Influence of morbid obesity on the single-dose pharmacokinetics of daptomycin

Fixed dose daptomycin: An opportunity for pharmacokinetic/pharmacodynamic optimization in Staphylococcus aureus infections

BACKGROUND

Daptomycin is a high-use intravenous antimicrobial agent affording the convenience of once-daily dosing. Prior studies suggest an opportunity to use a more operationally convenient fixed rather than weight-based dosing but this approach has not been studied prospectively.

METHODS

This study quantified the probability of toxicity and efficacy end points by prospectively testing a fixed dose regimen of daptomycin (750 mg) in obese and non-obese adults. At least, three daptomycin concentrations were measured at steady-state for each patient. A population pharmacokinetic model was constructed to evaluate concentration-time profiles and investigate covariates of daptomycin clearance. Simulations were performed to evaluate the probability of achieving efficacy (24-h area under the curve (AUC0-24) ≥ 666 mg∙h/L) and toxicity (minimum concentration (C min) ≥24.3 mg/L) targets for fixed (500-1000 mg) and weight-based (6-12 mg/kg) daptomycin doses.

RESULTS

Thirty-one patients (16 females, 15 males) with median (interquartile range (IQR)) age of 50 (30, 62) years and weight of 74 (54, 156) kg were included in the final analysis. Fixed dose daptomycin (750 mg) resulted in similar exposure across weights with a median (IQR) AUC0-24 of 819 (499, 1501) mg∙h/L and 749 (606, 1265) mg∙h/L in patients weighing ≤74 kg and >74 kg, respectively. Overall, male sex and increased kidney function necessitate higher fixed and weight-based doses to achieve efficacy. Creatine phosphokinase elevation was observed in two patients (6.5%) and predicted to be lower with fixed versus weight-based regimens.

CONCLUSIONS

Fixed daptomycin dosing adjusted for sex and kidney function is expected to improve the efficacy-to-toxicity ratio, transitions of care, and costs compared to weight-based doses. However, no empiric dosing approach is predicted to achieve ≥90% efficacy while minimizing the risk of toxicity, so therapeutic drug monitoring should be considered on a patient-specific basis.

A Machine Learning Algorithm to Predict the Starting Dose of Daptomycin

BACKGROUND AND OBJECTIVE

The dosage of daptomycin is usually based on body weight. However, it has been shown that this approach yields too high an exposure in obese patients. Pharmacokinetic and pharmacodynamic indexes (PK/PD) have been proposed for daptomycin's antibacterial effect (AUC/CMI >666) and toxicity (C0 > 24.3 mg/L). We previously developed machine learning (ML) algorithms to predict starting doses based on Monte Carlo simulations. We propose a new way to perform probability of target attainment based on an ML algorithm to predict the daptomycin starting dose.

METHODS

The Dvorchik model of daptomycin was implemented in the mrgsolve R package and 4950 pharmacokinetic profiles were simulated with doses ranging from 4 to 12 mg/kg. We trained and benchmarked four machine learning algorithms and selected the best to iteratively search for the optimal dose of daptomycin maximizing the event (AUC/CMI > 666 and C0 < 24.3 mg/L). The ML algorithm was evaluated in simulations and an external database of real patients in comparison with population pharmacokinetics.

RESULTS

The performance of the Xgboost algorithms developed to predict the event (ROC AUC) in the training and test set were 0.762 and 0.761, respectively. The most important prediction variables were dose, creatinine clearance, body weight and sex. In the external database of real patients, the starting dose administered based on the ML algorithm significantly improved the target attainment by 7.9% (p-value = 0.02929) in comparison with the dose administered based on body weight.

CONCLUSION

The developed algorithm improved the target attainment for daptomycin in comparison with weight-based dosing. We built a Shiny app to calculate the optimal starting dose.

A machine learning approach to predict daptomycin exposure from two concentrations based on Monte Carlo simulations

Daptomycin is a concentration-dependent lipopeptide antibiotic for which exposure/effect relationships have been shown. Machine learning (ML) algorithms, developed to predict the individual exposure to drugs, have shown very good performances in comparison to maximum a posteriori Bayesian estimation (MAP-BE). The aim of this work was to predict the area under the blood concentration curve (AUC) of daptomycin from two samples and a few covariates using XGBoost ML algorithm trained on Monte Carlo simulations. Five thousand one hundred fifty patients were simulated from two literature population pharmacokinetics models. Data from the first model were split into a training set (75%) and a testing set (25%). Four ML algorithms were built to learn AUC based on daptomycin blood concentration samples at pre-dose and 1 h post-dose. The XGBoost model (best ML algorithm) with the lowest root mean square error (RMSE) in a 10-fold cross-validation experiment was evaluated in both the test set and the simulations from the second population pharmacokinetic model (validation). The ML model based on the two concentrations, the differences between these concentrations, and five other covariates (sex, weight, daptomycin dose, creatinine clearance, and body temperature) yielded very good AUC estimation in the test (relative bias/RMSE = 0.43/7.69%) and validation sets (relative bias/RMSE = 4.61/6.63%). The XGBoost ML model developed allowed accurate estimation of daptomycin AUC using C0, C1h, and a few covariates and could be used for exposure estimation and dose adjustment. This ML approach can facilitate the conduct of future therapeutic drug monitoring (TDM) studies.

Model-Informed Approaches to Support Drug Development for Patients With Obesity: A Regulatory Perspective

Obesity, which is defined as having a body mass index of 30 kg/m2 or greater, has been recognized as a serious health problem that increases the risk of many comorbidities (eg, heart disease, stroke, and diabetes) and mortality. The high prevalence of individuals who are classified as obese calls for additional considerations in clinical trial design. Nevertheless, gaining a comprehensive understanding of how obesity affects the pharmacokinetics (PK), pharmacodynamics (PD), and efficacy of drugs proves challenging, primarily as obese patients are seldom selected for enrollment at the early stages of drug development. Over the past decade, model-informed drug development (MIDD) approaches have been increasingly used in drug development programs for obesity and its related diseases as they use and integrate all available sources and knowledge to inform and facilitate clinical drug development. This review summarizes the impact of obesity on PK, PD, and the efficacy of drugs and, more importantly, provides an overview of the use of MIDD approaches in drug development and regulatory decision making for patients with obesity: estimating PK, PD, and efficacy in specific dosing scenarios, optimizing dose regimen, and providing evidence for seeking new indication(s). Recent review cases using MIDD approaches to support dose selection and provide confirmatory evidence for effectiveness for patients with obesity, including pediatric patients, are discussed. These examples demonstrate the promise of MIDD as a valuable tool in supporting clinical trial design during drug development and facilitating regulatory decision-making processes for the benefit of patients with obesity.

Pharmacokinetics of obese adults: Not only an increase in weight

Obesity is a pathophysiological state defined by a body mass index > 30 kg/m2 and characterized by an adipose tissue accumulation leading to an important weight increased. Several pathologies named comorbidities such as cardiovascular disease, type 2 diabetes and cancer make obesity the fifth cause of death in the world. Physiological changes impact the four main phases of pharmacokinetics of some drugs and leads to an inappropriate drug-dose. For absorption, the gastrointestinal transit is accelerated, and the gastric empty time is shortened, that can reduce the solubilization and absorption of some oral drugs. The drug distribution is probably the most impacted by the obesity-related changes because the fat mass (FM) increases at the expense of the lean body weight (LBW), leading to an important increase of the volume of distribution for lipophilic drugs and a low or moderately increase of this parameter for hydrophilic drugs. This modification of the distribution may require drug-dose adjustments. By various mechanisms, the metabolism and elimination of drugs are impacted by obesity and should be considered as similar or lower than that non-obese patients. To better understand the necessary drug-dose adjustments in obese patients, a narrative review of the literature was conducted to highlight the main elements to consider in the therapeutic management of adult obese patients.

Reporting of Drug-Induced Myopathies Associated with the Combination of Statins and Daptomycin: A Disproportionality Analysis Using the US Food and Drug Administration Adverse Event Reporting System

BACKGROUND

Myopathy is one of the most common adverse reactions of daptomycin and statins. We aimed to evaluate the muscular toxicity of the combination therapy of daptomycin and statins in a large pharmacovigilance database.

METHODS

This was a retrospective disproportionality analysis based on real-world data. All cases reported between the first quarter of 2004 and the fourth quarter of 2022 where daptomycin and statins were reported were gathered from the US Food and Drug Administration Adverse Event Reporting System (FAERS) database. Disproportionality analyses were conducted by estimating the proportional reporting ratios (PRRs), reporting odds ratio (ROR), and information component (IC).

RESULTS

A total of 971,861 eligible cases were collected from the FAERS database. Data analysis showed that rosuvastatin (ROR: 124.39, 95% CI: 87.35-178.47), atorvastatin (ROR: 68.53, 95% CI: 51.93-90.43), and simvastatin (ROR: 94.83, 95% CI: 71.12-126.46) combined with daptomycin increased the reporting frequency of myopathy. Moreover, myopathy was reported more frequently with the 3-drug combination (ROR: 598.01, 95% CI: 231.81-1542.71). For rhabdomyolysis, the frequency of reports also increased when daptomycin was combined with rosuvastatin (ROR: 156.34, 95% CI: 96.21-254.05), simvastatin (ROR: 72.65, 95% CI: 47.36-111.44), and atorvastatin (ROR: 66.31, 95% CI: 44.06-99.81).

CONCLUSIONS

The combination of daptomycin and statins increased the association of myopathy and rhabdomyolysis, especially with rosuvastatin, simvastatin, and atorvastatin.

Characterization of plasma daptomycin in patients with serum highly glycated albumin and obesity

PURPOSE

Plasma daptomycin has not been fully characterized in diabetic and obese patients. This study aimed to evaluate the associations of plasma daptomycin with glycation of serum albumin and obesity.

METHODS

Infectious patients (n = 70) receiving intravenous daptomycin were enrolled. The plasma concentration of total and free daptomycin were determined using liquid chromatograph-tandem mass spectrometer. The associations of the plasma concentrations of daptomycin with clinical factors including serum albumin fractionations and physical status (obese including overweight, body mass index ≥ 25.0) were investigated. Daptomycin doses were adjusted using total body-weight.

RESULTS

The serum albumin level was positively and negatively correlated with the plasma concentration of total daptomycin and its free fraction proportion, respectively. The serum non-glycated albumin was negatively correlated with the free fraction proportion. The dose-normalized plasma concentration of total daptomycin was higher in the obese patients than in non-obese patients when the body-weight was corrected with total and adjusted values. For the dose adjustment with lean body-weight, no difference was observed in the dose-normalized plasma concentration of total daptomycin between the physical statuses. For each body-weight correction method, physical status did not affect the dose-normalized plasma concentration of free daptomycin.

CONCLUSION

The glycation of serum albumin and obesity did not associate with dose-normalized plasma free daptomycin. In obese patients, daptomycin dosage adjustment with total body-weight and adjusted body-weight may lead to an apparent excessive exposure resulting in overdosage compared to lean body-weight.

Drug pharmacokinetics in the obese population: challenging common assumptions on predictors of obesity-related parameter changes

INTRODUCTION

Obesity is associated with many physiological changes. We review available evidence regarding five commonly accepted assumptions to a priori predict the impact of obesity on drug pharmacokinetics (PK).

AREAS COVERED

The investigated assumptions are: 1) lean body weight is the preferred descriptor of clearance and dose adjustments; 2) volume of distribution increases for lipophilic, but not for hydrophilic drugs; 3) CYP-3A4 activity is suppressed and UGT activity is increased, implying decreased and increased dose requirements for substrates of these enzyme systems, respectively; 4) glomerular filtration rate is enhanced, necessitating higher doses for drugs cleared through glomerular filtration; 5) drug dosing information from obese adults can be extrapolated to obese adolescents.

EXPERT OPINION

Available literature contradicts, or at least limits the generalizability, of all five assumptions. Clinical studies should focus on quantifying the impact of duration and severity of obesity on drug PK in adults and adolescents, and also include oral bioavailability and pharmacodynamics in these studies. Physiologically-based PK approaches can be used to predict PK changes for individual drugs, but can also be used to define in general terms based on patient characteristics and drug properties, when certain assumptions can or cannot be expected to be systematically accurate.

Real-Time Therapeutic Drug Monitoring-Based Pharmacokinetic/Pharmacodynamic Optimization of Complex Antimicrobial Therapy in a Critically Ill Morbidly Obese Patient. Grand Round/A Case Study

The authors present the case of a critically ill morbidly obese patient (body mass index, 51.2 kg/m) who suffered from methicillin-resistant Staphylococcus epidermidis, and Candida albicans bloodstream infections. Initial treatment with caspofungin and daptomycin was deemed inappropriate, because blood cultures remained positive for both isolates after 14 days. The clinical pharmacological consultant suggested adding fluconazole and ceftobiprole to the ongoing antimicrobial therapy, and starting a real-time therapeutic drug monitoring program of daptomycin, ceftobiprole, and fluconazole, aimed at optimizing plasma exposures. Punctual minimum inhibitory concentration knowledge on the clinical isolates allowed attainment of the desired pharmacodynamic efficacy targets. Within few days, the patient greatly improved, as blood cultures became negative, and the inflammatory markers decreased to near normal values. This is a proof-of-concept of the importance of a therapeutic drug monitoring-based multidisciplinary approach in the proper management of complex antimicrobial therapy in special populations.

Clinical Pharmacokinetics of Daptomycin

Due to the low level of resistance observed with daptomycin, this antibiotic has an important place in the treatment of severe Gram-positive infections. It is the first-in-class of the group of calcium-dependent, membrane-binding lipopeptides, and is a cyclic peptide constituted of 13 amino acids and an n-decanoyl fatty acid chain. The antibacterial action of daptomycin requires its complexation with calcium. Daptomycin is not absorbed from the gastrointestinal tract and needs to be administered parenterally. The distribution of daptomycin is limited (volume of distribution of 0.1 L/kg in healthy volunteers) due to its negative charge at physiological pH and its high binding to plasma proteins (about 90%). Its elimination is mainly renal, with about 50% of the dose excreted unchanged in the urine, justifying dosage adjustment for patients with renal insufficiency. The pharmacokinetics of daptomycin are altered under certain pathophysiological conditions, resulting in high interindividual variability. As a result, therapeutic drug monitoring of daptomycin may be of interest for certain patients, such as intensive care unit patients, patients with renal or hepatic insufficiency, dialysis patients, obese patients, or children. A target for the ratio of the area under the curve to the minimum inhibitory concentration > 666 is usually recommended for clinical efficacy, whereas in order to limit the risk of undesirable muscular effects the residual concentration should not exceed 24.3 mg/L.

Pharmacokinetics and Pharmacodynamics of Drugs in Obese Pediatric Patients: How to Map Uncharted Clinical Territories

Clinicians are increasingly faced with challenges regarding the pharmacological treatment of obese pediatric patients. To provide guidance for these treatments, a better understanding of the impact of obesity on pharmacological processes in children is needed. Results on pharmacological studies in adults show however ambiguous patterns regarding the impact of obesity on ADME processes or on drug pharmacodynamics. Additionally, based on the limited research performed in obese pediatric patients, it becomes clear that findings from obese adults cannot be expected to always translate directly to similar findings in obese children. To improve knowledge on drug pharmacology in obese pediatric patients, studies should focus on quantifying the impact of maturation, obesity, and other relevant variables on primary pharmacological parameters and on disentangling systemic (renal and/or hepatic) and presystemic (gut and/or first-pass hepatic) clearance. For this, data is required from well-designed clinical trials that include patients with not only a wide range in age but also a range in excess body weight, upon oral and intravenous dosing. Population modelling approaches are ideally suitable for this purpose and can also be used to link the pharmacokinetics to pharmacodynamics and to derive drug dosing regimens. Generalizability of research findings can be achieved by including mechanistic aspects in the data analysis, for instance, using either extrapolation approaches in population modelling or by applying physiologically based modelling principles. It is imperative that more and smarter studies are performed in obese pediatric patients to provide safe and effective treatment for this special patient population.

Evaluation of treatment options for methicillin-resistant Staphylococcus aureus infections in the obese patient

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a major cause of infection in both the hospital and community setting. Obesity is a risk factor for infection, and the prevalence of this disease has reached epidemic proportions worldwide. Treatment of infections in this special population is a challenge given the lack of data on the optimal antibiotic choice and dosing strategies, particularly for treatment of MRSA infections. Obesity is associated with various physiological changes that may lead to altered pharmacokinetic parameters. These changes include altered drug biodistribution, elimination, and absorption. This review provides clinicians with a summary of the literature pertaining to the pharmacokinetic and pharmacodynamic considerations when selecting antibiotic therapy for the treatment of MRSA infections in obese patients.

Comparison of the Drug-Drug Interaction Potential of Daptomycin in Combination with Rifampin in Healthy Adult Volunteers

We evaluated the effects of rifampin coadministration and MDR1 single nucleotide polymorphisms on the disposition of daptomycin in twelve healthy adults. There were no significant changes from baseline in the clearance (0.53 versus 0.55 liters/h, P = 1.00), volume of distribution (7.0 versus 7.2 liter, P = 0.62), or half-life (9.7 versus 9.6 h, P = 0.89) of daptomycin after exposure to rifampin. The tested MDR1 polymorphisms were not associated with significant differences in daptomycin disposition.

Development and validation of sensitive and selective quantification of total and free daptomycin in human plasma using ultra-performance liquid chromatography coupled to tandem mass spectrometry

Recently, several studies on pharmacokinetics parameters of daptomycin reported that plasma trough concentration was linked to efficacy and adverse effects, suggesting the usefulness of therapeutic drug monitoring. Although some methods for determining total daptomycin concentration using liquid chromatography coupled to tandem mass spectrometry were established previously, no sensitive quantification method for free drug concentration was established. In this study, we aimed to develop a quantitative method of measuring both total and free daptomycin concentrations using ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS), by which both trough and maximum concentrations can be measured. Plasma samples were prepared by solid phase extraction. Free fractions were obtained by ultrafiltration. The assay fulfilled the requirements of US Food and Drug Administration and the European Medicines Agency for assay validation. The methods for total and free drug showed good fit over wide ranges of 0.5-200 and 0.04-40 μg/mL, with lower limits of quantitation of 0.5 and 0.04 μg/mL, respectively. Recovery rate of free daptomycin from ultrafiltration was approximately 100%. Extraction recovery rates of total and free drug measurements ranged from 57.1 to 67.4% and 54.6 to 62.3%, while matrix effect varied between 111.9 and 118.7% and 104.0 and 127.1%, respectively. The maximum and trough concentrations of total and free daptomycin in plasma from two patients in intensive care unit were successfully determined, demonstrating the feasibility of clinical application of the novel methods for determining plasma total and free daptomycin concentrations. In conclusion, we succeeded to develop a sensitive and selective method using UPLC-MS/MS for quantitative measurement of total and free daptomycin concentrations in plasma.

Effect of Statin Coadministration on the Risk of Daptomycin-Associated Myopathy

Background

Daptomycin-associated myopathy has been identified in 2%-14% of patients, and rhabdomyolysis is a known adverse effect. Although risk factors for daptomycin-associated myopathy are poorly defined, creatine phosphokinase (CPK) monitoring and temporary discontinuation of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, or "statins," has been recommended.

Methods

We conducted a single-center, retrospective, matched case-control risk factor analysis in adult and pediatric patients from 2004 to 2015. Patients in whom myopathy (defined as CPK values above the upper limit of normal) developed during daptomycin treatment were matched 1:1 to no-myopathy controls with at least the same duration of therapy. Risk factors independently associated with myopathy were determined using multivariable conditional logistic regression. Secondary analysis was performed in patients with rhabdomyolysis, defined as CPK values ≥10 times the upper limit of normal.

Results

Of 3042 patients reviewed, 128 (4.2%) were identified as having daptomycin-associated myopathy, 25 (0.8%) of whom had rhabdomyolysis; 121 (95%) of the 128 were adults, and the mean duration of therapy before CPK elevation was 16.7 days (range, 1-58 days). In multivariate analysis, deep abscess treatment (odds ratio, 2.80; P = .03), antihistamine coadministration (3.50; P = .03), and statin coadministration (2.60; P = .03) were independent risk factors for myopathy. Obesity (odds ratio, 3.28; P = .03) and statin coadministration (4.67; P = .03) were found to be independent risk factors for rhabdomyolysis, and older age was associated with reduced risk (0.97; P = .05).

Conclusions

Statin coadministration with daptomycin was independently associated with myopathy and rhabdomyolysis. This is the first study to provide strong evidence supporting this association. During coadministration, we recommend twice-weekly CPK monitoring and consideration of withholding statins.

Obesity and drug pharmacology: a review of the influence of obesity on pharmacokinetic and pharmacodynamic parameters

INTRODUCTION

The rising prevalence of obesity confronts clinicians with dosing problems in the (extreme) overweight population. Obesity has a great impact on key organs that play a role in the pharmacokinetics (PK) and pharmacodynamics (PD) of drugs, however the ultimate impact of these changes on how to adapt the dose may not always be known. Areas covered: In this review, physiological changes associated with obesity are discussed. An overview is provided on the alterations in absorption, distribution, drug metabolism and clearance in (morbid) obesity focusing on general principles that can be extracted from pharmacokinetic studies. Also, relevant pharmacodynamic considerations in obesity are discussed. Expert opinion: Over the last two decades, increased knowledge is generated on PK and PD in obesity. Future research should focus on filling in the knowledge gaps that remain, especially in connecting obesity-related physiological changes with changes in PK and/or PD and vice versa. Ultimately, this knowledge can be used to develop physiologically based PK and PD models on the basis of quantitative systems pharmacology principles. Moreover, efforts should focus on thorough prospective evaluation of developed model-based doses with subsequent implementation of these dosing recommendations in clinical practice.

Association of Higher Daptomycin Dose (7 mg/kg or Greater) with Improved Survival in Patients with Methicillin-Resistant Staphylococcus aureus Bacteremia

STUDY OBJECTIVE

Current guidelines recommend higher daptomycin doses than the daptomycin label dose of 6 mg/kg for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia; however, the evidence supporting this recommendation is from in vitro and case series studies. This study evaluated the comparative effectiveness of the daptomycin label dose versus higher daptomycin doses in patients with MRSA bacteremia.

DESIGN

Retrospective national cohort study.

SETTING

Veterans Affairs medical centers.

PATIENTS

A total of 371 adults with MRSA bacteremia who were admitted between 2002 and 2015 and treated initially with vancomycin within 24 hours of initial culture collection and then switched to daptomycin therapy within 7 days; 138 patients (37.2%) received daptomycin doses higher than the daptomycin label dose (7 mg/kg or greater), and 233 (62.8%) received the daptomycin label dose (6 mg/kg).

MEASUREMENTS AND MAIN RESULTS

Clinical outcomes were compared among those who received the daptomycin label dose and those who received the higher dose using propensity score-matched Cox proportional hazards regression models. To identify dose partitioning associated with optimal survival, classification and regression tree (CART) analysis was used among patients, controlling for confounding with a 30-day mortality disease risk score. Propensity score-matched 30-day mortality was 8.6% (6/70 patients) among the higher dose group versus 18.6% (13/70 patients) among the label dose group (hazard ratio 0.31, 95% confidence interval 0.10-0.94). No significant differences were observed in inpatient mortality, length of stay, 30-day readmission, or 30-day S. aureus reinfection between groups. CART analysis resulted in doses of 7 mg/kg or greater providing benefit only among patients with higher (more than 51%) predicted probabilities of 30-day mortality (p<0.001).

CONCLUSION

To our knowledge, this is the first comparative effectiveness study of daptomycin doses in patients with MRSA bacteremia. Survival benefits were observed with doses higher than the daptomycin label dose (7 mg/kg or greater) for the treatment of MRSA bacteremia. These data suggest that higher doses than the daptomycin label dose may be preferred over the label dose for improving clinical outcomes in patients with MRSA bacteremia.

No role for patient body weight on renal function assessment for drug dosing

Objectives

To evaluate the ability of body-weight-driven renal function assessment (RFA) formulae to predict on-target elimination rate ranges for gentamicin in patients with varying degrees of renal function.

Methods

A 6 year retrospective pharmacokinetic study was conducted at a university teaching hospital.

Results

A total of 85 patients met the inclusion criteria and 127 pharmacokinetic files were analysed from patients on medical-surgical wards (53%) and medical-surgical ICUs (13%) receiving intravenous gentamicin for treatment, as well as those for patients receiving it for surgical prophylaxis (34%). Each RFA formula was examined against standard dosing tables for gentamicin. A table of acceptable elimination rates was generated using a traditional peak of 8 mg/L and trough between 0.5 and 2 mg/L associated with each of the dosing interval extensions. The ability of each RFA formula to select on-target elimination rates was evaluated. The RFA formula assuming a normalized body weight of 72 kg and a modified creatinine reagent adjustment factor of 90% provided the most accurate on-target elimination rate selection. This method was superior to dosing interval selection based on the Modification in Diet Renal Disease (MDRD) formula, Sanford's guide method, as well as the Cockcroft-Gault formulae using total body weight, ideal body weight or lean body weight ( P  <   0.0001).

Conclusions

Based on the use of gentamicin as a surrogate guide for renally adjusted drugs, these results support dosing interval selection based on a normalized body weight method and a formula reagent adjustment factor of 90% within the Cockcroft-Gault formula.

The Surgical Infection Society Revised Guidelines on the Management of Intra-Abdominal Infection

BACKGROUND

Previous evidence-based guidelines on the management of intra-abdominal infection (IAI) were published by the Surgical Infection Society (SIS) in 1992, 2002, and 2010. At the time the most recent guideline was released, the plan was to update the guideline every five years to ensure the timeliness and appropriateness of the recommendations.

METHODS

Based on the previous guidelines, the task force outlined a number of topics related to the treatment of patients with IAI and then developed key questions on these various topics. All questions were approached using general and specific literature searches, focusing on articles and other information published since 2008. These publications and additional materials published before 2008 were reviewed by the task force as a whole or by individual subgroups as to relevance to individual questions. Recommendations were developed by a process of iterative consensus, with all task force members voting to accept or reject each recommendation. Grading was based on the GRADE (Grades of Recommendation Assessment, Development, and Evaluation) system; the quality of the evidence was graded as high, moderate, or weak, and the strength of the recommendation was graded as strong or weak. Review of the document was performed by members of the SIS who were not on the task force. After responses were made to all critiques, the document was approved as an official guideline of the SIS by the Executive Council.

RESULTS

This guideline summarizes the current recommendations developed by the task force on the treatment of patients who have IAI. Evidence-based recommendations have been made regarding risk assessment in individual patients; source control; the timing, selection, and duration of antimicrobial therapy; and suggested approaches to patients who fail initial therapy. Additional recommendations related to the treatment of pediatric patients with IAI have been included.

SUMMARY

The current recommendations of the SIS regarding the treatment of patients with IAI are provided in this guideline.

Pediatric Obesity: Pharmacokinetic Alterations and Effects on Antimicrobial Dosing

Limited data exist for appropriate drug dosing in obese children. This comprehensive review summarizes pharmacokinetic (PK) alterations that occur with age and obesity, and these effects on antimicrobial dosing. A thorough comparison of different measures of body weight and specific antimicrobial agents including cefazolin, cefepime, ceftazidime, daptomycin, doripenem, gentamicin, linezolid, meropenem, piperacillin-tazobactam, tobramycin, vancomycin, and voriconazole is presented. PubMed (1966-July 2015) and Cochrane Library searches were performed using these key terms: children, pharmacokinetic, obesity, overweight, body mass index, ideal body weight, lean body weight, body composition, and specific antimicrobial drugs. PK studies in obese children and, if necessary, data from adult studies were summarized. Knowledge of PK alterations stemming from physiologic changes that occur with age from the neonate to adolescent, as well as those that result from increased body fat, become an essential first step toward optimizing drug dosing in obese children. Excessive amounts of adipose tissue contribute significantly to body size, total body water content, and organ size and function that may modify drug distribution and clearance. PK studies that evaluated antimicrobial dosing primarily used total (or actual) body weight (TBW) for loading doses and TBW or adjusted body weight for maintenance doses, depending on the drugs' properties and dosing units. PK studies in obese children are imperative to elucidate drug distribution, clearance, and, consequently, the dose required for effective therapy in these children. Future studies should evaluate the effects of both age and obesity on drug dosing because the incidence of obesity is increasing in pediatric patients.

Evaluation of a standardized daptomycin dosing nomogram

PURPOSE

Implementation of a standardized daptomycin dosing protocol in a community teaching hospital to determine potential cost savings, effectiveness, and safety is presented.

METHODS

A retrospective review of randomly selected patients receiving daptomycin therapy from October 2013 to January 2014 was performed to establish a preimplementation patient control group. A specific time for preparing daptomycin in the i.v. room was used based on a standardized administration time of 4 p.m. Reconstituted doses were stored for up to 48 hours in the refrigerator in plastic syringes. All daptomycin doses were given by rapid i.v. administration. For all patients who received daptomycin, the protocol specified that a baseline creatine phosphokinase level be evaluated within 24 hours of the start date and on day 3, day 7, and weekly thereafter until daptomycin therapy was completed or discontinued.

RESULTS

The most frequent indications for daptomycin use preimplementation and postimplementation were related to catheter use or persistent bacteremia and skin and soft tissue infections. Through the implementation of the standardized dosing nomogram and optimization of i.v. room workflow, the amount of waste decreased by 21,500 mg and generated a savings of $13,845 over the course of the four-month study period, which can be extrapolated to $41,535 annually. The infection cure rate at completion of therapy was 56.7% in the preimplementation population compared with 70.0% in the postimplementation population. Daptomycin was well tolerated at the standardized doses used in the study.

CONCLUSION

Implementation of a standardized dosing nomogram reduced the amount of daptomycin wasted and resulted in cost savings. The standardized dosing nomogram did not impair the rate of clinical effectiveness or cause adverse events.

Significant publications on infectious diseases pharmacotherapy in 2014

PURPOSE

The most important articles on infectious diseases (ID) pharmacotherapy published in the peer-reviewed literature in 2014, as nominated and selected by panels of pharmacists and others with ID expertise, are summarized.

SUMMARY

Members of the Houston Infectious Diseases Network were asked to nominate articles published in 2014 from prominent peer-reviewed journals that were felt to have a major impact in the field of ID pharmacotherapy. A list of 19 nominated articles on general ID-related topics and 9 articles specifically related to human immunodeficiency virus (HIV) infection or acquired immunodeficiency syndrome (AIDS) was compiled. In a national online survey, members of the Society of Infectious Diseases Pharmacists (SIDP) were asked to select from the list 10 general ID articles believed to have made a significant contribution to the field of ID pharmacotherapy and 1 article contributing to HIV/AIDS pharmacotherapy. Of the 291 SIDP members surveyed, 134 (46%) and 56 (19%) participated in the selection of general ID-related articles and HIV/AIDS-related articles, respectively. The 11 highest-ranked papers (10 general ID-related articles, 1 HIV/AIDS-related article) are summarized here.

CONCLUSION

With the vast number of articles published each year, it is difficult to remain up-to-date on current, significant ID pharmacotherapy publications. This review of significant publications in 2014 may be helpful by lessening this burden.

Advances in antibiotic therapy in the critically ill

Infections occur frequently in critically ill patients and their management can be challenging for various reasons, including delayed diagnosis, difficulties identifying causative microorganisms, and the high prevalence of antibiotic-resistant strains. In this review, we briefly discuss the importance of early infection diagnosis, before considering in more detail some of the key issues related to antibiotic management in these patients, including controversies surrounding use of combination or monotherapy, duration of therapy, and de-escalation. Antibiotic pharmacodynamics and pharmacokinetics, notably volumes of distribution and clearance, can be altered by critical illness and can influence dosing regimens. Dosing decisions in different subgroups of patients, e.g., the obese, are also covered. We also briefly consider ventilator-associated pneumonia and the role of inhaled antibiotics. Finally, we mention antibiotics that are currently being developed and show promise for the future.

Daptomycin: an evidence-based review of its role in the treatment of Gram-positive infections

Infections caused by Gram-positive pathogens remain a major public health burden and are associated with high morbidity and mortality. Increasing rates of infection with Gram-positive bacteria and the emergence of resistance to commonly used antibiotics have led to the need for novel antibiotics. Daptomycin, a cyclic lipopeptide with rapid bactericidal activity against a wide range of Gram-positive bacteria including methicillin-resistant Staphylococcus aureus, has been shown to be effective and has a good safety profile for the approved indications of complicated skin and soft tissue infections (4 mg/kg/day), right-sided infective endocarditis caused by S. aureus, and bacteremia associated with complicated skin and soft tissue infections or right-sided infective endocarditis (6 mg/kg/day). Based on its pharmacokinetic profile and concentration-dependent bactericidal activity, high-dose (>6 mg/kg/day) daptomycin is considered an important treatment option in the management of various difficult-to-treat Gram-positive infections. Although daptomycin resistance has been documented, it remains uncommon despite the increasing use of daptomycin. To enhance activity and to minimize resistance, daptomycin in combination with other antibiotics has also been explored and found to be beneficial in certain severe infections. The availability of daptomycin via a 2-minute intravenous bolus facilitates its outpatient administration, providing an opportunity to reduce risk of health care-associated infections, improve patient satisfaction, and minimize health care costs. Daptomycin, not currently approved for use in the pediatric population, has been shown to be widely used for treating Gram-positive infections in children.

Effect of obesity on the pharmacokinetics of antimicrobials in critically ill patients: A structured review

The increased prevalence of obesity presents challenges for clinicians aiming to provide optimised antimicrobial dosing in the intensive care unit. Obesity is likely to exacerbate the alterations to antimicrobial pharmacokinetics when the chronic diseases associated with obesity exist with the acute pathophysiological changes associated with critical illness. The purpose of this paper is to review the potential pharmacokinetic (PK) changes of antimicrobials in obese critically ill patients and the implications for appropriate dosing. We found that hydrophilic antimicrobials (e.g. β-lactams, vancomycin, daptomycin) were more likely to manifest altered pharmacokinetics in critically ill patients who are obese. In particular for β-lactam antibiotics, obesity is associated with a larger volume of distribution (V(d)). In obese critically ill patients, piperacillin is also associated with a lower drug clearance (CL). For doripenem, these PK changes have been associated with reduced achievement of pharmacodynamic (PD) targets when standard drug doses are used. For vancomycin, increases in Vd are associated with increasing total body weight (TBW), meaning that the loading dose should be based on TBW even in obese patients. For daptomycin, an increased Vd is not considered to be clinically relevant. For antifungals, little data exist in obese critically ill patients; during fluconazole therapy, an obese patient had a lower V(d) and higher CL than non-obese comparators. Overall, most studies suggested that standard dosage regimens of most commonly used antimicrobials are sufficient to achieve PD targets. However, it is likely that larger doses would be required for pathogens with higher minimum inhibitory concentrations.

A Review of the Toxicologic Implications of Obesity

The increasing prevalence of obesity in developed nations has far-reaching implications for medical toxicology. The management of obese patients is complicated by comorbid illnesses, changes in cardiovascular and respiratory physiology, alterations in pharmacokinetics, and a lack of studies to identify appropriate dosing for current therapeutics and antidotes. In this review article, we examine obesity-associated physiologic and pharmacokinetic changes that may increase the vulnerability of obese patients to overdose. Further research is needed to characterize the relationship between drug toxicity and obesity.

Antimicrobial Stewardship Intervention and Feedback to Infectious Disease Specialists: A Case Study in High-Dose Daptomycin

Infectious Diseases specialists have used high-dose daptomycin (≥6 mg/kg/day) in select patients with difficult to treat methicillin-resistant Staphylococcus aureus (MRSA) or vancomycin-resistant Enterococcus (VRE) infections to optimize outcomes. Antimicrobial stewardship programs enforce antimicrobial formulary restrictions; however, interventions specifically aimed at Infectious Disease specialists can be particularly challenging. The purpose of this study was to create a high-dose daptomycin algorithm for Infectious Disease specialists that are consistent with best-practices. Daptomycin prescribing habits pre- and post-daptomycin algorithm implementation were evaluated using a quasi-experimental study design. Patients were included if ≥18 years of age and received daptomycin for ≥48 h. Patients were excluded if daptomycin was initiated on an outpatient setting. During the 12-month pre-intervention phase, 112 patients were included, with 73 patients in the 12-month post-intervention phase. A statistically significant decrease in the mean daptomycin dose from 9.01 mg/kg to 7.51 mg/kg (p < 0.005) was observed, resulting in an annual drug cost-savings of over $75,000 without adversely affecting readmission rates due to infection. Creation of a daptomycin algorithm with consideration of pathogen, disease state, and prior treatment, is an effective means of influencing prescribing habits of Infectious Disease specialists.

Musculoskeletal safety outcomes of patients receiving daptomycin with HMG-CoA reductase inhibitors

Daptomycin, a cyclic lipopeptide antibiotic, and 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins) are commonly administered in the inpatient setting and are associated with creatine phosphokinase (CPK) elevations, myalgias, and muscle weakness. Safety data for coadministration of daptomycin with statins are limited. To determine the safety of coadministration of daptomycin with statin therapy, a multicenter, retrospective, observational study was performed at 13 institutions in the Southeastern United States. Forty-nine adult patients receiving statins concurrently with daptomycin were compared with 171 patients receiving daptomycin without statin therapy. Detailed information, including treatment indication and duration, infecting pathogen, baseline and subsequent CPK levels, and presence of myalgias or muscle complaints, was collected. Myalgias were noted in 3/49 (6.1%) patients receiving combination therapy compared with 5/171 (2.9%) of patients receiving daptomycin alone (P = 0.38). CPK elevations of >1,000 U/liter occurred in 5/49 (10.2%) patients receiving combination therapy compared to 9/171 (5.3%) patients receiving daptomycin alone (P = 0.32). Two of five patients experiencing CPK elevations of >1,000 U/liter in the combination group had symptoms of myopathy. Three patients (6.1%) discontinued therapy due to CPK elevations with concurrent myalgias in the combination group versus 6 patients (3.5%) in the daptomycin-alone group (P = 0.42). CPK levels and myalgias reversed upon discontinuation of daptomycin therapy. Overall musculoskeletal toxicity was numerically higher in the combination group but this result was not statistically significant. Further prospective study is warranted in a larger population.

Impact of hospital guideline for weight-based antimicrobial dosing in morbidly obese adults and comprehensive literature review

WHAT IS KNOWN AND OBJECTIVE

Obesity is a significant burden on the healthcare system in the United States, and determining the appropriate antimicrobial dosing regimen in morbidly obese patients is challenging. Morbidly obese patients have documented differences in pharmacokinetic and pharmacodynamic properties compared to normal-weight patients, which impact antibiotic efficacy and toxicity. The Food and Drug Administration does not recognize obesity as a special population and does not require pharmaceutical companies to perform studies specific to obese patients. However, there are an increasing number of post-approval studies in obese patients, and this manuscript reviews available clinical and pharmacokinetic literature regarding weight-based antimicrobial agents. Additionally, we describe a single-centre approach to optimize dosing in morbidly obese patients.

METHODS

A comprehensive literature search was performed on 15 weight-based antimicrobials in the setting of obesity: acyclovir, aminoglycosides, amphotericin B, cidofovir, colistimethate, daptomycin, flucytosine, foscarnet, ganciclovir, quinupristin/dalfopristin, trimethoprim/sulfamethoxazole, vancomycin and voriconazole. A weight-based antimicrobial dosing guideline for morbidly obese patients was developed. An analysis of guideline compliance and cost analysis were performed following guideline implementation.

RESULTS AND DISCUSSION

This review describes the pharmacokinetic changes that occur in obese patients, including increased volume of distribution, altered hepatic metabolism, renal excretion and changes in protein binding. The majority of weight-based antimicrobials result in increased serum concentrations in morbidly obese patients compared to normal-weight patients when the calculated dose is based on actual body weight.

WHAT IS NEW AND CONCLUSION

This review demonstrates different antibiotic pharmacokinetic properties are altered in obese patients that could impact efficacy and toxicity. A single-centre guideline for weight-based antimicrobial dosing in obesity was developed and provides recommendations for using ideal body weight, adjusted body weight or actual body weight when calculating antimicrobial doses. However, more research is needed to better elucidate optimal dosing of weight-based antimicrobials in obesity, with particular focus on efficacy and toxicity.

Daptomycin dosing strategies in patients receiving thrice-weekly intermittent hemodialysis

OBJECTIVE

To determine the optimal dosing regimen of daptomycin in patients receiving thrice-weekly hemodialysis.

DATA SOURCES

Literature was accessed via PubMed using the terms daptomycin and hemodialysis through July 2013. Reference citations from publications identified were reviewed.

STUDY SELECTION AND DATA EXTRACTION

English language articles meeting the search criteria were evaluated. Studies were included if they addressed either thrice-weekly or intradialytic daptomycin administration.

DATA SYNTHESIS

Daptomycin is approved for the treatment of bloodstream infections due to methicillin-resistant Staphylococcus aureus and other Gram-positive organisms. Rapid bactericidal activity and limited potential for drug interactions make daptomycin an attractive agent. However, the daptomycin prescribing information recommends dosing every 48 hours in patients receiving hemodialysis, which results in dyssynchrony of dosing and dialysis sessions every other week. Studies evaluating a dosing regimen of daptomycin thrice weekly, coinciding with dialysis, indicate that pharmacokinetic and pharmacodynamic parameters are appropriate for therapeutic success. However, to maintain adequate serum drug concentrations throughout the 72-hour interdialytic period, an additional 50% of the dose should be provided to account for the longer interval. Intradialytic dosing, with the administration of daptomycin infusion beginning during the final 30 minutes of dialysis, may also require a dose increase. Limited clinical outcomes data have been reported, but no significant safety concerns have been identified.

CONCLUSIONS

Administration of daptomycin doses thrice weekly on hemodialysis days appears to be both safe and reasonable. Doses should be increased preceding the 72-hour interdialytic period or if daptomycin is infused during dialysis.

Daptomycin-induced rhabdomyolysis and acute liver injury

Daptomycin use is a known cause of rhabdomyolysis; its role in liver injury is less certain. We report a case of daptomycin-induced rhabdomyolysis with liver injury. This report indicates a role for liver function monitoring while receiving daptomycin, as well as the importance of promptly considering drug toxicities in acute and emergency care settings.

Simplified equations using two concentrations to calculate area under the curve for antimicrobials with concentration-dependent pharmacodynamics: daptomycin as a motivating example

The effects of several antimicrobial agents are predicted by the ratio of the area under the concentration-time curve (AUC) to the MIC (AUC/MIC). Peak (Cp) and trough (Ct) concentrations are often measured clinically as surrogates of AUC because actual computation of AUC from 1 or 2 samples requires sophisticated mathematical methods. Given that the effects of daptomycin are predicted by AUC/MIC, our objective was to compare simple equation calculated AUC based on Cp and Ct to model integrated AUC. A standard population pharmacokinetic model was used to simulate 5,000 daptomycin concentration-time profiles after 5 doses of 6 mg/kg of body weight/day (0.5-h infusions). The AUC for the 24-h period was computed by integration and by equations with 110 Cp-Ct combination pairs. The Cp time points were in 15-min increments between 0.5 h and 3 h and Ct in 15-min increments within an hour of the end of the dosing interval for each dose. The precision and bias of the calculated AUC relative to the integrated AUC were determined to identify Cp-Ct pairs associated with the lowest bias and highest precision. The equations were further validated using two daptomycin concentration-time data sets from healthy volunteers and critically ill patients. The precision and bias of calculated AUC were based primarily on Cp, and use of a daptomycin Cp 1.5 h to 3 h from the start of infusion was associated with a bias of <10% and an R(2) of >0.95. Data from the healthy volunteers and critically ill patients also demonstrated declining bias with use of Cp ≥ 1.5 h from the start of infusion with relatively good precision. Simplified equations using a daptomycin Cp approximately 2 h from the start of infusion and a Ct within an hour of the end of the dosing interval should yield precise and unbiased estimates of daptomycin AUC.

Successful Treatment of Infective Panniculitis With Daptomycin in a Pregnant, Morbidly Obese Patient

Objective: To report a case of infective panniculitis in a morbidly obese, pregnant woman, which was successfully treated with daptomycin. Case Summary: A 34-year-old, 27-week pregnant, morbidly obese woman with a history of skin/soft-tissue infections and diabetes mellitus, presented with panniculitis. Initial treatment with β-lactam antibiotics did not result in clinical improvement. Methicillin-resistant Staphylococcus aureus was suspected, and 14 days of daptomycin 4 mg/kg (using total body weight) resulted in a clinical cure, without any adverse effects on the mother or the neonate. Discussion: Panniculitis is a type of skin/soft-tissue infection that is often caused by Gram-positive microorganisms. Daptomycin is one of the recommended agents for the treatment of skin/soft-tissue infections in hospitalized patients; however, it has not been extensively studied in pregnancy or morbid obesity. Some data suggest that exposure to daptomycin is significantly increased in morbidly obese persons because of the higher total dose received in this patient population. Animal data suggest that this drug is safe in pregnancy (category B), and at the time of publication, 3 prior cases of safe use of daptomycin in pregnancy have been reported. Conclusions: This case provides additional evidence for the use of daptomycin in pregnancy as well as morbid obesity.

Normalization of creatine kinase values in a case of rhabdomyolysis during daptomycin treatment

A 41-year-old woman presented in the Emergency Department with suspected compartment syndrome of lower left leg (creatine kinase [CK]: 12,502 IU/L, Cr: 4.31 mg/dL). Fasciotomy of the four limb compartments was conducted. By day 2, the patient presented oliguria during previous 24 h, so daily intermittent dialysis was carried out. On day 12, the patient presented an episode of bacteremia due to Staphylococcus hominis. Treatment with vancomycin was initiated and was changed after 4 days to daptomycin due to unsatisfactory clinical progression (6 mg/kg every 48 h, according to renal function and patient's weight) (CK: 2,972 IU/L). After 15 days of treatment, the dose of daptomycin was increased to 6 mg/kg every 24 h (CrCL: 46 mL/min, CK: 83 IU/L). The antibiotic was continued for another 4 days. Fourteen days later, the patient was discharged (CK: 26 IU/L). Daptomycin could be prescribed in some patients with elevated CK values. A cut-off value of baseline CK for use of daptomycin needs to be determined.

Daptomycin dosing based on ideal body weight versus actual body weight: comparison of clinical outcomes

Daptomycin use at our institution changed to ideal body weight dosing based on a published analysis of pharmacokinetic-pharmacodynamic efficacy target attainment, bacterial ecology, and a desire to reduce drug toxicity. The current study compared outcomes between actual body weight and ideal body weight dosing of daptomycin before and after this intervention. In the evaluable group, 69 patients received doses based on actual body weight and 48 patients received doses based on ideal body weight. Patients were treated for documented Enterococcus species, Staphylococcus aureus, or coagulase-negative Staphylococcus infections, including bloodstream, intraabdominal, skin and soft tissue, urinary, and bone. There was no statistically significant difference in clinical success between the groups (88.9% for actual body weight compared to 89.1% for ideal body weight, P = 0.97). After we adjusted for gender, age, body mass index, concomitant 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors, infection type, and organism type, clinical success rates remained similar between groups (adjusted odds ratio of 0.68 in favor of actual body weight, 95% confidence interval [CI] of 0.13 to 3.55). Microbiological outcomes, length of stay, mortality, and adverse effects were also similar between groups. Further studies are warranted to confirm that ideal body weight dosing provides similar outcomes to actual body weight dosing for all patients and types of infections and organisms.

Population pharmacokinetics of daptomycin in patients affected by severe Gram-positive infections

A population pharmacokinetic analysis of daptomycin was performed based on therapeutic drug monitoring (TDM) data from 58 patients receiving doses of 4-12 mg/kg for the treatment of severe Gram-positive infections. At a daily dose of 8 mg/kg, daptomycin plasma concentrations (mean ± S.D.) were 76.9 ± 9.8 mg/L at the end of infusion and 52.7 ± 15.4 mg/L and 11.4 ± 5.4 mg/L at 0.5 h and 23 h after drug administration, respectively. The final model was a one-compartmental model with first-order elimination, with estimated clearance (CL) of 0.80 ± 0.14 L/h and a volume of distribution (V(d)) of 0.19 ± 0.05 L/kg. Creatinine clearance (CL(Cr)) was identified as having a significant influence on daptomycin CL, and a decrease in CL(Cr) of 30 mL/min from the median value (80 mL/min) was associated with a reduction of daptomycin CL from 0.80 L/h to 0.73 L/h. These results confirm that the presence of severe infection may be associated with an altered disposition of daptomycin, with an increased Vd. MICs were available in 41 patients and results showed that 38 and 31 subjects achieved AUC/MIC values associated with bacteriostatic (>400) and bactericidal effects (>800), respectively. Of note, 31 of these 41 subjects experienced a clinical improvement or were cured. Although daptomycin pharmacokinetics may be influenced by infections, effective AUC/MIC values were achieved in the majority of patients. The present model may be applied in clinical settings for a TDM routine on the basis of a sparse blood sampling protocol.

Safety and efficacy of high-dose daptomycin as salvage therapy for severe gram-positive bacterial sepsis in hospitalized adult patients

Background

Increasing the dosage of daptomycin may be advantageous in severe infection by enhancing bactericidal activity and pharmacodynamics. However, clinical data on using daptomycin at doses above 6 mg/kg in Asian population are limited.

Methods

A retrospective observational cohort study of all hospitalized adult patients treated with daptomycin (> 6 mg/kg) for at least 72 hours was performed in Taiwan.

Results

A total of 67 patients (40 males) with a median age of 57 years received a median dose of 7.61 mg/kg (range, 6.03-11.53 mg/kg) of daptomycin for a median duration of 14 days (range, 3–53 days). Forty-one patients (61.2%) were in intensive care units (ICU). Sites of infections included complicated skin and soft tissue infections (n = 16), catheter-related bacteremia (n = 16), endocarditis (n = 11), primary bacteremia (n = 10), osteomyelitis and septic arthritis (n = 9), and miscellaneous (n = 5). The median Pitt bacteremia score among the 54 (80.6%) patients with bacteremia was 4. The most common pathogen was methicillin-resistant Staphylococcus aureus (n = 38). Fifty-nine patients (88.1%) were treated with daptomycin after glycopepetide use. Overall, 52 (77.6%) patients achieved clinical success. The all-cause mortality rate at 28 day was 35.8%. In multivariate analysis, the significant predictors of in-hospital mortality in 54 bacteremic patients were malignancies (P = 0.01) and ICU stay (P = 0.02). Adverse effects of daptomycin were generally well-tolerated, leading to discontinuation in 3 patients. Daptomycin-related creatine phosphokinase (CPK) elevations were observed in 4 patients, and all received doses > 8 mg/kg.

Conclusions

Treatment with high dose daptomycin as salvage therapy was generally effective and safe in Taiwan. CPK level elevations were more frequent in patients with dose > 8 mg/kg.

Pharmacokinetics of Antimicrobials in Obese Children

INTRODUCTION

Childhood obesity is common and results in substantial morbidity. The most commonly prescribed drugs in obese children are antibiotics. However, physiologic changes associated with childhood obesity can alter antibiotic pharmacokinetics and optimal body size measures to guide dosing in his population are ill defined. This combination can result in therapeutic failures or drug-related toxicities. This review summarizes pharmacokinetic information for antibiotics in obese children and implications for dosing.

METHODS

We conducted a comprehensive literature search of PubMed, EMBASE, and International Pharmaceutical Abstracts to identify pharmacokinetic studies of antimicrobial agents in obese children. We included the following search terms: obesity, pharmacokinetics, pharmacodynamics, drug toxicity, dosing, anti-infective agents, antiviral agents, and antifungal agents.

RESULTS

We identified four pharmacokinetic studies of antibiotics in obese children: one for cefazolin and tobramycin, one for gentamicin, and two for vancomycin. Only the cefazolin/tobramycin trial was prospective. The drugs studied differ in their tissue and body water distribution characteristics. Two of the studies (tobramycin and gentamicin) reported pharmacokinetic differences and required dosing modifications in obese children.

DISCUSSION

The lack of pharmacokinetic studies in obese children is pronounced. The scarcity of pharmacokinetic data limits the ability to predict drug disposition using drug physicochemical properties and impedes a rational approach to selection of appropriate body size measures for dosing. Given this knowledge gap, additional trials in obese children are urgently needed and is a public health concern.

CONCLUSION

Pharmacokinetic studies of antimicrobials in obese children are desperately needed to guide dosing and avoid therapeutic failures or unwanted toxicities.

Impact of obesity on drug metabolism and elimination in adults and children

The prevalence of obesity in adults and children is rapidly increasing across the world. Several general (patho)physiological alterations associated with obesity have been described, but the specific impact of these alterations on drug metabolism and elimination and its consequences for drug dosing remains largely unknown. In order to broaden our knowledge of this area, we have reviewed and summarized clinical studies that reported clearance values of drugs in both obese and non-obese patients. Studies were classified according to their most important metabolic or elimination pathway. This resulted in a structured review of the impact of obesity on metabolic and elimination processes, including phase I metabolism, phase II metabolism, liver blood flow, glomerular filtration and tubular processes. This literature study shows that the influence of obesity on drug metabolism and elimination greatly differs per specific metabolic or elimination pathway. Clearance of cytochrome P450 (CYP) 3A4 substrates is lower in obese as compared with non-obese patients. In contrast, clearance of drugs primarily metabolized by uridine diphosphate glucuronosyltransferase (UGT), glomerular filtration and/or tubular-mediated mechanisms, xanthine oxidase, N-acetyltransferase or CYP2E1 appears higher in obese versus non-obese patients. Additionally, in obese patients, trends indicating higher clearance values were seen for drugs metabolized via CYP1A2, CYP2C9, CYP2C19 and CYP2D6, while studies on high-extraction-ratio drugs showed somewhat inconclusive results. Very limited information is available in obese children, which prevents a direct comparison between data obtained in obese children and obese adults. Future clinical studies, especially in children, adolescents and morbidly obese individuals, are needed to extend our knowledge in this clinically important area of adult and paediatric clinical pharmacology.