Pharmacokinetics of vancomycin in adult cystic fibrosis patients

Population pharmacokinetics and target attainment analysis of vancomycin after intermittent dosing in adults with cystic fibrosis

Vancomycin is the first-line agent to treat pulmonary infections caused by methicillin-resistant Staphylococcus aureus (MRSA) in people with cystic fibrosis (PwCF). However, there is no consensus on vancomycin initial dosing in this population among health institutions, and there is a large variability in initial dosing across the United States. In this study, we characterized the pharmacokinetics (PK) of vancomycin in PwCF using a population PK approach. The clinical PK data to develop the population PK model were obtained from vancomycin therapeutic monitoring data from PwCF undergoing treatment for infections due to MRSA. The population PK model was then used to perform comprehensive Monte Carlo simulations to evaluate the probability of target attainment (PTA) of 12 different initial dosing scenarios. The area under the curve to minimum inhibitory concentration (MIC) ratio ≥400 mg*h/L and <650 mg*h/L were used as efficacy and toxicity targets for PTA analysis. A total of 181 vancomycin plasma concentrations were included in the analysis. A one-compartment model with first-order elimination best described the data. Weight significantly influenced the vancomycin PK (P < 0.05). In the final model, clearance was estimated as 5.52 L/h/70 kg, and the volume of distribution was 31.5 L/70 kg. The PTA analysis showed that at MIC = 1 µg/mL, doses 1,500 q8h and 2,000 q12h showed the highest %PTA in achieving both efficacy and toxicity targets. The PTA results from this study may potentially inform the initial dosing regimens of vancomycin to treat pulmonary infections due to MRSA in PwCF.

The pharmacokinetics and pharmacodynamics of continuous infusion vancomycin in adult people with cystic fibrosis

BACKGROUND

The American Thoracic Society Guidelines recommend vancomycin as first line option for treatment of methicillin-resistant Staphylococcus aureus. Two studies have described the pharmacokinetics (PK) of intermittent intravenous (IV) vancomycin in adult people with cystic fibrosis (PwCF). Currently, there have not been any studies describing the PK of continuous infusion vancomycin in PwCF. Our study aimed to describe the PK of continuous infusion vancomycin in adult PwCF.

METHODS

Included patients were adult PwCF, who were admitted to University of Utah Hospital between May 11, 2014 and August 31, 2020, and received continuous infusion vancomycin for the treatment of an pulmonary exacerbations. The primary outcome was to describe vancomycin clearance rate (CLvanco ) and total daily dose (TDD). Secondary outcomes included rates of acute kidney injury (AKI), liver injury, and infusion-related reactions.

RESULTS

Twenty patients were included in this study. The mean CLvanco was 5.08 L/h on Day 3 and 4.58 L/h on Day 7 (p = .04), and the TDD increased from 2444 mg on Day 3 to 2556 on Day 7, although not statistically significant (p = 0.26). Zero patients experienced an AKI, two patients experienced liver injury, and no patients experienced infusion-related reactions.

CONCLUSIONS

This study demonstrates that continuous infusion vancomycin PK, namely CLvanco , is similar to previously reported CLvanco for intermittent dosed IV vancomycin in adult PwCF. This study suggests that continuous infusion vancomycin is likely safe to use in adult PwCF.

Pharmacokinetics of intermittent dosed intravenous vancomycin in adult persons with cystic fibrosis

BACKGROUND

Antibiotics have altered pharmacokinetics (PK) in persons with cystic fibrosis (PwCF) during treatment for an acute pulmonary exacerbation (APE). The Cystic Fibrosis Foundation Pulmonary Guidelines-Treatment of Pulmonary Exacerbations do not provide specific recommendations for treatment of methicillin-resistant Staphylococcus aureus (MRSA) lung infections. However, the American Thoracic Society Guidelines recommend vancomycin as the first-line therapy. Only one study has previously described a single dose of intravenous (IV) vancomycin PK in adult PwCF. Our study aimed to describe intermittent IV vancomycin PK at steady-state in adult PwCF.

METHODS

Adult PwCF who were admitted to University of Utah Hospital between May 11, 2014 and August 31, 2020, and received intermittent IV vancomycin for the treatment of an APE were included in this study. The primary outcome was to describe the drug volume of distribution (Vd), drug clearance, elimination half-life, and total daily dose of vancomycin. Secondary outcomes were rates of acute kidney injury (AKI), liver injury, and infusion-related reactions.

RESULTS

Thirteen patients were included. The mean Vd was 0.54 L/kg on Day 3 and 0.53L/kg on Day 7. CL_vanco was 5.11L/h on Day 3 and 4.69 L/h on Day 7. Zero patients experienced an AKI, two patients experienced liver injury, and no patients experienced infusion-related reactions.

CONCLUSIONS

Our results demonstrate that in PwCF intermittent IV vancomycin steady-state PK are similar to previously reported single-dose IV vancomycin. Additionally, CL_vanco minimally changes from Day 3 to Day 7, although this study was not powered to detect a difference.

Two Innovative Approaches to Optimize Vancomycin Dosing Using Estimated AUC after First Dose: Validation Using Data Generated from Population PK Model Coupled with Monte-Carlo Simulation and Comparison with the First-Order PK Equation Approach

The revised consensus guidelines for optimizing vancomycin doses suggest that maintaining the area under the concentration-time curve to minimal inhibitory concentration ratio (AUC/MIC) of 400–600 mg·h/L is the target pharmacokinetic/pharmacodynamic (PK/PD) index for efficacy. AUC-guided dosing approach uses a first-order pharmacokinetics (PK) equation to estimate AUC using two samples obtained at steady state and one-compartment model, which can cause inaccurate AUC estimation and fail to achieve the effective PK/PD target early in therapy (days 1 and 2). To achieve an efficacy target from the third or fourth dose, two innovative approaches (Method 1 and Method 2) to estimate vancomycin AUC at steady state (AUCSS) using two-compartment model and three or four levels after the first dose are proposed. The feasibility of the proposed methods was evaluated and compared with another published dosing algorithm (Method 3), which uses two samples and a one-compartment approach. Monte Carlo simulation was performed using a well-established population PK model, and concentration-time profiles for virtual patients with various degrees of renal function were generated, with 1000 subjects per group. AUC extrapolated to infinity (AUC0–∞) after the first dose was estimated using the three methods, whereas reference AUC (AUCref) was calculated using the linear-trapezoidal method at steady state after repeated doses. The ratio of AUC0–∞: AUCref and % bias were selected as the indicators to evaluate the accuracy of three methods. Sensitivity analysis was performed to examine the influence of change in each sampling time on the estimated AUC0–∞ using the two proposed approaches. For simulated patients with various creatinine clearance, the mean of AUC0–∞: AUCref obtained from Method 1, Method 2 and Method 3 ranged between 0.98 to 1, 0.96 to 0.99, and 0.44 to 0.69, respectively. The mean bias observed with the three methods was −0.10% to −2.09%, −1.30% to −3.59% and −30.75% to −55.53%, respectively. The largest mean bias observed by changing sampling time while using Method 1 and Method 2 were −4.30% and −10.50%, respectively. Three user-friendly and easy-to-use excel calculators were built based on the two proposed methods. The results showed that our approaches ensured sufficient accuracy and achieved target PK/PD index early and were superior to the published methodologies. Our methodology has the potential to be used for vancomycin dose optimization and can be easily implemented in clinical practice.

State of the art in cystic fibrosis pharmacology optimization of antimicrobials in the treatment of cystic fibrosis pulmonary exacerbations: III. Executive summary

Acute pulmonary exacerbations are complications of cystic fibrosis (CF) and are associated with increased morbidity and mortality. Methicillin-resistant Staphylococcus aureus (MRSA) and Aspergillus fumigatus are organisms that have been detected in the lungs of CF patients. The focus of this review is to provide an overview of the classes of antimicrobials used for MRSA and allergic bronchopulmonary aspergillosis (ABPA), a hypersensitivity reaction caused by A. fumigatus. The current anti-MRSA antibiotics and medications for ABPA dosing recommendations are discussed. This article also reviews the findings from the MRSA utilization surveys and the pharmacokinetic and pharmacodynamic differences between CF and non-CF patients. Antimethicillin S. aureus antibiotics include ceftaroline, clindamycin, fluoroquinolone derivatives (ciprofloxacin, levofloxacin), glycopeptide derivatives (telavancin, vancomycin), linezolid, rifampin, sulfamethoxazole/trimethoprim, and tetracycline derivatives (doxycycline, minocycline, tigecycline). Medications used for ABPA include corticosteroids, amphotericin B, azole antifungals (isavuconazole, itraconazole, posaconazole, voriconazole), and a monoclonal antibody, omalizumab.

Pharmacokinetic and Pharmacodynamic Optimization of Antibiotic Therapy in Cystic Fibrosis Patients: Current Evidences, Gaps in Knowledge and Future Directions

Antibiotic therapy is one of the main treatments for cystic fibrosis (CF). It aims to eradicate bacteria during early infection, calms down the inflammatory process, and leads to symptom resolution of pulmonary exacerbations. CF can modify both the pharmacokinetic (PK) and pharmacodynamic (PD) profiles of antibiotics, therefore specific PK/PD endpoints should be determined in the context of CF. Currently available data suggest that optimal PK/PD targets cannot be attained in sputum with intravenous aminoglycosides. Continuous infusion appears preferable for β-lactam antibiotics, but optimal concentrations in sputum are unlikely to be reached, with some possible exceptions such as meropenem and ceftolozane. Usual doses are likely suboptimal for fluoroquinolones and linezolid, whereas daily doses of 45-60 mg/kg and 200 mg could be convenient for vancomycin and doxycycline, respectively. Weekly azithromycin doses of 22-30 mg/kg could also be appropriate for its anti-inflammatory effect. The difficulty with achieving optimal concentrations supports the use of combined treatments and the inhaled administration route, as very high local concentrations, concomitantly with low systemic exposure, can be obtained with the inhaled route for aminoglycosides, colistin, and fluoroquinolones, thus minimizing the risk of toxicity.

The pharmacokinetics of antibiotics in cystic fibrosis

INTRODUCTION

Dosing of antibiotics in people with cystic fibrosis (CF) is challenging, due to altered pharmacokinetics, difficulty of lung tissue penetration, and increasing presence of antimicrobial resistance.

AREAS COVERED

The purpose of this work is to critically review original data as well as previous reviews and guidelines on pharmacokinetics of systemic and inhaled antibiotics in CF, with the aim to propose strategies for optimization of antibacterial therapy in both children and adults with CF.

EXPERT OPINION

For systemic antibiotics, absorption is comparable in CF patients and non-CF controls. The volume of distribution (Vd) of most antibiotics is similar between people with CF with normal body composition and healthy individuals. However, there are a few exceptions, like cefotiam and tobramycin. Many antibiotic class-dependent changes in drug metabolism and excretion are reported, with an increased total body clearance for ß-lactam antibiotics, aminoglycosides, fluoroquinolones, and trimethoprim. We, therefore, recommend following class-specific guidelines for CF, mostly resulting in higher dosages per kg bodyweight in CF compared to non-CF controls. Higher local antibiotic concentrations in the airways can be obtained by inhalation therapy, with which eradication of bacteria may be achieved while minimizing systemic exposure and risk of toxicity.

Comparison of Vancomycin Pharmacokinetics in Cystic Fibrosis Patients Pre and Post-lung Transplant

Background:

Vancomycin is commonly used to treat acute cystic fibrosis (CF) exacerbations associated with methicillin-resistant Staphylococcus aureus (MRSA). Multiple studies have demonstrated pharmacokinetic differences of antimicrobials in the CF population. Very little data exist regarding pharmacokinetics postlung transplant, but 2 studies have noted changes in tobramycin pharmacokinetics. No such studies exist evaluating vancomycin in CF patients postlung transplant.

Methods:

A retrospective cohort review of CF patients who underwent lung transplantation and received vancomycin pre- and posttransplant was conducted. CF patients who underwent transplant between 2007 and 2016 at 4 medical centers throughout the United States were included. The primary endpoint was the change in elimination rate constant. The secondary endpoints were subgroup analyses of patients grouped by age, time posttransplant, and number of nephrotoxic medications.

Results:

A total of 25 patients were included, of which just under half were pediatric. Patients were significantly older and heavier posttransplant and had higher serum creatinine and number of nephrotoxic medications. The change in elimination rate constant from pre- to posttransplant was −0.50 hr⁻¹ which was statistically significant (P < .001). This significant decrease was consistent among all subgroups of patients evaluated with the exception of pediatric patients.

Conclusion:

Vancomycin pharmacokinetics are significantly altered in CF patients in the posttransplant setting as evidenced by a decrease in elimination rate constant. This decrease may be related to a decrease in renal clearance and higher numbers of nephrotoxic medications posttransplant. Regardless, pretransplant vancomycin regimens may not predict appropriate posttransplant regimens.

State of the art in cystic fibrosis pharmacology-Optimization of antimicrobials in the treatment of cystic fibrosis pulmonary exacerbations: I. Anti-methicillin-resistant Staphylococcus aureus (MRSA) antibiotics

Acute pulmonary exacerbations (APE) are a complication of cystic fibrosis (CF) and are associated with morbidity and mortality. Methicillin-resistant Staphylococcus aureus (MRSA) is one of many organisms that has been detected in the airways of patients with CF. This review provides an evidence-based summary of pharmacokinetic/pharmacodynamic (PK/PD), tolerability, and efficacy studies utilizing anti-MRSA antibiotics (ie, ceftaroline, clindamycin, fluoroquinolone derivatives (ciprofloxacin, levofloxacin), glycopeptide derivatives (telavancin, vancomycin), linezolid, rifampin, sulfamethoxazole/trimethoprim (SMZ/TMP), and tetracycline derivatives (doxycycline, minocycline, tigecycline) in the treatment of APE and identifies areas where further study is warranted. A recent utilization study of antimicrobials for anti-MRSA has shown some CF Foundation accredited care centers and affiliate programs are using doses higher than the FDA-approved doses. Further studies are needed to determine the PK/PD properties in CF patients with clindamycin, minocycline, rifampin, SMZ/TMP, telavancin, and tigecycline; as well as, efficacy and tolerability studies with ciprofloxacin, clindamycin, doxycycline, levofloxacin, minocycline, rifampin, SMZ/TMP, in CF patients with MRSA.

Antimicrobial Treatment of Staphylococcus aureus in Patients With Cystic Fibrosis

Staphylococcus aureus is a ubiquitous human commensal pathogen. It is commonly isolated in cystic fibrosis (CF) patients and is considered one of the main causes of the recurrent acute pulmonary infections and progressive decline in lung function that characterize this inherited life-threatening multisystem disorder. However, the true role of S. aureus in CF patients is not completely understood. The main aim of this narrative review is to discuss the present knowledge of the role of S. aureus in CF patients. Literature review showed that despite the fact that the availability and use of drugs effective against S. aureus have coincided with a significant improvement in the prognosis of lung disease in CF patients, clearly evidencing the importance of S. aureus therapy, how to use old and new drugs to obtain the maximal effectiveness has not been precisely defined. The most important problem remains that the high frequency with which S. aureus is carried in healthy subjects prevents the differentiation of simple colonization from infection. Moreover, although experts recommend antibiotic administration in CF patients with symptoms and in those with persistent detection of S. aureus, the best antibiotic approach has not been defined. All these problems are complicated by the evidence that the most effective antibiotic against methicillin-resistant S. aureus (MRSA) cannot be used in patients with CF with the same schedules used in patients without CF. Further studies are needed to solve these problems and to assure CF patients the highest level of care.

An Evaluation of Vancomycin Area Under the Curve Estimation Methods for Children Treated for Acute Pulmonary Exacerbations of Cystic Fibrosis Due to Methicillin-Resistant Staphylococcus aureus

The prevalence of pulmonary methicillin-resistant Staphylococcus aureus infections in patients with cystic fibrosis (CF) has increased over the last 2 decades. Two concentrations-a postdistributive and a trough-are currently used to estimate the area under the curve (AUC) of vancomycin, an antibiotic routinely used to treat these infections, to achieve the target AUC/minimum inhibitory concentration of ≥400 mg·h/L in ensuring optimal dosing of this drug. This study evaluated precision and bias in estimating vancomycin AUCs obtained either from a population pharmacokinetic (PK) model by using a single trough concentration or from standard PK equation-based 2-point monitoring approach. AUCs were either obtained from a single trough concentration-fitted model or derived from a model fitted by 2 concentration points. Children ≥2 years of age with CF received intravenous vancomycin at 2 centers from June 2012 to December 2014. A population PK model was developed in Pmetrics to quantify the between-subject variability in vancomycin PK parameters, define the sources of PK variability, and leverage information from the population to improve individual AUC estimates. Twenty-three children with CF received 27 courses of vancomycin. The median age was 12.3 (interquartile range [IQR] 8.5-16.6) years. From the individual vancomycin PK parameter estimates from the population PK model, median AUC was 622 (IQR 529-680) mg·h/L. Values were not significantly different from the AUC calculated using the standard PK equation-based approach (median 616 [IQR 540-663] mg·h/L) (P = .89). A standard PK equation-based approach using 2 concentrations and a population PK model-based approach using a single trough concentration yielded unbiased and precise AUC estimates. Findings suggest that options exist to implement AUC-based pediatric vancomycin dosing in patients with CF. The findings of this study reveal that several excellent options exist for centers to implement AUC-based pediatric vancomycin dosing for patients with CF.

Vancomycin Dosing and Monitoring in the Treatment of Cystic Fibrosis: Results of a National Practice Survey

OBJECTIVES

Vancomycin is commonly used in patients with cystic fibrosis (CF) to treat acute pulmonary exacerbations, but few guidelines exist to help dose and monitor patients. The objective of this study was to assess vancomycin use and monitoring strategies at Cystic Fibrosis Foundation (CFF)-accredited centers in hopes of developing and implementing vancomycin dosing and monitoring standards.

METHODS

An anonymous national cross-sectional survey of pharmacists affiliated with CFF-accredited pediatric and/or adult centers was performed by using Surveymonkey.com. The survey consisted of 3 sections: (1) CF Center Demographic Information (10 questions); 2) vancomycin use in pediatric CF patients (31 questions); and 3) vancomycin use in adult CF patients (29 questions); it was administered from March 9, 2015, to April 13, 2015.

RESULTS

The survey was completed by 31/69 (45%) pharmacists and 28 (90.3%) reported using vancomycin in the pediatric population. The most common initial starting dose for pediatric patients was 15 mg/kg/dose (57.1%) and every 6 hours was the most common dosing frequency (67.9%). The most common monitoring strategy was collection of a trough concentration (92.9%) with 57.7% of pharmacist targeting a range of 15 to 20 mg/L. The most common initial starting vancomycin dose in adults with CF was 15 mg/kg/dose (61.5%), and initial frequency of every 8 hours (73.1%). The most common monitoring strategy was a trough concentration (96.2%) with 83.3% of pharmacists reporting a goal trough range of 15 to 20 mg/L.

CONCLUSIONS

The most common vancomycin dosing reported was 15 to 20 mg/kg/dose every 6 hours (pediatric) and 15 to 20 mg/kg/dose every 8 to 12 hours (adults). Serum concentrations measured to meet monitoring parameters of trough concentrations of 15 to 20 mg/L, or area under the curve to minimum inhibitory concentration ratio > 400, were the same in both pediatric and adult patients.

The cumulative effects of intravenous antibiotic treatments on hearing in patients with cystic fibrosis

BACKGROUND

Aminoglycosides (AGs) and glycopeptides are antibiotics essential for treating life-threatening respiratory infections in patients with cystic fibrosis (CF). The goal of this study was to examine the effects of cumulative intravenous (IV)-AG (amikacin and/or tobramycin) and/or glycopeptide (vancomycin) dosing on hearing status in patients with CF.

METHODS

Hearing thresholds were measured from 0.25 to 16.0kHz, in 81 participants with CF. Participants were categorized into two groups: normal hearing in both ears (≤25dB HL for all frequency bands) or hearing loss (>25dB HL for any frequency band in either ear). Participants were also characterized into quartiles by their cumulative IV-AG (with or without vancomycin) exposure. Dosing was calculated using two strategies: (i) total number of lifetime doses, and (ii) total number of lifetime doses while accounting for the total doses per day. This was referred to as the "weighted" method.

RESULTS

Participants in the hearing loss group were significantly older than those in the normal-hearing group. After adjusting for gender and age at the time of hearing test, participants in the two highest-quartile exposure groups were almost 5 X more likely to have permanent sensorineural hearing loss than those in the two lowest-quartile exposure groups. There was a small group of CF patients who had normal hearing despite high exposure to IV-antibiotics.

CONCLUSIONS

Cumulative IV-antibiotic dosing has a significant negative effect on hearing sensitivity in patients with CF, when controlling for age and gender effects. A trend for increasing odds of hearing loss was associated with increasing cumulative IV-antibiotic dosing.

Optimizing the Clinical Use of Vancomycin

The increasing number of infections produced by beta-lactam-resistant Gram-positive bacteria and the morbidity secondary to these infections make it necessary to optimize the use of vancomycin. In 2009, the American Society of Health-System Pharmacists, the Infectious Diseases Society of America, and the Society of Infectious Disease Pharmacists published specific guidelines about vancomycin dosage and monitoring. However, these guidelines have not been updated in the past 6 years. This review analyzes the new available information about vancomycin published in recent years regarding pharmacokinetics and pharmacodynamics, serum concentration monitoring, and optimal vancomycin dosing in special situations (obese people, burn patients, renal replacement therapy, among others). Vancomycin efficacy is linked to a correct dosage which should aim to reach an area under the curve (AUC)/MIC ratio of ≥400; serum trough levels of 15 to 20 mg/liter are considered a surrogate marker of an AUC/MIC ratio of ≥400 for a MIC of ≤1 mg/liter. For Staphylococcus aureus strains presenting with a MIC >1 mg/liter, an alternative agent should be considered. Vancomycin doses must be adjusted according to body weight and the plasma trough levels of the drug. Nephrotoxicity has been associated with target vancomycin trough levels above 15 mg/liter. Continuous infusion is an option, especially for patients at high risk of renal impairment or unstable vancomycin clearance. In such cases, vancomycin plasma steady-state level and creatinine monitoring are strongly indicated.

Vancomycin pharmacokinetic models: informing the clinical management of drug-resistant bacterial infections

This review aims to critically evaluate the pharmacokinetic literature describing the use of vancomycin in the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections. Guidelines recommend that trough concentrations be used to guide vancomycin dosing for the treatment of MRSA infections; however, numerous in vitro, animal model and clinical studies have demonstrated that the therapeutic effectiveness of vancomycin is best described by the area under the concentration versus time curve (AUC) divided by the minimum inhibitory concentration (MIC) of the infecting organism (AUC/MIC). Among patients with lower respiratory tract infections, an AUC/MIC ≥400 was associated with a superior clinical and bacteriological response. Similarly, patients with MRSA bacteremia who achieved an Etest AUC/MIC ≥320 within 48 h were 50% less likely to experience treatment failure. For other patient populations and different clinical syndromes (e.g., children, the elderly, patients with osteomyelitis, etc.), pharmacokinetic/pharmacodynamic studies and prospective clinical trials are needed to establish appropriate therapeutic targets.

Inhaled anti-infective chemotherapy for respiratory tract infections: successes, challenges and the road ahead

One of the most common causes of illnesses in humans is from respiratory tract infections caused by bacterial, viral or fungal pathogens. Inhaled anti-infective drugs are crucial for the prophylaxis and treatment of respiratory tract infections. The benefit of anti-infective drug delivery via inhalation is that it affords delivery of sufficient therapeutic dosages directly to the primary site of infection, while minimizing the risks of systemic toxicity or avoiding potential suboptimal pharmacokinetics/pharmacodynamics associated with systemic drug exposure. This review provides an up-to-date treatise of approved and novel developmental inhaled anti-infective agents, with particular attention to effective strategies for their use, pulmonary pharmacokinetic properties and safety.

Antibiotic Management of Methicillin-Resistant Staphylococcus aureus–Associated Acute Pulmonary Exacerbations in Cystic Fibrosis

Objective: To review the treatment of methicillin-resistant Staphylococcus aureus (MRSA)–associated acute pulmonary exacerbations (APEs) in cystic fibrosis (CF). Data Sources: A search of PubMed, MEDLINE, Cochrane Library and Clinicaltrials.gov databases through November 2014 was conducted using the search terms Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, pulmonary exacerbations, and cystic fibrosis. Study Selection and Data Extraction: All English-language research articles, case reports, and case series were evaluated. A total of 185 articles were identified related to MRSA and CF; 30 articles that studied treatments of MRSA APE in CF were included. Data Synthesis: The persistent presence of MRSA in the respiratory tract of patients with CF has been associated with higher morbidity and an increased risk of death. Limited clinical data exist supporting the efficacy of any specific antimicrobial currently available for the treatment of APE secondary to MRSA. Conclusions: Data extrapolated from other populations suggest that vancomycin and linezolid are appropriate first-line treatment options for the treatment of APE secondary to MRSA. Second-line options include doxycycline or minocycline and trimethoprim/sulfamethoxazole, each of which may be useful in patients coinfected with other respiratory pathogens, for which they may provide overlapping coverage. Ceftaroline and ceftobiprole are newer antibiotics that appear to have a potential role in the treatment of APE in CF, but the latter is not currently available to the US market. Although potentially useful, clindamycin is limited by high rates of resistance, telavancin is limited by its toxicity profile, and tigecycline is limited by a lack of demonstrated efficacy for infections that are similar to that seen in the CF population. Studies investigating the clinical utility of the above-cited antibiotics for APE in CF secondary to MRSA are desperately needed to broaden the treatment armamentarium for this medical condition.

Intravenous and Inhaled Antimicrobials at Home in Cystic Fibrosis Patients

The primary clinical characteristics of cystic fibrosis (CF) are malnutrition caused by malabsorption secondary to pancreatic insufficiency, chronic pulmonary infections, and male infertility. The major cause of morbidity and mortality are bronchiectasis and obstructive pulmonary disease. Lung disease in CF is manifested by this chronic lung disease progression, with intermittent episodes of acute worsening of symptoms called pulmonary exacerbations. Once the patient has stabilized, and if suitable care can be arranged, these interventions are often transitioned to the home. This review summarizes important points pertinent to the use of intravenous and inhaled antimicrobials that may be encountered by prescribers, nurses, technicians, and case managers in the home health setting. Appropriate dosing, indications, adverse drug reactions, monitoring parameters, and practicality of both intravenous and inhaled antimicrobials are discussed.

Pharmacokinetic and Pharmacodynamic Aspects of Antibiotic Use in High-Risk Populations

The study of pharmacokinetics includes the absorption, distribution, metabolism, and elimination of drugs. The pharmacologic effect that a medication has on the body is known as pharmacodynamics. With antimicrobials, pharmacokinetic and pharmacodynamic parameters become especially important because of the association between host drug concentrations, microorganism eradication, and resistance. This article focuses on the pharmacokinetic changes that can occur with antimicrobials when they are used in patients at high risk of infections and how they influence pharmacodynamic effects. The populations described here include patients with obesity and diabetes mellitus, renal or hepatic failure, chronic lung disease, severe burns, and long-term prosthetic devices and the elderly.

Pulmonary administration of perfluorodecaline- gentamicin and perfluorodecaline- vancomycin emulsions

The aim of this study was to examine pharmacokinetics and pulmonary antibiotic tissue concentrations (PATC) of gentamicin and vancomycin after intrapulmonary administration of a perfluorodecaline (PFD)-gentamicin and a PFD-vancomycin emulsion during partial liquid ventilation (PLV). PLV was initiated in 19 healthy rabbits and 18 surfactant-depleted rabbits. The animals were randomized to receive either 5 mg/kg gentamicin and 15 mg/kg vancomycin intravenously, or 5 mg/kg gentamicin intrapulmonary, or 15 mg/kg vancomycin intrapulmonary. Antibiotic plasma levels were measured after 15, 30, 45, and 60 min, and hourly thereafter. After 5 h animals were sacrificed and lungs were removed to evaluate PATC and histology. PATC were significantly higher after intrapulmonary administration of both gentamicin and vancomycin. In healthy rabbits, peak plasma concentrations were lower and 5 h plasma concentrations were higher after intrapulmonary administration, whereas plasma concentrations were not different in surfactant-depleted rabbits. There were no differences in lung histology, hemodynamics, lung mechanics, or gas exchange between the treatment groups. We conclude that during PLV, higher PATC can be achieved after intrapulmonary administration of PFD-antibiotic emulsions compared with intravenous administration of the same dose without apparent short-term adverse effects. We speculate that intrapulmonary antibiotic administration during PLV may be beneficial in treating severe pneumonia.

Basis of anti-infective therapy: pharmacokinetic-pharmacodynamic criteria and methodology for dual dosage individualisation

Antimicrobial therapy should be designed on the basis of microbiological, as well as pharmacokinetic, criteria; microbiological parameters provide information about the susceptibility of the pathogen responsible for the infectious process while pharmacokinetic parameters give information about the potential ability of the drug in question to reach and remain at the sites of infection in the body. Microbiological parameters such as the minimum inhibitory concentration, minimum bactericidal concentration, bacterial titre, bactericidal rate and 'post-antibiotic effect' (PAE) must be considered. Among the pharmacokinetic parameters, the maximum serum concentration at steady state (CmaxSS), area under the concentration-time curve (AUC) and length of time that the serum concentrations exceed a particular value are the most useful in this context. Different relationships between these parameters, known as efficacy indices, have been established to predict the potential efficacy of antibacterial therapy. Antimicrobial dosage individualisation should be based on the optimisation of the efficacy index that best correlates with patient response. It seems appropriate to establish the degree of correlation among the different efficacy indices and clinical response observed in patients by means of a correlation analysis. This type of analysis can be either retrospective or prospective and may be based on linear or maximum response models. Simulation of the plasma concentration curves obtained with the particular regimen administered offers a methodology which is easy to apply and provides the pharmacokinetic information necessary to calculate the different efficacy indices. Information about the susceptibility of the pathogen to the antibacterial in question and about the response to the treatment used is also necessary for the correlation analysis. This type of analysis determines which of the indices is best correlated with efficacy and, hence, is the index to be optimised when attempting to individualise antibacterial therapy for different situations.

Pharmacokinetic optimisation of antibacterial treatment in patients with cystic fibrosis. Current practice and suggestions for future directions

Antibacterials play a central role in the medical management of patients with cystic fibrosis (CF). Administration of adequate dosages of antibacterials results in pronounced beneficial effects on the morbidity and mortality of this patient group. The dosage of the antibacterial that is needed for optimal treatment depends on the individual patient's pharmacokinetics and the pharmacokinetic-pharmacodynamic effect on the micro-organism of relevance in the host. In general, the disposition of antibacterial drugs in patients with CF is not as 'atypical' as once thought. Recent research with adequately matched controls demonstrated that, for a few beta-lactam antibacterials only, a CF-specific increase of the total body clearance seems to exist and that the large volumes of distribution observed are the result of malnutrition and the relative lack of adipose tissue. Pharmacokinetic-pharmacodynamic relationships in patients with CF are less well studied. Apart from the pharmacokinetics, there is a need for optimisation of antibacterial therapy. For the aminoglycosides, pharmacokinetic optimisation based on measured serum drug concentrations is common practice. The Sawchuk-Zaske method based on peak and trough drug concentrations is widely used. A more sophisticated approach is the 'goal-oriented model-based Bayesian adaptive control' method, where integration of mathematically determined optimally (D-optimally) sampled serum drug concentrations and a population model results in the most likely set of individual pharmacokinetic parameter values suitable for further pharmacokinetic optimisation of the therapy. A future development is the integration of changing serum drug concentrations and killing rates of the target micro-organism to a pharmacokinetic-pharmacodynamic surrogate relationship to optimise drug therapy. The latter approach may be extremely useful in deciding on the frequency of aminoglycoside administration as well as the optimal use of the beta-lactam antibacterials and fluoroquinolones.