How can we predict bacterial eradication?

New insights into the treatment of acute otitis media

INTRODUCTION

Acute otitis media (AOM) affects most (80%) children by 5 years of age and is the most common reason children are prescribed antibiotics. The epidemiology of AOM has changed considerably since the widespread use of pneumococcal conjugate vaccines, which has broad-reaching implications for management.

AREAS COVERED

In this narrative review, we cover the epidemiology of AOM, best practices for diagnosis and management, new diagnostic technology, effective stewardship interventions, and future directions of the field. Literature review was performed using PubMed and ClinicalTrials.gov.

EXPERT OPINION

Inaccurate diagnoses, unnecessary antibiotic use, and increasing antimicrobial resistance remain major challenges in AOM management. Fortunately, effective tools and interventions to improve diagnostic accuracy, de-implement unnecessary antibiotic use, and individualize care are on the horizon. Successful scaling of these tools and interventions will be critical to improving overall care for children.

Pharmacokinetics of amoxicillin in obese and nonobese subjects

AIMS

To compare the pharmacokinetics of amoxicillin (AMX) in obese and nonobese subjects, given as single dose 875-mg tablets.

METHODS

A prospective, single-centre, open-label, clinical study was carried out involving 10 nonobese and 20 obese subjects given a dose of an AMX 875-mg tablet. Serial blood samples were collected between 0 and 8 hours after administration of AMX and plasma levels were quantified by liquid chromatography-tandem mass spectrometry. The pharmacokinetic parameters (PK) were calculated by noncompartmental analysis and means of the 2 groups were compared using Student t-test. Analysis of correlation between covariates and PK was performed using Pearson's correlation coefficient.

RESULTS

Ten nonobese subjects (mean age 30.6 ± 7.12 y; body mass index 21.56 ± 1.95 kg/m² ) and 20 obese subjects (mean age 34.47 ± 7.03 y; body mass index 33.17 ± 2.38 kg/m² ) participated in the study. Both maximum concentration (C_max ; 12.12 ± 4.06 vs. 9.66 ± 2.93 mg/L) and area under the curve (AUC)_0-inf (34.18 ± 12.94 mg.h/L vs. 26.88 ± 9.24 mg.h/L) were slightly higher in nonobese than in obese subjects, respectively, but differences were not significant. The volume of distribution (V/F) parameter was statistically significantly higher in obese compared to nonobese patients (44.20 ± 17.85 L vs. 27.57 ± 12.96 L). Statistically significant correlations were observed for several weight metrics vs. AUC, C_max , V/F and clearance, and for creatinine clearance vs. AUC, C_max and clearance.

CONCLUSION

In obese subjects, the main altered PK was V/F as a consequence of greater body weight. This may result in antibiotic treatment failure if standard therapeutic regimens are administered.

Is the penetration of clindamycin into the masseter muscle really enough to treat odontogenic infections?

OBJECTIVES

This study aims to determine the penetration of clindamycin into the masseter muscle of rats by microdialysis and correlate with the main microorganisms involved in odontogenic infections.

MATERIALS AND METHODS

Tissue concentrations of clindamycin in healthy muscle tissue were measured by microdialysis after administration of a single intravenous dose of 51 mg/kg and multiple doses of 17 mg/kg (8/8 h). It was quantified in plasma after a single administration of 51 mg/kg. Microdialysis samples were collected at 30-min intervals and clindamycin was assayed by LC-MS. Pharmacokinetic parameters and tissue penetration were determined. Pharmacokinetic/pharmacodynamic index (ƒ%T > minimum inhibitory concentration (MIC)) was considered to assess dosing regimens.

RESULTS

The pharmacokinetic parameters determined by non-compartmental plasma analysis for the dose of 51 mg/kg were similar to that determined by compartmental analysis. The maximum free interstitial concentration (C_max) of clindamycin in muscle tissue was 14.20 (10.63-14.89) and 4.82 (3.35-6.66) mg/L for 51 mg/kg and 17 mg/kg 8/8 h, respectively. In addition, the area under the curve (AUC_0-inf) for plasma and tissue of clindamycin were 44.78 (28.82-65.65) and 16.54 (13.83-18.35) h.mg/L for 51 mg/kg, respectively, and the tissue penetration factor determined was 1.10. Considering that the main bacteria that cause odontogenic infections generally present MIC ≤ 0.5 mg/L, the ƒ%T > MIC index is reached when the dose regimen of 17 mg/kg 8/8 h is employed.

CONCLUSIONS

This investigation showed that clindamycin excellently penetrates muscle tissue of rats. It provides effective antibacterial concentrations at the target site when 17 mg/kg 8/8 h is employed and can be applied to treat the main bacteria causing odontogenic infections.

CLINICAL RELEVANCE

It reinforces the use of clindamycin in odontogenic infections with significant tissue penetration.

Reduced bioavailability of oral amoxicillin tablets compared to suspensions in Roux-en-Y gastric bypass bariatric subjects

AIMS

To evaluate the relative bioavailability of oral amoxicillin (AMX) tablets in comparison to AMX suspension in Roux-en-Y gastric bypass bariatric subjects.

METHODS

A randomized, double-blind, cross-over study was performed on the bioavailability of oral AMX tablets and suspension in Roux-en-Y gastric bypass subjects operated at least 3 months previously . Doses of 875 mg of the AMX tablet or 800 mg of the AMX suspension were given to all the subjects, allowing a washout of 7 days between the periods. Blood samples were collected at 0, 0.25, 0.5, 1, 1.5, 2, 4, 6 and 8 hours after drug administration and the AMX levels were quantified by liquid chromatography coupled with triple quadrupole tandem mass spectrometry. The pharmacokinetic parameters were calculated by noncompartmental analysis, normalized to an 875 mg dose and the bioavailability of the AMX from the tablets was compared to that from the suspension formulation.

RESULTS

Twenty subjects aged 42.65 ± 7.21 years and with a body mass index of 29.88 ± 4.36 kg/m² were enrolled in the study. The maximum AMX plasma concentration of the tablets and the suspension (normalized to 875 mg) were 7.42 ± 2.99 mg/L and 8.73 ± 3.26 mg/L (90% confidence interval of 70.71-99.11), and the total area under the curve from time zero to infinity were 23.10 ± 7.41 mg.h/L and 27.59 ± 8.32 mg.h/L (90% confidence interval of 71.25-97.32), respectively.

CONCLUSION

The tablets presented a lower bioavailability than the suspension formulation and the total absorbed amount of AMX in these subjects was lower in comparison to the standard AMX absorption rates in nonbariatric subjects, regardless of the formulation.

Evidence-Based Recommendations for Antimicrobial Nasal Washes in Chronic Rhinosinusitis

Background

Chronic rhinosinusitis (CRS) refractory to medical and surgical therapy is a difficult problem for patients and physicians. Topical antimicrobial nasal irrigations are commonly used for treatment with great variation in methodology and without clear scientific support for current treatment formulations. The purpose of this study was to develop a scientific rationale for creating standardized recommendations for clinical practice in the use of topical antimicrobial washes for CRS.

Methods

An extensive review of basic science and clinical literature on the treatment of CRS with topical antimicrobial washes was completed. Pharmacokinetics of and organism susceptibility to appropriate topically applied antimicrobial agents were reviewed.

Results

The most common organisms associated with CRS were identified. The relevant pharmacokinetics of drugs targeted at these organisms are presented. Susceptibility breakpoints set by the National Committee for Clinical Laboratory Standards are identified to help establish the most effective concentration of the identified drugs. Recommendations for agent selection, agent concentration, length of treatment, dosing schedule, and methods of irrigation are presented.

Conclusion

Antimicrobial nasal washes provide a potentially effective treatment for the growing population of patients who remain symptomatic after appropriate medical and surgical intervention. This study establishes the basic principles supporting this treatment option and offers rational, evidence-based treatment guidelines. The study has identified additional areas that need to be investigated before prospective clinical trials can be effectively undertaken.

Role of Honey in Topical and Systemic Bacterial Infections

BACKGROUND

The development of bacterial resistance to antibiotics has made it more difficult and expensive to treat infections. Honey is getting worldwide attention as a topical therapeutic agent for wound infections and potential future candidate for systemic infections.

OBJECTIVES

The purpose of this review was to summarise different antibacterial bio-active compounds in honey, their synergistic interaction and their clinical implications in topical and systemic infections. In addition, contemporary testing methods for evaluating peroxide and non-peroxide antibacterial activity of honey were also critically appraised.

DESIGN

MEDLINE, EMBASE, Cochrane Library, Pub Med, reference lists and databases were used to review the literature.

RESULTS

Honey contains several unique antibacterial components. These components are believed to act on diverse bacterial targets, are broad spectrum, operate synergistically, prevent biofilm formation, and decrease production of virulence factors. Moreover, honey has the ability to block bacterial communication (quorum sensing), and therefore, it is unlikely that bacteria develop resistance against honey. Bacterial resistance against honey has not been documented so far. Unlike conventional antibiotics, honey only targets pathogenic bacteria without disturbing the growth of normal gastrointestinal flora when taken orally. It also contains prebiotics, probiotics, and zinc and enhances the growth of beneficial gut flora. The presence of such plethora of antibacterial properties in one product makes it a promising candidate not only in wound infections but also in systemic and particularly for gastrointestinal infections. Agar diffusion assay, being used for evaluating antibacterial activity of honey, is not the most appropriate and sensitive assay as it only detects non-peroxide activity when present at a higher level. Therefore, there is a need to develop more sensitive techniques that may be capable of detecting and evaluating different important components in honey as well as their synergistic interaction.

CONCLUSIONS

Keeping in view the current guidelines for treatment of diarrhea, honey is considered one of the potential candidates for treatment of diarrhea because it contains a natural combination of probiotics, prebiotics, and zinc. Therefore, it would be worthwhile if such a combination is tested in RCTs for treatment of diarrhea.

Pharmacokinetics and residue depletion of erythromycin in gilthead sea bream Sparus aurata L. after oral administration

Erythromycin (ERY) is an antibiotic effective against Streptococcus iniae, a microorganism responsible for significant losses in aquaculture. No data are available on the pharmacokinetics and residue depletion of ERY in sea bream. The aim of this study was thus to evaluate the pharmacokinetics of ERY in this species after a single oral administration at 75 mg kg(-1) b.w. and to assess its residue depletion from tissues after prolonged treatment for 10 days. ERY was rapidly absorbed in sea bream (Cmax  = 10.04 μg g(-1) and Tmax =1 h), with a half-life of 9.35 h and an AUC0-24 of 56.81 (h μg mL(-1) ). The data obtained and the evaluation of pharmacokinetic/pharmacodynamic parameters allowed us to hypothesize that dosage used in this study should be effective against S. iniae. A rapid reduction in erythromycin concentrations was observed in tissues, with the drug being detectable only during the first day post-treatment. In Europe, the use of ERY in aquaculture is allowed by off-label prescription with a withdrawal time of 500 °C day(-1) . The absence of ERY residues in tissues already at 24 h post-treatment suggests that ERY in sea bream should not pose human food safety issues.

Extended release amoxicillin/clavulanate: optimizing a product for respiratory infections based on pharmacodynamic principles

Acute bacterial respiratory tract infections cause a great deal of human morbidity and mortality. Treatment guidelines for these infections include macrolides, doxycycline, beta-lactams and beta-lactam/beta-lactamase inhibitor combinations such as amoxicillin/clavulanic acid to provide coverage for the common respiratory pathogens, including penicillin and macrolide nonsusceptible Streptococcus pneumoniae, as well as beta-lactamase-producing Haemophilus influenzae and Moraxella catarrhalis. In response to recent guidelines recommending higher dose amoxicillin to extend coverage to a higher percentage of S. pneumoniae, a new formulation of amoxicillin/clavulanic acid was developed. This formulation includes a higher amoxicillin dose, with part of the amoxicillin dose being in an extended release formulation, without increasing the clavulanate dose, for twice-daily oral treatment of these infections. Clinical studies of community-acquired pneumonia and acute rhinosinusitis have shown that the new formulation is well tolerated and highly efficacious, with clinical outcomes equivalent to comparators.

Pharmacokinetics and residue depletion of erythromycin in rainbow trout Oncorhynchus mykiss (Walbaum)

Erythromycin (ERY) is a drug active against Gram-positive bacteria such as Lactococcus garvieae, a pathogen responsible for an important disease that may cause a substantial decrease in rainbow trout Oncorhynchus mykiss (Walbaum) production, the species of fish most commonly produced in Italy. In the literature, studies on the kinetics behaviour of ERY in fish are limited. Therefore, the aim of the present study was to evaluate the pharmacokinetics of ERY in rainbow trout after a single oral treatment with 75 mg kg⁻¹ body weight (b.w.) of ERY and the residue depletion after multiple oral administration of 75 mg kg⁻¹ b.w. day⁻¹ of ERY for 10 days. Blood concentrations of ERY increased up to 20.24 ± 13.32 μg mL⁻¹ at 6 h, then decreased to 5.97 ± 3.89 μg mL⁻¹ at 24 h. The time during which the antibiotic remains in the bloodstream at concentrations exceeding the MIC (T > MIC) and the area under the serum concentration-time curve (AUC)/MIC are both pharmacokinetic-pharmacodynamic (PK/PD) predictors of ERY efficacy, and the data obtained allowed us to hypothesize that a dosage of 75 mg kg⁻¹ b.w. day⁻¹ of ERY could treat the lactococcosis in trout. Regarding the study of ERY depletion, rapid elimination was observed in tissue (muscle plus adherent skin); in fact the concentrations were below the limit of quantification in all samples (except two) by day 10 post-treatment. ERY is not licensed in Europe for use in aquaculture, and its use is possible only by off-label prescription with a precautionary withdrawal time of 500 degree-days, as established by Directive 2004/28/EC. From the data obtained in this study, a withdrawal time of 8.90 days was calculated, corresponding, in our experimental conditions, to 117.5 degree-days, a value significantly lower than that established by the European directive.

Evaluation of Antimicrobial Treatments in Children with Acute Otitis Media in Spain: A Pharmacokinetic-Pharmacodynamic (PK/PD) Approach

Pharmacokinetic/pharmacodynamic (PK/PD) principles are priceless tools for evaluating the effectiveness of different antimicrobial treatments for different infections. However, very few studies deal with pediatric dosages and take into account the unbound drug serum levels. Our study is focused on the most frequent antibiotic dosing schedules used in Spain for the treatment of acute otitis media (AOM) in children, where high rates of penicillin and macrolide resistance exist among pneumococcal isolates. Pharmacokinetic parameters of antibiotics in children where obtained from the literature. The minimum inhibitory concentrations (MIC90) of antibiotics for pediatric strains of Streptococcus pneumoniae and Haemophilus influenzae were obtained from the SAUCE 2 project. Only ceftriaxone (50 mg/kg single intramuscular dose) and high doses of co-amoxiclav (27-33 mg/kg q8h) provided adequate efficacy indexes (tss(%)>MIC) for both S. pneumoniae and H. influenzae in AOM in children. These results are consistent with MEF (medium ear fluid) levels obtained from the literature. Our results confirm the utility of serum unbound levels to predict efficacy of antibiotics in children with AOM.

Pharmacodynamics for predicting therapeutic outcome and countering resistance spread: The cefditoren case

The relationship between pharmacokinetics and pharmacodynamics is a key instrument to improve antimicrobial stewardship and should be aimed to identification of the drug exposure measure that is closely associated not only with the ability to kill organisms but also to suppress the emergence of resistant subpopulations. This article reviews published studies for efficacy prediction with cefditoren and those aimed to explore its potential for countering resistance spread, focusing on the three most prevalent community-acquired isolates from respiratory infections: Streptococcus pneumoniae (S. pneumoniae), Haemophilus influenzae (H. influenzae) and Streptococcus pyogenes (S. pyogenes). Studies for efficacy prediction include in vitro pharmacodynamic simulations (using physiological concentrations of human albumin) and mice models (taking advantage of the same protein binding rate in mice and humans) to determine the value of the pharmacodynamic indices predicting efficacy, and Monte Carlo simulations to explore population pharmacodynamic coverage, as weapons for establishing breakpoints. Studies exploring the potential of cefditoren (free concentrations obtained with 400 mg cefditoren bid administration) for countering spread of resistance showed its capability for countering (1) intra-strain spread of resistance linked to ftsI gene mutations in H. influenzae; (2) the spread of H. influenzae resistant strains (with ftsI gene mutations) in multi-strain H. influenzae niches or of S. pneumoniae strains with multiple resistance traits in multi-strain S. pneumoniae niches; and (3) for overcoming indirect pathogenicity linked to β-lactamase production by H. influenzae that protects S. pyogenes in multibacterial niches. This revision evidences the ecological potential for cefditoren (countering resistance spread among human-adapted commensals) and its adequate pharmacodynamic coverage of respiratory pathogens (including those resistant to previous oral compounds) producing community-acquired infections.

Bioadhesive controlled metronidazole release matrix based on chitosan and xanthan gum

Metronidazole, a common antibacterial drug, was incorporated into a hydrophilic polymer matrix composed of chitosan xanthan gum mixture. Hydrogel formation of this binary chitosan-xanthan gum combination was tested for its ability to control the release of metronidazole as a drug model. This preparation (MZ-CR) was characterized by in vitro, ex vivo bioadhesion and in vivo bioavailability study. For comparison purposes a commercial extended release formulation of metronidazole (CMZ) was used as a reference. The in vitro drug-release profiles of metronidazole preparation and CMZ were similar in 0.1 M HCl and phosphate buffer pH 6.8. Moreover, metronidazole preparation and CMZ showed a similar detachment force to sheep stomach mucosa, while the bioadhesion of the metronidazole preparation was higher three times than CMZ to sheep duodenum. The results of in vivo study indicated that the absorption of metronidazole from the preparation was faster than that of CMZ. Also, MZ-CR leads to higher metronidazole C(max) and AUC relative to that of the CMZ. This increase in bioavailability might be explained by the bioadhesion of the preparation at the upper part of the small intestine that could result in an increase in the overall intestinal transit time. As a conclusion, formulating chitosan-xanthan gum mixture as a hydrophilic polymer matrix resulted in a superior pharmacokinetic parameters translated by better rate and extent of absorption of metronidazole.

Ocular pharmacokinetics of AzaSite Xtra-2% azithromycin formulated in a DuraSite delivery system

PURPOSE

The pharmacokinetics of a 2% ocular solution of azithromycin in DuraSite was evaluated in rabbits to determine whether the PK/PD parameters support a once-a-day for three-day therapeutic regimen against bacterial conjunctivitis.

MATERIALS AND METHODS

Mean levels of azithromycin were determined in tears, bulbar conjunctiva, cornea, and plasma following a single drop of 2% azithromycin. The levels were determined by HPLC-MS.

RESULTS

Concentrations of azithromycin peaked at 30 minutes. At the end of 24 hours, ocular tissue concentrations exceeded the MIC breakpoint for the most common causative pathogens of bacterial conjunctivitis by at least 7-fold.

CONCLUSION

The PK/PD profile of 2% azithromycin suggests efficacy against common causative bacteria with just one dose per day for three days.

Antimicrobial breakpoint estimation accounting for variability in pharmacokinetics

Background

Pharmacokinetic and pharmacodynamic (PK/PD) indices are increasingly being used in the microbiological field to assess the efficacy of a dosing regimen. In contrast to methods using MIC, PK/PD-based methods reflect in vivo conditions and are more predictive of efficacy. Unfortunately, they entail the use of one PK-derived value such as AUC or Cmax and may thus lead to biased efficiency information when the variability is large. The aim of the present work was to evaluate the efficacy of a treatment by adjusting classical breakpoint estimation methods to the situation of variable PK profiles.

Methods and results

We propose a logical generalisation of the usual AUC methods by introducing the concept of "efficiency" for a PK profile, which involves the efficacy function as a weight. We formulated these methods for both classes of concentration- and time-dependent antibiotics. Using drug models and in silico approaches, we provide a theoretical basis for characterizing the efficiency of a PK profile under in vivo conditions. We also used the particular case of variable drug intake to assess the effect of the variable PK profiles generated and to analyse the implications for breakpoint estimation.

Conclusion

Compared to traditional methods, our weighted AUC approach gives a more powerful PK/PD link and reveals, through examples, interesting issues about the uniqueness of therapeutic outcome indices and antibiotic resistance problems.

A probabilistic approach for the evaluation of pharmacological effect induced by patient irregular drug intake

Fine individual drug intake data, generally collected by electronic monitoring devices, reveal that individual marked random patterns are likely to persist through long therapeutic periods. This work aims to establish the relationship between irregularity in drug intake and its potential impact on therapeutic outcomes, which will also serve as a basis for more objective interventions. First we proposed a direct way to extract the necessary information representing the patient drug intake history. To provide a fair evaluation of the pharmacological performance, we revisited several classical pharmacological indices and proposed new ones in the stochastic context of patient's drug intake irregularity. To illustrate our procedure, we have considered two cases of HIV treatment using a combination of lopinavir/ritonavir (Kaletra@) for once daily and twice daily regimens. We have quantified the impact on therapeutic effect of various characteristics in dosing histories, namely missing doses and deviations from nominal times. Using our newly defined pharmacological indices, we clearly showed the ability of our probabilistic approach in measuring the impact of noncompliance. As a direct fallout, we have discussed strategies to attenuate the impact of noncompliance through an optimal design of dosing regimen.

New semiphysiological absorption model to assess the pharmacodynamic profile of cefuroxime axetil using nonparametric and parametric population pharmacokinetics

Cefuroxime axetil is widely used to treat respiratory tract infections. We are not aware of a population pharmacokinetic (PK) model for cefuroxime axetil. Our objectives were to develop a semiphysiological population PK model and evaluate the pharmacodynamic profile for cefuroxime axetil. Twenty-four healthy volunteers received 250 mg oral cefuroxime as a suspension after a standardized breakfast. Liquid chromatography-tandem mass spectrometry was used for drug analysis, NONMEM and S-ADAPT (results reported) were used for parametric population PK modeling, and NPAG was used for nonparametric population PK modeling. Monte Carlo simulations were used to predict the duration for which the non-protein-bound-plasma concentration was above the MIC (fT(>MIC)). A model with one disposition compartment, a saturable and time-dependent drug release from the stomach, and fast drug absorption from the intestine yielded precise (r > 0.992) and unbiased curve fits and an excellent predictive performance. The apparent clearance was 21.7 liters/h (19.8% coefficient of variation [CV]) and the volume of distribution 38.7 liters (18.3% CV). Robust (>or=90%) probabilities of target attainment (PTAs) were achieved by 250 mg cefuroxime given every 12 h (q12h) or q8h for MICs of <or=0.375 mg/liter or <or=0.5 mg/liter, respectively, for the bacteriostasis target fT(>MIC) of >or=40% and for MICs of <or=0.094 mg/liter or <or=0.375 mg/liter, respectively, for the near-maximal-killing target fT(>MIC) of >or=65%. For the >or=40% fT(>MIC) target, the PTAs for 250 mg cefuroxime q12h were >or=97.8% for Streptococcus pyogenes and penicillin-susceptible Streptococcus pneumoniae. Cefuroxime at 250 mg q12h or q8h achieved PTAs below 73% or 92%, respectively, for Haemophilus influenzae, Moraxella catarrhalis, and penicillin-intermediate S. pneumoniae for susceptibility data from various countries. Depending on the MIC distribution, 250 mg oral cefuroxime q8h instead of q12h should be considered, especially for more-severe infections that require near-maximal killing by cefuroxime.

Beta-lactam activity against penicillin-resistant Streptococcus pneumoniae strains exhibiting higher amoxicillin versus penicillin minimum inhibitory concentration values: an in vitro pharmacodynamic simulation

BACKGROUND

Activity of simulated serum concentrations after oral therapy with 400 mg cefditoren pivoxil b.i.d., 500 mg cefuroxime axetil b.i.d. and 875/125 mg amoxicillin/clavulanic acid b.i.d. and t.i.d. regimens was explored over 24 h against Streptococcus pneumoniae.

METHODS

Computerized pharmacodynamic simulations were performed against strains with penicillin/amoxicillin/cefuroxime/cefditoren minimum inhibitory concentrations (MICs, microg/ml) and serotypes: strain 1 (0.25/0.12/1/0.12; serotype 6A), strain 2 (2/4/ 2/0.25; serotype 6B), strain 3 (4/16/4/0.5; serotype 14), and strain 4 (4/16/8/1; serotype 14).

RESULTS

Bactericidal activity (> or =3 log(10) reduction) at 12 and 24 h was obtained against all strains with cefditoren, against strains 1 and 2 with cefuroxime and amoxicillin/clavulanic acid t.i.d., but only against strain 1 with amoxicillin/clavulanic acid b.i.d.. Bactericidal activity at 24 h was related to T > MIC of >30% dosing interval, 1.7-2.0 log(10) reductions with T > MIC of 20-30%, and <1 log(10) reduction or regrowth with T > MIC of 0%.

CONCLUSIONS

It is difficult to achieve pharmacodynamic coverage and bactericidal activity by physiological concentrations of oral beta-lactams against penicillin-resistant pneumococcal strains exhibiting higher amoxicillin versus penicillin MICs. Cefditoren may offer alternatives.

Cost-effectiveness of empirical prescribing of antimicrobials in community-acquired pneumonia in three countries in the presence of resistance

OBJECTIVES

To assess the cost-effectiveness of empirical outpatient treatment options for community-acquired pneumonia (CAP) in France, the USA and Germany, representing high, moderate and low antimicrobial resistance prevalence, respectively.

METHODS

A decision analytic model was developed for mild-to-moderate CAP outpatient treatment. Treatment algorithms incorporated follow-up after treatment failure due to resistance or other reasons. First-line treatment included moxifloxacin, beta-lactams, macrolides or doxycycline; second-line treatment used a different antimicrobial class. Country-specific resistance and co-resistance prevalences to first- and second-line therapy for the major CAP pathogens were derived from surveillance studies. Clinical failure rates due to antimicrobial-susceptible and -resistant pathogens were obtained from the literature or estimated. Total costs were estimated using standard sources and a third-party payer perspective. Outcome measures included first-line clinical failures avoided, second-line treatments avoided and hospitalizations avoided. Incremental cost-effectiveness ratios (ICERs) were calculated.

RESULTS

First-line moxifloxacin treatment followed by co-amoxiclav dominated all other treatments in France, the USA and in Germany for all outcome measures. Sensitivity analyses maintained moxifloxacin dominance in France and the USA but affected ICERs in some cases in Germany.

CONCLUSIONS

Antimicrobial resistance/spectrum have a significant impact on outcomes and costs in empirical outpatient CAP treatment. Despite low acquisition costs for generic antibiotics, first-line treatment effective against the major CAP pathogens, including strains resistant to other antimicrobials, resulted in better clinical outcomes in all countries and lower treatment costs for all.

Susceptibility of Staphylococcus aureus to fusidic acid: Canadian data

BACKGROUND

Ongoing antimicrobial surveillance is important to ensure proper management of infectious diseases. There are inherent issues in estimating the relevant incidence of antimicrobial resistance from surveillance data and special issues for topical preparations.

OBJECTIVE

To perform semiannual surveillance of fusidic acid susceptibility of Staphylococcus aureus strains in a Canadian tertiary care hospital.

METHODS

S. aureus strains were collected twice yearly from routine cultures. Routine antimicrobial susceptibility testing was performed by an automated method. Fusidic acid susceptibility testing was performed by disk diffusion.

RESULTS

Between 1999 and 2005, 2,302 S. aureus strains were tested, of which 240 were methicillin resistant (MRSA). Among all strains tested, 65 (2.8%) were resistant to fusidic acid. Ten of the MRSA strains (4.2%) were resistant to fusidic acid. Although from different patients, these were shown to be part of a hospital outbreak and were epidemiologically linked.

CONCLUSIONS

There has been no trend toward increasing fusidic acid resistance in our hospital over this period.

Review of the spectrum and potency of orally administered cephalosporins and amoxicillin/clavulanate

The antimicrobial spectrum and in vitro potency of the most frequently prescribed orally administered cephalosporins (cefaclor, cefdinir, cefpodoxime, cefprozil, cefuroxime axetil, cephalexin) and amoxicillin/clavulanate are reviewed. These beta-lactam agents have been widely used in the outpatient arena for the treatment of community-acquired respiratory tract and other mild-to-moderate infections. The data presented here were obtained from critical review articles on each of these compounds. Cephalexin and cefaclor were among the least potent and had the narrowest antimicrobial spectrums against the pathogens evaluated. In contrast, cefdinir, cefpodoxime, cefprozil, and cefuroxime were highly active against penicillin-susceptible Streptococcus pneumoniae and retained some activity against penicillin-intermediate strains, whereas amoxicillin/clavulanate was the most active against S. pneumoniae, including most penicillin nonsusceptible strains. Amoxicillin/clavulanate and cefdinir were the most potent compounds against methicillin (oxacillin)-susceptible Staphylococcus aureus, whereas cefpodoxime was the most potent compound against Haemophilus influenzae. Amoxicillin/clavulanate, cefdinir, and cefpodoxime were also active against Moraxella catarrhalis, including beta-lactamase-producing strains. In summary, orally administered "3rd-generation" or extended spectrum cephalosporins exhibited more balanced spectrums of activity against the principal bacterial pathogens responsible for outpatient respiratory tract and other infections when compared with other widely used oral cephalosporins of earlier generations or amoxicillin alone.

In vitro susceptibility testing versus in vivo effectiveness

The clinical relevance of susceptibility testing has always been questioned because of the difficulty of correlating in vitro susceptibility testing with in vivo clinical effectiveness. Clearly there have always been host/pathogen factors that influence the clinical outcome that cannot be predicted by the results of susceptibility testing. However, improved understanding of pharmacodynamic and pharmacokinetic parameters has greatly improved the use of antimicrobial agents. Most importantly, the integration of these pharmacodynamic and pharmacokinetic indices has greatly improved the correlation between in vitro susceptibility testing and in vivo clinical effectiveness and allows more realistic breakpoints. Finally, the clinical microbiology laboratory has advanced with improved methods as well as the adaptation of breakpoints that are more realistic.

Use of in vitro critical inhibitory concentration, a novel approach to predict in vivo synergistic bactericidal effect of combined amikacin and piperacillin against Pseudomonas aeruginosa in a systemic rat infection model

PURPOSE

This study was undertaken to explore the use of in vitro critical inhibitory concentration (CIC) as a surrogate marker relating the pharmacokinetic (PK) parameters to in vivo bactericidal synergistic effect [pharmacodynamic (PD)] of amikacin + piperacillin combination against Pseudomonas aeruginosa in a systemic rat infection model.

METHODS

The in vitro antibacterial activities of amikacin and piperacillin, alone and in combinations at various ratios of the concentrations, were tested against a standard [5 x 10(5) colony-forming units (CFU)/ml] and a large (1.5 x 10(8) CFU/ml) inoculum of P. aeruginosa ATCC 9027 using a modified survival-time method. The CIC of each individual antibiotic for the different combinations was determined using a cup-plate method. In vivo studies were performed on Sprague-Dawley rats using a systemic model of infection with P. aeruginosa ATCC 9027. PK profiles and in vivo killing effects of the combination at different dosing ratios were studied.

RESULTS

An inoculum effect was observed with the antibiotics studied. Synergy was seen against both the inocula at the following concentration ratios: 70% C(ami) + 30% C(pip) and 75% C(ami) + 25% C(pip), where C(ami) and C(pip) are the concentrations of amikacin and piperacillin to produce a 1000-fold decrease in bacterial population over 5 h, respectively. The CIC values determined corroborated with the order of in vitro bacterial killing observed for the antibiotic combinations. The dosing ratio of 12.6 mg/kg amikacin + 36 mg/kg piperacillin (a 70:30 ratio of the individual doses) exhibited the greatest killing in vivo when compared to the other ratios. The PK-PD relationships were described by simple, linear regression equations using the area under the in vivo killing curve as a PD marker and the AUCIC(ami)/CIC(ami) + AUCIC(pip)/CIC(pip), AUC(ami)/CIC(ami) + AUC(pip)/CIC(pip), C(max,ami)/CIC(ami) + C(max,pip)/CIC(pip), and AUCIC(ami)/MIC(ami) + AUCIC(pip)/MIC(pip) as PK markers for the amikacin + piperacillin combination.

CONCLUSION

The combination of amikacin and piperacillin exhibited synergistic killing effect on P. aeruginosa that could be modeled using CIC as a surrogate marker relating the PK parameters to in vivo bactericidal effect.

In vitro and in vivo studies on mucoadhesive microspheres of amoxicillin

Amoxicillin mucoadhesive microspheres (Amo-ad-ms) were prepared using ethylcellulose (Ec) as matrix and carbopol 934P as mucoadhesive polymer for the potential use of treating gastric and duodenal ulcers, which were associated with Helicobacter pylori. The morphological characteristics of the mucoadhesive microspheres were studied under scanning electron microscope. In vitro release test showed that amoxicillin released faster in pH 1.0 hydrochloric acid (HCl) than in pH 7.8 phosphate buffer. Yet, it would be degraded to some extent in a pH 1.0 HCl medium at 37 degrees C, which indicated that amoxicillin was not stable in an acidic surrounding. It was also found that amoxicillin entrapped within the microspheres could keep stable. In vitro and in vivo mucoadhesive tests showed that Amo-ad-ms adhered more strongly to gastric mucous layer than nonadhesive amoxicillin microspheres (Amo-Ec-ms) did and could retain in gastrointestinal tract for an extended period of time. Amo-ad-ms and amoxicillin powder were orally administered to rats. The amoxicillin concentration in gastric tissue was higher in the Amo-ad-ms group. In vivo H. pylori clearance tests were also carried out by administering, respectively, Amo-ad-ms or amoxicillin powder, to H. pylori infectious BALB/c mice under fed conditions at single or multiple dose(s) in oral administration. The results showed that Amo-ad-ms had a better clearance effect than amoxicillin powder did. In conclusion, the prolonged gastrointestinal residence time and enhanced amoxicillin stability resulting from the mucoadhesive microspheres of amoxicillin might make contribution to H. pylori clearance.

Comparative bacteriological efficacy of pharmacokinetically enhanced amoxicillin-clavulanate against Streptococcus pneumoniae with elevated amoxicillin MICs and Haemophilus influenzae

A new pharmacokinetically enhanced formulation of amoxicillin-clavulanate (2,000 mg of amoxicillin/125 mg of clavulanate twice a day; ratio 16:1) has been designed, with sustained-release technology, to allow coverage of bacterial strains with amoxicillin-clavulanic acid MICs of at least 4/2 mug/ml. The bacteriological efficacy of amoxicillin-clavulanate, 2,000/125 mg twice a day, ratio 16:1, was compared in a rat model of respiratory tract infection versus four other amoxicillin-clavulanate formulations: 8:1 three times a day (1,000/125 mg), 7:1 three times a day (875/125 mg), 7:1 twice a day (875/125 mg), and 4:1 three times a day (500/125 mg); levofloxacin (500 mg once a day); and azithromycin (1,000 mg on day 1 followed thereafter by 500 mg once a day). Bacterial strains included Streptococcus pneumoniae, with amoxicillin-clavulanic acid MICs of 2/1 (one strain), 4/2, or 8/4 microg/ml (three strains each), and Haemophilus influenzae, one beta-lactamase-positive strain and one beta-lactamase-negative, ampicillin-resistant strain. Animals were infected by intrabronchial instillation. Antibacterial treatment commenced 24 h postinfection, with doses delivered by computer-controlled intravenous infusion to approximate the concentrations achieved in human plasma following oral administration. Plasma concentrations in the rat corresponded closely with target human concentrations for all antimicrobials tested. Amoxicillin-clavulanate, 2,000/125 mg twice a day, ratio 16:1, was effective against all S. pneumoniae strains tested, including those with amoxicillin-clavulanic acid MICs of up to 8/4 microg/ml and against beta-lactamase-producing and beta-lactamase-negative ampicillin-resistant H. influenzae. These results demonstrate the bacteriological efficacy of pharmacokinetically enhanced amoxicillin-clavulanate 2,000/125 mg twice a day (ratio 16:1) against S. pneumoniae with amoxicillin-clavulanic acid MICs of at least 4/2 microg/ml and support clavulanate 125 mg twice a day as sufficient to protect against beta-lactamase in this rat model.

Pharmacodynamic studies of amoxicillin against Streptococcus pneumoniae: comparison of a new pharmacokinetically enhanced formulation (2000 mg twice daily) with standard dosage regimens

OBJECTIVES

To compare the pharmacodynamic effects of a pharmacokinetically enhanced formulation of amoxicillin 2000 mg twice daily, with amoxicillin 875 mg twice daily, 875 mg three times daily and 500 mg three times daily against Streptococcus pneumoniae with different susceptibility to amoxicillin in an in vitro kinetic model.

METHODS

Strains of S. pneumoniae with amoxicillin MICs of 1, 2, 4 and 8 mg/L at an initial inoculum of approximately 10(5) cfu/mL were exposed to amoxicillin in an in vitro kinetic model simulating the human serum concentration-time profile of the pharmacokinetically enhanced formulation twice daily (C(max) 17 mg/L after 1.5 h). All isolates were also exposed to amoxicillin with concentration-time profiles correlating to the human dosage of 875 mg twice daily (C(max) 15 mg/L after 1 h), 875 mg three times daily and 500 mg (C(max) 8 mg/L after 1 h) three times daily with simulated half-life of 1 h. Repeated samples were taken regularly during 24 h and viable counts were carried out.

RESULTS

Overall, the pharmacokinetically enhanced formulation was more effective at reducing bacterial counts than any of the other formulations evaluated. Eradication was achieved with the enhanced formulation for strains with a MIC of < or =2 mg/L, however, regrowth occurred with the other dosing regimens. In the experiments with the strain with a MIC of 4 mg/L, the enhanced formulation kept the bacterial counts < or =10(2) cfu/mL for at least 14 out of 24 h tested. In contrast, none of the other formulations reduced the bacterial counts down to < or =10(2) cfu/mL at any point. None of the regimens was able to eradicate the strain with an MIC of 8 mg/L, even though an initial substantial kill was noted with the enhanced formulation after both doses. The least effective dosage regimen for all strains was 875 mg twice daily.

Comparative in vitro activity of a pharmacokinetically enhanced oral formulation of amoxicillin/clavulanic acid (2000/125 mg twice daily) against 9172 respiratory isolates collected worldwide in 2000

OBJECTIVES

A new, pharmacokinetically enhanced, oral formulation of amoxicillin/clavulanic acid has been developed to overcome resistance in the major bacterial respiratory pathogen Streptococcus pneumoniae, while maintaining excellent activity against Haemophilus influenzae and Moraxella catarrhalis, including beta-lactamase producing strains. This study was conducted to provide in vitro susceptibility data for amoxicillin/clavulanic acid and 16 comparator agents against the key respiratory tract pathogens.

METHODS

Susceptibility testing was performed on 9172 isolates collected from 95 centers in North America, Europe, Australia, and Hong Kong by broth microdilution MIC determination, according to NCCLS methods, using amoxicillin/clavulanic acid and 16 comparator antimicrobial agents. Results were interpreted according to NCCLS breakpoints and pharmacokinetic/pharmacodynamic (PK/PD) breakpoints based on oral dosing regimens.

RESULTS

Overall, 93.5% of Streptococcus pneumoniae isolates were susceptible to amoxicillin/clavulanic acid at the current susceptible breakpoint of < or =2 microg/mL and 97.3% at the PK/PD susceptible breakpoint of < or =4 microg/mL for the extended release formulation. Proportions of isolates that were penicillin intermediate and resistant were 13% and 16.5%, respectively, while 25% were macrolide resistant and 21.8% trimethoprim/sulfamethoxazole resistant. 21.9% of Haemophilus influenzae were beta-lactamase producers and 16.8% trimethoprim/sulfamethoxazole resistant, >99% of isolates were susceptible to amoxicillin/clavulanic acid, cefixime, ciprofloxacin and levofloxacin at NCCLS breakpoints. The most active agents against Moraxella catarrhalis were amoxicillin/clavulanic acid, macrolides, cefixime, fluoroquinolones, and doxycycline. Overall, 13% of Streptococcus pyogenes were resistant to macrolides.

CONCLUSION

The extended release formulation of amoxicillin/clavulanic acid has potential for empiric use against many respiratory tract infections worldwide due to its activity against species resistant to many agents currently in use.

Overview of newer antimicrobial formulations for overcoming pneumococcal resistance

The pharmacokinetic (PK) and pharmacodynamic (PD) profile of an antimicrobial agent provides important information that can be used to maximize bacteriologic and clinical efficacy, minimize selective pressure for the development of antimicrobial resistance, and determine an optimal dosing regimen. Judicious selection of an antimicrobial based on local susceptibility data and PK and PD parameters is imperative in this era of increasing resistance among Streptococcus pneumoniae, a leading cause of community-acquired respiratory tract infections. The beta-lactam antimicrobials display time-dependent bacterial killing with minimal to no persistent effects. Ketolides and fluoroquinolones display concentration-dependent bacterial killing, and tetracyclines and macrolides display time-dependent killing. All have prolonged persistent effects (e.g., postantibiotic effect) that retard or prevent bacterial regrowth when free drug levels fall below the minimum inhibitory concentration (MIC). New high-dose and/or extended-release formulations of traditional antimicrobials have been added to the current armamentarium for treatment of community-acquired respiratory tract infections. These formulations include amoxicillin-clavulanate potassium powder for oral suspension 90/6.4 mg/kg per day divided every 12 hours (Augmentin ES-600; GlaxoSmithKline, Research Triangle Park, NC), amoxicillin-clavulanate potassium extended-release tablets 2 x 1,000 mg/62.5 mg every 12 hours (Augmentin XR; GlaxoSmithKline), clarithromycin extended-release tablets 2 x 500 mg once daily (Biaxin XL; Abbott Laboratories, North Chicago, IL), and cefaclor extended-release tablets 375 mg or 500 mg every 12 hours (Ceclor CD; Eli Lilly Pharmaceuticals, Indianapolis, IN). Of these agents, only amoxicillin-clavulanate potassium powder for oral suspension and amoxicillin-clavulanate potassium extended-release tablets were designed to treat infections caused by penicillin-resistant pneumococci (penicillin MIC < or =2 microg/mL). Extended-release clarithromycin does not provide higher daily doses than its immediate-release counterpart; rather, it allows for once-daily dosing of this agent because of its slower absorption following oral administration. Extended-release cefaclor is considered clinically equivalent to 250 mg of immediate-release cefaclor pulvules administered 3 times daily; it cannot be used interchangeably with 500 mg 3-times-daily dosages of other cefaclor formulations. Thus, despite providing a similar or higher total daily dose than its immediate-release counterpart, extended-release cefaclor is indicated only for the treatment of patients with mild to moderate infections caused by susceptible strains of certain organisms.

Antibacterial effects of amoxicillin-clavulanate against Streptococcus pneumoniae and Haemophilus influenzae strains for which MICs are high, in an in vitro pharmacokinetic model

The antibacterial effect of amoxicillin-clavulanate in two formulations, pharmacokinetically enhanced 16:1 amoxicillin-clavulanate twice a day (b.i.d.) and standard 7:1 amoxicillin-clavulanate b.i.d., were studied in an in vitro pharmacokinetic model of infection. Five strains of Streptococcus pneumoniae and two of Haemophilus influenzae, all associated with raised MICs (2 to 8 mg/liter), were used. The antibacterial effect was measured over 24 h by the area under the bacterial kill curve (AUBKC) and the log change in viable count at 24 h (Delta24). A high 10(8) CFU/ml and low 10(6) CFU/ml initial inocula were used. Employing the Delta24 effect measure, the time above MIC (T>MIC) 50% maximum effect (EC(50)) for S. pneumoniae was in the range 21 to 28% with an 80% maximal response of 41 to 51%, for the AUBKC measure, the value was 26 to 39%, irrespective of inoculum. For H. influenzae, the T>MIC EC(50) was 28 to 37%, and the 80% maximum response was 32 to 48% for the Delta24 measure and 20 to 48% for AUBKC. The maximum response occurred at a T>MIC of 50 to 60% for both species and inocula. The S. pneumoniae data were analyzed by analysis of variance to assess the effect of inoculum, formulation, and MIC on antibacterial effect. Standard and enhanced formulations had different effects depending on MIC, with the standard formulation less effective at higher amoxicillin-clavulanate MICs. This is explained by the greater T>MICs of the enhanced formulation. Although resistant to amoxicillin-clavulanate by conventional breakpoints, S. pneumoniae and H. influenzae strains for which MICs are 2 or 4 mg/liter may well respond to therapy with pharmacokinetically enhanced formulation amoxicillin-clavulanate.

Building in efficacy: developing solutions to combat drug-resistant S. pneumoniae

The development of our understanding of the pharmacokinetic (PK) and pharmacodynamic (PD) principles that determine antimicrobial efficacy has advanced substantially over the last 10 years. We are now in a position to use PK/PD principles to set targets for antimicrobial design and optimisation so that we can predict eradication of specific pathogens or resistant variants when agents are used clinically. Optimisation of PK/PD parameters to enable the treatment of resistant pathogens with oral agents may not be possible with many current agents, such as some cephalosporins, macrolides and fluoroquinolones. Aminopenicillins, however, such as amoxicillin, have linear PK and have a good safety profile even at high doses. The new pharmacokinetically enhanced oral formulation of amoxicillin/clavulanate, 2000/125 mg twice daily, was designed using PK/PD principles to be able to eradicate Streptococcus pneumoniae with amoxicillin MICs of up to and including 4 mg/L, which includes most penicillin-resistant isolates. For amoxicillin and amoxicillin/clavulanate, a time above MIC (T > MIC) of 35-40% of the dosing interval (based on blood levels) is predictive of high bacteriological efficacy. This target was met by the design of a unique bilayer tablet incorporating 437.5 mg of sustained-release sodium amoxicillin in one layer plus 562.5 mg of immediate-release amoxicillin trihydrate and 62.5 mg of clavulanate potassium in the second layer, with two tablets administered for each dose. This unique design extends the bacterial killing time by increasing the T > MIC to 49% of the dosing interval against pathogens with MICs of 4 mg/L, and 60% of the dosing interval against pathogens with MICs of 2 mg/L. Based on these results, this new amoxicillin/clavulanate formulation should be highly effective in treating respiratory tract infections due to drug-resistant S. pneumoniae as well as beta-lactamase-producing pathogens, such as Haemophilus influenzae and Moraxella catarrhalis.

Introduction: standards of antibacterial performance

The development and clinical use of antimicrobial agents continue to evolve in line with new science, understanding and needs. While antimicrobial resistance remains an important determinant for drug development and therapeutic choice, pharmacokinetic and pharmacodynamic parameters are having an ever-increasing importance in defining performance targets for new and established agents. Recently licensed new therapies are largely directed at serious hospital-associated Gram-positive infections, whereas in the community, therapeutic choice remains dependent on well-established agents from limited classes of antimicrobials. In order to maximise the benefits from such agents, it is appropriate that dosage regimens and antibacterial choices be reviewed in the light of new knowledge, particularly in the area of pharmacokinetics and pharmacodynamics. Antimicrobial resistance continues to evolve, notably within respiratory pathogens, therefore steps must be taken to maintain optimum therapeutic outcomes and also limit the development and spread of resistant strains. Whilst changes in patient and physician attitudes and behaviour towards better quality prescribing are important, new agents must also be developed to provide adequate coverage for resistant pathogens. Development times for novel agents and classes of antimicrobials are long, with uncertain safety profiles and chances of success. Thus, the development of new formulations of existing agents, designed to overcome current resistance patterns, constitutes a potentially important additional strategy towards appropriate prescribing.