Stability of doripenem, imipenem and meropenem at elevated room temperatures

Comprehensive stability analysis of 13 β-lactams and β-lactamase inhibitors in in vitro media, and novel supplement dosing strategy to mitigate thermal drug degradation

Non-clinical antibiotic development relies on in vitro susceptibility and infection model studies. Validating the achievement of the targeted drug concentrations is essential to avoid under-estimation of drug effects and over-estimation of resistance emergence. While certain β-lactams (e.g., imipenem) and β-lactamase inhibitors (BLIs; clavulanic acid) are believed to be relatively unstable, limited tangible data on their stability in commonly used in vitro media are known. We aimed to determine the thermal stability of 10 β-lactams and 3 BLIs via LC-MS/MS in cation-adjusted Mueller Hinton broth at 25 and 36°C as well as agar at 4 and 37°C, and in water at -20, 4, and 25°C. Supplement dosing algorithms were developed to achieve broth concentrations close to their target over 24 h. During incubation in broth (pH 7.25)/agar, degradation half-lives were 16.9/21.8 h for imipenem, 20.7/31.6 h for biapenem, 29.0 h for clavulanic acid (studied in broth only), 23.1/71.6 h for cefsulodin, 40.6/57.9 h for doripenem, 46.5/64.6 h for meropenem, 50.8/97.7 h for cefepime, 61.5/99.5 h for piperacillin, and >120 h for all other compounds. Broth stability decreased at higher pH. All drugs were ≥90% stable for 72 h in agar at 4°C. Degradation half-lives in water at 25°C were >200 h for all drugs except imipenem (14.7 h, at 1,000 mg/L) and doripenem (59.5 h). One imipenem supplement dose allowed concentrations to stay within ±31% of their target concentration. This study provides comprehensive stability data on β-lactams and BLIs in relevant in vitro media using LC-MS/MS. Future studies are warranted applying these data to antimicrobial susceptibility testing and assessing the impact of β-lactamase-related degradation.

Estimating the prevalence of poor-quality anti-TB medicines: a neglected risk for global TB control and resistance

OBJECTIVES

Tuberculosis (TB) remains a major global public health problem, especially with the recent emergence of multidrug-resistant TB and extensively drug-resistant TB. There has been little consideration of the extent of substandard and falsified (SF) TB medicines as drivers of resistance. We assessed the evidence on the prevalence of SF anti-TB medicines and discussed their public health impact.

MATERIALS/METHODS

We searched Web of Science, Medline, Pubmed, Google Scholar, WHO, US Pharmacopeia and Medicines Regulatory Agencies websites for publications on anti-TB medicines quality up to 31 October 2021. Publications reporting on the prevalence of SF anti-TB drugs were evaluated for quantitative analysis.

RESULTS

Of the 530 screened publications, 162 (30.6%) were relevant to anti-TB medicines quality; of those, 65 (40.1%) described one or more TB quality surveys in a specific location or region with enough information to yield an estimate of the local prevalence of poor-quality TB medicines. 7682 samples were collected in 22 countries and of those, 1170 (15.2%) failed at least one quality test. 14.1% (879/6255) of samples failed in quality surveys, 12.5% (136/1086) in bioequivalence studies and 36.9% (87/236) in accelerated biostability studies. The most frequently assessed were rifampicin monotherapy (45 studies, 19.5%) and isoniazid monotherapy (33, 14.3%), rifampicin-isoniazid-pyrazinamide-ethambutol fixed dose combinations (28, 12.1%) and rifampicin-isoniazid (20, 8.6%). The median (IQR) number of samples collected per study was 12 (1-478).

CONCLUSIONS

SF, especially substandard, anti-TB medicines are present worldwide. However, TB medicine quality data are few and are therefore not generalisable that 15.2% of global anti-TB medicine supply is SF. The evidence available suggests that the surveillance of the quality of TB medicines needs to be an integral part of treatment programmes. More research is needed on the development and evaluation of rapid, affordable and accurate portable devices to empower pharmacy inspectors to screen for anti-TB medicines.

Outpatient parenteral antimicrobial therapy with continuous infusion of meropenem: A retrospective analysis of three years of clinical experience

INTRODUCTION

Data regarding outpatient parenteral antimicrobial therapy (OPAT) with continuous infusion of meropenem (CIM) remain scarce and controversial. We aimed to analyze its outcomes.

METHODS

We conducted a retrospective analysis of a cohort of patients who received OPAT with CIM during a three-year period at a single center in northwest Spain. Demographics, clinical data and OPAT outcomes were recorded.

RESULTS

Since January 2017-December 2019, 34 patients received 35 OPAT episodes with CIM. The median age was 75 years, and 18 (51.4%) had a Charlson comorbidity index>2. Twelve (34.3%) had respiratory infection, 11 (31.4%) urinary tract infection, and 12 (34.3%) other infections. Twenty-one (60%) received a dose of 6g/day, and 27 (77.1%) received combined antibiotic therapy. The duration of OPAT with CIM was 10 median days. Pseudomonas aeruginosa was the most frequently (34.3%) isolated microorganism and 10 (28.6%) infections were polymicrobial. During OPAT and hospital at home unit admission, 4 (11.4%) patients had any adverse reaction that required CIM withdrawal, 2 (5.7%) were readmitted, and 3 (8.8%) died (2 infection-related deaths). After 30 days from discharge 6 (18.8%) of 32 not-censored patients had unplanned readmissions (2 infection-related), 6 (18.8%) developed recurrence (3 relapses, 3 reinfections) and 1 (3.1%) died (none-infection-related death). Twenty-three (71.9%) of these 32 patients did not experience unplanned readmission, recurrence or death.

CONCLUSION

CIM can be an option to be administrated in OPAT programs in selected patients. Further studies are warranted to increase evidence regarding its use, and to externally validate our findings.

Inter-species interactions alter antibiotic efficacy in bacterial communities

The efficacy of antibiotic treatments targeting polymicrobial communities is not well predicted by conventional in vitro susceptibility testing based on determining minimum inhibitory concentration (MIC) in monocultures. One reason for this is that inter-species interactions can alter the community members' susceptibility to antibiotics. Here we quantify, and identify mechanisms for, community-modulated changes of efficacy for clinically relevant antibiotics against the pathogen Pseudomonas aeruginosa in model cystic fibrosis (CF) lung communities derived from clinical samples. We demonstrate that multi-drug resistant Stenotrophomonas maltophilia can provide high levels of antibiotic protection to otherwise sensitive P. aeruginosa. Exposure protection to imipenem was provided by chromosomally encoded metallo-β-lactamase that detoxified the environment; protection was dependent upon S. maltophilia cell density and was provided by S. maltophilia strains isolated from CF sputum, increasing the MIC of P. aeruginosa by up to 16-fold. In contrast, the presence of S. maltophilia provided no protection against meropenem, another routinely used carbapenem. Mathematical ordinary differential equation modelling shows that the level of exposure protection provided against different carbapenems can be explained by differences in antibiotic efficacy and inactivation rate. Together, these findings reveal that exploitation of pre-occurring antimicrobial resistance, and inter-specific competition, can have large impacts on pathogen antibiotic susceptibility, highlighting the importance of microbial ecology for designing successful antibiotic treatments for multispecies communities.

Enhancing the stability of active pharmaceutical ingredients by the cocrystal strategy

Cocrystal strategies to achieve excellent physiochemical performance under different environmental stress were highlighted here. The lattice energy and the energy barrier of degradation reactions are two pillars in a stable cocrystal construction.

Influence of Concentration and Temperature on Stability of Imipenem Focused on Solutions for Extended Infusion

Background

Imipenem remains active against most Gram-positive and Gram-negative organisms. This study aimed to evaluate chemical stability of imipenem in 2 commonly used concentrations when stored in 3 various temperatures.

Methods

Imipenem injection powder was used to prepare 5 mL and 10 mg/mL of imipenem in .9% sodium chloride solution. Prepared solutions in PVC bags were stored at 25°C, 30°C, and 40°C. The solutions were investigated over 0, 1, 2, 3, 4, and 6 hours using HPLC analysis. The association between drug stability, temperature, and concentration was determined.

Results

The 5 mg/mL solutions of brand A and B imipenem mL were stable for 6 hours at 25°C, 30°C, and 40°C, respectively. For 10 mg/mL, the solution of brand A was stable for 3 hours and brand B was stable for 6 hours at 25°C. Also, brand A and B imipenem solutions at the concentration of 10 mg/mL were stable for less than 1 hour at 30°C and 40°C.

Conclusion

The stability of imipenem injection solution was affected by temperature and concentration. Increasing in temperature and drug concentration resulted in decreased stability of imipenem. Suitable temperature and drug concentration should be concerned when this drug is given by extended infusion.

Simultaneous determination of meropenem and imipenem in rat plasma by LC-MS/MS and its application to a pharmacokinetic study

An efficient and reliable method using LC-MS/MS was established and validated for the simultaneous quantification of meropenem and imipenem in rat plasma. An electronic spray ion source in the positive multiple reaction monitoring mode was used for the detection and the transitions were m/z 384.6 → m/z 141.2 for meropenem, m/z 300.1 → m/z 141.8 for imipenem and m/z 423.4 → m/z 207.1 for matrine (IS). The calibration curves of meropenem and imipenem were linear in the range of 0.50-200 μg/mL. Satisfactory separation was achieved with a total run time of 3.0 min, the injection volume was 3 μl. The retention times of meropenem, imipenem and IS were 1.19, 1.14 and 1.13 min, respectively. Meropenem and imipenem are easily hydrolyzed in plasma. HEPES was used as a stabilizer and added to the plasma samples immediately after centrifugation. Extractions of meropenem, imipenem and IS were carried out by protein precipitation with acetonitrile. The specificity, precision and accuracy, stability, recovery and matrix effects were within acceptance limits. This method was successfully applied to investigate the pharmacokinetics of intravenous injection of meropenem and imipenem single administration or combined with sulbactam in rats. We found that sulbactam has no influence on the pharmacokinetics behavior of meropenem or imipenem.

Population Pharmacokinetics and Dose Optimization of Ceftazidime and Imipenem in Patients with Acute Exacerbations of Chronic Obstructive Pulmonary Disease

Background: Ceftazidime and imipenem have been increasingly used to treat Acute Exacerbations of Chronic Obstructive Pulmonary Disease (AECOPD) due to their extended-spectrum covering Pseudomonas aeruginosa. This study aims to describe the population pharmacokinetic (PK) and pharmacodynamic (PD) target attainment for ceftazidime and imipenem in patients with AECOPD. Methods: We conducted a prospective PK study at Bach Mai Hospital (Viet Nam). A total of 50 (ceftazidime) and 44 (imipenem) patients with AECOPD were enrolled. Population PK analysis was performed using Monolix 2019R1 and Monte Carlo simulations were conducted to determine the optimal dose regimen with respect to the attainment of 60% and 40% fT>MIC for ceftazidime and imipenem, respectively. A dosing algorithm was developed to identify optimal treatment doses. Results: Ceftazidime and imipenem PK was best described by a one-compartment population model with a volume of distribution and clearance of 23.7 L and 8.74 L/h for ceftazidime and 15.1 L and 7.88 L/h for imipenem, respectively. Cockcroft–Gault creatinine clearance represented a significant covariate affecting the clearance of both drugs. Increased doses with prolonged infusion were found to cover pathogens with reduced susceptibility. Conclusions: This study describes a novel and versatile three-level dosing algorithm based on patients’ renal function and characteristic of the infective pathogen to explore ceftazidime and imipenem optimal regimen for AECOPD.

Home intravenous antibiotherapy and the proper use of elastomeric pumps: Systematic review of the literature and proposals for improved use

Over several decades, the economic situation and consideration of patient quality of life have been responsible for increased outpatient treatment. It is in this context that outpatient antimicrobial treatment (OPAT) has rapidly developed. The availability of elastomeric infusion pumps has permitted prolonged or continuous antibiotic administration by dint of a mechanical device necessitating neither gravity nor a source of electricity. In numerous situations, its utilization optimizes administration of time-dependent antibiotics while freeing the patient from the constraints associated with infusion by gravity, volumetric pump or electrical syringe pump and, more often than not, limiting the number of nurse interventions to one or two a day. That much said, the installation of these pumps, which is not systematically justified, entails markedly increased OPAT costs and is liable to expose the patient to a risk of therapeutic failure or adverse effects due to the instability of the molecules utilized in a non-controlled environment, instability that necessitates close monitoring of their use. More precisely, a prescriber must take into consideration the stability parameters of each molecule (infusion duration, concentration following dilution, nature of the diluent and pump temperature). The objective of this work is to evaluate the different means of utilization of elastomeric infusion pumps in intravenous antibiotic administration outside of hospital. Following a review of the literature, we will present a tool for optimized antibiotic prescription, in a town setting by means of an infusion device.

ChromID® CARBA Agar Fails to Detect Carbapenem-Resistant Enterobacteriaceae With Slightly Reduced Susceptibility to Carbapenems

After first detections of carbapenemase-producing Enterobacteriaceae (CPE) in animals, the European Union Reference Laboratory for Antimicrobial Resistance has provided a protocol for the isolation of carbapenemase-producing Escherichia (E.) coli from cecum content and meat. Up to now, only few isolates were recovered using this procedure. In our experience, the choice of the selective agar is important for the efficacy of the method. Currently, the use of the prevailing method fails to detect CPE that exhibit a low resistance against carbapenems. Thus, this study aims to evaluate the suitability of selective media with antibiotic supplements and commercial ChromID^® CARBA agar for a reliable CPE detection. For comparative investigations, detection of freeze-dried carbapenemase-resistant bacteria was studied on different batches of the ChromID^® CARBA agar as well as on MacConkey agar supplemented with 1 mg/L cefotaxime and 0.125 mg/L meropenem (McC+CTX+MEM). The suitability of the different media was assessed within a time of 25 weeks, starting at least six weeks before expiration of the media. Carbapenem-resistant isolates exhibiting a serine-based hydrolytic resistance mechanism (e.g., bla _KPC genes) were consistently detected over 25 weeks on the different media. In contrast, carbapenemase producers with only slightly reduced susceptibility and exhibiting a zinc-catalyzed activity (e.g., bla _VIM, bla _NDM, and bla _IMP) could only be cultivated on long-time expired ChromID^® CARBA, but within the whole test period on McC+CTX+MEM. Thus, ChromID^® CARBA agar appears to be not suitable for the detection of CPE with slightly increased minimum inhibitory concentrations (MIC) against carbapenems, which have been detected in German livestock and thus, are of main interest in the national monitoring programs. Our data are in concordance with the results of eleven state laboratories that had participated in this study with their ChromID^® CARBA batches routinely used for the German CPE monitoring. Based on the determined CPE detection rate, we recommend the use of McC+CTX+MEM for monitoring purposes. This study indicates that the use of ChromID^® CARBA agar might lead to an underestimation of the current CPE occurrence in food and livestock samples.

Comparative in vitro antimicrobial potency, stability, colouration and dissolution time of generics versus innovator of meropenem in Europe

Meropenem generics are often imposed on prescribers, however scarce information is available on key properties such as antimicrobial potency, stability and colouration in solution, and dissolution time. This study aimed to generate comparative information for products available in Europe. The originator (ASTRA) and four generics (HOSPIRA, SANDOZ, FRESENIUS and AUROVIT) were compared for: (i) MICs against Pseudomonas aeruginosa clinical isolates (range, 0.125-191 mg/L); (ii) colouration (visual and photometry) and stability of concentrated solutions for prolonged or continuous infusion and maintained at 25-37 °C for up to 8 h (acceptable limit, ≥90% of original concentration); and (iii) dissolution time of concentrated solutions (50 mg/mL [for bolus administration]: turbidimetry and nursing personnel assessment). No significant difference was observed for MICs (except 2/80 isolates). For concentrated solutions storage: (i) SANDOZ produced about two times more yellow-coloured degradation products than the other preparations; (ii) meropenem loss was time-, concentration- and temperature-dependent; (iii) FRESENIUS was the least stable (limit for 1 g/48 mL, ~8 h at 25 °C and 4.5 h at 37 °C); (iv) at 2 g/48 mL, the storage time limit was 5-6 h at 25 °C and ~3 h at 37 °C for all preparations. Complete dissolution (turbidimetry) required 240 s for generics (120 s for ASTRA), and nurses reported longer but highly variable times for generics. Substantial differences between innovator and generics have been identified that could impact on their clinical use and/or make multicentric studies difficult to interpret, requiring suitability studies in the environments of their intended use.

Evaluation of Tobramycin and Ciprofloxacin as a Synergistic Combination Against Hypermutable Pseudomonas Aeruginosa Strains via Mechanism-Based Modelling

Hypermutable Pseudomonas aeruginosa strains have a greatly increased mutation rate and are prevalent in chronic respiratory infections. Initially, we systematically evaluated the time-course of total and resistant populations of hypermutable (PAO∆mutS) and non-hypermutable (PAO1) P. aeruginosa strains in 48-h static concentration time-kill studies with two inocula. Both strains were exposed to clinically relevant concentrations of important antibiotics (aztreonam, ceftazidime, imipenem, meropenem, tobramycin, and ciprofloxacin) in monotherapy. The combination of tobramycin and ciprofloxacin was subsequently assessed in 48-h static concentration time-kill studies against PAO1, PAO∆mutS, and two hypermutable clinical P. aeruginosa strains. Mechanism-based mathematical modelling was conducted to describe the time-course of total and resistant bacteria for all four strains exposed to the combination. With all monotherapies, bacterial regrowth and resistant populations were overall more pronounced for PAO∆mutS compared to PAO1. The combination of tobramycin and ciprofloxacin was synergistic, with up to 10^6.1 colony forming units (CFU)/mL more bacterial killing than the most active monotherapy for all strains, and largely suppressed less-susceptible populations. This work indicates that monotherapies against hypermutable P. aeruginosa strains are not a viable option. Tobramycin with ciprofloxacin was identified as a promising and tangible option to combat hypermutable P. aeruginosa strains.

Systematic review of stability data pertaining to selected antibiotics used for extended infusions in outpatient parenteral antimicrobial therapy (OPAT) at standard room temperature and in warmer climates

Aim

To determine if there are sufficient stability data to confirm appropriate prescribing of antibiotics commonly used in outpatient parenteral antimicrobial therapy (OPAT) in warmer climates.

Data sources

Four databases were systematically searched using the terms 'beta-lactams', or 'antibiotics', or 'anti-bacterial agents' and 'drug stability' or drug storage' for studies specific to drug stability published between 1966 and February 2018.

Study selection

The search strategy initially identified 2879 potential articles. After title and abstract review, the full-texts of 137 potential articles were assessed, with 46 articles matching the inclusion and exclusion criteria included in this review.

Results

A large volume of stability data is available for the selected drugs. Stability data at temperatures higher than 25°C were available for several of the medications, however few drugs demonstrated stability in warmer climates of 34°C or higher. Only buffered benzylpenicillin, cefoxitin and buffered flucloxacillin were found to have stability data supporting OPAT in warmer climates. Sequential data, profiling the drug for an extended period in solution under refrigeration prior to the run-out period at the higher temperatures, are also lacking.

Limitations

This study was limited by including only peer reviewed articles. There may be further grey literature supporting the stability of some of the drugs mentioned.

Conclusion

There are insufficient stability data of antibiotic use in warmer climates. Studies to verify the stability and appropriate use of many antibiotics used in OPAT at standard room temperature and in warmer climates are urgently required. Several drugs in current use in the OPAT settings are lacking stability data.

Implications

Further research in this field is needed to develop structured evidence-based guidelines. Results of this review should be further compared with observed patient outcomes in current clinical practice.

Pharmacokinetics of Doripenem in Healthy Koreans and Monte Carlo Simulations to Explore Optimal Dosage Regimens in Patients With Normal and Enhanced Renal Function

Supplemental Digital Content is Available in the Text.

Background:

Dose adjustment is often required in patients with normal or enhanced renal function. The aim of this study is to investigate the pharmacokinetic (PK) properties of doripenem and explore optimal dosing regimens in patients with normal or enhanced renal function according to various minimum inhibitory concentrations (MICs).

Methods:

The authors conducted a clinical trial and analyzed PK samples in 11 healthy Korean subjects applying noncompartmental analysis and a population approach. The population PK parameter estimates were used in Monte Carlo simulations to explore optimal dosing regimens for a probability of target attainment of 90% at 40% fT_MIC (free drug concentrations above MIC).

Results:

The time course of doripenem concentrations was well described by a 2-compartment model. The population typical values of clearance and steady-state volume were 22.9 L/h and 19.1 L, respectively, and were consistent with our noncompartmental analysis results. When the MIC was greater than 1 mcg/mL, at least increasing the dose or prolonging the infusion time was essential in patients with normal or enhanced renal function.

Conclusions:

These results suggest that dosage adjustment such as increasing the dose or lengthening the infusion time should be considered in patients with normal or enhanced renal function.

Meropenem Combined with Ciprofloxacin Combats Hypermutable Pseudomonas aeruginosa from Respiratory Infections of Cystic Fibrosis Patients

Hypermutable Pseudomonas aeruginosa organisms are prevalent in chronic respiratory infections and have been associated with reduced lung function in cystic fibrosis (CF); these isolates can become resistant to all antibiotics in monotherapy. This study aimed to evaluate the time course of bacterial killing and resistance of meropenem and ciprofloxacin in combination against hypermutable and nonhypermutable P. aeruginosa Static concentration time-kill experiments over 72 h assessed meropenem and ciprofloxacin in mono- and combination therapies against PAO1 (nonhypermutable), PAOΔmutS (hypermutable), and hypermutable isolates CW8, CW35, and CW44 obtained from CF patients with chronic respiratory infections. Meropenem (1 or 2 g every 8 h [q8h] as 3-h infusions and 3 g/day as a continuous infusion) and ciprofloxacin (400 mg q8h as 1-h infusions) in monotherapies and combinations were further evaluated in an 8-day hollow-fiber infection model study (HFIM) against CW44. Concentration-time profiles in lung epithelial lining fluid reflecting the pharmacokinetics in CF patients were simulated and counts of total and resistant bacteria determined. All data were analyzed by mechanism-based modeling (MBM). In the HFIM, all monotherapies resulted in rapid regrowth with resistance at 48 h. The maximum daily doses of 6 g meropenem (T_>MIC of 80% to 88%) and 1.2 g ciprofloxacin (area under the concentration-time curve over 24 h in the steady state divided by the MIC [AUC/MIC], 176), both given intermittently, in monotherapy failed to suppress regrowth and resulted in substantial emergence of resistance (≥7.6 log₁₀ CFU/ml resistant populations). The combination of these regimens achieved synergistic killing and suppressed resistance. MBM with subpopulation and mechanistic synergy yielded unbiased and precise curve fits. Thus, the combination of 6 g/day meropenem plus ciprofloxacin holds promise for future clinical evaluation against infections by susceptible hypermutable P. aeruginosa.

A Natural Deep Eutectic Solvent Formulated to Stabilize β-Lactam Antibiotics

β-lactam antibiotics, such as penicillin share a very unstable chemical structure. In water-based solutions, such as those used for clinical applications, the β-lactam ring is readily opened due to a nucleophilic or electrophilic attack, leading to the loss of antimicrobial activity. Since the achievement and maintenance of optimum therapeutic levels of β-lactam antibiotics is critical for the resolution of many infectious clinical situations, and to avoid antibiotic resistance generation, the design of new non-aqueous dosage forms is urgent. Recently, natural deep eutectic solvents (NADES) have emerged as alternative non-toxic and non-aqueous solvents for different biomedical applications. In this work, we formulated and characterized a NADES composed by betaine and urea (BU). Using this solvent, we evaluated the stability of clavulanic acid (CLV) and imipenem (IMP) and characterized their antimicrobial activities calculating the minimal inhibitory concentration. Characterization of BU solvent by infrared spectroscopy (IR) and nuclear magnetic resonance spectroscopy (NMR) indicated that the obtained solvent has a microstructure mainly based on hydrogen bonding interactions and water addition strongly affects its dynamic. The stability of β-lactam antibiotic IMP and CLV using this solvent was increased by 7 fold and 2.5 fold respectively compared to water when analysed seven days after being dissolved. Microbiological assays showed that antibacterial activity at day seven was significantly decreased for both CLV and IMP when dissolved in water, while no change in their antibacterial properties was observed when antibiotics were dissolved in BU. The increased stability of IMP and CLV in BU may be related to the inert behaviour of the solvent and the higher dynamic restriction that helps antibiotics to maintain a more stable conformation. These data suggest the potential use of BU as a solvent to prevent degradation of β-lactam antibiotics.

Pharmacokinetics and Extracorporeal Membrane Oxygenation in Adults: A Literature Review

Extracorporeal membrane oxygenation is a rapidly emerging treatment for respiratory or cardiac failure and is used as a bridge to recovery, transplant, or destination therapy. Adult patients receiving extracorporeal membrane oxygenation also receive significant amounts of pharmacotherapy. Although the body of literature on extra-corporeal membrane oxygenation in general is extensive, only a few publications focus on pharmacokinetic changes related to extracorporeal membrane oxygenation in adults. Understanding pharmacokinetics in adult patients receiving extracorporeal membrane oxygenation is important to correctly select and dose medications in this patient population. This article reviews published studies of the effects of extracorporeal membrane oxygenation on pharmacokinetics in adults.

Population Pharmacokinetic Analysis of Doripenem after Intravenous Infusion in Korean Patients with Acute Infections

We investigated the population pharmacokinetics (PK) of doripenem in Korean patients with acute infections and determined an appropriate dosing regimen using a Monte Carlo simulation for predicting pharmacodynamics (PD). Patients (n = 37) with a creatinine clearance (CL_CR) of 20 to 50 ml/min or >50 ml/min who received a 250-mg or 500-mg dose of doripenem over the course of 1 h every 8 h, respectively, were included in this study. Blood samples were taken predosing and 0 h, 0.5 h, and 4 to 6 h after the fourth infusion. A nonlinear mixed-effect modeling tool was used for the PK analysis and pharmacodynamic simulation; doripenem PK were well described by a one-compartment model. The population mean values of the body weight (WT)-normalized clearance (CL/WT) and the body weight-normalized volume of distribution (V/WT) were 0.109 liter/h/kg of body weight (relative standard error, 9.197%) and 0.280 liter/kg (relative standard error, 9.56%), respectively. Doripenem CL was significantly influenced by CL_CR The proposed equation to estimate doripenem CL in Korean patients was CL/WT = 0.109 × WT × (CL_CR/57)^0.688, where CL/WT is in liters per hour per kilogram. CL in Korean patients was expected to be lower than that in Caucasian patients, regardless of renal function. The Monte Carlo simulation showed that 90% attainment of target PK/PD magnitudes could be achieved with the usual dosing regimens when the MIC was ≤1 mg/liter. However, prolonged infusions (4 h) should be considered, especially when patients have augmented renal function and for patients infected with pathogens with a high MIC. Our results provide an individualized doripenem dosing regimen for patients with various renal functions and for patients infected with bacteria with decreased susceptibility.

Stability of doripenem in reconstituted solution - thermal and oxidative decomposition kinetics and degradation products by LC-MS

A ultra-fast liquid chromatography method applied to quantitation of doripenem in powder for injection was validated. Validation parameters were assayed and a rapid analysis was established by a reversed-phase system comprising a C₁₈ column endcapped (50 × 4.0 mm, 2.0 μm), mobile phase consisting of phosphoric acid 0.01% (pH 3.8) and acetonitrile (98:02, v/v) and a flow rate of 0.4 mL min^-1 . Drug stability was studied through submission to forced conditions, allowing the major degradation products to be detected and the kinetics parameters to be established. Thermal and oxidative degradation were determined, and indicated a kinetic decomposition following first and second order, respectively. The main degradation products were identified by LC-MS analysis, and the results were evaluated in order to suggest the chemical structures corresponding to respective masses and fragmentations. Six compounds were identified, with m/z 411, 427, 437, 634, 650 and 664. All of them resulted from cleavage of β-lactam ring and alcoholic chain and/or dimerization. These experimental results provide valuable information about the stability of doripenem reconstituted solution and procedures for its handling and storage.

Is continuous infusion of imipenem always the best choice?

Monte Carlo simulations allow prediction and comparison of concentration-time profiles arising from different dosing regimens in a defined population, provided a population pharmacokinetic model has been established. The aims of this study were to evaluate the population pharmacokinetics of imipenem in critically ill patients with hospital-acquired pneumonia (HAP) and to assess the probability of target attainment (PTA) and cumulative fraction of response (CFR) using EUCAST data. A two-compartment model based on a data set of 19 subjects was employed. Various dosage regimens at 0.5-h and 3-h infusion rates and as continuous infusion were evaluated against the pharmacodynamic targets of 20%fT_>MIC, 40%fT_>MIC and 100%fT_>MIC. For the target of 40%fT_>MIC, all 0.5-h infusion regimens achieved optimal exposures (CFR ≥ 90%) against Escherichia coli and Staphylococcus aureus, with nearly optimal exposure against Klebsiella pneumoniae (CFR ≥ 89.4%). The 3-h infusions and continuous infusion exceeded 97% CFR against all pathogens with the exception of Pseudomonas aeruginosa and Acinetobacter spp., where the maximum CFRs were 85.5% and 88.4%, respectively. For the 100%fT_>MIC target, only continuous infusion was associated with nearly optimal exposures. Higher PTAs for the targets of 40%fT_>MIC and 100%fT_>MIC were achieved with 3-h infusions and continuous infusion in comparison with 0.5-h infusions; however, continuous infusion carries a risk of not reaching the MIC of less susceptible pathogens in a higher proportion of patients. In critically ill patients with HAP with risk factors for Gram-negative non-fermenting bacteria, maximum doses administered as extended infusions may be necessary.

Compatibility of Meropenem with Different Commercial Peritoneal Dialysis Solutions

♦ BACKGROUND: Intraperitoneal administration of antimicrobial agents is recommended for the treatment of peritoneal dialysis (PD)-related peritonitis. For home-based antimicrobial therapy it is common to supply patients with PD fluid bags with admixed antibiotic. Thus, the compatibility of meropenem with different PD fluids (PDFs), namely Extraneal, Physioneal 1.36% and Physioneal 2.27% (all Baxter Healthcare Corp., Deerfield, IL, USA), was investigated under varying storage conditions. ♦ METHODS: Meropenem (Venus Pharma, Werne, Germany) was stored at 6°C and 25°C over 14 days and at 37°C over 24 hours. Drug concentration over time was determined using high performance liquid chromatography, drug activity by a diffusion disk method, diluent stability by visual inspection and drug adsorption was calculated. Blank PD fluids and deionized water were used as comparator solutions. ♦ RESULTS: Compared to water, the stability of meropenem was minimally lower in Extraneal but markedly reduced in both Physioneal solutions. No significant drug adsorption was detected for any PDF investigated. ♦ CONCLUSIONS: Meropenem is stable and compatible with Extraneal and might be stored for up to a week at refrigeration temperature (6°C). A loss of ~20% of meropenem after 2 days at room temperature should be considered. Mixed Physioneal appears not suitable for storage at any temperature after meropenem has been admixed. A considerable drug degradation due to the warming up to body temperature through heating plates should further be taken into account in clinical practice.

Preparing and administering injectable antibiotics: How to avoid playing God

The emergence of bacterial resistance and the lack of new antibiotics in the pipeline represent a public health priority. Maximizing the quality of antibiotic prescriptions is therefore of major importance in terms of adequate preparation and administration modalities. Adequate preparation prevents the inactivation of antibiotics and is a prerequisite to maximizing their efficacy (taking into account the pharmacokinetic/pharmacodynamic relationship) and to minimizing their toxicity. Many antibiotic guidelines address the choice of drugs and treatment duration but none of them exclusively address preparation and administration modalities. These guidelines are based on the available literature and offer essential data for a proper antibiotic preparation and administration by physicians and nurses. They may lead to a better efficacy and to a reduced antibiotic resistance. Such guidelines also contribute to a proper use of drugs and improve the interaction between inpatient and outpatient care for a better overall management of patients.

Relative contribution of biological variation and technical variables to zone diameter variations of disc diffusion susceptibility testing

OBJECTIVES

Disc diffusion is still largely based on manual procedures. Technical variations originate from inoculum preparation, variations in materials, individual operator plate streaking and reading accuracy. Resulting measurement imprecision contributes to categorization errors. Biological variation resembles the natural fluctuation of a measured parameter such as antibiotic susceptibility around a mean value. It is deemed to originate from factors such as genetic background or metabolic state. This study analysed the relative contribution of different technical and biological factors to total disc diffusion variation.

METHODS

For calculation of relative error factor contribution to disc diffusion variability, five experiments were designed keeping different combinations of error factors constant. A mathematical model was developed to analyse the individual error factor contribution to disc diffusion variation for each of the tested drug-species combinations.

RESULTS

The contribution of biological variation to total diameter variance ranged from 10.4% to 98.8% for different drug-species combinations. Highest biological variation was found for Enterococcus faecalis WT and vancomycin (98.8%) and for penicillinase-producing Staphylococcus aureus and penicillin G (96.0%). Average imprecision of automated zone reading revealed that 1.4%-5.3% of total imprecision was due to technical variation, while materials, i.e. antibiotic discs and agar plates, contributed between 2.6% and 3.9%. Inoculum preparation and manual plate streaking contributed 6.8%-24.8% and 6.6%-24.3%, respectively, to total imprecision.

CONCLUSIONS

This study illustrates the relative contributions of technical factors that account for a significant part of total variance in disc diffusion. The highest relative contribution originated from the operator, i.e. manual inoculum preparation and plate streaking. Further standardization of inoculum preparation and plate streaking by automation could potentially increase the precision of disc diffusion and improve the correlation of susceptibility reports with clinical outcome.

The Use of a Combination Antibiogram to Assist with the Selection of Appropriate Antimicrobial Therapy for Carbapenemase-Producing Enterobacteriaceae Infections

Combination antibiograms can be used to evaluate organism cross-resistance among multiple antibiotics. As combination therapy is generally favored for the treatment of carbapenemase-producing Enterobacteriaceae (CPE), combination antibiograms provide valuable information about the combination of antibiotics that achieve the highest likelihood of adequate antibiotic coverage against CPE.

Determination of meropenem in bacterial media by LC-MS/MS

To support the development of a dynamic in vitro human pharmacokinetic/pharmacodynamic simulation model for biofilm-mediated infections and study stability of meropenem, an LC-MS/MS method for the determination of meropenem in Luria Bertani (LB) media was developed and validated in an API2000 LC-MS/MS system. A partial validation was also performed in M9 media. Sample aliquots of 100μL (or 25μL for M9 media) were mixed with the internal standard (IS) ceftazidime and filtered. The filtrate was directly injected onto a C8 column eluted with ammonium formate (10mM, pH 4) and acetonitrile (0.1% formic acid) in a gradient mode. ESI(+) and MRM with ion pair m/z 384→68 for meropenem and m/z 547→468 for the IS were used for quantification. The calibration curve concentration range was 50 to 25,000ng/mL. The recovery was over 98%. In LB media, significant signal suppression was observed throughout the time period of detection when compared with mobile phase solvents, but the matrix effect was compensated well with the IS. In M9 media, much less signal suppression was observed. The method is simple, fast, and reliable. Using the method, stability of meropenem in LB and M9 media were tested. No significant degradation was observed for at least 8h in both LB media (37°C) and M9 media (30°C), but more than 15% degradation was observed overnight (∼20h). The method was transferred to an API5000 LC-MS/MS system using meropenem-d6 as the IS.

Dosing nomograms for attaining optimum concentrations of meropenem by continuous infusion in critically ill patients with severe gram-negative infections: a pharmacokinetics/pharmacodynamics-based approach

The worrisome increase in Gram-negative bacteria with borderline susceptibility to carbapenems and of carbapenemase-producing Enterobacteriaceae has significantly undermined their efficacy. Continuous infusion may be the best way to maximize the time-dependent activity of meropenem. The aim of this study was to create dosing nomograms in relation to different creatinine clearance (CL(Cr)) estimates for use in daily clinical practice to target the steady-state concentrations (C(ss)s) of meropenem during continuous infusion at 8 to 16 mg/liter (after the administration of an initial loading dose of 1 to 2 g over 30 min). The correlation between meropenem clearance (CL(m)) and CL(Cr) was retrospectively assessed in a cohort of critically ill patients (group 1, n = 67) to create a formula for dosage calculation to target C(ss). The performance of this formula was validated in a similar cohort (group 2, n = 56) by comparison of the observed and the predicted C(ss)s. A significant relationship between CL(m) and CL(Cr) was observed in group 1 (r = 0.72, P < 0.001). The application of the formula to meropenem dosing in group 2, infusion rate (g/24 h) = [0.078 × CL(Cr) (ml/min) + 2.85] × target C(ss) × (24/1,000), led to a significant correlation between the observed and the predicted C(ss)s (r = 0.92, P < 0.001). Dosing nomograms based on CL(Cr) were created to target the meropenem C(ss) at 8, 12, and 16 mg/liter in critically ill patients. These nomograms could be helpful in improving the treatment of severe Gram-negative infections with meropenem, especially in the presence of borderline susceptible pathogens or even of carbapenemase producers and/or of pathophysiological conditions which may enhance meropenem clearance.

Synergistic killing of multidrug-resistant Pseudomonas aeruginosa at multiple inocula by colistin combined with doripenem in an in vitro pharmacokinetic/pharmacodynamic model

Combination therapy may be required for multidrug-resistant (MDR) Pseudomonas aeruginosa. The aim of this study was to systematically investigate bacterial killing and emergence of colistin resistance with colistin and doripenem combinations against MDR P. aeruginosa. Studies were conducted in a one-compartment in vitro pharmacokinetic/pharmacodynamic model for 96 h at two inocula (~10(6) and ~10(8) CFU/ml) against a colistin-heteroresistant reference strain (ATCC 27853) and a colistin-resistant MDR clinical isolate (19147 n/m). Four combinations utilizing clinically achievable concentrations were investigated. Microbiological response was examined by log changes and population analysis profiles. Colistin (constant concentrations of 0.5 or 2 mg/liter) plus doripenem (peaks of 2.5 or 25 mg/liter every 8 h; half-life, 1.5 h) substantially increased bacterial killing against both strains at the low inoculum, while combinations containing colistin at 2 mg/liter increased activity against ATCC 27853 at the high inoculum; only colistin at 0.5 mg/liter plus doripenem at 2.5 mg/liter failed to improve activity against 19147 n/m at the high inoculum. Combinations were additive or synergistic against ATCC 27853 in 16 and 11 of 20 cases (4 combinations across 5 sample points) at the 10(6)- and 10(8)-CFU/ml inocula, respectively; the corresponding values for 19147 n/m were 16 and 9. Combinations containing doripenem at 25 mg/liter resulted in eradication of 19147 n/m at the low inoculum and substantial reductions in regrowth (including to below the limit of detection at ∼50 h) at the high inoculum. Emergence of colistin-resistant subpopulations of ATCC 27853 was substantially reduced and delayed with combination therapy. This investigation provides important information for optimization of colistin-doripenem combinations.

Clinically relevant plasma concentrations of colistin in combination with imipenem enhance pharmacodynamic activity against multidrug-resistant Pseudomonas aeruginosa at multiple inocula

The use of combination antibiotic therapy may be beneficial against rapidly emerging resistance in Pseudomonas aeruginosa. The aim of this study was to systematically investigate in vitro bacterial killing and resistance emergence with colistin alone and in combination with imipenem against multidrug-resistant (MDR) P. aeruginosa. Time-kill studies were conducted over 48 h using 5 clinical isolates and ATCC 27853 at two inocula (~10(6) and ~10(8) CFU/ml); MDR, non-MDR, and colistin-heteroresistant and -resistant strains were included. Nine colistin-imipenem combinations were investigated. Microbiological response was examined by log changes at 6, 24, and 48 h. Colistin combined with imipenem at clinically relevant concentrations increased the levels of killing of MDR and colistin-heteroresistant isolates at both inocula. Substantial improvements in activity with combinations were observed across 48 h with all colistin concentrations at the low inoculum and with colistin at 4× and 16× MIC (or 4 and 32 mg/liter) at the high inoculum. Combinations were additive or synergistic against imipenem-resistant isolates (MICs, 16 and 32 mg/liter) at the 10(6)-CFU inoculum in 9, 11, and 12 of 18 cases (i.e., 9 combinations across 2 isolates) at 6, 24, and 48 h, respectively, and against the same isolates at the 10(8)-CFU inoculum in 11, 7, and 8 cases, respectively. Against a colistin-resistant strain (MIC, 128 mg/liter), combinations were additive or synergistic in 9 and 8 of 9 cases at 24 h at the 10(6)- and 10(8)-CFU inocula, respectively, and in 5 and 7 cases at 48 h. This systematic study provides important information for optimization of colistin-imipenem combinations targeting both colistin-susceptible and colistin-resistant subpopulations.

Carbapenemase-producing Klebsiella pneumoniae: (when) might we still consider treating with carbapenems?

Infections caused by carbapenemase-producing Klebsiella pneumoniae (CPKP) are increasing in frequency worldwide. CPKP isolates exhibit extensive drug resistance phenotypes, complicate therapy, and limit treatment options. Although CPKP isolates are often highly resistant to carbapenems, a proportion of these have relatively low MICs for carbapenems, raising the question of whether this class of agents has any therapeutic potential against CPKP infections. Results from animal studies and patient outcome data indicate that carbapenems retain meaningful in vitro activity against CPKP isolates with carbapenem MICs of ≤ 4 mg/L. Accumulating clinical experience also suggests that the therapeutic efficacy of carbapenems against CPKP isolates with MICs of ≤ 4 mg/L is enhanced when these agents are administered in combination with another active antibiotic. The results of human pharmacokinetic/pharmacodynamic studies are in line with the above observations; it is highly probable that a high-dose/prolonged-infusion regimen of a carbapenem would attain a time above the MIC value of 50% for CPKP isolates with MICs up to 4 mg/L, ensuring acceptable drug exposure and favourable treatment outcome. The analyses summarized in this review support the notion that carbapenems have their place in the treatment of CPKP infections and that the currently proposed EUCAST clinical breakpoints could direct physicians in making treatment decisions.