New formulations of amoxicillin/clavulanic acid: a pharmacokinetic and pharmacodynamic review

Amoxicillin-Clavulanate Breakpoints Against Enterobacterales: Rationale for Revision by the Clinical and Laboratory Standards Institute

Amoxicillin-clavulanate (AMC) is among the most frequently prescribed antibiotics globally. It has broad antibacterial activity against gram-positive, gram-negative, and anaerobic bacteria and has been used to treat infections caused by a broad range of pathogens. AMC breakpoints against Enterobacterales were initially set in the 1980s. However, since that time, increases in antibiotic resistance, advances in pharmacokinetic/pharmacodynamic analyses, and publication of additional clinical data prompted a reassessment by the Clinical and Laboratory Standards Institute (CLSI) Subcommittee on Antimicrobial Susceptibility Testing. Based on this contemporary reappraisal, the CLSI retained the Enterobacterales breakpoints but revised comments regarding dosing associated with use of the AMC breakpoints in the 2022 supplement of M100. This viewpoint provides insight into the CLSI breakpoint reevaluation process and summarizes the data and rationale used to support these revisions to the AMC Enterobacterales breakpoint.

[Antibacterial therapy for acute streptococcal tonsillopharyngitis: results of a randomized comparative clinical trial with amoxicillin + clavulanic acid EXPRESS]

BACKGROUND

Acute tonsillopharyngitis is one of the most common types of respiratory tract infections. In case of bacterial etiologies of the disease, penicillin antibiotics are prescribed, in particular amoxicillin + clavulanic acid. Dispersible forms of antibiotics have a number of advantages over film-coated tablets and are characterized by better pharmacokinetic parameters that increase the effectiveness and safety of treatment, as well as patient compliance.

AIM

To compare the effectiveness and safety of Amoxicillin + Clavulanic acid EXPRESS in the form of dispersible tablets and amoxicillin with clavulanic acid in film-coated tablets in the treatment of acute streptococcal tonsillopharyngitis.

MATERIALS AND METHODS

A randomized comparative clinical study involved 60 adult patients diagnosed with acute streptococcal tonsillopharyngitis. Group 1 (n=30) received the Amoxicillin + Clavulanic acid EXPRESS, dispersible tablets, 875+125 mg 2 times a day at the beginning of meals. Group 2 (n=30) received Amoxiclav, film-coated tablets, 875+125 mg 2 times a day at the beginning of meals. The duration of the treatment was 10 days. The following procedures were performed to all participants: general clinical and otorhinolaryngological examinations, an express test to detect group A streptococcal antigens in a smear from the posterior pharyngeal wall (streptatest), assessment of symptoms of acute tonsillopharyngitis on the McIsaac scale, severity of sore throat, difficulty swallowing, swelling of the throat, measurement of body temperature, assessment of the clinical global impression of the therapy, adherence to treatment, frequency of the adverse reactions before treatment, 3 days after the beginning of therapy and after the course completion (day 10).

RESULTS

Recovery occurred in 96.6% of patients in group 1 according to examination on the 10th day of treatment and in 93.3% of patients in group 2. The rate of fever regression was higher in group 1 - on the 3rd day of treatment, normalization of temperature was observed in 36.6% and 30% of patients in the comparison group. Pain syndrome, symptoms of throat swelling and difficulty swallowing significantly (p<0.01) regressed by the 10th day in patients of both treatment groups. The incidence of adverse reactions on the 10th day of treatment in group 1 was 10%, in group 2 - 33.3% (p=0.03).

CONCLUSION

Amoxicillin + Clavulanic acid EXPRESS has high therapeutic efficacy in the treatment of acute streptococcal tonsillopharyngitis, comparable to the Amoxiclav in film-coated tablets. At the same time, dispersible tablets of Amoxicillin + Clavulanic acid EXPRESS demonstrated a significantly higher safety profile compared to the simple tablet form.

What if amoxicillin/clavulanic acid reduces the cisplatin anticancer impact on oral cancer treatment?

Antibiotics-chemotherapeutics combination have become on the table for many cancer treatments. For this reason, we thought that further progress and development of studies to support chemotherapeutic approaches with the use of antibiotics may be beneficial in the clinical field. Cell lines (SCC-15, HTB-41, and MRC-5) were treated with 5-100 μM/ml concentrations of cisplatin (cisp) and amoxicillin/clavulanic acid (amx/cla) with combination (amx/cla-cisp) and alone in three different incubation periods. The all-cells viability was examined with WST-1 and apoptotic activity of the drugs were investigated via cell death ELISA assay kit. The cytotoxic impact of the 100 μM amx/cla-cisp combination was found to be reduced by up to 21.8%, which was significant given that the cytotoxic effect of only cisplatin therapy was 86.1%. Because our findings demonstrated that solo amx/cla therapy have almost no impact on proliferation or death, we focused on the amx/cla-cisp combination effect. It was found that the amx/cla-cisp combination has reduced the apoptotic fragment when comparing with the solely cisp-treated cells. Due to amx/cla-cisp combination on both cells but significantly on SCC-15 recovered the sole cisplatin effect, we believe that there might be a second thought when prescribing antibiotics while treating cancer patients. Not only the antibiotic's type but also the cancer type might interact to lessen the chemotherapeutic agent's impact which is clinically a dilemma to focus on.

Pharmaceutical and Pharmacological Evaluation of Amoxicillin after Solubility Enhancement Using the Spray Drying Technique

The dose frequency of drugs belonging to class II is usually high and associated with harmful effects on the body. The study aimed to enhance the solubility of the poorly water-soluble drug amoxicillin (AM) by the solid dispersion (SD) technique. Six different SDs of AM, F1-F6, were prepared by the spray drying technique using two other carriers, HP-β-CD (F1-F3) and HPMC (F4-F6), in 1:1, 1:2, and 1:3 drug-to-polymer ratios. These SDs were analyzed to determine their practical yield, drug content, and aqueous solubility using analytical techniques such as Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and powder X-ray diffraction. The effect of polymer concentration on SDs was determined using aqueous solubility, in vitro dissolution, and in vivo studies. The results showed no drug-polymer interactions in SDs. Solubility studies showed that SDs based on the drug-to-polymer ratio of 1:2 (F2 and F5) were highly soluble in water compared to those with ratios of 1:1 and 1:3. In vitro dissolution studies also showed that SDs with a ratio of 1:2 released the highest drug concentration from both polymeric systems. The SDs based on HPMC confirmed the more sustained release of the drug as compared to that of HP-β-CD. All the SDs were observed as stable and amorphous, with a smooth spherical surface. In vivo studies reveal the enhancement of pharmacokinetics parameters as compared to standard AM. Hence, it is confirmed that spray drying is an excellent technique to enhance the solubility of AM in an aqueous medium. This may contribute to the enhancement of the pharmacokinetic behaviors of SDs.

CYP2B6 allelic variants and non-genetic factors influence CYP2B6 enzyme function

Human CYP2B6 enzyme although constitutes relatively low proportion (1–4%) of hepatic cytochrome P450 content, it is the major catalyst of metabolism of several clinically important drugs (efavirenz, cyclophosphamide, bupropion, methadone). High interindividual variability in CYP2B6 function, contributing to impaired drug-response and/or adverse reactions, is partly elucidated by genetic polymorphisms, whereas non-genetic factors can significantly modify the CYP2B6 phenotype. The influence of genetic and phenoconverting non-genetic factors on CYP2B6-selective activity and CYP2B6 expression was investigated in liver tissues from Caucasian subjects (N = 119). Strong association was observed between hepatic S-mephenytoin N-demethylase activity and CYP2B6 mRNA expression (P < 0.0001). In less than one third of the tissue donors, the CYP2B6 phenotype characterized by S-mephenytoin N-demethylase activity and/or CYP2B6 expression was concordant with CYP2B6 genotype, whereas in more than 35% of the subjects, an altered CYP2B6 phenotype was attributed to phenoconverting non-genetic factors (to CYP2B6-specific inhibitors and inducers, non-specific amoxicillin + clavulanic acid treatment and chronic alcohol consumption, but not to the gender). Furthermore, CYP2B6 genotype–phenotype mismatch still existed in one third of tissue donors. In conclusion, identifying potential sources of CYP2B6 variability and considering both genetic variations and non-genetic factors is a pressing requirement for appropriate elucidation of CYP2B6 genotype–phenotype mismatch.

Simultaneous solid-liquid separation and primary purification of clavulanic acid from fermentation broth of Streptomyces clavuligerus using salting-out extraction system

Clavulanic acid (CA) is usually used together with other β-lactam antibiotics as combination drugs to inhibit bacterial β-lactamases, which is mainly produced from the fermentation of microorganism such as Streptomyces clavuligerus. Recently, it is still a challenge for downstream processing of low concentration and unstable CA from fermentation broth with high solid content, high viscosity, and small cell size. In this study, an integrated process was developed for simultaneous solid-liquid separation and primary purification of CA from real fermentation broth of S. clavuligerus using salting-out extraction system (SOES). First, different SOESs were investigated, and a suitable SOES composed of ethanol/phosphate was chosen and further optimized using the pretreated fermentation broth. Then, the optimal system composed of 20% ethanol/15% K2HPO4 and 10% KH2PO4 w/w was used to direct separation of CA from untreated fermentation broth. The result showed that the partition coefficient (K) and recovery yield (Y) of CA from untreated fermentation broth were 29.13 and 96.8%, respectively. Simultaneously, the removal rates of the cells and proteins were 99.8% and 63.3%, respectively. Compared with the traditional method of membrane filtration or liquid-liquid extraction system, this developed SOES showed the advantages of simple operation, shorter operation time, lower process cost and higher recovery yield of CA. These results demonstrated that the developed SOES could be used as an attractive alternative for the downstream processing of CA from real fermentation broth.

Geminal Diheteroatomic Motifs: Some Applications of Acetals, Ketals, and Their Sulfur and Nitrogen Homologues in Medicinal Chemistry and Drug Design

Acetals and ketals and their nitrogen and sulfur homologues are often considered to be unconventional and potentially problematic scaffolding elements or pharmacophores for the design of orally bioavailable drugs. This opinion is largely a function of the perception that such motifs might be chemically unstable under the acidic conditions of the stomach and upper gastrointestinal tract. However, even simple acetals and ketals, including acyclic molecules, can be sufficiently robust under acidic conditions to be fashioned into orally bioavailable drugs, and these structural elements are embedded in many effective therapeutic agents. The chemical stability of molecules incorporating geminal diheteroatomic motifs can be modulated by physicochemical design principles that include the judicious deployment of proximal electron-withdrawing substituents and conformational restriction. In this Perspective, we exemplify geminal diheteroatomic motifs that have been utilized in the discovery of orally bioavailable drugs or drug candidates against the backdrop of understanding their potential for chemical lability.

Opportunities for Stewardship in the Transition From Intravenous to Enteral Antibiotics in Hospitalized Pediatric Patients

BACKGROUND/OBJECTIVE

Pediatric patients hospitalized with bacterial infections often receive intravenous (IV) antibiotics. Early transition to enteral antibiotics can reduce hospital duration, cost, and complications. We aimed to identify opportunities to transition from IV to enteral antibiotics, describe variation of transition among hospitals, and evaluate feasibility of novel stewardship metrics.

METHODS

This multisite retrospective cohort study used the Pediatric Health Information System to identify pediatric patients hospitalized with pneumonia, neck infection, orbital infection, urinary tract infection (UTI), osteomyelitis, septic arthritis, or skin and soft tissue infection (SSTI) between 2017 and 2018. Opportunity days were defined as days on which patients received both IV antibiotics and enteral medications, suggesting enteral tolerance. Percent opportunity was defined as opportunity days divided by days on any antibiotics. Both outcomes excluded IV antibiotics that have no alternative oral formulation. We evaluated outcomes per infection and antibiotic and assessed across-hospital variation.

RESULTS

We identified 88,522 aggregate opportunity days in 100,103 hospitalizations. On 57% of the antibiotic days, there was an opportunity to switch patients to enteral therapy, with greatest opportunity days in SSTI, neck infection, and pneumonia encounters, and with clindamycin, ceftriaxone, and ampicillin-sulbactam. Percent opportunity varied by infection (73% in septic arthritis to 40% in pneumonia). There was significant across-hospital variation in percent opportunity for all infections.

CONCLUSION

This multicenter study demonstrated the potential opportunity to transition from IV to enteral therapy in over half of antibiotic days. Opportunity varied by infection, antibiotic, and hospital. Across-hospital variation demonstrated likely missed opportunities for earlier transition and the need to define optimal transition times. Stewardship efforts promoting earlier transition for highly bioavailable antibiotics could reduce healthcare utilization and promote high-value care. We identified feasible stewardship metrics.

Antibiotic treatment in acute exacerbation of COPD: patient outcomes with amoxicillin vs. amoxicillin/clavulanic acid-data from 43,636 outpatients

BACKGROUND

For antibiotic treatment of Acute exacerbations of COPD (AECOPD) the National guidelines in Denmark recommend either first choice amoxicillin 750 mg TID (AMX) or amoxicillin with clavulanic acid 500 mg/125 mg TID (AMC). Addition of clavulanic acid offers a broader spectrum; opposite, AMX alone in a higher dose may offer more time above MIC. The aim of this study was to determine which of these regimens is associated with better outcome.

METHODS

The Danish Registry of COPD (DrCOPD), a nationwide outpatient COPD registry, was crosslinked with medication data and hospital contacts. The first prescription of AMX or AMC after inclusion in DrCOPD was used as exposure variable. Adjusted Cox proportional hazards models were used to analyze the risk of hospitalization or death (combined) within 30 days and other endpoints.

RESULTS

For the first treatment of AECOPD 12,915 received AMX, and 30,721 patients received AMC. AMX was associated with a decreased risk of pneumonia hospitalization or death (aHR 0.6, 95% CI 0.5-0.7; p < 0.0001) compared to AMC.

CONCLUSION

In AECOPD, empirically adding clavulanic acid to amoxicillin is not associated with a better outcome; it seems safe for these patients to be treated with amoxicillin alone.

Penicillin - getting prescribing right for children

Penicillins are commonly prescribed to children. Recommendations in the product information may not be the most appropriate doses for children and may list clinical indications that are preferably treated with other antibiotics

Reputable guidelines, for example Therapeutic Guidelines: Antibiotic, offer up-to-date advice on optimal choice, route, dosage and duration of oral penicillins in children

In most instances, the child’s weight should be used to calculate the dose in mg per kg without exceeding the maximum adult dose

When prescribing higher weight-based doses of amoxicillin or flucloxacillin, check the volume of oral liquid required to complete a treatment course to ensure adequate supply

Population pharmacokinetics of ticarcillin in critically ill patients receiving extended daily diafiltration

The aim of this study was to describe the population pharmacokinetics of ticarcillin during extended daily diafiltration (EDDf) in critically ill patients with acute kidney injury. Blood samples were collected from critically ill patients prescribed ticarcillin during one to two dosing intervals during which EDDf was performed. Plasma samples were measured using a validated ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method. Concentration-time data were analysed using a population pharmacokinetics approach with Pmetrics®. A total of 53 blood samples were collected from six critically ill patients (three male). The mean ± standard deviation patient age, weight and body mass index (BMI) was 43 ± 22 years, 88 ± 14 kg and 31 ± 5 kg/m², respectively. A two-compartment linear model adequately described the data. Median population pharmacokinetic parameter estimates were as follows: clearance in the presence of EDDf (CL_EDDf), 6.41 L/h; clearance of EDDf (CL_non-EDDf), 4.97 L/h; volume of distribution of the central compartment (V_c), 56.46 L; intercompartmental clearance from the central to peripheral compartment (k_CP), 13.54 L/h; and intercompartmental clearance from the peripheral to central compartment (k_PC), 21.93 L/h. This is the first population pharmacokinetic model of ticarcillin in patients receiving EDDf. Large pharmacokinetic variability was found, supporting further investigation of the pharmacokinetics of less-studied β-lactam antibiotics in prolonged intermittent renal replacement therapy.

Pharmacokinetic drug interaction and safety after coadministration of clarithromycin, amoxicillin, and ilaprazole: a randomised, open-label, one-way crossover, two parallel sequences study

Purpose

Ilaprazole, the latest proton pump inhibitor, can be used with clarithromycin and amoxicillin as a triple therapy regimen for eradicating Helicobacter pylori. The aim of this study was to evaluate pharmacokinetic drug interactions and safety profiles after coadministration of clarithromycin, amoxicillin, and ilaprazole.

Methods

A randomised, open-label, one-way crossover, two parallel sequences study was conducted in 32 healthy subjects. In part 1, the subjects received a single dose of ilaprazole 10 mg in period 1 and clarithromycin 500 mg and amoxicillin 1000 mg twice daily for 6 days in period 2. In part 2, the subjects received clarithromycin 500 mg and amoxicillin 1000 mg once in period 1 and ilaprazole 10 mg twice daily for 6 days in period 2. In both sequences, the three drugs were coadministrated once on day 5 in period 2. Pharmacokinetic evaluations of ilaprazole (part 1), and clarithromycin and amoxicillin (part 2) were conducted.

Results

Twenty-eight subjects completed the study. For ilaprazole, the peak concentration (C_max) slightly decreased from 479 (ilaprazole alone) to 446 ng/mL (triple therapy) [Geometric least square mean ratio (90% confidence interval), 0.93 (0.70–1.22)]. The area under the concentration-time curve from 0 h to the last measurable concentration (AUC_last) slightly increased from 3301 to 3538 μg·h/mL [1.07 (0.85–1.35)]. For clarithromycin, the C_max slightly decreased from 1.87 to 1.72 μg/mL [0.90 (0.70–1.15)], and AUC_last slightly increased from 14.6 to 16.5 μg·h/mL [1.09 (0.87–1.37)]. For amoxicillin, the C_max slightly decreased from 9.37 to 8.14 μg/mL [0.86 (0.74–1.01)], and AUC_last slightly decreased from 27.9 to 26.7 μg·h/mL [0.98 (0.83–1.16)]. These changes in the PK parameters of each drug were not statistically significant.

Conclusions

The coadministration of ilaprazole, clarithromycin, and amoxicillin was tolerable and did not cause a significant PK drug interaction. Thus, a triple therapy regimen comprising ilaprazole, clarithromycin, and amoxicillin may be an option for the eradication of H. pylori.

Clinicaltrials.govnumber: NCT02998437.

Electronic supplementary material

The online version of this article (10.1007/s00228-018-2489-2) contains supplementary material, which is available to authorized users.

Optimization of Antimicrobial Treatment to Minimize Resistance Selection

Optimization of antimicrobial treatment is a cornerstone in the fight against antimicrobial resistance. Various national and international authorities and professional veterinary and farming associations have released generic guidelines on prudent antimicrobial use in animals. However, these generic guidelines need to be translated into a set of animal species- and disease-specific practice recommendations. This article focuses on prevention of antimicrobial resistance and its complex relationship with treatment efficacy, highlighting key situations where the current antimicrobial drug products, treatment recommendations, and practices may be insufficient to minimize antimicrobial selection. The authors address this topic using a multidisciplinary approach involving microbiology, pharmacology, clinical medicine, and animal husbandry. In the first part of the article, we define four key targets for implementing the concept of optimal antimicrobial treatment in veterinary practice: (i) reduction of overall antimicrobial consumption, (ii) improved use of diagnostic testing, (iii) prudent use of second-line, critically important antimicrobials, and (iv) optimization of dosage regimens. In the second part, we provided practice recommendations for achieving these four targets, with reference to specific conditions that account for most antimicrobial use in pigs (intestinal and respiratory disease), cattle (respiratory disease and mastitis), dogs and cats (skin, intestinal, genitourinary, and respiratory disease), and horses (upper respiratory disease, neonatal foal care, and surgical infections). Lastly, we present perspectives on the education and research needs for improving antimicrobial use in the future.

Antibiotic stability over six weeks in aqueous solution at body temperature with and without heat treatment that mimics the curing of bone cement

OBJECTIVES

Thermal stability is a key property in determining the suitability of an antibiotic agent for local application in the treatment of orthopaedic infections. Despite the fact that long-term therapy is a stated goal of novel local delivery carriers, data describing thermal stability over a long period are scarce, and studies that avoid interference from specific carrier materials are absent from the orthopaedic literature.

METHODS

In this study, a total of 38 frequently used antibiotic agents were maintained at 37°C in saline solution, and degradation and antibacterial activity assessed over six weeks. The impact of an initial supplementary heat exposure mimicking exothermically curing bone cement was also tested as this material is commonly used as a local delivery vehicle. Antibiotic degradation was assessed by liquid chromatography coupled to mass spectrometry, or by immunoassays, as appropriate. Antibacterial activity over time was determined by the Kirby-Bauer disk diffusion assay.

RESULTS

The heat exposure mimicking curing bone cement had minimal effect on stability for most antibiotics, except for gentamicin which experienced approximately 25% degradation as measured by immunoassay. Beta-lactam antibiotics were found to degrade quite rapidly at 37°C regardless of whether there was an initial heat exposure. Excellent long-term stability was observed for aminoglycosides, glycopeptides, tetracyclines and quinolones under both conditions.

CONCLUSIONS

This study provides a valuable dataset for orthopaedic surgeons considering local application of antibiotics, and for material scientists looking to develop next-generation controlled or extended-release antibiotic carriers.Cite this article: E. Samara, T. F. Moriarty, L. A. Decosterd, R. G. Richards, E. Gautier, P. Wahl. Antibiotic stability over six weeks in aqueous solution at body temperature with and without heat treatment that mimics the curing of bone cement. Bone Joint J 2017;6:296-306. DOI: 10.1302/2046-3758.65.BJR-2017-0276.R1.

Bacterial responses to antibiotics and their combinations

Antibiotics affect bacterial cell physiology at many levels. Rather than just compensating for the direct cellular defects caused by the drug, bacteria respond to antibiotics by changing their morphology, macromolecular composition, metabolism, gene expression and possibly even their mutation rate. Inevitably, these processes affect each other, resulting in a complex response with changes in the expression of numerous genes. Genome-wide approaches can thus help in gaining a comprehensive understanding of bacterial responses to antibiotics. In addition, a combination of experimental and theoretical approaches is needed for identifying general principles that underlie these responses. Here, we review recent progress in our understanding of bacterial responses to antibiotics and their combinations, focusing on effects at the levels of growth rate and gene expression. We concentrate on studies performed in controlled laboratory conditions, which combine promising experimental techniques with quantitative data analysis and mathematical modeling. While these basic research approaches are not immediately applicable in the clinic, uncovering the principles and mechanisms underlying bacterial responses to antibiotics may, in the long term, contribute to the development of new treatment strategies to cope with and prevent the rise of resistant pathogenic bacteria.

Influence of pharmacokinetics/pharmacodynamics of antibacterials in their dosing regimen selection

The choice of antimicrobial dosing in clinical practice in the past was based upon a 'penicillin mentality', that is, on the assumption that the in vivo antimicrobial efficacy is dependent on the duration of drug levels above the minimum inhibitory concentration of target microorganisms. Really, a rational antimicrobial therapy is strongly related to a basic understanding of the influence the patient has on the antibiotic (pharmacokinetics [PKs]) and the patient's response to the specific drug effects (pharmacodynamics [PDs]). PK/PD parameters are essential in facilitating the translation of microbiological activity into clinical situations, ensuring a successful outcome. This review will analyze the typical patterns of antimicrobial activity and the corresponding PK/PD parameters, with a special focus on a PK/PD dosing approach with the most commonly utilized antimicrobial agent classes.

Evaluation of drug formularies for pediatric intensive care

OBJECTIVES

To evaluate availability and reliability of pediatric drug dosing guidelines in selected formularies for intensive care patients. Most drugs used in the pediatric intensive care unit are prescribed off-label, often on the guidance of limited information from commonly used drug formularies.

DESIGN

Availability of dosing information on prescribed drugs in a Dutch intensive care unit from January 1, 2005 to December 31, 2006 was compared among four selected formularies (Micromedex, Lexi-Comp, Drug Formulary for Children, Drug Doses). Reliability of dosing guidelines was assessed by evaluating labeling status and literature data for the three most (midazolam, acetaminophen, and amoxicillin/clavulanic acid) and the three least (bosentan, ketanserin, and iloprost) prescribed drugs.

MEASUREMENTS AND MAIN RESULTS

The selected formularies covered 68% to 86% of all 257 prescribed drugs. Guidelines differ widely on daily doses per kilogram, dose description, dosing regimen, and age ranges. For the three most prescribed and one of the least prescribed drugs (bosentan), dosing guidelines adequately reflected labeling status and existing (but scarce) literature. No dosing guidelines were available for iloprost, and only one dosing guideline was available for ketanserin.

CONCLUSIONS

This study shows that four commonly used drug formularies give few and widely differing dosing guidelines for drugs prescribed in the intensive care unit. If guidelines exist, they seem to reflect labeling status (if present) and limited literature available. Findings from this study likely reflect the scarcity of drug studies in this population. Physicians should be aware of the limitations of these formularies for daily practice in this group of vulnerable patients.

Potassium clavulanate

The title salt, K(+)·C(8)H(8)NO(5) (-) [systematic name: potassium (2R,5R,Z)-3-(2-hy-droxy-ethyl-idene)-7-oxo-4-oxa-1-aza-bicyclo-[3.2.0]heptane-2-carb-oxyl-ate], a widely used β-lactam anti-biotic, is usually chemically unstable even in the solid state owing to its tendency to be hydrolysed. In the crystal structure, the potassium cations are arranged along the a axis, forming inter-actions to the carboxyl-ate and hy-droxy groups, resulting in one-dimensional ionic columns. These columns are arranged along the b axis, connected by O-H⋯O hydrogen bonds, forming a layer in the ab plane.

Variations in amoxicillin pharmacokinetic/pharmacodynamic parameters may explain treatment failures in acute otitis media

Pharmacokinetic/pharmacodynamic (PK/PD) modeling and Monte Carlo simulations suggest that amoxicillin should rarely fail as therapy for Streptococcus pneumoniae and Haemophilus influenzae acute otitis media (AOM) infections except when the S. pneumoniae are highly penicillin resistant or the H. influenzae are beta-lactamase producing. However, important and not infrequent exceptions to this expectation have been described. The objective of this review was to define the biologic variations in amoxicillin PK/PD parameters for the treatment of AOM in children and assess whether these variations could explain why the commonly employed amoxicillin PK/PD model is imperfect in predicting outcome for every patient in this clinical setting. To this end, a literature search of MEDLINE (1966-2006) and EMBASE (1974-2006) was conducted to identify studies that evaluated ampicillin or amoxicillin intestinal absorption, serum concentrations, and/or middle ear fluid (MEF) concentrations. Analysis of studies identified for review showed that the intestinal bioavailability of amoxicillin depends on passive diffusion and a saturable 'pump' mechanism that produces variable serum concentrations of the antibacterial agent. Indeed, substantial differences from patient to patient in serum (5- to 30-fold) and MEF (up to 20-fold) concentrations of amoxicillin occur following oral administration, and 15-35% of children have no detectable amoxicillin in MEF. These findings suggest that variability in PK/PD parameters may impact amoxicillin concentrations in serum and MEF, possibly explaining some AOM treatment failures.

Influence of posture on pharmacokinetics

INTRODUCTION

Body position may influence physiological characteristics, such as perfusion, gastrointestinal function and plasma volume. These characteristics may interact with key factors determining the pharmacokinetics of drugs (dissolution, absorption, distribution, metabolism, excretion).

OBJECTIVES

Based on a systematic literature search, current data on the effect of posture on physiological characteristics and/or pharmacokinetics are summarized, and the relevance of possible effects, such as those presenting in clinical practice and clinical pharmacokinetic studies, is assessed.

RESULTS

Postures which favour rapid gastric emptying (sitting, standing, recumbent right) accelerate the absorption of orally administered drugs. Consequently, these postures favour a shorter time to reach peak plasma drug concentration (t(max)) and a higher maximum plasma drug concentration (C(max)) and--in the case of transient saturation of first-pass metabolism--total exposure (area under the concentration-time curve, AUC) in comparison to recumbent left and supine positions (e.g. nifedipine: AUC 30 and 38% higher in standing and right lateral position vs. left lateral position; C(max) 149 and 80% higher, respectively). The magnitude of these postural effects depends strongly on the nature and amount of liquids and food ingested before drug administration and is most pronounced in the fasting state and after administration with a nonnutrient liquid. Changes in splanchnic-hepatic blood flow (e.g. reduction of estimated hepatic perfusion by 37% in standing vs. supine position) may substantially affect the metabolism of orally administered drugs, especially of those with a high/saturable first-pass metabolism. For highly protein-bound drugs (e.g. phenytoin, imipramine), the total plasma concentration has been found to be approximately 10% higher in standing than lying subjects due to changes in plasma volume.

CONCLUSIONS

Positioning of a patient may be an effective method of enhancing or retarding absorption of some drugs in appropriate clinical situations (e.g. toxic ingestions, bedridden patients). In clinical pharmacokinetic trials, such as bioequivalence studies, defining and maintaining posture precisely is a useful approach for reducing within- and between-subject variability.

Combination drugs, an emerging option for antibacterial therapy

The emerging and sustained resistance to antibiotics and the poor pipeline of new antibacterials is creating a major health issue worldwide. Bacterial pathogens are increasingly becoming resistant even to the most recently approved antibiotics. Few antibiotics are being approved by regulatory organizations, which reflects both the difficulty of developing such agents and the fact that antibiotic discovery programs have been terminated at several major pharmaceutical companies in the past decade. As a result, the output of the drug pipelines is simply not well positioned to control the growing army of resistant pathogens, although academic institutions and smaller companies are trying to fill that gap. An emerging option to fight such pathogens is combination therapy. Combinations of two antibiotics or antibiotics with adjuvants are emerging as a promising therapeutic approach. This article provides and discusses clinical and scientific challenges to support the development of combination therapy to treat bacterial infections.

[Evaluation of the in vitro activity of two betalactams on the oxidative metabolism of polymorphonuclear neutrophils]

STUDY AIMS

The aim was to evaluate the in vitro effects of amoxicillin and its combination with clavulanic acid, two beta-lactams intravenously injected, on the oxidative metabolism of polymorphonuclear neutrophils. These cells play the major role in the "respiratory burst" as they produce superoxide anion to kill the infectious agent. An activation of this process by the injected antibiotics could enhance the bactericidal action or explain some of adverse effects.

MATERIALS AND METHODS

Two models were used to estimate the O(2)(-) amounts produced in the presence of the antimicrobial agents. In the cellular model, O(2)(-) was generated by neutrophils artificially stimulated or not (separated by a gradient centrifugation through Histopaque 1077). In the acellular model, O(2)(-) was produced by the xanthine-xanthine oxidase system. O(2)(-) was measured by spectrophotometry using the ferricytochrome C reduction.

RESULTS

The O(2)(-) production by polymorphonuclear neutrophils was increased when both antibiotics were added to the reaction mixture. A significant activation of the cell oxidative metabolism was observed with amoxicillin using various stimulating agents, that was higher without stimulation and lower when amoxicillin and clavulanic acid were associated.

CONCLUSION

Amoxicillin could either activate polymorphonuclear neutrophils NADPH-oxidase or cause its activation by a membrane effect, or interfere with the zymosan activation way. It could then be supposed that this antimicrobial agent intensified the bactericidal effects.

Antimicrobial resistance trends among sinus isolates of Streptococcus pneumoniae in the United States (2001-2005)

OBJECTIVE

To test the susceptibility of Streptococcus pneumoniae sinus isolates collected across the United States against commonly used antimicrobial agents.

STUDY DESIGN AND SETTING

S. pneumoniae sinus isolates (N = 847) collected as part of the Tracking Resistance in the US Today Surveillance Program from 2001 to 2005 were tested against 8 antimicrobial agents.

RESULTS

In ascending order, the relative activities (% susceptible) were penicillin (51.8%), trimethoprim/sulfamethoxazole (TMP/SMX) (57.6%), erythromycin (59.5%), cefuroxime (62.0%), amoxicillin/clavulanate (85.5%), clindamycin (86.1%), levofloxacin (99.4%), and linezolid (100%; for 2004 and 2005 respiratory seasons, only). Resistance rates over the 5 years remained generally stable, although resistance to amoxicillin/clavulanate nearly doubled (from 6.5% to 12.9%). Forty percent of isolates were resistant to >or=2 agents tested.

CONCLUSIONS AND SIGNIFICANCE

Susceptibility trends among sinus S. pneumoniae isolates appear to have stabilized over the past 5 years. Resistance rates remain elevated for penicillin and macrolides, whereas the high prevalence of multidrug resistance remains a concern.