Parenteral antibiotic therapy in the treatment of lower respiratory tract infections. Strategies to minimize the development of antibiotic resistance

Quantification of beta-lactam antibiotics cefuroxime and flucloxacillin in human synovial fluid, using ultra-performance convergence chromatography-tandem mass spectrometry

Total hip- and knee arthroplasty generally result in successful outcomes. A small percentage of patients however suffer from periprosthetic joint infections (PJI) postoperatively, often with severe consequences. The standard treatment of chronic PJIs consists of a staged arthroplasty exchange during which antibiotic therapy plays a crucial role. For successful antibiotic treatment, adequate concentrations at the infection site are a prerequisite. Regarding the treatment of PJIs, knowledge is lacking with respect to the relationship between administered dosages and plasma- and infection site concentrations of the antibiotics. To gain insight into the antibiotic exposure at the infection site, validated analytical methods for analysis of the antibiotics in matrices at the site of the PJI are essential. We describe a validated ultra-performance convergence chromatography-tandem mass spectrometry (UPC2-MS/MS) method for quantification of the beta-lactam antibiotics cefuroxime and flucloxacillin in synovial fluid. This method was successfully validated for antibiotic quantification in synovial fluids according to the EMA guidelines and consists of a simple sample preparation. For both antibiotics, the accuracy and precision were within requirements (RSD < 15%). In addition, matrix effects and recovery were within the range of 80-120%. Carry over was less than 20% and stability in -80 °C was at least 2 months for standards and quality controls. The limits of quantification were adequate (1-100 mg/L) to cover potential cefuroxime and flucloxacillin concentrations in synovial fluid as described in literature (r > 0.995). The method has a run time of 4.5 min and 50 μL synovial fluid is needed and the validated method will be applied during a PK/PD study to determine the exposure of the study antibiotics in synovial fluid at the site of PJIs.

Pharmacokinetic/pharmacodynamic approaches to drug delivery design for inhalation drugs

Introduction: Inhaled drugs are important in the treatment of many lung pathologies, but to be therapeutically effective they must reach unbound concentrations at their effect site in the lung that are adequate to interact with their pharmacodynamic properties (PD) and exert the pharmacological action over an appropriate dosing interval. Therefore, the evaluation of pharmacokinetic (PK)/PD relationship is critical to predict their possible therapeutic effect.Areas covered: We review the approaches used to assess the PK/PD relationship of the major classes of inhaled drugs that are prescribed to treat pulmonary pathologies.Expert opinion: There are still great difficulties in producing data on lung concentrations of inhaled drugs and interpreting them as to their ability to induce the desired therapeutic action. The structural complexity of the lungs, the multiplicity of processes involved simultaneously and the physical interactions between the lungs and drug make any PK/PD approach to drug delivery design for inhalation medications extremely challenging. New approaches/methods are increasing our understanding about what happens to inhaled drugs, but they are still not ready for regulatory purposes. Therefore, we must still rely on plasma concentrations based on the axiom that they reflect both the extent and the pattern of deposition within the lungs.

Delivering Antibacterials to the Lungs

An important determinant of clinical outcome of a lower respiratory tract infection may be sterilization of the infected lung, which is also dependent on sustained antibacterial concentrations achieved in the lung. For this reason, recently there has been increased interest in measuring the concentration of antimicrobial agents at different potential sites of infection in the lung. Levels of antibacterials are now measured in bronchial mucosa, epithelial lining fluid (ELF) and alveolar macrophages, as well as in sputum. Penicillins and cephalosporins reach only marginal concentrations in bronchial secretions, whereas fluoroquinolones and macrolides have been shown to achieve high concentrations. The extent of penetration of different antibacterials into the bronchial mucosa is relatively high. This is also true for beta-lactams, although their tissue concentrations never reach blood concentrations. Antibacterials penetrate less into the ELF than into the bronchial mucosa, but fluoroquinolones appear to concentrate more into alveolar lavage than into bronchial mucosa. Pulmonary pharmacokinetics is a very useful tool for describing how drugs behave in the human lung, but it does not promote an understanding of the pharmacological effects of a drug. More important, instead, is the correlation between pulmonary disposition of the drug and its minimum inhibitory concentration (MIC) values for the infectious agent. The addition of bacteriological characteristics to in vivo pharmacokinetic studies has triggered a 'pharmacodynamic approach'. Pharmacodynamic parameters integrate the microbiological activity and pharmacokinetics of an anti-infective drug by focusing on its biological effects, particularly growth inhibition and killing of pathogens. Drugs that penetrate well and remain for long periods at the pulmonary site of infection often induce therapeutic responses greater than expected on the basis of in vitro data. However, although the determination of antibacterial concentrations at the site of infection in the lung has been suggested to be important in predicting the therapeutic efficacy of antimicrobial treatment during bacterial infections of the lower respiratory tract, some studies have demonstrated that pulmonary bacterial clearance is correlated more closely to concentrations in the serum than to those in the lung homogenates, probably because they better reflect antibacterial concentration in the interstitial fluid.

Comparative study of the disposition of levofloxacin, netilmicin and cefepime in the isolated rat lung

An experimental model of artificially perfused and mechanically ventilated lung has been applied to compare the kinetic behaviour of levofloxacin, cefepime and netilmicin in this body tissue. The study has been performed to explore the usefulness of the isolated lung technique in the pharmacokinetic field, particularly to study the disposition of antibiotics in pulmonary tissue. The lung was perfused with Krebs-Henseleit medium containing 3% bovine albumin at a flow rate of 5 mL min−1. It was ventilated at 60 respirations/min with a 2-mL tidal volume of air previously humidified and warmed to 37°C. The concentrations of the above antibiotics were determined by HPLC techniques and the outflow curves were analysed by stochastic, as well as by model-dependent, methods. The results show pharmacokinetic differences among these antibiotics, which are in accordance with previously reported data, levofloxacin being the drug with the highest distribution coefficient in this tissue (1.25 ± 0.14 vs 0.39 ± 0.07 and 0.41 ± 0.06 mL g−1 for netilmicin and cefepime, respectively). Accordingly, the isolated lung of the rat, under the experimental conditions used here, constitutes an alternative model to be incorporated to pharmacokinetic studies with a great potential use for those drugs that show a pharmacological or toxicological action depending on the kinetic profile in the lung tissue.

Pharmacodynamics of Levofloxacin in Patients With Acute Exacerbation of Chronic Bronchitis

STUDY OBJECTIVES

Levofloxacin is a fluoroquinolone antimicrobial agent for which pharmacodynamic relationships between the maximum serum antibiotic concentration (Cmax)/minimum inhibitory concentration (MIC) ratio and/or the area under the serum concentration-time curve during a 24-h dosing period (AUC(0-24))/MIC ratio and clinical and/or microbiological outcomes have been developed. In this study we examined the relationship between the in vitro bacterial susceptibility to levofloxacin, the achieved levofloxacin serum and sputum concentrations, and the in vivo bacterial eradication in patients with acute exacerbations of chronic bronchitis.

PATIENTS AND INTERVENTIONS

Thirty patients received levofloxacin, 500 mg/d po for 7 days. Samples of venous blood and sputum for the determination of levofloxacin concentrations were collected on day 1 immediately prior to dosing, and then at 1, 4, 8, 12, and 24 h.

RESULTS

The mean peak concentration in serum (6.5 mg/L) was found 1 h after administration, and at 4 h after administration in sputum (5.1 mg/L). Levofloxacin was always detectable 24 h after administration from both samples. Successful treatment occurred in 90% (27 of 30 patients) when assessed both clinically and bacteriologically. Treatment was successful in eight patients when the AUC(0-24)/MIC ratio was > 40 for serum, and in nine patients when it was > 30 for sputum. Treatment was also successful in seven patients when the Cmax/MIC ratio was > 5.01 for serum, and in nine patients when the Cmax/MIC ratio was > 4.01 for sputum. Treatment was successful in 90% (27 of 30 patients) when the AUC(0-24)/MIC ratio was > 125 for serum and > 100 for sputum, and when Cmax/MIC was > 10.01 for serum and > 8.01 for sputum following the first dose.

CONCLUSIONS

The pharmacodynamics values that we have obtained in sputum with levofloxacin may be used as predictors of therapy outcomes.

The future challenges facing the development of new antimicrobial drugs

The emergence of resistance to antibacterial agents is a pressing concern for human health. New drugs to combat this problem are therefore in great demand, but as past experience indicates, the time for resistance to new drugs to develop is often short. Conventionally, antibacterial drugs have been developed on the basis of their ability to inhibit bacterial multiplication, and this remains at the core of most approaches to discover new antibacterial drugs. Here, we focus primarily on an alternative novel strategy for antibacterial drug development that could potentially alleviate the current situation of drug resistance--targeting non-multiplying latent bacteria, which prolong the duration of antimicrobial chemotherapy and so might increase the rate of development of resistance.