Pharmacokinetics, Safety, and Tolerability of Imipenem/Cilastatin/Relebactam in Children with Confirmed or Suspected Gram-Negative Bacterial Infections: A Phase 1b, Open-Label, Single-Dose Clinical Trial

Imipenem/cilastatin/relebactam is approved for the treatment of serious gram-negative bacterial infections in adults. This study assessed the pharmacokinetics (PK), safety, and tolerability of a single dose of imipenem/cilastatin/relebactam (with a fixed 2:1 ratio of imipenem/cilastatin to relebactam, and with a maximum dose of 15 mg/kg imipenem and 15 mg/kg cilastatin [≤500 mg imipenem and ≤500 mg cilastatin] and 7.5 mg/kg relebactam [≤250 mg relebactam]) in children with confirmed/suspected gram-negative bacterial infections receiving standard-of-care antibacterial therapy. In this phase 1, noncomparative study (ClinicalTrials.gov identifier, NCT03230916), PK parameters from 46 children were analyzed using both population modeling and noncompartmental analysis. The PK/pharmacodynamic (PD) target for imipenem was percent time of the dosing interval that unbound plasma concentration exceeded the minimum inhibitory concentration (%fT>MIC) of ≥30% (MIC = 2 mcg/mL). For relebactam, the PK/PD target was a free drug area under the plasma concentration-time curve (AUC) normalized to MIC (at 2 mcg/mL) of ≥8.0 (equivalent to an AUC from time zero extrapolated to infinity of ≥20.52 mcg·h/mL). Safety was assessed up to 14 days after drug infusion. For imipenem, the ranges for the geometric mean %fT>MIC and maximum concentration (Cmax ) across age cohorts were 56.5%-93.7% and 32.2-38.2 mcg/mL, respectively. For relebactam, the ranges of the geometric mean Cmax and AUC from 0 to 6 hours across age cohorts were 16.9-21.3 mcg/mL and 26.1-55.3 mcg·h/mL, respectively. In total, 8/46 (17%) children experienced ≥1 adverse events (AEs) and 2/46 (4%) children experienced nonserious AEs that were deemed drug related by the investigator. Imipenem and relebactam exceeded plasma PK/PD targets; single doses of imipenem/cilastatin/relebactam were well tolerated with no significant safety concerns identified. These results informed imipenem/cilastatin/relebactam dose selection for further pediatric clinical evaluation.

Kidney-Protector Lipidic Cilastatin Derivatives as Structure-Directing Agents for the Synthesis of Mesoporous Silica Nanoparticles for Drug Delivery

Mesoporous silica nanomaterials have emerged as promising vehicles in controlled drug delivery systems due to their ability to selectively transport, protect, and release pharmaceuticals in a controlled and sustained manner. One drawback of these drug delivery systems is their preparation procedure that usually requires several steps including the removal of the structure-directing agent (surfactant) and the later loading of the drug into the porous structure. Herein, we describe the preparation of mesoporous silica nanoparticles, as drug delivery systems from structure-directing agents based on the kidney-protector drug cilastatin in a simple, fast, and one-step process. The concept of drug-structure-directing agent (DSDA) allows the use of lipidic derivatives of cilastatin to direct the successful formation of mesoporous silica nanoparticles (MSNs). The inherent pharmacological activity of the surfactant DSDA cilastatin-based template permits that the MSNs can be directly employed as drug delivery nanocarriers, without the need of extra steps. MSNs thus synthesized have shown good sphericity and remarkable textural properties. The size of the nanoparticles can be adjusted by simply selecting the stirring speed, time, and aging temperature during the synthesis procedure. Moreover, the release experiments performed on these materials afforded a slow and sustained drug release over several days, which illustrates the MSNs potential utility as drug delivery system for the cilastatin cargo kidney protector. While most nanotechnology strategies focused on combating the different illnesses this methodology emphasizes on reducing the kidney toxicity associated to cancer chemotherapy.

Nontherapeutic equivalence of a generic product of imipenem-cilastatin is caused more by chemical instability of the active pharmaceutical ingredient (imipenem) than by its substandard amount of cilastatin

Background

We demonstrated therapeutic nonequivalence of “bioequivalent” generics for meropenem, but there is no data with generics of other carbapenems.

Methods

One generic product of imipenem-cilastatin was compared with the innovator in terms of in vitro susceptibility testing, pharmaceutical equivalence, pharmacokinetic (PK) and pharmacodynamic (PD) equivalence in the neutropenic mouse thigh, lung and brain infection models. Both pharmaceutical forms were then subjected to analytical chemistry assays (LC/MS).

Results and conclusion

The generic product had 30% lower concentration of cilastatin compared with the innovator of imipenem-cilastatin. Regarding the active pharmaceutical ingredient (imipenem), we found no differences in MIC, MBC, concentration or potency or AUC, confirming equivalence in terms of in vitro activity. However, the generic failed therapeutic equivalence in all three animal models. Its E_max against S. aureus in the thigh model was consistently lower, killing from 0.1 to 7.3 million less microorganisms per gram in 24 hours than the innovator (P = 0.003). Against K. pneumoniae in the lung model, the generic exhibited a conspicuous Eagle effect fitting a Gaussian equation instead of the expected sigmoid curve of the Hill model. In the brain infection model with P. aeruginosa, the generic failed when bacterial growth was >4 log₁₀ CFU/g in 24 hours, but not if it was less than 2.5 log₁₀ CFU/g. These large differences in the PD profile cannot be explained by the lower concentration of cilastatin, and rather suggested a failure attributable to the imipenem constituent of the generic product. Analytical chemistry assays confirmed that, besides having 30% less cilastatin, the generic imipenem was more acidic, less stable, and exhibited four different degradation masses that were absent in the innovator.

Pharmacokinetic–Pharmacodynamic Modeling and Simulation for in Vivo Bactericidal Effect in Murine Infection Model

A pharmacokinetic (PK)/pharmacodynamic (PD) modeling strategy to simulate in vivo bactericidal effects for three carbapenem antibiotics, doripenem (DRPM), meropenem (MEPM)/cilastatin (CS), and imipenem (IPM)/CS, against a Pseudomonas aeruginosa (P. aeruginosa) strain is proposed. The PD model we have already developed to explain in vitro time-kill profiles was modified to incorporate the growth rate, bactericidal activities, and PK profiles in murine lung infection models. Plasma concentration data and bacterial time-kill data for each antibiotic consist of six and eight time points, respectively, at one dose regimen (four or five mouse/point). In vivo time-kill curves could be well simulated for each antibiotic by the PK/PD model. Simulated bacterial counts at 24 h and PK/PD indices derived from total drug concentrations (time above the minimum inhibitory concentration (MIC) (T > MIC), C(max)/MIC, and AUC/MIC) for various dose regimens were examined for MEPM/CS and IPM/CS. Simulated bacterial counts correlated only with T > MIC (correlation coefficient: 0.951 for MEPM/CS, 0.982 for IPM/CS) and T > MIC values to achieve a bacteriostatic effect and a 2-log killing effect for both antibiotics were estimated to be approximately 15 and 20%, respectively, which are similar to previously reported results. These findings suggested that the proposed PK/PD model is a good tool for predicting in vivo bactericidal effects.

Population pharmacokinetics and pharmacodynamics of continuous versus short-term infusion of imipenem-cilastatin in critically ill patients in a randomized, controlled trial

Beta-lactams are regularly administered in intermittent short-term infusions. The percentage of the dosing interval during which free drug concentrations exceed the MIC (fT(>MIC)) is the measure of drug exposure that best correlates with clinical outcome for beta-lactams. Therefore, administration by continuous infusion has gained increasing interest recently. We studied 20 critically ill patients with nosocomial pneumonia and investigated whether continuous infusion with a reduced total dose, compared to the standard regimen of intermittent short-term infusion, results in a superior probability of target attainment as assessed by the fT(>MIC) value of imipenem. In this prospective, randomized, controlled clinical study, patients received either a loading dose of 1 g/1 g imipenem and cilastatin (as a short-term infusion) at time zero, followed by 2 g/2 g imipenem-cilastatin per 24 h as a continuous infusion for 3 days (n = 10), or 1 g/1 g imipenem-cilastatin three times per day as a short-term infusion for 3 days (total daily dose, 3 g/3 g; n = 10). Imipenem concentrations in plasma were determined by using a validated liquid chromatography-tandem mass spectrometry assay. A two-compartment open model was employed for population pharmacokinetic modeling. We simulated 10,000 intensive-care-unit patients via Monte Carlo simulations for pharmacodynamic evaluation using the target 40% fT(>MIC). The probability of target attainment by MIC for intermittent infusion was robust (>90%) up to MICs of 1 to 2 mg/liter. The corresponding value for continuous infusion was 2 to 4 mg/liter. Although all 20 patients had an fT(>MIC) of 100%, 3 patients died. Patient survival was best described by employing a sepsis-related organ failure assessment score as a covariate in a logistic regression analysis. Larger clinical trials are warranted for evaluation of continuous infusions at a reduced dose of imipenem for critically ill patients.

Using imipenem and cilastatin during continuous renal replacement therapy

AIM

To identify and review studies which have sought to define the pharmacokinetics of imipenem and cilastatin in patients receiving continuous renal replacement therapy (CRRT).

METHOD

Literature was primarily identified using Pharmline, Embase and Medline databases using the search terms "imipenem," "haemofiltration," "haemodialysis" and "pharmacokinetics." Papers that discussed only intermittent haemodialysis were excluded.

RESULTS

Seven papers were identified which described the pharmacokinetics of imipenem in patients receiving CRRT. Four different modes of CRRT were used. The methods of sampling, dosages used and assumptions made during pharmacokinetic calculations varied widely between the studies. Total body clearance of imipenem during CRRT in patients suffering from acute renal failure was found to range between 89 and 149 ml/min. Total body clearance of cilastatin ranged between 9 and 32 ml/min. Total body clearance of both imipenem and cilastatin was reduced in patients with chronic renal failure. Total body clearance of cilastatin was also reduced by impaired liver function. Dose recommendations made ranged between 500 mg 6-hourly and 500 mg 12-hourly.

CONCLUSIONS

The heterogeneity of the studies identified prevents them being analysed as a single group. For meaningful dosage recommendations to be made, further studies are required using larger populations and with more detail regarding liver dysfunction and duration of renal failure.

Pharmacodynamic Modeling of Imipenem-Cilastatin, Meropenem, and Piperacillin-Tazobactam for Empiric Therapy of Skin and Soft Tissue Infections: A Report from the OPTAMA Program

BACKGROUND

The bactericidal exposures necessary for positive clinical outcomes among skin and soft tissue infections are largely dependent on interpatient pharmacokinetic variability and pathogen drug susceptibility. By simulating the probability of achieving target bactericidal exposures, the pharmacodynamics of three beta-lactam agents were compared against a range of pathogens implicated commonly in complicated skin and soft tissue infections.

METHODS

Using Monte Carlo simulation, pharmacodynamic target attainment expressed as the percentage of the time interval during which the antibiotic concentration exceeded the minimal inhibitory concentration (%T > MIC) in serum and blister fluid was calculated for 5,000 simulated patients receiving imipenem-cilastatin 0.5 g q8h, meropenem 0.5 g q8h, piperacillin-tazobactam 3.375 g q6h, and piperacillin-tazobactam 4.5 g q8h. The pharmacokinetics for each antibiotic were derived from previously published healthy volunteer studies. The MICs for Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Enterobacter sp., Klebsiella sp., coagulase-negative staphylococci, Proteus sp., beta-hemolytic streptococci, and Serratia sp. were taken from the MYSTIC 2003 surveillance study and weighted by the prevalence of each pathogen among 1,404 isolates collected from skin and soft tissue infections during the 2000 SENTRY study. The prevalence of methicillin-resistant Staphylococcus aureus (MRSA) was added into the model at increasing resistance rates.

RESULTS

Imipenem-cilastatin, meropenem, and piperacillin-tazobactam 3.375 g q6h achieved greater than 90% likelihood of achieving bactericidal exposure in serum and blister fluid until the prevalence of MRSA increased beyond 10%. Piperacillin-tazobactam 4.5 g q8h achieved a lower probability of achieving bactericidal exposure than the other regimens (88.7%, p < 0.001).

CONCLUSIONS

When the incidence of MRSA is low, imipenem-cilastatin, meropenem and piperacillin-tazobactam 3.375 g q6h would be optimal choices for the empiric treatment of complicated skin and soft tissue infections among the regimens studied. When MRSA is suspected, a drug that retains activity against this pathogen should be considered.

Pharmacodynamic Modeling of β-lactam Antibiotics for the Empiric Treatment of Secondary Peritonitis: A Report from the OPTAMA Program

BACKGROUND

In this report of the OPTAMA (Optimizing Pharmacodynamic Target Attainment using the MYSTIC Antibiogram) program, we utilized Monte Carlo simulation to compare the probabilities of achieving bactericidal time above the minimum inhibitory concentration (MIC) (%T > MIC) exposures for imipenem-cilastatin 500 mg q6h and 1000 mg q8h, meropenem 500 mg q6h and 1000 mg q8h and piperacillin/tazobactam 3.375 g q6h and 4.5 g q8h in the empiric treatment of secondary peritonitis.

METHODS

The prevalence of pathogens causing secondary peritonitis was identified from the primary surgical and infectious diseases literature. Data for these pathogens with respect to MIC were obtained from the 2003 MYSTIC surveillance study and weighted by the prevalence of each pathogen. A sensitivity analysis varying the prevalence of P. aeruginosa was performed with two additional models to determine the robustness of the data. Pharmacokinetic parameters, obtained from previously published studies in healthy volunteers were used to simulate the %T > MIC for 10,000 patients receiving imipenem-cilastatin, meropenem, and piperacillin/tazobactam. The likelihood of obtaining bactericidal exposure is reported.

RESULTS

Empiric utilization of imipenem-cilastatin and meropenem 500 mg q6h and 1000 mg q8h regimens achieved 99.6%-99.7% likelihood of bactericidal exposure. Piperacillin/ tazobactam 3.375 g q6h and 4.5 g q8h produced bactericidal target attainments of 92.9% and 85.2%, respectively. Models simulating higher prevalence of P. aeruginosa reduced the likelihood of bactericidal exposure for piperacillin/tazobactam regimens significantly and had little effect on the carbapenems.

CONCLUSION

All of the beta-lactams used in the current analysis were predicted to achieve high target attainment consistently for the empiric treatment of secondary peritonitis. However, imipenem-cilastatin 500 mg q6h and 1000 mg q8h, meropenem 1000 mg q8h and 500 mg q6h, and piperacillin/tazobactam 3.375 g q6h achieved the highest likelihood. These, in particular, would be effective choices for the empiric treatment of secondary peritonitis.

Pharmacokinetics of imipenem-cilastatin following intravenous administration in healthy adult horses

In two studies, six healthy adult horses were given imipenem-cilastatin by slow intravenous (i.v.) infusion at an imipenem dosage of 10 mg/kg (study 1) and 20 mg/kg (study 2). The same horses were used in each dosage schedule, with a 2-week washout period between studies. In each dosage group, serial blood and synovial fluid samples were collected for 6 h after completion of the infusion. HPLC was used to determine the imipenem concentration in all samples. Imipenem was well tolerated by all horses at both dosages; no adverse effects were noted during the study period or during the 24-hour postinfusion observation period. The pharmacokinetic profiles of imipenem in the plasma and synovial fluid indicate that an imipenem dosage of 10-20 mg/kg by slow i.v. infusion q6h (every 6 h) is appropriate for most susceptible pathogens.

Pharmacodynamic evaluation of extending the administration time of meropenem using a Monte Carlo simulation

A Monte Carlo simulation demonstrated that 1 g of meropenem (MEM) every 8 h (q8h) (3-h infusion) has a higher target attainment rate against Pseudomonas aeruginosa than either 500 mg of MEM q8h (3-h infusion) or 0.5 g of imipenem-cilastatin (I-C) q6h (1-h infusion). For other pathogens, 500 mg of MEM q8h was equivalent or superior to I-C.

[Investigation on administration method of carbapenems]

Seventy-two women diagnosed as parametritis were enrolled in this study and examined on the effective administration method of carbapenems, imipenem/cilastatin (IPM/CS), panipenem/betamipron (PAPM/BP) and meropenem (MEPM). The total dosage of each carbapenem was 1.5 g/day, and administration frequency was twice a day (0.75 g x 2) or three times a day (0.5 g x 3). We reviewed the highest body temperature, white blood cell count and CRP value, before treatment and the fourth day after the start of treatment. Three times a day method was statistically superior to twice a day method in the highest body temperature, and CRP value. When we use carbapenem antimicrobial agents, the basis of PK/PD of time above MIC would lead to the increasing clinical effects.

The in vitro elution characteristics of vancomycin combined with imipenem-cilastatin in acrylic bone-cements: a pharmacokinetic study

The aim of this in vitro study was to compare the elution characteristics of vancomycin alone and in combination with imipenem-cilastatin from 3 acrylic bone-cements (CMW1 [DePuy International, Blackpool, UK], Palacos R [Schering-Plough, Wehrheim, Germany], and Simplex P [Howmedica International, London, UK]). Six groups of 3 antibiotic-loaded cement disks were prepared, incorporating 2 g of vancomycin (3 groups) and 2 g of vancomycin plus 2 g of imipenem-cilastatin (3 groups). The disks were placed in saline baths for 5 weeks, with the baths being sampled periodically and the elution rates calculated. The total amount of vancomycin released by the cements treated with vancomycin alone was 7.98 mg for CMW1, 7.74 mg for Palacos R, and 6.76 mg for Simplex P; with the addition of imipenem-cilastatin, the total amount of vancomycin released by the 3 cements increased by 30.58%, 50.52%, and 50.15%. CMW1 had better elution characteristics than the other cements when treated with vancomycin alone; the elution of Palacos R and Simplex P was better than that of CMW1 when vancomycin was combined with imipenem-cilastatin.

Effects of parenterally administered ciprofloxacin in a murine model of pulmonary Pseudomonas aeruginosa infection mimicking ventilator-associated pneumonia

BACKGROUND AND METHODS

We compared the bacteriological, pharmacological and histopathological effects of parenterally administered ciprofloxacin (CPFX) to those of imipenem/cilastatin (IMP/CS) and cefozopran (CZOP) in a murine model of mucoid Pseudomonas aeruginosa pneumonia mimicking ventilator-associated pneumonia.

RESULTS

The minimum inhibitory concentrations (MICs) of CPFX, IMP and CZOP were 1.0, 1.0 and 4.0 mg/l, respectively. Treatment with CPFX resulted in a significant decrease in the number of viable bacteria [control, IMP/CS, CZOP and CPFX (mean +/- SEM): 5.02 +/- 0.20, 4.96 +/- 0.38, 5.44 +/- 0.13 and 3.27 +/- 0.02 log(10) colony-forming units lung, respectively]. Histopathological examination revealed that inflammatory changes in the CPFX-treated group were less marked than in other groups. Of the drugs analyzed, the pharmacokinetic parameters of area under the time-concentration curve (AUC)/MIC, AUC exceeding MIC and the time that lung concentrations of drug remained above the MIC were highest for CPFX.

CONCLUSION

Our results suggest that parenterally administered ciprofloxacin is effective in ventilator-associated P. aeruginosa pneumonia.

[Study on the pharmacokinetics of Imipenem cilastatin in burn patients during the acute phase]

OBJECTIVE

To investigate the pharmacokinetic characteristics of Imipenem/cilastatin in burn patients during the acute phase.

METHODS

Imipenem concentrations in the plasma, blister and, interstitial fluids and urine of 6 burn patients (P group) were determined during the acute phase by high performance liquid chromatography after the first initial dose. Pharmacokinetic parameters were thus produced and statistically analyzed by program package STAT 5. Ten healthy volunteers served as control group (C group).

RESULTS

Compared to those in control group, pharmacokinetic parameters of Imipenem exhibited evident difference, such as prolonged half-life [(1.56 plus minus 0.55) h vs (1.06 plus minus 0.24) h] and enlarged distributing volume (16.16 plus minus 4.26) vs (13.96 plus minus 7.10). Imipenem could be detected in the blister and interstitial fluids of burn patients 1 hr after the initial dose. Renal clearance of Imipenem was positively correlated to creatinine clearance (r = 0.5834).

CONCLUSION

The intervals between doses should better be prolonged when loaded-dosage of Imipenem was administered in burn patients during the acute phase. Imipenem could penetrate II and III degree burn wound when given in the acute phase. Attention should be paid to renal function when Imipenem was given.

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.

[The clinical efficacy of imipenem/cilastatin sodium in orthopedic infections and drug levels in the bone tissue]

We evaluated the clinical efficacy of imipenem/cilastatin sodium (IPM/CS--a carbapenem antibiotic) against orthopedic infections, and the drug levels of the bone tissues were determined. The clinical efficacies for 6 patients in the infection group were good in 3 cases, and fair in the other 3; giving an efficacy rate of 50%. Bacteriologically, 8 strains were isolated from patients with the infection and an eradication rate of 87.5% was obtained upon the treatment. In 39 patients that were given the drug prophylactically, no postoperative infections occurred. Mean IPM levels in the bone and the bone marrow at 1 hour after administration in 5 patients of the prophylactic group were 17.3 micrograms/ml and 5.9 micrograms/g, respectively. The ratio of concentrations the bone to those in the bone marrow was 34.6%. The results of this study suggest that IMP/CS reaches to the bone tissue providing sufficient concentrations and that the drug is efficacious for the prophylaxis and the treatment of orthopedic infections.

Pharmacokinetics of meropenem in animals, healthy volunteers, and patients

Meropenem is a carbapenem antibiotic that appears to be widely distributed in tissues and is eliminated by both excretion and metabolism. Approximately 70% of meropenem is excreted via the kidneys, thus dosage adjustments are required for patients with renal impairment. The pharmacokinetic parameters for meropenem are similar to those for imipenem/cilastatin, with the exception of meropenem's smaller volume of distribution. The urinary recovery of meropenem is as high as that of imipenem in combination with cilastatin, an inhibitor of renal dehydropeptidase. Therefore, unlike imipenem, meropenem can be used without dehydropeptidase inhibitors to obtain a consistently high concentration in the urine without nephrotoxic effects.

Pharmacokinetics of imipenem and cilastatin during continuous venovenous hemodialysis in patients who are critically ill

The objective of this study is to study the pharmacokinetics of imipenem-cilastatin in patients with anuria related to multiorgan failure during continuous venovenous hemodialysis (CVVHD) at a fixed blood flow rate of 60 ml/min, fixed dialysate flow rate of 20 ml/min, and drainage flow rate of 1-3 mil/min. A prospective open label study was designed in an intensive care unit in a university hospital. Six patients who required mechanical ventilation and inotropic agents and exhibited acute anuric renal failure were examined. Intravenous imipenem-cilastatin, 500/500 mg, was administered over 30 mins. Blood samples were obtained from the inlet and the outlet of the dialyzer and dialysate samples from the outlet before and at 0.0, 0.5, 1.0, 2.0, 3.0, 6.0, 9.0, and 12.0 hrs after infusion ended. The peak and trough concentrations of imipenem were 32.47 +/- 6.69 micrograms/ml and 1.12 +/- 0.46 micrograms/ml, respectively, whereas those of cilastatin were 50.05 micrograms/ml +/- 14.80 and 9.53 +/- 3.25 micrograms/ml, respectively. The half life was 2.79 +/- 0.3 hr for imipenem, and 6.67 +/- 0.93 hr for cilastatin. Total body clearance of imipenem was 89.4 +/- 17.5 ml/min, including the clearance by CVVHD of 18.7 +/- 1.2 ml/min, and corresponding values for cilastatin were 31.7 +/- 9.0 ml/min and 13.7 +/- 3.4 ml/min. In conclusion, in patients with anuria, the elimination of imipenem-cilastatin was constant during CVVHD. The recommended regimen in patients with anuria who receive CVVHD in this setting was estimated as intravenous imipenem-cilastatin, 500/500 mg, every 12 hrs.

Aerosolization of imipenem/cilastatin prevents pseudomonas-induced acute lung injury

Aerosolization of imipenem/cilastatin was compared with continuous intravenous infusions of the antibiotic for pharmacokinetic/pharmacodynamic analysis. The concentrations of imipenim/cilastatin in bronchoalveolar lavage fluids (BAL) obtained from rats exposed to the aerosolized antibiotic were significantly greater than the concentrations in BAL in the rats that had received intravenous infusions of imipenem/cilastatin. The two methods of antibiotic delivery were compared for their effects on bacterial-induced lung injury in rats that had Pseudomonas aeruginosa instilled into their airspaces. The aerosolization of antibiotic was associated with significantly decreased bacterial-induced lung injury. The high concentrations of antibiotic in the airspaces secondary to aerosolization appears to kill bacteria more quickly and preserve lung epithelial and endothelial integrity better than systemic delivery of the same antibiotic.

Pharmacokinetics in nonhuman primates of a prototype carbapenem active against methicillin-resistant Staphylococcus aureus

Pharmacokinetic parameters were determined for imipenem-cilastatin and a carbapenem antibiotic, L-695,256, active against methicillin-resistant Staphylococcus aureus in rhesus monkeys and a chimpanzee. L-695,256 had larger areas under the concentration-time curve than imipenem-cilastatin (30 +/- 5 versus 24 +/- 1 micrograms.h/ml in the rhesus monkeys and 77 versus 60 micrograms.h/ml in the chimpanzee) and a longer half-life at beta phase (1.2 +/- 0.1 versus 0.6 +/- 0.1 h in the rhesus monkeys and 1.0 versus 0.8 h in the chimpanzee). Resistance to hydrolysis by the renal dehydropeptidase-I allowed L-695,256 to be administered as a single agent.

Serum bactericidal activities and comparative pharmacokinetics of meropenem and imipenem-cilastatin

The pharmacokinetics and serum bactericidal activities (SBAs) of imipenem and meropenem were investigated in a randomized crossover study. Twelve healthy male volunteers received a constant 30-min infusion of either 1 g of imipenem plus 1 g of cilastatin or 1 g of meropenem. The concentrations of the drugs in serum and urine were determined by bioassay and high-pressure liquid chromatography. Pharmacokinetic parameters were based on an open two-compartment model and a noncompartmental technique. At the end of infusion, the mean concentrations of imipenem and meropenem measured in serum were 61.2 +/- 9.8 and 51.6 +/- 6.5 mg/liter, respectively; urinary recoveries were 48.6% +/- 8.2% and 60.0% +/- 6.5% of the dose in 12 h, respectively; and the areas under the concentration-time curve from time zero to infinity were 96.1 +/- 14.4 and 70.5 +/- 10.3 mg.h/liter, respectively (P < or = 0.02). Imipenem had a mean half-life of 66.7 +/- 10.4 min; that of meropenem was 64.4 +/- 6.9 min. The volumes of distribution at steady state of imipenem and meropenem were 15.3 +/- 3.3 and 18.6 +/- 3.0 liters/70 kg, respectively, and the mean renal clearances per 1.73 m2 were 85.6 +/- 17.6 and 144.6 +/- 26.0 ml/min, respectively. Both antibiotics were well tolerated in this single-dose administration study. The SBAs were measured by the microdilution method of Reller and Stratton (L. B. Reller and C. W. Stratton, J. Infect. Dis. 136:196-204, 1977) against 40 clinically isolated strains. Mean reciprocal bactericidal titers were measured 1 and 6 h after administration. After 1 and 6 h the median SBAs for imipenem and meropenem, were 409 and 34.9 and 97.9 and 5.8, respectively, against Staphylococcus aureus, 19.9 and 4.4 and 19.4 and 4.8, respectively, against Pseudomonas aeruginosa, 34.3 and 2.2 and 232 and 15.5, respectively, against Enterobacter cloacae, and 13.4 and 2.25 and 90.7 and 7.9, respectively, against Proteus mirabilis. Both drugs had rather short biological elimination half-lives and a predominantly renal route of elimination. Both carbapenems revealed high SBAs against clinically important pathogens at 1 h; meropenem had a higher SBA against E. cloacae and P. mirabilis, and the SBA of imipenem against S. aureus was greater than the SBA of meropenem.

Imipenem/cilastatin: an update of its antibacterial activity, pharmacokinetics and therapeutic efficacy in the treatment of serious infections

The prototype carbapenem antibacterial agent imipenem has a very broad spectrum of antibacterial activity, encompassing most Gram-negative and Gram-positive aerobes and anaerobes, including most beta-lactamase-producing species. It is coadministered with a renal dehydropeptidase inhibitor, cilastatin, in order to prevent its renal metabolism in clinical use. Extensive clinical experience gained with imipenem/cilastatin has shown it to provide effective monotherapy for septicaemia, neutropenic fever, and intra-abdominal, lower respiratory tract, genitourinary, gynaecological, skin and soft tissues, and bone and joint infections. In these indications, imipenem/cilastatin generally exhibits similar efficacy to broad-spectrum cephalosporins and other carbapenems and is at least equivalent to standard aminoglycoside-based and other combination regimens. Imipenem/cilastatin is generally well tolerated by adults and children, with local injection site events, gastrointestinal disturbances and dermatological reactions being the most common adverse events. Seizures have also been reported, occurring mostly in patients with impaired renal function or CNS pathology, or with excessive dosage. Although it is no longer a unique compound, as newer carbapenems such as meropenem are becoming available, imipenem/cilastatin nevertheless remains an important agent with established efficacy as monotherapy for moderate to severe bacterial infections. Its particular niche is in treating infections known or suspected to be caused by multiresistant pathogens.

Mucosal pharmacokinetics and pilot study of short course of parenteral imipenem in the eradication of Helicobacter pylori

Eradication of Helicobacter pylori infection is known to reduce the incidence of duodenal ulcer recurrence. The most commonly used regimen for H. pylori infection is triple antimicrobial therapy for 1-2 weeks. This treatment is associated with frequent side effects and hence unsatisfactory compliance. As in vitro data showed that H. pylori is sensitive to imipenem, the pharmacokinetics of this drug in the gastric milieu, and the clinical efficacy of imipenem with omeprazole in eradicating H. pylori infection were studied. Imipenem/cilastatin levels in serum, gastric secretion and gastric mucosa were assayed in four patients after intravenous injection of a bolus dose of 500 mg. The serum and gastric secretion levels of imipenem achieved were more than 10 times the minimum inhibitory concentration of the drug for H. pylori. Gastric mucosal levels of imipenem vary considerably with time, which probably indicates rapid elimination of the drug into the gastric lumen. In the second part of this study, imipenem/cilastatin was given intravenously for the first 2 days after diagnosis of H. pylori infection in patients with endoscopically confirmed duodenal ulcers. The patients were also treated with 4 weeks of omeprazole. Clearance of H. pylori was initially achieved at the end of 2 days in 20 out of 22 (91%) patients. However, when the biopsies were repeated at 8 weeks, recurrence of H. pylori infection was evident in 19 cases (86.3%) indicating a failure of eradication. It was concluded that imipenem/cilastatin in combination with omeprazole failed to eradicate H. pylori infection.

Comparison of simulated and in-vivo plasma levels of cilastatin following intravenous in-line drug administration

The primary objective of this work was to establish a method to simulate the plasma levels of cilastatin, a model drug, following an intravenous in-line delivery scheme. In-vivo data in dogs obtained from this work were used to demonstrate the validity of the proposed approach. The in-line drug delivery system consists of a drug containing device which is placed between a large volume parenteral and a patient. Numerous advantages have been identified for this automatic in-line reconstitution delivery system. The numerical convolution integral algorithm was used in this work to perform plasma profile simulation. The results indicated that the simulated cilastatin plasma profile following in-line delivery closely agreed with the in-vivo data.

Pharmacokinetic profiles of intravenous imipenem/cilastatin during slow hemodialysis in critically ill patients

The pharmacokinetics of imipenem/cilastatin were determined in 7 critically ill patients undergoing slow hemodialysis (HD). All patients were anuric. Following intravenous administration of 500 mg of imipenem/cilastatin, concentrations of the drugs in the serum and dialysate were monitored during slow HD. The elimination phase half-life of imipenem was 3.1 +/- 0.3 h and that of cilastatin was 9.7 +/- 1.2 h. The total body clearance of imipenem and cilastatin was 84.0 +/- 7.2 and 32.2 +/- 2.4 ml/min, respectively. Clearance of imipenem and cilastatin during slow HD was 24.3 +/- 2.4 and 54.3 +/- 3.1%, respectively, of total body clearance. After the 10.5-h session of slow HD, serum concentrations of imipenem and cilastatin were 2.3 +/- 0.4 and 16.0 +/- 1.2 mg/l, respectively. It appears that at least 500 mg of imipenem may be needed as a supplemental dose after a session of slow HD or the application interval should be shortened to maintain a therapeutic concentration.

Clinical pharmacokinetics during continuous haemofiltration

Continuous haemofiltration is an extracorporeal technique that is increasingly used to remove fluid, electrolytes, and other waste products from the blood supply of critically ill patients with acute renal failure. Continuous arteriovenous haemofiltration (CAVH), where the blood exits the body from an artery and re-enters through a vein, is widely used. Continuous venovenous haemofiltration (CVVH), where blood both exits and enters through a vein by way of a mechanical pump, avoids problems that result from the variable ultrafiltration rate found during CAVH. Continuous arteriovenous or venovenous haemodiafiltration (CAVHD or CVVHD) combine continuous haemofiltration and haemodialysis. All methods involve ultrafiltration of the patient's blood through a filter that is highly permeable to water and small molecules. Drug elimination by haemofiltration depends mainly on the rate of ultrafiltration, the drug protein binding and the sieving coefficient of the membrane. Because patients undergoing continuous haemofiltration have impaired renal function, dosage reduction is often recommended so that adverse drug reactions are avoided. In contrast, if drug removal by haemofiltration is significant, dosage supplementation may be required to ensure therapeutic efficacy of the drug. Therefore, knowledge of the impact of continuous haemofiltration on drug elimination and the pharmacokinetic profile of drugs is essential to good clinical management. The currently available information on the clinical pharmacokinetic aspects of drug therapy during continuous haemofiltration are summarised. Drugs commonly associated with haemofiltration therapy are tabulated with updated pharmacokinetics and drug-monitoring information.

Pharmacokinetic evaluation of imipenem combined with cilastatin in cystic fibrosis

The pharmacokinetics of imipenem (MK-787) and cilastatin (MK-791) were studied in 30 patients with cystic fibrosis (CF) receiving the drug for therapeutic purposes at doses of 11 mg/kg given as a 30-min infusion. The serum concentrations and urine elimination were studied after the first dose and during steady state. The concentrations were assayed by high-pressure liquid chromatography. The total areas under the imipenem serum concentration curves (AUCs) to infinity were 30.4 +/- 6.8 mg.h/l after the first dose compared with 29.1 +/- 7.1 mg.h/l during steady state (NS). The cilastatin AUCs on the 2 days were 40.3 +/- 9.3 and 38.3 +/- 0.4 mg.h/l (NS), respectively. The urinary recovery of imipenem was 47.8 +/- 17.8% after the first dose and 57.8 +/- 24.2% during steady state (NS). The amounts of cilastatin eliminated in the urine during 6 h were 6/7.3 +/- 22.9% after the first dose and 60.5 +/- 17.0% of the dose during steady state (NS). The mean half-life of imipenem in these CF patients was 1.2 +/- 0.4 h on the first day of the examination and within the same range during steady state. The distribution volume (Vd beta) was in the range of 28 liters, the total body clearance was 16.3 liters/h (285 ml/min) on the first day. The t1/2 of cilastatin was 0.59 +/- 0.14 h after the first dose and 0.61 +/- 0.14 h during steady state. Thus patients with CF eliminated cilastatin more quickly than imipenem.

Synergic activity of imipenem/cilastatin combined with cefotiam against methicillin-resistant Staphylococcus aureus

The synergic activity of imipenem/cilastatin combined with cefotiam was studied in a mouse bacteraemia model. Combinations of imipenem plus cefotiam in ratios from 1:5 to 1:160 were more effective than either imipenem alone or cefotiam alone (P < 0.05). Synergy was observed against both beta-lactamase producing and beta-lactamase non-producing MRSA. Staggered combinations of imipenem with cefotiam (each drug was administered at a different time) were studied in an in-vitro pharmacokinetic system to clarify relationships between killing kinetics and pharmacodynamics of the combinations. In the in-vitro system, cefotiam (1 g over 30 min) administered 2 h after imipenem administration (250 mg over 30 min) reduced viable cell counts to an undetectable level and maintained this for 4 h, while the simultaneous administration of imipenem and cefotiam maintained an undetectable cell count for only 2 h. Furthermore, imipenem administered after cefotiam showed no synergy. These results indicate that the timing of dosing of each antibiotic influences synergy, and administration of cefotiam 2 h after imipenem is more effective than the other regimens.

[Chemotherapy with imipenem/cilastatin for severe infections accompanied by malignant hematological disorders]

The clinical and bacteriological efficacy of imipenem/cilastatin (IPM/CS) was evaluated in 30 cases of serious infections associated with hematological malignancies. 1. Among 28 evaluable cases, excellent efficacy was obtained in 6 cases and good effectiveness in 10 cases, resulting in a high clinical efficacy rate (57.1%). The clinical effectiveness of IPM/CS was not dependent on neutrophil count in peripheral blood. A 53.8% efficacy rate was observed in 26 cases which had received pretreatment with other antibiotics. 2. Antibacterial activities of IPM/CS have so far been evaluated against organisms isolated in 20 of 28 cases: 2 strains of coagulase-negative Staphylococcus, 2 strains of methicillin-resistant Staphylococcus aureus, 2 strains of Enterococcus faecalis, 9 strains of Enterobacter cloacae, and 8 other strains. 3. Among 3 evaluable cases treated with IPM/CS alone, response was good in 1 case. Among 25 patients receiving IPM/CS in combination with an aminoglycoside or a penicillin, the efficacy rate was 60%. 4. Five patients had IPM/CS-related adverse events; nausea and vomiting in 2 cases, seizures in 1 case, small increases in GOT and GPT in 2 cases, and the appearance of casts in urine sediment in 1 case. These patients, however, tolerated the complete course of therapy with IPM/CS except the 2 cases with nausea and vomiting. These results indicate that chemotherapy with IPM/CS is effective for the treatment of severe infectious diseases accompanied by hematological disorders.

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

Imipenem is an antibacterial agent of the carbapenem class of beta-lactams, with a very broad spectrum of activity that includes most Gram-negative and Gram-positive pathogens, aerobes and anaerobes, and with marked activity against species producing beta-lactamases. It is coadministered with cilastatin, a renal dehydropeptidase inhibitor that prevents renal metabolism of imipenem. As initial monotherapy, imipenem/cilastatin provides effective and well-tolerated treatment of moderate to severe infections in various body systems, including intra-abdominal, obstetric and gynaecological, lower respiratory tract, skin and soft tissue, and urinary tract infections, and also in bacteraemia and septicaemia, and in patients with malignancy-related febrile neutropenia. It is likely to be of particular benefit in cases where bacterial pathogens have not yet been identified, such as in the treatment of serious infections in immunocompromised patients, or in an intensive care setting. Thus, imipenem/cilastatin is effective as initial monotherapy of a variety of infections, including infections in neutropenic patients, with a clear role in empirical treatment of mixed infection.

Effect of biliary obstruction on the hepatic excretion of imipenem-cilastatin

The biliary excretion of imipenem-cilastatin studied by endoscopic cannulation of the common bile duct in patients with complete obstruction and in a group without obstruction showed that despite a 24-h prophylaxis, the bile obtained from patients with obstruction immediately after cannulation contained neither imipenem nor cilastatin, while there were 2 and 5% of peak concentrations in serum for imipenem and cilastatin, respectively, in the bile from patients without obstruction. Biliary excretion of both compounds increased rapidly after decompression, reaching a maximum of 15% of peak levels in serum within 2 h. Twenty-four hours after drainage, the biliary excretion of the drugs further improved. We conclude that since biliary obstruction impairs excretion of antibiotics, drainage is necessary for the control of sepsis in obstructed cholangitis.

Pharmacokinetics of imipenem/cilastatin sodium in children with peritonitis

Fifteen children (3-12 years) with peritonitis were given imipenem/cilastatin intravenously (15 or 25 mg/kg) every six hours for 3-14 days. One day during treatment days 2-8, multiple blood and urine samples were collected from each individual over a six hour dosing interval. Twelve children completed the study. The urinary recovery of imipenem and cilastatin averaged 50-70% of the administered dose. The plasma t1/2 for imipenem averaged 55 min. while that for cilastatin was even more rapid (approximately 38 min.). Little or no accumulation of either imipenem or cilastatin was observed for this regimen in this age group of paediatric patients. Steady state conditions prevailed within 2 days of initiation of therapy. The pharmacokinetics of imipenem and cilastatin in paediatric patients 3-12 years of age appear similar to those observed for adults.

Pharmacokinetics of imipenem in serum and skin window fluid in healthy adults after intramuscular or intravenous administration

The pharmacokinetic profiles of imipenem after intramuscular (i.m.) and intravenous injections were examined in adult volunteers. Levels of imipenem in serum after i.m. injection of a microcrystalline suspension of imipenem-cilastatin (500 mg each) reached a peak (8.0 micrograms/ml) at 1.5 h after administration, and concentrations were maintained in excess of 1.5 micrograms/ml for 6 h. Serum elimination half-life (1.3 h), volume of distribution (14.5 liters), and area under the curve (AUC; 27.8 micrograms.h/ml) after i.m. injection did not significantly differ from those of a comparable dose given by intravenous infusion. Bioavailability after i.m. injection was 89%. Imipenem levels in skin window fluid after i.m. administration were maximal (4.3 micrograms/ml) at 4 h after injection, at which time imipenem concentrations exceeded those produced by intravenous infusion. The AUCskin window/AUCserum ratio for skin window fluid after i.m. injection was 68%, indicating good penetration of the drug into skin fluid. This study shows that i.m. injection of 500 mg of imipenem-cilastatin results in concentrations of imipenem in serum and skin fluid that are, for at least 6 h, consistent with antimicrobial activity against susceptible organisms.

Clearance of imipenem/cilastatin in acute renal failure patients treated by continuous hemodiafiltration (CAVHD)

In patients with acute renal failure, who were treated with continuous arteriovenous hemofiltration (CAVH) or continuous arteriovenous hemodiafiltration (CAVHD), we measured clearance rates of imipenem and cilastatin (Tiënam-500). Literature data on volume of distribution and on the endogenous clearance in normals and in anuric patients and the observed clearance rates by CAVH/CAVHD were used to develop guidelines for dose adaptations. Based on the desired peak levels of imipenem, normal subjects should receive the fixed imipenem/cilastatin dose combination (500 mg/500 mg) q.i.d. and patients with acute renal failure should receive the same dose b.i.d. After starting treatment with either CAVH, CAVHD or continuous venovenous hemofiltration (CVVH), no further dose adjustment is necessary. The non-renal clearance rate of cilastatin is very low compared to that of imipenem. If a patient develops anuria, the clearance rate of imipenem decreases from the normal value of 245 ml/min to 116 ml/min. Clearance rate of cilastatin, however, decreases from 230 ml/min to 3 ml/min. Therefore, in patients with renal failure accumulation of cilastatin will occur. On the other hand, if the patient is treated by CAVHD, the relative contribution of the dialyser clearance to the total drug clearance is much greater for cilastatin than for imipenem. As a result, the accumulation of cilastatin is reversed. During treatment by CAVHD, the clearance rate of imipenem raises 15%-25% and that of cilastatin 335%-600%. For this reason, we conclude that the use of the fixed dose combination (500 mg/500 mg) b.i.d. in patients with acute renal failure treated by CAVHD may be justified.

Removal of imipenem and cilastatin by hemodialysis in patients with end-stage renal failure

The removal of imipenem and cilastatin by hemodialysis was studied in 14 (for imipenem) and 6 (for cilastatin) subjects. Following intravenous infusion of imipenem and cilastatin at a combined concentration of 10 mg/kg of body weight, drug levels in plasma were determined serially during off- and on-hemodialysis periods, which were 2 and 4 h, respectively. The biexponential decay of the drug levels in plasma was evident in each subject for both imipenem and cilastatin. Hemodialysis accelerated the elimination of both imipenem and cilastatin: the mean elimination-phase half-life of imipenem was shortened from 200 to 78 min, and that of cilastatin was shortened from 445 to 115 min. Hemodialysis clearance of imipenem and cilastatin was calculated by five different methods, each with intrinsic assumptions. The mean hemodialysis clearance of imipenem was estimated to be 74.08 +/- 13.29 ml/min, and that of cilastatin was estimated to be 65.0 +/- 8.6 ml/min, after consideration of various methodological limitations. It was estimated that in a hypothetical anephric patient weighing 60 kg, a 4-h hemodialysis treatment would remove 54.8% of the imipenem and 62.9% of the cilastatin present in the body at the start of dialysis.

[A clinical phase I study on intramuscular imipenem/cilastatin sodium]

The safety and pharmacokinetics of imipenem/cilastatin sodium (IPM/CS) were evaluated in comparative studies using single intramuscular injection, intravenous infusion or multiple intramuscular administration. The studies were done employing 30 healthy volunteers. Adverse effects were observed in 5 of 18 volunteers in the single intramuscular dose study. One of them complained of mild itching and mild pain at the injection site, and the other 4 volunteers had mild pain at the injection sites. With the other methods of administration, no adverse effects were observed. No other abnormal physical findings nor abnormal laboratory test values were observed in any of the studies. Imipenem (IPM) was absorbed rather slowly through the muscles, resulting in a low maximum plasma concentration (Cmax) and a prolonged half life (T1/2) upon intramuscular injection compared to the results obtained upon intravenous infusion. The total areas under the curves obtained with these 2 methods were similar, however. Cilastatin (CS) was absorbed rapidly after intramuscular injection, and the Cmax obtained was higher than that obtained for IPM. The T1/2 and the AUC of CS obtained with intramuscular injection were similar to those obtained with intravenous infusion. Cumulative urinary recovery rates obtained with these 2 different routes of administration were not different. Detectable urinary levels of IPM were maintained much longer upon intramuscular injection than upon intravenous infusion. In the multiple dose study, neither IPM nor CS showed tendency to accumulate.

Steady-state pharmacokinetics of intramuscular imipenem-cilastatin in elderly patients with various degrees of renal function

We studied the concentrations in plasma and pharmacokinetics of imipenem and cilastatin in elderly patients (greater than 65 years old) who had various degrees of renal function and who were hospitalized with soft tissue infections. Three groups of patients received imipenem-cilastatin (500/500 mg) intramuscularly every 12 h: group I consisted of eight patients with a creatinine clearance (CLCR) of greater than 50 ml/min (range, 51 to 84 ml/min; mean, 65.8 ml/min); group II consisted of three patients with a CLCR of 20 to 50 ml/min; and group III consisted of two patients with a CLCR of less than 20 ml/min. Imipenem and cilastatin concentrations were measured at steady state on day 5. Mean peak and trough plasma imipenem concentrations were 5.28 +/- 1.78 and 1.43 +/- 0.76 micrograms/ml in group I, 6.25 +/- 0.78 and 2.50 +/- 0.00 micrograms/ml in group II, and 14.3 +/- 0.71 and 6.85 +/- 1.06 micrograms/ml in group III, respectively. Mean peak and trough plasma cilastatin concentrations were 11.8 +/- 2.85 and 0.31 +/- 0.43 microgram/ml in group I, 15.5 +/- 2.48 and 2.03 +/- 2.05 micrograms/ml in group II, and 24.5 +/- 6.72 and 10.7 +/- 5.94 micrograms/ml in group III, respectively. Mean imipenem AUCss (area under the concentration-time curve over a dosage interval at steady state) values were 38.7 +/- 7.9 micrograms.h/ml for group I, 52.3 +/- 7.3 micrograms.h/ml for group II, and 143.7 +/- 11.9 micrograms.h/ml for group III. Mean cilastatin AUCss values were 45.6 +/- 12.5 micrograms.h/ml for group I, 93.8 +/- 51.2 micrograms.h/ml for group II, and 217.5 +/- 57.8 micrograms.h/ml for group III. Cilastatin mean apparent body clearance values (normalized to weight) were 2.78 +/- 0.67 ml/min for group I, 1.43 +/- 0.81 ml/min for group II, and 0.71 +/- 0.24 ml/min for group III. Imipenem open-lactam metabolite levels were all below the level of detective of the assay (<3.9 micrograms/ml). There was a progressive increase in plasma imipenem and cilastatin levels and AUCss and there was a decline in body clearance as renal function declined.

Pharmacokinetics of meropenem compared to imipenem-cilastatin in young, healthy males

Imipenem combined with cilastatin and meropenem was given as intravenous infusions of 1 g to eight young, healthy males on two separate occasions. Blood and urine samples were collected for up to 12 h. The terminal half-lives in plasma were 0.98 h and 1.11 h for meropenem and imipenem, respectively. The volume of distribution was smaller for meropenem than for imipenem (12.5 l and 14.4 l, respectively). The plasma clearance for meropenem was 188 (SD 31) ml/min and for imipenem 183 (SD 25) ml/min. Renal clearance was on average 139 (SD 24) ml/min and 135 (SD 11) ml/min, respectively. About 75% of the administered dose of both compounds was eliminated unchanged in urine. Non-renal clearance accounted for approximately 25% of the total clearance for both drugs. The kinetics of meropenem are very similar to those of imipenem given with cilastatin, and meropenem is as stable against renal metabolic degradation as imipenem combined with cilastatin.

Pharmacokinetics of parenteral imipenem/cilastatin in patients on continuous ambulatory peritoneal dialysis

We investigated the pharmacokinetics of two intravenous (iv) dose regimens of imipenem/cilastatin in Chinese patients on chronic ambulatory peritoneal dialysis (CAPD), who had an average creatinine clearance of 3.2 ml/min/1.73 m2. Doses of 0.5 and 1.0 g produced mean peak serum imipenem concentrations of 30 and 70 mg/l respectively, about 60% of cilastatin. Peritoneal dialysis fluid (PDF) imipenem concentrations reached 20-30% of the serum peak 4-5 h after iv injection, and the lowest maximum PDF concentrations were 2 mg/l after the 0.5 g dose and 14 mg/l after 1.0 g. Thus both regimes produced PDF imipenem concentrations above the MICs of susceptible pathogens. The half-life of imipenem was 6.4 h and the plasma clearance 66 ml/min; serum and PDF imipenem were in equilibration after about 5 h. Cilastatin had a prolonged half-life of 19 h and a plasma clearance of 10 ml/min, and accumulated in both serum and PDF. With a 0.5 g dose, the pharmacokinetics of imipenem/cilastatin suggest that the combination may prove an effective treatment for peritonitis associated with CAPD.

Imipenem/cilastatin: evolution of the sustained-release intramuscular formulation

Since 1983, numerous studies have confirmed the efficacy of imipenem/cilastatin as monotherapy for polymicrobial and multiresistant infections. Doses range from 1 to 4 g/day, usually given in 3-4 intravenous infusions. Recently, a sustained-release, intramuscular formulation of imipenem/cilastatin sodium has been developed. Investigations in both animals and healthy human volunteers have shown that this formulation maintains plasma concentrations of imipenem above susceptibility breakpoints for nearly twice the duration provided by similar intravenous doses. Although peak concentrations are lower with the intramuscular formulation, current research suggests that the efficacy of beta-lactam antibiotics is more closely related to the duration that levels are sustained above minimum inhibitory concentrations, rather than to the magnitude of peak concentrations over minimum inhibitory concentrations. Hence, the intramuscular formulation of imipenem/cilastatin sodium holds promise as an efficient, effective regimen in patients with serious infections of mild to moderate severity.

Intramuscular imipenem as adjuvant therapy for acute cholecystitis and perforated or gangrenous appendicitis

An open-label prospective study was performed employing intramuscularly administered imipenem as an adjunct to surgery in 20 patients with acute cholecystitis and 24 patients with perforated or gangrenous appendicitis. Three (12.5%) septic failures occurred in appendicitis patients and 2 (10%) failures in cholecystitis patients. There were no deaths. Adverse effects were minor, and there was no toxicity. Although failures were not associated with in vitro resistance, Pseudomonas spp. were recovered from 2 of 3 appendicitis failures. Intramuscular imipenem appeared to be an effective single-drug antimicrobial when used as an adjunct to surgery in patients with acute cholecystitis or perforated appendicitis. It should be a more cost-effective alternative to the current multiple-drug therapy frequently employed in patients with intra-abdominal sepsis.

Twice daily intramuscular imipenem/cilastatin in the treatment of skin and soft tissue infections

One hundred and two patients were enrolled in an open-label evaluation of intramuscular imipenem/cilastatin using doses of either 500 or 750 mg every 12 h in the treatment of mild to moderately severe skin and soft tissue infections. Seventy-four of 102 patients were clinically evaluable. Thirty-one patients had abscesses, 20 had cellulitis and 23 had wound infections. One hundred seventy-eight isolates were recovered from these 74 patients (average 2.4 isolates/patient). Sixty of 74 evaluable patients (82%) were cured; 12 of 74 (16%) were improved. Two patients failed to improve. Therapy was well tolerated. Adverse effects occurred in 8 patients. All of these effects were minor, and none required discontinuation of therapy. Eighty-two percent of patients reported no pain with injections. Therapy did not need to be interrupted or discontinued in the remaining 18% of patients reporting moderate local pain with injections. Peak and trough serum imipenem levels were measured in 15 patients receiving a 500-mg intramuscular dose of imipenem/cilastatin. The mean peak imipenem concentration in 15 patients was 10.7 micrograms/ml (range 3.3-17.8); the mean trough concentration was 2.1 micrograms/ml (range 0.8-4.9). The trough levels were higher than those found in healthy volunteers and may reflect the age and mild renal dysfunction in this group of treated patients. Imipenem/cilastatin used for mild or moderate skin and soft tissue infections was both efficacious and well tolerated. Intramuscular therapy with this agent offers advantages over intravenous therapy because of its long apparent half-life and pharmacokinetics.

Quantification of imipenem's primary metabolite in plasma by postcolumn chemical rearrangement and UV detection

Imipenem (thienamycin formamidine) is an antibiotic active against a broad spectrum of bacteria. Its primary metabolite arises from cleavage of the lactam ring. The metabolite can be formed in-vitro by acid-catalyzed or enzymatic hydrolysis. In animals and man, this metabolite can be generated systemically as well as in the kidneys following the excretion of imipenem into the urine. In man, this dehydropeptidase-catalyzed renal metabolism is minimized by the coadministration of cilastatin, a competitive inhibitor. A specific HPLC assay has been developed to evaluate the disposition of this metabolite in humans having normal or end-stage renal function. The assay employs ion-pair, reversed-phase chromatography, and post-column acid treatment of the analyte for ultraviolet detection.