance of imipenem between patients with ARF and ESRF and (ii) to the additional clearance by the hemofilter. Since the total clearance of cilastatin was low, marked accumulation occurred, and this was particularly pronounced in patients with additional liver dysfunction. Thus, in patients with ARF managed by CVVH, rather high imipenem doses are required, and these inevitably result in a marked accumulation of cilastatin. The doses of imipenem recommended for patients with ESRF, however, will lead to underdosing and inadequate antibiotic therapy.

Activities of levofloxacin, ofloxacin, and ciprofloxacin, alone and in combination with amikacin, against acinetobacters as determined by checkerboard and time-kill studies

A total of 101 Acinetobacter genospecies (77 Acinetobacter baumannii strains and 24 non-A. baumannii strains) were tested for their susceptibilities to levofloxacin, ofloxacin, and ciprofloxacin and for synergy between the quinolones and amikacin by checkerboard titration and time-kill analyses. The MICs at which 50% of the isolates are inhibited (MIC50)/MIC90s for the 101 strains were as follows (in micrograms per milliliter): levofloxacin, 0.25/16.0; ofloxacin, 0.5/32.0; ciprofloxacin, 0.25/> 64.0; and amikacin, 1.0/> 32.0. At empiric breakpoints of < or = 2.0 microg/ml, 61% of the strains were susceptible to all three quinolones. At a breakpoint of < or = 16.0 microg/ml, 84% of the strains were susceptible to amikacin. Checkerboard titrations yielded synergistic fractional inhibitory concentration (FIC) indices (< or = 0.5) for one strain with levofloxacin and amikacin and for two strains with ofloxacin and amikacin. Indices of > 0.5 to 1.0 were seen for 57, 54, and 55 strains with levofloxacin plus amikacin, ofloxacin plus amikacin, and ciprofloxacin plus amikacin, respectively, and indices of > 1.0 in 43, 45, and 46 strains, respectively, were found with the above three combinations. No strains yielded antagonistic FIC indices (> 4.0). Most FIC results of > 1.0 occurred in strains for which the quinolone MICs were > 2.0 microg/ml and for which the amikacin MICs were > or = 32.0 microg/ml. By contrast, synergy (defined as > or = 2 log10 decrease compared to the more active compound alone by time-kill analysis) was found in all seven strains tested for which the quinolone MICs were < or = 2.0 microg/ml. For eight other strains for which the quinolone MICs were > 2.0 microg/ml as determined by time-kill analysis, quinolone and amikacin concentrations in combination were usually too high to permit clinical use. Time-kill analysis was found to be more sensitive in detecting synergy than was the checkerboard method.

Xanthomonas maltophilia and Pseudomonas cepacia in lower respiratory tracts of patients in critical care units

Xanthomonas maltophilia and Pseudomonas cepacia are Gram-negative bacilli that are considered to opportunistic pathogens. These bacteria may cause colonization and infection, especially in acutely ill patients. Between 1 July 1990 and 30 June 1992 sputum [correction of suptum] culture results from patients in the critical care units were surveyed daily. During the 2 year period, sputum from 27 patients grew X. maltophilia. It was hospital-acquired in 26 patients. A total of 26 patients were mechanically ventilated for between 1 day and 8 months (median 19 days) before sputum cultures grew X. maltophilia. Various antimicrobial agents were prescribed for 25 of the 27 patients before they acquired X. maltophilia infection. The case fatality was 44.4%. Sputum from 79 patients grew P. cepacia. It was hospital-acquired in all who were ventilated for between 1 day and 50 days (median 9 days) before sputum cultures grew P. cepacia. Several antimicrobial agents were given to 77 patients before P. cepacia was isolated from them. The case fatality rate was 51.9%. In the majority of cases, the positive cultures indicated colonization. Patients with APACHE II scores >15 experienced a higher fatality (55.6% vs. 22.2%, P<0.05 for X. maltophilia and 56.9% vs.28.6%, P<0.05 for P. cepacia).

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.

Antibiotic choices in surgical intensive care unit patients

Antibiotics have dramatically changed the care of the critically ill patient over the last 60 years. Patients with complex physiological conditions present with infectious processes requiring the effective use of antimicrobial drugs. In many situations, the inability to eradicate the infectious process is complicated by the progressive development of resistance among the causative organisms. Systemic antibiotic prophylaxis is warranted only for the prevention of wound infections. Regimens in these cases should use large doses of nontoxic antibiotics covering the spectrum of organisms likely to contaminate the wound. The duration of wound prophylaxis should be short, essentially covering only the period of active wound closure; this is usually less than 24 hours. Prevention of most other infections in the ICU depends on the recognition and correction of the various disturbances of host defenses. Topical antibiotic therapy may reduce the level of colonization for a few specific types of infection. Initial empiric antibiotic therapy should be started for clear indications. The antibiotics chosen should be those most likely to be effective against the probable organisms, those which have the lowest toxicity, and those with the smallest likelihood of inducing multiresistance. They must be adjusted promptly based on the microbiologic sensitivities observed. The realization that the physiology of critical illness may alter the normal relations between drug dosages and the tissue antibiotic levels obtained mandates a different approach to the treatment of these patients. The drug volumes of distribution are generally markedly expanded in these patients. Furthermore, these patients require high tissue antibiotic concentrations to improve the chances for successful therapy. Thus, the antibiotics selected must be capable of providing these levels without significant toxicity to the host. Therapy should be continued based on the clinical response observed. Premature cessation of effective therapy often results in relapse.

In vitro antibacterial activity and beta-lactamase stability of the new carbapenem LJC10,627

In in vitro susceptibility tests the new carbapenem LJC10,627 showed potent antibacterial activity against gram-positive and gram-negative bacteria, except that most methicillin-resistant Staphylococcus aureus strains tested were found to be resistant to LJC10,627. LJC10,627 showed high activity against Pseudomonas aeruginosa and was active against Enterobacter cloacae and Citrobacter freundii strains which were resistant to ceftazidime and cefpirome. The Ki values of LJC10,627 for penicillinase Type I, cephalosporinase and oxyiminocephalosporinase were low, whereas the Ki value for L-1 enzyme from Xanthomonas maltophilia was high.

In vitro antibacterial activity and beta-lactamase stability of the new carbapenem SM-7338

The in vitro activity of the new carbapenem SM-7338 was tested in comparison with imipenem, ceftazidime, cefotaxime, flomoxef, cefuzonam and cefmetazole against 2850 clinical bacterial isolates. SM-7338 showed good activity against a broad spectrum of gram-positive and gram-negative bacteria. SM-7338 was very active against gram-negative bacteria, inhibiting all Enterobacteriaceae, except 25% of Serratia marcescens isolates, at a concentration of 0.78 mg/l. SM-7338 inhibited the majority of Pseudomonas spp. at concentrations of less than or equal to 3.13 mg/l, its activity being twofold higher than that of imipenem. However, the activity of SM-7338 against gram-positive cocci was about one-fourth that of imipenem. Against anaerobes, SM-7338 also had the best activity of the beta-lactams tested. The compound was inactive against methicillin-resistant staphylococci, Enterococcus faecium, Xanthomonas maltophilia and Flavobacterium spp., as were the other beta-lactams. SM-7338 was quite stable in the presence of various types of beta-lactamase, but was hydrolyzed by Xanthomonas maltophilia beta-lactamase, as was imipenem. This high degree of stability was responsible for the potent activity of SM-7388 against beta-lactamase-producing species such as Enterobacter cloacae, Citrobacter freundii and Proteus vulgaris. SM-7338 also showed bactericidal activity against clinical isolates at the MIC or at concentrations slightly above the MIC.

Emergence of resistance to imipenem in Pseudomonas aeruginosa

The emergence of resistance to imipenem by Pseudomonas aeruginosa was investigated with four pairs of isolates. Each pair represented pretherapy (susceptible) and posttherapy (resistant) specimens. In all cases, the imipenem-resistant isolates did not demonstrate changed susceptibilities to other beta-lactams. Agarose gel electrophoresis revealed no change in plasmid profiles between any pair of isolates. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the Sarkosyl-insoluble membrane protein revealed the loss of an outer membrane protein of apparent molecular mass 48 to 49 kilodaltons in posttherapy strains when grown with imipenem selection (5 micrograms/ml). There was no significant difference in the binding of [14C]imipenem to the penicillin-binding proteins of the pre- and posttherapy strains. Trichloroacetic acid precipitation of membranes isolated after growth in the presence of [14C]imipenem revealed that significantly less drug was bound to Sarkosyl-soluble membrane protein in three of the four posttherapy strains than the membrane proteins of the respective pretherapy strains. beta-Lactamase activity against imipenem at 100 or 3 microM was not detected in any isolate either with or without induction. These data suggest that resistance to imipenem is associated with the loss of a 48- to 49-kilodalton outer membrane protein accompanied by, in three of four cases, decreased penetration of the antibiotic across the outer membrane.

The epidemiology of Pseudomonas cepacia in patients with cystic fibrosis

Pseudomonas cepacia has emerged as an important nosocomial pathogen colonizing and infecting the respiratory tract of patients with cystic fibrosis (CF). Although assessment of outcomes associated with P. cepacia colonization has been difficult, controlled studies have shown that colonized patients experience more adverse outcomes compared with those not colonized. In the United States, an increasing trend in national incidence and prevalence of P. cepacia colonization has been shown, but cases have been unevenly distributed in a few centers. These estimates, however, may be biased by intercenter differences in laboratory methods for detecting P. cepacia in patient sputum. The source and mode of transmission of P. cepacia have not been adequately demonstrated, and may vary from center to center. Until further studies elucidate the epidemiology of P. cepacia in patients with CF, it may be prudent for CF centers to consider the use of selective media to isolate P. cepacia from sputa of patients with CF, to conduct investigations of clusters of P. cepacia-colonized patients, and to consider adopting infection control precautions recommended for control of multiply resistant gram negative organisms.

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.

In vitro activity of imipenem against enterococci and staphylococci and evidence for high rates of synergism with teicoplanin, fosfomycin, and rifampin

The in vitro activities of imipenem alone and in combination with teicoplanin, fosfomycin, and rifampin were tested against clinical isolates of enterococci and staphylococci. In both groups of organisms, the three combinations demonstrated high rates of synergism in both checkerboard and time-kill studies.

In vitro additive effect of imipenem combined with vancomycin against multiple-drug resistant, coagulase-negative Staphylococci

Imipenem combined with vancomycin resulted in a marked additive effect in vitro against 9 clinical isolates of multiple-drug resistant (MDR), coagulase-negative staphylococci, including strains resistant against imipenem. The additive effect was documented with the aid of checkerboard MIC determinations and with time kill curve experiments. In contrast, imipenem combined with vancomycin merely yielded weak additive or indifferent effects against 10 MDR isolates of Staphylococcus aureus, all of which were susceptible to imipenem.

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.

[Efficacy and tolerance of imipenem/cilastatin in the treatment of surgical infections with and without bone involvement]

Imipenem/cilastatin in a doses of 1.5/day was used to treat 31 moderate to severe infections, predominantly soft tissue infections with bone involvement, in 30 surgical patients. A clinical success was achieved in 93% of the patients. In one patient with diabetic gangrene of the foot, imipenem/cilastatin treatment performed as a last resort was not able to prevent amputation. One patient died from his underlying disease while on therapy. All isolates except one Pseudomonas diminuta strain regarded as contaminant were initially sensitive to imipenem. Two Pseudomonas aeruginosa strains developed resistance by the end of therapy. Staphylococcus aureus and coagulase-negative staphylococci were the most common aetiologic agents. Only few clinical and biochemical side-effects were observed: in two cases an allergic rash appeared following several days' treatment. Four patients developed thrombocytopenia, which, however, was completely reversible after the end of therapy.

[Imipenem/cilastatin in surgical intensive medicine]

26 patients from the surgical intensive care unit, University Hospital Lübeck, received imipenem/cilastatin for severe abdominal, respiratory or urogenital infections. 500 mg imipenem/cilastatin were infused i.v. over 30 min q. i. d. The treatment was successful in 84,6% of the patients suffering from severe infections. Two cases were considered to be failures. 36 of the 43 isolated pathogens (83.7%) were eliminated. Transitory elevations of liver enzymes were the most frequent side-reactions observed; an increase in serum creatinine, diarrhoea or fungal colonization were less common.

[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.

[Bone concentrations of imipenem after a dose of imipenem/cilastatin]

The concentration of imipenem in organic bone, determined in 16 patients by bioassay after short infusion (15 min) of 1 g imipenem/cilastatin was 4.3 +/- 2.06 mg/kg (geometric mean +/- standard deviation, n = 13) after 45 minutes, and 2.8 +/- 1.86 mg/kg (n = 26) after 88 minutes. Imipenem penetrates into inorganic hydroxylapatite (imbution), however, its antimicrobial activity is lost. The mean serum concentration in 12 patients (mean age 77 years) with normal renal and hepatic function 15 minutes after the beginning of the infusion was 93.1 mg/l imipenem. The mean serum half life t (1/2 beta) was 1.32 hours, the total body clearance 108.6 1/h, and the volume of distribution during the beta phase V(beta) 12.4 1.

[Dosage of imipenem/cilastatin]

Imipenem/cilastatin was used for the treatment of 594 bacterial infections in 545 patients at a dosage of 1.5 g/day (n = 283), 2.0 g/day (n = 129), 3.0 g/day (n = 102), or 4 g/day (n = 11). The most common indications for therapy were nosocomial pneumonias followed by intraabdominal postoperative infections, and skin and soft tissue infections. Out of 1171 bacterial strains isolated from 932 patients, seven showed primary resistance to imipenem. The causative agent was eliminated in 87% of the patients. Treatment failed in 24 of the 594 patients. In 35 patients therapy was stopped because of side effects. The most frequent side effect was local irritation at the site of intravenous application.

Tentative interpretive criteria for in vitro antibacterial susceptibility testing with imipenem

Imipenem is a member of a new class of highly potent beta-lactam antibiotics, carbapenems, with a very broad antibacterial spectrum. This study was undertaken to determine tentative interpretive criteria for in vitro susceptibility testing with 10-micrograms imipenem disks. A careful examination of the zone diameters and the corresponding MICs for 489 clinical isolates by regression-line analysis and the error rate-bounded classification scheme suggested the following guidelines: greater than or equal to 16 mm with an MIC correlate of less than or equal to 4 micrograms/ml for susceptible, 14 to 15 mm (8 micrograms/ml) for moderately susceptible, and less than or equal to 13 mm (greater than or equal to 16 micrograms/ml) for resistant. Lack of cross-resistance between imipenem and broad-spectrum cephalosporins such as cefotaxime and ceftazidime argues against their use as class disks to predict in vitro susceptibility of bacterial species to carbapenems.