The pharmacokinetics of aztreonam and penetration into the bronchial secretions of critically ill patients

Liquid Chromatography Mass Spectrometry Detection of Antibiotic Agents in Sputum from Persons with Cystic Fibrosis

Antibiotic therapy is expected to impact host microbial communities considerably, yet many studies focused on microbiome and health are often confounded by limited information about antibiotic exposure. Given that antibiotics have diverse pharmacokinetic and antimicrobial properties, investigating the type and concentration of these agents in specific host specimens would provide much needed insight into their impact on the microbes therein. Here, we developed liquid chromatography mass spectrometry (LC-MS) methods to detect 18 antibiotic agents in sputum from persons with cystic fibrosis. Antibiotic spike-in control samples were used to compare three liquid extraction methods on the Waters Acquity Quattro Premier XE. Extraction with dithiothreitol captured the most antibiotics and was used to detect antibiotics in sputum samples from 11 people with cystic fibrosis, with results being compared to the individuals' self-reported antibiotic use. For the sputum samples, two LC-MS assays were used; the Quattro Premier detected nanomolar or micromolar concentrations of 16 antibiotics, whereas the Xevo TQ-XS detected all 18 antibiotics, most at subnanomolar levels. In 45% of tested sputum samples (71/158), at least one antibiotic that was not reported by the subject was detected by both LC-MS methods, a discordance largely explained by the thrice weekly administration and long half-life of azithromycin. For ∼37% of samples, antibiotics reported as taken by the individual were not detected by either instrument. Our results provide an approach for detecting a variety of antibiotics at the site of infection, thereby providing a means to include antibiotic usage data into microbiome studies.

Therapeutic Drug Monitoring of Prolonged Infusion Aztreonam for Multi-Drug Resistant Pseudomonas aeruginosa: A Case Report

Aztreonam, a broad-spectrum monobactam, is typically reserved for multidrug resistant (MDR) infections. Pharmacokinetic (PK) data to guide dosing in children, however, are limited to healthy volunteers or nonintensive care unit (ICU) patients. Impaired antibiotic delivery into tissue remains a major concern and may explain the high morbidity and mortality associated with MDR infections. Therefore, evaluating the PK changes in pediatric ICU patients is necessary to elucidate the most appropriate antimicrobial regimen. We describe the PK of prolonged infusion aztreonam in a patient with MDR Pseudomonas aeruginosa empyema. The 16-year-old tetraplegic male with a cervical spinal cord injury, chronic respiratory failure, and tracheostomy was admitted with a 2-day history of fever and hypoxemia. Chest x-ray revealed a left lower lobe infiltrate. On hospital day 2, computed tomography scan noted a massive collapse of the left lung with bronchiectasis and hepatization with a pneumatocele. He underwent bronchoscopy on days 2, 6, and 10 and the cultures subsequently grew P aeruginosa only sensitive to aztreonam (minimum inhibitory concentration [MIC] of 2-6 mg/L). A regimen of aztreonam 2 grams intravenously (IV) every 6 hours (each dose infused over 4 hours) and polymyxin B 1,000,000 units IV every 12 hours (each dose infused over 30 minutes) was initiated on day 3. On day 8, the aztreonam serum plateau concentration was 71 mg/L. Repeat respiratory and bronchoscopy cultures from days 19 to 37 remained negative. Aztreonam clearance was 2.3 mL/kg/min, which was significantly increased when compared with the 1.3 mL/kg/min suggested in the prescribing information based on adult data. A prolonged infusion of 2 grams of aztreonam every 6 hours (each dose infused over 4 hours) successfully attained 100% of the target serum and lung concentrations above the MIC for at least 40% of the dosing interval, and was associated with successful treatment of MDR P aeruginosa empyema.

A review of the pharmacokinetics and pharmacodynamics of aztreonam

The monobactam aztreonam is currently being re-examined as a therapeutic agent in light of the global spread of carbapenem resistance in aerobic Gram-negative bacilli and aztreonam's stability to Ambler class B metallo-β-lactamases. Of particular interest are the pharmacokinetic and pharmacodynamic properties of aztreonam alone and in combination with β-lactamase inhibitors. The choice of inhibitor may vary depending on the spectrum of β-lactamases produced by Enterobacteriaceae. The monobactam ring is also being used to produce new developmental monobactams. Thus, a greater understanding of aztreonam pharmacokinetics and dynamics is of great relevance in drug development. This review summarizes the pharmacokinetic profile of aztreonam in man and its pharmacodynamics in human and pre-clinical studies when studied alone and with β-lactamase inhibitors.

Treatment of community-acquired pneumonia

Community-acquired pneumonia is the sixth leading cause of death in the USA. Adherence to the 2007 Infectious Diseases Society of America/American Thoracic Society community-acquired pneumonia guidelines has been associated with improved clinical outcomes. However, choice between guideline-recommended treatments is at the discretion of the prescribing clinician. This review is intended to discuss the characteristics of these treatment options including dosing frequency, dose adjustment for renal/hepatic dysfunction, serious/common adverse events, drug interactions, lung penetration, pharmacokinetic-pharmacodynamic target and effect of obesity to help guide antimicrobial selection. An increasing portion of patients are receiving expanded empiric coverage for methicillin-resistant Staphylococcus aureus as recommended by the American Thoracic Society and Infectious Diseases Society of America for healthcare-associated pneumonia. However, this expanded coverage may not be achieving the desired improvements in clinical outcomes. We expect this increasingly diverse spectrum of patients with pneumonia to eventually result in the merger of these two guidelines to include all patients with pneumonia.

Pharmacokinetics and pharmacodynamics of aerosolized antibacterial agents in chronically infected cystic fibrosis patients

Bacteria adapt to growth in lungs of patients with cystic fibrosis (CF) by selection of heterogeneously resistant variants that are not detected by conventional susceptibility testing but are selected for rapidly during antibacterial treatment. Therefore, total bacterial counts and antibiotic susceptibilities are misleading indicators of infection and are not helpful as guides for therapy decisions or efficacy endpoints. High drug concentrations delivered by aerosol may maximize efficacy, as decreased drug susceptibilities of the pathogens are compensated for by high target site concentrations. However, reductions of the bacterial load in sputum and improvements in lung function were within the same ranges following aerosolized and conventional therapies. Furthermore, the use of conventional pharmacokinetic/pharmacodynamic (PK/PD) surrogates correlating pharmacokinetics in serum with clinical cure and presumed or proven eradication of the pathogen as a basis for PK/PD investigations in CF patients is irrelevant, as minimization of systemic exposure is one of the main objectives of aerosolized therapy; in addition, bacterial pathogens cannot be eradicated, and chronic infection cannot be cured. Consequently, conventional PK/PD surrogates are not applicable to CF patients. It is nonetheless obvious that systemic exposure of patients, with all its sequelae, is minimized and that the burden of oral treatment for CF patients suffering from chronic infections is reduced.

Effects of antibiotic therapy on Pseudomonas aeruginosa-induced lung injury in a rat model

The effect of antibiotics on the acute lung injury induced by virulent Pseudomonas aeruginosa PA103 was quantitatively analyzed in a rat model. Lung injury was induced by the instillation of PA103 directly into the right lower lobes of the lungs of anesthetized rats. The alveolar epithelial injury, extravascular lung water, and total plasma equivalents were measured as separate, independent parameters of acute lung injury. Four hours after the instillation of PA103, all the parameters were increased linearly depending on the dose of P. aeruginosa. Next, we examined the effects of intravenously administered antibiotics on the parameters of acute lung injury in D-galactosamine-sensitized rats. One hour after the rats received 10(7) CFU of PA103, an intravenous bolus injection of aztreonam (60 mg/kg) or imipenem-cilastatin (30 mg/kg) was administered. Despite an MIC indicating resistance, imipenem-cilastatin improved all the measurements of lung injury; in contrast, aztreonam, which had an MIC indicating sensitivity, did not improve any of the lung injury parameters. The antibiotics did not generate different quantities of plasma endotoxin; therefore, endotoxin did not appear to explain the differences in lung injury. This in vivo model is useful to quantitatively compare the efficacies of parenteral antibiotic administration on Pseudomonas airspace infections.

Outcome assessment of minimizing vancomycin monitoring and dosing adjustments

An approach to minimize monitoring of vancomycin therapy was evaluated in 120 patients, and results were compared with data from 120 patients in whom vancomycin therapy was monitored and adjusted based on serum peak and trough concentrations and traditional pharmacokinetic methods. Patients dosed by the nomogram (NM) had regimens adjusted based on actual body weight, estimated creatinine clearance, and a targeted trough concentration of 5-20 microg/ml. A single trough serum concentration was drawn only after 5 or more days of therapy. Overall, the average length of therapy was similar between groups (9.9 +/- 9.4 days NM and 8.6 +/- 7.2 days pharmacokinetic). The most common regimen for both groups was 1 g every 12 hours, although NM patients received significantly fewer grams/day (1.9 +/- 0.7 g/day) than the pharmacokinetic group (2.2 +/- 1.0 g/day, p<0.04). Patients dosed by NM also had significantly fewer regimen changes (0.63 +/- 0.96 vs pharmacokinetic 0.92 +/- 0.97, p=0.02) as well as significantly fewer serum concentrations measured/patient (1.08 +/- 1.9 vs 1.96 +/- 2.0, p=0.001). In addition, serum concentrations for NM patients were drawn later in therapy (5.4 +/- 2.5 vs 3.8 +/- 3.4 days, p=0.004). Of patients dosed by NM guidelines, 77 had trough concentrations drawn; these data were used to validate the nomogram. Seventy-two patients (94%) had trough concentrations in the target range of 5-20 microg/ml. No differences were found between groups with respect to cure, improvement, failure, or days to eradication, or with respect to nephrotoxicity. Finally, total drug cost/patient was not different between groups. A considerable cost savings to our institution was noted for patients dosed by NM compared with pharmacokinetics ($232.5 +/- 50.74 vs $403.75 +/- 70.97/mo, p=0.009) based on levels saved. Caution should be applied when generalizing our results to other patient populations.

Differential distributions in tissues and efficacies of aztreonam and ceftazidime and in vivo bacterial morphological changes following treatment

The differential tissue distributions of aztreonam and ceftazidime within fibrin clots infected with Pseudomonas aeruginosa, Enterobacter cloacae, and Serratia marcescens, their efficacies, and the in vivo bacterial morphological changes induced by these drugs were evaluated. Rabbits were given intravenously a single dose of 100 mg of either agents/kg of body weight. In the cores of the clots, the peak levels of both drugs were much lower than those observed in the peripheries and in serum. Aztreonam's half-lives within the peripheries and in the cores of the fibrin clots were up to six times higher than observed in serum, while ceftazidime's half-lives in clots were twice that observed in serum. This resulted in a much greater penetration ratio for aztreonam than for ceftazidime. Both drugs controlled the growth of P. aeruginosa in vivo, but E. cloacae and S. marcescens responded better to ceftazidime. Morphological changes were more abundant in the peripheries than in the cores of the clots. In the control group, P. aeruginosa's morphology in the cores was different than that in the peripheries of the clots. Against P. aeruginosa, aztreonam did induce morphological changes in the cores while ceftazidime did not. Electron microscopic studies revealed that morphological changes associated with aztreonam seemed different than those of ceftazidime. Along with elongation of bacteria, more bow tie and herniated bacteria were observed with aztreonam. Though both agents selectively affect PBP 3, as manifested by elongated bacteria, they induce in the peripheries of the clots thickening, breaks, and detachment in bacterial cell walls, alterations which are generally associated with antibiotics affecting PBP 1a and 1b.

Clinical pharmacokinetics of aztreonam. An update

Plasma concentrations of aztreonam follow a 2-compartment open model with a distribution half-life of 0.20 hours after intravenous injection. The volume of distribution at steady-state (Vss) after intravenous and intramuscular injection is about 0.16 L/kg (0.42 L/kg for free drug). After intramuscular injection, absorption is almost complete. Absorption after intraperitoneal administration in patients with peritonitis is 92%. Over a large dosage range, plasma concentrations increase dose proportionally. In healthy individuals, about 56% of the drug is plasma protein bound. Diffusion into tissues is generally slow, and the ratio between mean tissue and plasma aztreonam concentration seems to depend mainly on tissue composition. Aztreonam penetrates into cerebrospinal fluid (CSF) more rapidly in patients with inflamed meninges than in those with noninflamed meninges. Diffusion through the placenta is poor, as is diffusion into breastmilk. Aztreonam is predominantly eliminated by the kidney, partly by active tubular excretion. Extrarenal clearance appears to be through hepatic excretion. Metabolism occurs to a very limited extent. Total plasma clearance (CLp) in healthy adults is about 5.6 L/h and the terminal elimination half-life is 1.7 to 2.0 hours. CLp is similar in both children and adults when expressed as a function of bodyweight. However, in neonates, especially in low birthweight infants, CLp is lower. In various disease states, the Vss of aztreonam is not appreciably different from that found in healthy individuals. However, patients with low serum albumin levels (e.g. burn patients, critically ill patients and those with cirrhosis of the liver) generally have an increased volume of distribution. The elimination half-life of the drug is dependent on renal function.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug treatment of pneumonia in the hospital. What are the choices?

Mortality and morbidity of nosocomial pneumonia remain high. Successful treatment of pulmonary infections depends on several factors including type of infection, offending pathogen, status of host defences, and adequate choice of antibiotic therapy. The physician's decision should aim at achieving antibiotic concentrations beyond the MIC at the site of infection. Gram-negative bacilli, notably Pseudomonos aeruginosa, Klebsiella pneumoniae and Escherichia coli, remain the most frequent agents in nosocomial pneumonia. Staphylococcus aureus and Streptococcus pneumoniae predominate among the Gram-positive cocci. Pneumocystis carinii predominates in immunocompromised patients. Protected sample bronchoscopy associated with quantitative cultures of samples, and quantification of intracellular microorganisms in cells recovered by broncho-alveolar lavage are two promising procedures which might replace previous, more aggressive methods. Penetration of antibiotics into lung tissue depends on physicochemical properties of the drug and the degree of inflammation of lung tissue. Quinolones, macrolides, tetracyclines and trimethoprim penetrate well into bronchial secretions. Penetration is moderate to low for aminoglycosides and beta-lactams. Fluoroquinolones and new beta-lactam agents, including third-generation cephalosporins imipenem, aztreonam and ticarcillin-clavulanate, showed comparative clinical efficacy in treatment of nosocomial pneumonia, with an efficacy rate close to 80%. Aminoglycosides should not be used alone. Combination therapy reduces but does not eliminate the risk of selection of Gram-negative resistant mutants. It should not be used routinely except for P. aeruginosa, Enterobacter cloacae and Serratia marcescens infections.

Aztreonam pharmacokinetics in burn patients

The pharmacokinetics of aztreonam in eight adult patients with severe burn injuries (total body surface area burn, 49% +/- 21% [mean +/- standard deviation]) were studied. The time of initiation of study following burn injury was 7.0 +/- 1.4 days. Four patients at first dose and at steady state were studied. Aztreonam concentrations were measured by high-performance liquid chromatography, and a two-compartment model was used to fit the data. No significant differences in any pharmacokinetic parameters between first dose and steady state were observed. Volume of distribution of the central compartment after first dose (0.14 liters/kg) and volume of distribution at steady state (0.31 liters/kg) were approximately 30% higher than those reported for other patient populations. Total drug clearance and renal drug clearance when normalized to creatinine clearance (CLCR) were similar to those previously reported for other critically ill patients. CLCR was strongly correlated with renal drug clearance (r = 0.94) and total drug clearance (r = 0.95). The extent and degree of burn (percent second or third degree burn) were poorly correlated with all pharmacokinetic parameters with the exception of the volume of distribution at steady state, which was correlated with both total body surface area burn (r = 0.95) and percent second degree burn (r = 0.83). Aztreonam pharmacokinetics are altered as a result of thermal injury; however, CLCR can be used to assess the clearance of aztreonam in burn patients.