Pharmacodynamic Target Research Articles

In Vivo Pharmacokinetic and Pharmacodynamic Profiles of Antofloxacin against Klebsiella pneumoniae in a Neutropenic Murine Lung Infection Model.

Antofloxacin is a novel broad-spectrum fluoroquinolone under development for the treatment of infections caused by a diverse group of bacterial species. We explored the pharmacodynamic (PD) profile and targets of antofloxacin against seven Klebsiella pneumoniae isolates by using a neutropenic murine lung infection model. Plasma and bronchopulmonary pharmacokinetic (PK) studies were conducted at single subcutaneous doses of 2.5, 10, 40, and 160 mg/kg of body weight. Mice were infected intratracheally with K. pneumoniae and treated using 2-fold-increasing total doses of antofloxacin ranging from 2.5 to 160 mg/kg/24 h administered in 1, 2, 3, or 4 doses. The Emax Hill equation was used to model the dose-response data. Antofloxacin could penetrate the lung epithelial lining fluid (ELF) with pharmacokinetics similar to those in plasma with linear elimination half-lives over the dose range. All study strains showed a 3-log10 or greater reduction in bacterial burden and prolonged postantibiotic effects (PAEs) ranging from 3.2 to 5.3 h. Dose fractionation response curves were steep, and the free-drug area under the concentration-time curve over 24 h (AUC0-24)/MIC ratio was the PD index most closely linked to efficacy (R2 = 0.96). The mean free-drug AUC0-24/MIC ratios required to achieve net bacterial stasis, a 1-log10 kill, and a 2-log10 kill for each isolate were 52.6, 89.9, and 164.9, respectively. When integrated with human PK data, these PD targets could provide a framework for further optimization of dosing regimens. This could make antofloxacin an attractive option for the treatment of respiratory tract infections involving K. pneumoniae.

Establishment of an AUC0-24 Threshold for Nephrotoxicity Is a Step towards Individualized Vancomycin Dosing for Methicillin-Resistant Staphylococcus aureus Bacteremia.

Unlike vancomycin trough concentrations, data on the utility of vancomycin pharmacokinetic (PK) parameters, namely, the area under the concentration-time curve from 0 to 24 h (AUC0-24), in predicting acute kidney injury (AKI) are limited. Our aim was to investigate this relationship in patients receiving vancomycin therapy for methicillin-resistant Staphylococcus aureus bacteremia (MRSA-B). A single-center retrospective observational cohort study involving 127 consecutive MRSA-B patients was conducted to examine the incidence of AKI (defined as serum creatinine of ≥0.5 mg/liter and a 50% increase from baseline) and vancomycin exposure parameters associated with nephrotoxicity. Bayesian estimation was used to predict individual vancomycin AUC0-24 All patients received vancomycin monotherapy for a minimum of 14 days following the diagnosis of MRSA-B. AKI was observed in 15.7% of patients (20/127). Clinical characteristics were similar between patients with and without AKI. At steady state, higher vancomycin trough concentrations were associated with AKI (17.2 mg/liter versus 13.1 mg/liter; P = 0.003). A vancomycin AUC0-24 threshold for AKI of >563 mg · h/liter was detected by classification and regression tree (CART) analysis; patients with exposures above this threshold were significantly more likely to experience AKI than patients with lower vancomycin exposures (40% [8/20] versus 11.2% [12/107]; P = 0.002). This parameter remained an independent predictor of AKI on multivariate logistic regression (odds ratio [OR], 5.07; 95% confidence interval [CI], 1.57 to 16.29; P = 0.006) and was a better predictor of nephrotoxicity than vancomycin trough concentrations. Overall, AKI is associated with higher vancomycin exposure as measured by AUC0-24 These results suggest that individualized patient dosing may be possible with dose modifications directed toward established pharmacodynamic targets while balancing AKI risks.

MP11-10 CLINICAL PHARMACOKINETICS OF BETA-LACTAM ANTIBIOTICS IN PROSTATE TISSUE, AND DOSING CONSIDERATIONS FOR PROSTATITIS BASED ON SITE-SPECIFIC PHARMACODYNAMICS

INTRODUCTION AND OBJECTIVES: Carbapenems (doripenem and meropenem) are a therapeutic option for bacterial prostatitis and antibacterial prophylaxis in prostatic surgery, especially in patients who are intolerant or resistant to quinolones. However, the clinical pharmacokinetics (PK) of the two carbapenems in prostate tissue and attainment of their pharmacodynamic (PD) targets at site of action had been unclear. This study thus examined, for the first time, the clinical PK of doripenem and meropenem in prostate tissue, and estimated their PD target attainment at this site. METHODS: Doripenem (0.25 g or 0.5 g) or meropenem (0.25 g or 0.5 g) was intravenously administered to 101 patients with benign prostatic hypertrophy prior to TURP. Blood samples and prostate tissue samples were collected 0.5, 1, 1.5, 2, 3, 4 and 5 h after starting a 0.5-h infusion. Drug concentrations in plasma and prostate tissue were measured using high-performance liquid chromatography, analyzed using a three-compartment population pharmacokinetic model, and used to estimate the probability of attaining a bactericidal target (40% of the time above the minimum inhibitory concentration [MIC] for bacteria). RESULTS: These carbapenems penetrated similarly into prostate tissue, independently of the dose, with mean prostate tissue/ plasma ratios of 0.166e0.173 (maximum drug concentration) and 0.177e0.187 (area under drug concentration-time curve). Despite this relatively low penetration by doripenem and meropenem, their usual regimens of 0.25 g three times daily and 0.5 g twice daily (0.5-h infusions) achieved a favorable target-attainment probability value of 90.8e95.9%, in prostate tissue, against clinical isolate populations of Escherichia coli and Klebsiella species (the two major causative bacteria in prostatitis). However, Pseudomonas aeruginosa isolate population needed 0.5 g three times daily for probability values of 55.9% for doripenem and 52.3% for meropenem. The prostatic pharmacodynamic-based breakpoint MIC (the highest MIC at which the targetattainment probability in prostate tissue was more than 90%) was 0.063 mg/L for 0.25 g three times daily and 0.125 mg/L for 0.5 g three times daily, for both drugs. CONCLUSIONS: These results define clinical pharmacokinetics of doripenem and meropenem in prostate tissue, while also rationalizing and optimizing their dosing regimens for prostatitis on the basis of site-specific pharmacodynamic target attainment.

Pharmacodynamic targets of psychotic patients treated with a long-acting therapy

IntroductionGiven the poor compliance of schizofrenic patients to antipsychotic therapies, are been developed drugs in long-acting formulation that for their pharmacokinetic ensures prolonged therapeutic activities. Currently, we consider that their efficacy depends on hereditary tracts, influencing both pharmacodynamic and pharmacokinetic parameters.ObjectiveInvestigate relationships between clinical efficacy and genetic polymorphims of long-acting drugs’ pharmacodynamic targets.MethodsSeventy-eight psychotic patients, treated with atypical long-acting antipsychotics (olanzapine pamoate, paliperidone palmitate, risperidon and aripiprazole), were examined. We carried out a blood sampling to evaluate dopaminergic DRD2 and glutamatergic GRM3 genetic receptors polymorphisms. PANSS and BPRS scales were used to assess clinical condition.ResultsRegarding the GRM3 genes, the study of rs2228595 and rs6465084 polymorphisms showed a prevalence of wild type genotypic frequency of 81.2% and 56.2%, respectively. The prevalence of the patients with mutated heterozygote genotype (rs6465084 polymorphisms) resulted high (40.6%). Considering rs1989796 e rs274622 polymorphisms, the sample showed a prevalence of mutated heterozygote genotype in the 53.1% e 45.3%, respectively, with a percentage of 43.7% of patients with a mutation in homozygosis. Considering the rs146812 polymorphism, the 53.1% of patients resulted with a wild type genotype. Finally, findings showed a prevalence of 56.2% for the mutated heterozygote genotype in the DRD2 rs6277 polymorphism. The genotypic categorization analysis demonstrated a significative association between the GRM3 rs274622 polymorphism and higher BPRS scores.ConclusionsThe relationship between rs274622 polymorphism and worse clinical conditions could indicate a major resistance to long-acting antipsychotics in patients with genotypic frequency CT (mutated heterozygosis) for this polymorphism.Disclosure of interestThe authors have not supplied their declaration of competing interest.

Population Pharmacokinetics and Pharmacodynamic Target Attainment of Ampicillin in Neonates with Hypoxemic-Ischemic Encephalopathy in the Setting of Controlled Hypothermia.

To describe the population pharmacokinetics and pharmacodynamic target attainment of ampicillin in neonates with hypoxic-ischemic encephalopathy (HIE) undergoing controlled hypothermia (CH). Prospective, open-label pharmacokinetic study. A 189-bed, freestanding children's tertiary care teaching hospital. Thirteen neonates (three females and 10 males) with HIE encephalopathy receiving CH and ampicillin 100 mg/kg/dose intravenously every 8 hours who were admitted to the neonatal intensive care unit between May 2013 and June 2014. Blood (0.5 ml) was collected at 8, 10, and 14 hours of life coinciding with other scheduled laboratory investigations for ampicillin concentration analysis, providing a total of three ampicillin serum concentrations/patient. The patients had a median gestational age of 39 weeks, mean ± SD birth weight of 3.34 ± 0.61 kg, and mean ± SD estimated glomerular filtration rate of 43 ± 12.6 ml/minute/1.73 m2 . Ampicillin concentrations were best described by a two-compartment model with gestational age as a covariate with allometric scaling on total body clearance. The mean ± SD total body clearance for the population was 0.43 ± 0.12 ml/minute/kg (median 0.36 ml/min/kg), volume of the central compartment was 0.35 ± 0.46 L/kg, and the calculated population estimate for the total volume of distribution (Vd ) was 0.52 ± 0.28 L/kg. The R2 , bias, and precision were 0.497, 0.538, and 10.5 μg/ml and 0.972, -0.125, and 0.938 μg/ml for the observed versus population and observed versus individual predicted concentrations, respectively. Monte Carlo simulation was conducted to determine the probability of target attainment for 12 simulated ampicillin dosing regimens using 50% and 100% of the dosing interval that free drug concentration remains above the minimum inhibitory concentration (fT > MIC) in 5000 simulated neonates with HIE receiving CH. Dosing regimens of 25 and 50 mg/kg/dose every 24 hours provided for an appropriate pharmacodynamic target attainment of 50% and 100% fT > MIC. To our knowledge, this study describes the first pharmacokinetic data of ampicillin in neonates with HIE receiving CH and demonstrates a reduced total body clearance and an increased Vd for ampicillin. Based on these data, modifications to the ampicillin dosing regimens seem appropriate during the period of CH. Dosing regimens of ampicillin 25 and 50 mg/kg/day were able achieve optimal probability of target attainment against all susceptible gram-negative and gram-positive bacteria in a population of neonates with HIE receiving CH for 50% and 100% fT > MIC.

Preclinical Pharmacokinetics and Pharmacodynamic Target of SCY-078, a First-in-Class Orally Active Antifungal Glucan Synthesis Inhibitor, in Murine Models of Disseminated Candidiasis.

ABSTRACTSCY-078 (MK-3118) is a novel, semisynthetic derivative of enfumafungin and represents the first compound of the triterpene class of antifungals. SCY-078 exhibits potent inhibition of β-(1,3)-d-glucan synthesis, an essential cell wall component of many pathogenic fungi, including Candida spp. and Aspergillus spp. SCY-078 is currently in phase 2 clinical development for the treatment of invasive fungal diseases. In vitro disposition studies to assess solubility, intestinal permeability, and metabolic stability were predictive of good oral bioavailability. Preclinical pharmacokinetic studies were consistent with once-daily administration to humans. After intravenous delivery, plasma clearance in rodents and dogs was low, representing <15% and <25% of hepatic blood flow, respectively. The terminal elimination-phase half-life was 5.5 to 8.7 h in rodents, and it was ∼9.3 h in dogs. The volume of distribution at steady-state was high (4.7 to 5.3 liters/kg), a finding suggestive of extensive tissue distribution. Exposure of SCY-078 in kidney tissue, a target organ for invasive fungal disease such as candidiasis, exceeded plasma by 20- to 25-fold for the area under the concentration-time curve from 0 h to infinity (AUC0–∞) and Cmax. SCY-078 achieved efficacy endpoints following oral delivery across multiple murine models of disseminated candidiasis. The pharmacokinetic/pharmacodynamic indices Cmax/MIC and AUC/MIC correlated with outcome. Target therapeutic exposure, expressed as the plasma AUC0–24, was comparable across models, with an upper value of 11.2 μg·h/ml (15.4 μM·h); the corresponding mean value for free drug AUC/MIC was ∼0.75. Overall, these results demonstrate that SCY-078 has the oral and intravenous (i.v.) pharmacokinetic properties and potency in murine infection models of disseminated candidiasis to support further investigation as a novel i.v. and oral treatment for invasive fungal diseases.

Review of Metronidazole Dosing in Preterm Neonates.

Metronidazole dosing recommendations vary significantly for premature infants in pediatric dosing references and can result in confusion for prescribers. We performed a literature search identifying articles evaluating the pharmacokinetics and dosing of metronidazole in premature infants. The search was limited to English-language articles in MEDLINE (January 1946 to December 2016), EMBASE (January 1974 to December 2016), and International Pharmaceutical Abstracts (January 1970 to December 2016). Reference citations from relevant articles were also reviewed. Six pharmacokinetic studies, representing 152 neonates, were included; however, only three of the well-defined studies were reviewed in depth, and the other three studies were considered foundational. The pharmacokinetic studies included in this review indicate that some published dosing recommendations in pediatric dosing references may result in subtherapeutic metronidazole concentrations. Therefore, postmenstrual age based dosing recommendations were provided by the authors of these pharmacokinetic studies based on a pharmacodynamic target of 6 to 8 mg/L; yet, these dosing recommendations differ from one another. The pharmacokinetic studies included in this review provide some guidance to dosing; however, a major limitation is that outcomes of clinical efficacy and safety were not evaluated. Future studies targeting the optimal dosing and serum concentrations required for clinical efficacy are needed.

Is continuous infusion of imipenem always the best choice?

Monte Carlo simulations allow prediction and comparison of concentration–time profiles arising from different dosing regimens in a defined population, provided a population pharmacokinetic model has been established. The aims of this study were to evaluate the population pharmacokinetics of imipenem in critically ill patients with hospital-acquired pneumonia (HAP) and to assess the probability of target attainment (PTA) and cumulative fraction of response (CFR) using EUCAST data. A two-compartment model based on a data set of 19 subjects was employed. Various dosage regimens at 0.5-h and 3-h infusion rates and as continuous infusion were evaluated against the pharmacodynamic targets of 20%fT>MIC, 40%fT>MIC and 100%fT>MIC. For the target of 40%fT>MIC, all 0.5-h infusion regimens achieved optimal exposures (CFR ≥ 90%) against Escherichia coli and Staphylococcus aureus, with nearly optimal exposure against Klebsiella pneumoniae (CFR ≥ 89.4%). The 3-h infusions and continuous infusion exceeded 97% CFR against all pathogens with the exception of Pseudomonas aeruginosa and Acinetobacter spp., where the maximum CFRs were 85.5% and 88.4%, respectively. For the 100%fT>MIC target, only continuous infusion was associated with nearly optimal exposures. Higher PTAs for the targets of 40%fT>MIC and 100%fT>MIC were achieved with 3-h infusions and continuous infusion in comparison with 0.5-h infusions; however, continuous infusion carries a risk of not reaching the MIC of less susceptible pathogens in a higher proportion of patients. In critically ill patients with HAP with risk factors for Gram-negative non-fermenting bacteria, maximum doses administered as extended infusions may be necessary.

Evaluation of Amikacin Pharmacokinetics and Pharmacodynamics for Optimal Initial Dosing Regimen.

Amikacin has been one of the important antimicrobial agents against Gram-negative pathogens. However, there is discrepancy regarding the amikacin initial dosage, with some reports recently recommending ≥25 mg/kg and others the conventional dosage (15–20 mg/kg). Hence, we evaluated the optimal initial dosing regimen of amikacin. Pharmacokinetic (PK) parameters were estimated using a population PK analysis. The pharmacodynamic (PD) target was a ratio of ≥8 between the concentration achieved 1 h after beginning the infusion (C peak) and the minimal inhibitory concentration (MIC) of the liable bacteria. Based on the population PK parameters, we simulated individual C peak for several dosing regimens by Monte Carlo method and analyzed the C peak/MIC ratio for MICs from 0.5 to 32 μg/mL. This study included 35 infected patients (25 males), with a median (range) age and body weight of 70 (15–95) years and 49.5 (32.5–78) kg, respectively. A two-compartment model was used, and total body clearance (CL) significantly correlated with creatinine clearance, and volume of distribution (V d) with body weight. Regarding the probability to achieve a C peak/MIC of ≥8, the 15 mg/kg regimen was sufficient to achieve the PK/PD target in ≥90% of patients for a MIC of 4 μg/mL or less. The cumulative fraction of response in Pseudomonas aeruginosa was that 76% of patients achieved a C peak/MIC of 8 with the amikacin dosage of 15 mg/kg/day. We suggest that the 15-mg/kg once-daily dosage of amikacin be recommended as the initial dosage. As its maintenance dosage, the 15 mg/kg/day amikacin dosage is needed for a MIC of ≤4 μg/mL, and amikacin monotherapy for a MIC of ≥8 μg/mL should be avoided.

Ex vivo Ceftolozane/Tazobactam Clearance during Continuous Renal Replacement Therapy

Background/Aims: To determine ceftolozane/tazobactam transmembrane clearances (CLTM) in continuous hemofiltration (CHF) and continuous hemodialysis (CHD) and to determine optimal ceftolozane/tazobactam dosing regimens for patients receiving continuous renal replacement therapy (CRRT). Method: Validated, ex vivo CHF and CHD bovine blood models using polysulfone (HF1400) and AN69 (Multiflow 150-M) hemofilters were used to evaluate adsorption and CLTM at different effluent flow rates. Monte Carlo simulations (MCS) using pharmacokinetic parameters from published studies and CLTM from this study were used to generate ceftolozane/tazobactam dosing for patients receiving CRRT. Results: CHF and CHD CLTM did not differ at equivalent effluent rates. CLTM approximated effluent flow rates. No adsorption of ceftolozane/tazobactam occurred for either hemofilter. Effluent flow was the most important determinant of MCS-derived doses. Conclusion: CRRT clearances of ceftolozane/tazobactam depended on effluent flow rates but not hemofilter types. MCS-derived ceftolozane/tazobactam doses of 750 (500/250)-1,500 (1,000/500) mg every 8 h met pharmacodynamic targets for virtual patients receiving CRRT at contemporary effluent rates.

Proportion of Staphylococcus aureus with a Vancomycin Minimum Inhibitory Concentration (MIC) of 1 mg/L Increases Between 2012 and 2017 in Singapore

Background Vancomycin is commonly used to treat methicillin-resistant Staphylococcus aureus (MRSA). Monte Carlo simulations in the literature suggest that vancomycin may not reach desired pharmacodynamic targets when typical dosing regimens are used to treat S. Aureus (SAU) with an MIC > 1 mg/L. Worse clinical outcomes have also been associated with methicillin-susceptible S. Aureus (MSSA) with higher vancomycin MICs, when treated with β-lactams.Methods Vancomycin MICs (VITEK 2) for SAU isolated from June 2012 to April 2017 were collated from the laboratory records at Tan Tock Seng Hospital, Singapore. Vancomycin MICs for MSSA are underrepresented as susceptibility tests for SAU isolated from blood are initially performed by direct disk diffusion. A reflex Vitek susceptibility is performed on MRSA but not MSSA blood isolates. All nonblood isolates are assessed by Vitek. Duplicates were removed.ResultsAll vancomycin MICs were within the susceptible range of ≤2 mg/L (Table 1). There was an overall temporal increase in proportions of both MRSA and MSSA isolates with an MIC 1 mg/L, from 9 to 30% and 14 to 37%, respectively. There was a reciprocal decrease in the proportion of isolates with MIC ≤ 0.5 mg/L (Figure 1). Proportions with MIC 2 mg/L showed a decreasing trend.Table 12012 (June–December)20132014201520162017 (January–April)MSSA isolates568972101110351152463 ≤0.5 mg/L437869802747833288 1 mg/L8390207282317173 2 mg/L48132622MRSA isolates513763753717633236 ≤0.5 mg/L414705631542544164 1 mg/L40371131698771 2 mg/L59219621These trends remained consistent when all SAU, both MSSA and MRSA together, were split into blood isolates and “other” groups (Figure 2).The data for MRSA bacteremia were analysed separately. The proportion with MIC 1 mg/L increased from 7% in 2012 to 27% in 2017. The proportion with MIC 2 mg/L decreased from 21% in 2012 to zero since 2016.Conclusion The proportion of Staphylococcus aureus isolates with an MIC of 1 mg/L increased more than threefold between 2012 and 2017. This trend is seen in both bloodstream and noninvasive isolates. As the proportion with MIC >1 mg/L has not increased, Monte Carlo simulations would suggest that clinical outcomes may not have been affected despite this upward creep.Disclosures All authors: No reported disclosures.

PUB011 A Potent, VEGFR2-Sparing RET Kinase Inhibitor for Treating Patients with RET-Dependent Lung Cancers

Activating mutations and fusions of the RET receptor tyrosine kinase have been identified in several cancer types, including fusions in ∼ 2% of lung adenocarcinomas. Furthermore, tyrosine kinase inhibitors (TKIs) that inhibit RET have activity in patients with RET-dependent cancers. However, current TKIs are only moderately potent against RET, cause toxicity through stronger inhibition of other kinases (e.g. KDR/VEGFR2) and poorly inhibit secondary resistance (e.g. gatekeeper) mutations. We aimed to design an inhibitor that targets diverse RET fusions and potential resistance mutations, with sparing of anti-targets and excellent drug-like properties. Lead RET inhibitor candidates were selected by determining: (1) activity against KIF5B- and CCDC6-RET fusions found in lung cancer and and V804 gatekeeper substitutions that casue acquried resistance to multikinase inhibitors; and (2) selectivity against a broad panel of kinase and other anti-targets. Activity in vivo was determined by measuring both pharmacodynamic target modulation and efficacy in diverse RET-dependent tumor models, including cancer cell line and patient-derived mouse xenografts (PDX). Our lead RET candidates possess nanomolar potency against diverse RET fusions and potential acquired resistance mutations, including challenging V804 gatekeeper substitutions. Furthermore, each is and at least 100-fold selective for the majority of kinases analyzed in vitro, and this high degree of selectivity is maintained against critical anti-targets in live cells, including KDR. These properties lead to significant efficacy in vivo in lung cancer xenografts harboring endogenous RET alterations and a RET-fusion PDX with acquired resistance to multikinase inhibitors mediated by V804M. Finally, daily oral dosing of mouse xenografts for more than three months produces continued tumor regression, without the development of acquired resistance or toxicity. The unique combination of high potency, broad activity against diverse RET alterations and minimal activity against anti-targets indicates the potential for continuous dosing, long-term efficacy and a wide therapeutic index in the clinic. We have developed potent and specific RET kinase inhibitors with favorable pharmaceutical properties and potent activity against diverse RET alterations in vitro and in vivo, including founder genetic alterations and resistance mutations that may arise following treatment with multikinase inhibitors. Together with significant sparing of other kinase and non-kinase anti-targets, they are predicted to robustly inhibit RET in patients at clinically relevant doses, and therefore offer the potential for more effective and safe treatment of patients with RET-dependent cancers. Loxo Oncology will be initiating clinical development of its lead RET inhibitor in patients with RET-fusion lung cancers in the coming months.

Population-based meta-analysis of roxithromycin pharmacokinetics: dosing implications of saturable absorption and protein binding.

The macrolide antibiotic roxithromycin has seen widespread clinical use for several decades; however, no population pharmacokinetic analysis has been published. Early studies indicated saturation of protein binding and absorption at doses within the approved range, which may impact pharmacodynamic target attainment since regimens of 150 mg twice daily and 300 mg once daily are used interchangeably in clinical practice. This study aimed to develop a population-based meta-analysis of roxithromycin pharmacokinetics, and utilize this model to inform optimal dosing regimens. Following an extensive search, roxithromycin pharmacokinetic data were collected or digitized from literature publications. Population pharmacokinetic modelling was undertaken with ADAPT. Dosing simulations were performed to investigate differences in exposure and pharmacodynamic target attainment between dosing regimens. A two-compartment model with saturable absorption described the data ( n = 63); changes in free drug exposure were simulated using a saturable protein binding model. Simulations indicated that a 300 mg daily regimen achieves a 37% and 53% lower total or free AUC ( f AUC), respectively, compared with 150 mg twice daily. These pharmacokinetic differences translated to significantly lower target attainment ( f AUC/MIC ratio >20) with a 300 mg daily regimen at MICs of 0.5 and 1 mg/L (51% and 7%) compared with patients receiving 150 mg twice daily (82% and 54%). Roxithromycin displays saturable absorption and protein binding leading to lower exposure and lower target attainment at MICs ≥0.5 mg/L with widely used once-daily dosing regimens, indicating that twice-daily regimens may be preferable for pathogens less susceptible to roxithromycin.

Piperacillin/tazobactam as an alternative antibiotic therapy to carbapenems in the treatment of urinary tract infections due to extended-spectrum β-lactamase-producing Enterobacteriaceae: an in silico pharmacokinetic study

Piperacillin/tazobactam (TZP) as an alternative treatment to carbapenems for infections involving extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae (ESBL-PE) remains debated. In this study, the probabilities of pharmacodynamic (PD) target attainment with different TZP regimens in ESBL-producing Escherichia coli (ESBL-Ec) and Klebsiella pneumoniae (ESBL-Kp) were evaluated in the context of pyelonephritis. Minimum inhibitory concentrations (MICs) of 144 ESBL-Ec and 111 ESBL-Kp from pyelonephritis were measured, and two previously published population pharmacokinetic models were used to determine by Monte Carlo simulation the probabilities of reaching two PD targets (50%fT>MIC and 100%fT>MIC) with TZP doses of 4 g three times daily and 4.5 g four times daily given as short (1 h) or prolonged (4 h) infusions or as 12–18 g/day continuous infusions. Only MICs of the 133 ESBL-Ec and 74 ESBL-Kp strains susceptible to TZP according to inhibition zone diameter were considered for the simulations. Results were similar with the two models, and only prolonged and continuous infusions allowed to reach 50%fT>MIC with a probability of >90% irrespective of bacterial species. Continuous infusion and prolonged infusion combined with the maximum dosage were the only condition allowing to achieve 100%fT>MIC with a probability of >70% with this population of ESBL-Ec. A probability of >90% to reach 100%fT>MIC with ESBL-Kp could be obtained only with the 18 g/day continuous-infusion regimen. TZP may be used for treatment for mild pyelonephritis involving susceptible ESBL-Ec provided that administration modalities are optimised. Conversely, for ESBL-Kp the risk of treatment failure may be higher, supporting the use of continuous infusion.

Population Pharmacokinetics and Pharmacodynamics of Doripenem in Obese, Hospitalized Patients.

Doripenem population pharmacokinetics and dosing recommendations are limited in obesity. To evaluate the population pharmacokinetics and pharmacodynamics of doripenem in obese patients. Hospitalized adults with a body mass index (BMI) ≥ 40 kg/m2 or total body weight (TBW) ≥45.5 kg over their ideal body weight received doripenem 500 mg every 8 hours, infused over 1 hour. Population pharmacokinetic analyses were performed using NONMEM, and Monte Carlo simulations were performed for 5 intermittent and prolonged infusion dosing regimens to calculate probability of target attainment (PTA) at 40% and 100% fT>MIC (free drug concentrations above the minimum inhibitory concentration). A total of 20 patients were studied: 10 in an intensive care unit (ICU) and 10 in a non-ICU. A 2-compartment model with first-order elimination best described the serum concentration-time data. Doripenem clearance (CL) was significantly associated with creatinine CL (CRCL), volume of the central compartment with TBW and ICU residence, and volume of the peripheral compartment with TBW ( P < 0.05). Using 40% fT>MIC, PTA was >90% for all simulated dosing regimens at MICs ≤2 mg/L. Using 100% fT>MIC, prolonged infusions of 1 g every 6 hours and 2 g every 8 hours achieved >90% PTA at MICs ≤2 mg/L. CRCL, ICU residence, and TBW are significantly associated with doripenem pharmacokinetics. Currently approved dosing regimens provide adequate pharmacodynamic exposures at 40% fT>MIC for susceptible bacteria in obese patients. However, prolonged infusions of larger doses are needed if a higher pharmacodynamic target is desired.

Total and unbound ceftriaxone pharmacokinetics in critically ill Australian Indigenous patients with severe sepsis

In the absence of specific data to guide optimal dosing, this study aimed to describe the pharmacokinetics of ceftriaxone in severely septic Australian Indigenous patients and to assess achievement of the pharmacodynamic target of the regimens prescribed. A pharmacokinetic study was conducted in a remote hospital intensive care unit in patients receiving ceftriaxone dosing of 1 g every 12 h (q12h). Serial blood and urine samples were collected over one dosing interval on two consecutive days. Samples were assayed using a validated chromatography method for total and unbound concentrations. Concentration–time data collected were analysed with a non-compartmental approach. A total of 100 plasma samples were collected from five subjects. Ceftriaxone clearance, volume of distribution at steady-state, elimination half-life and elimination rate constant estimates were 0.9 (0.6–1.5) L/h, 11.2 (7.6–13.4) L, 9.5 (3.2–10.2) h and 0.07 (0.07–0.21) h–1, respectively. The unbound fraction of ceftriaxone ranged between 14% and 43%, with a higher unbound fraction present at higher total concentrations. The unbound concentrations at 720 min from the initiation of infusion for the first and second dosing intervals were 7.2 (4.8–10.7) mg/L and 7.8 (4.7–12.1) mg/L respectively, which exceeds the minimum inhibitory concentration of all typical target pathogens. In conclusion, the regimen of ceftriaxone 1 g q12h is adequate for critically ill Australian Indigenous patients with severe sepsis caused by non-resistant pathogens.

Impact of a high loading dose of amikacin in patients with severe sepsis or septic shock.

BackgroundThe therapeutic effect of aminoglycosides is highest and optimal when the peak plasma concentration (C max)/minimal inhibitory concentration (MIC) ratio is between 8 and 10. The French guidelines recommend to use high doses of aminoglycosides for empiric antibiotic therapy in patients suffering from severe sepsis or septic shock. In clinical practice, the recommended target is an amikacin C max between 60 and 80 mg/L, which corresponds to approximately 8 times the MIC breakpoint, as defined by the European Committee on Antimicrobial Susceptibility Testing. The aim of this study was to assess the incidence and impact on mortality of an amikacin concentration between 60 and 80 mg/L in patients suffering from severe sepsis or septic shock.MethodsThis was a prospective observational cohort study conducted in two intensive care units (ICU). Patients receiving amikacin at a loading dose of 30 mg/kg for severe sepsis or septic shock were enrolled in the cohort. The target C max for amikacin was between 60 and 80 mg/L, as recommended by French guidelines (i.e. C max/MIC breakpoint = 8–10).ResultsOver the study period, the amikacin C max was <60 mg/L, between 60 and 80 mg/L, and >80 mg/L in 20 (18.2%), 46 (41.8%) and 44 (40%) of the 110 selected patients, respectively. Mortality rate was 40, 28.3 and 56.8% in the groups of patients with C max < 60 mg/L, 60 mg/L < C max < 80 mg/L and C max > 80 mg/L, respectively. Following multivariate analysis, mortality rate was significantly lower in the group of patients with amikacin C max between 60 and 80 mg/L than in the group of patients with amikacin C max > 80 mg/L (P = 0.004). The multivariate analysis also revealed that the factors independently associated with a higher in-ICU mortality rate were age (P = 0.02) and norepinephrine dose (P = 0.0001).Conclusions With a loading dose of 30 mg/kg of amikacin, concentration was potentially suboptimal (C max < 60 mg/L) in only 18.2% of patients. The pharmacodynamic target (60 mg/L < C max < 80 mg/L) recommended by French guidelines was reached in 41.8% of patients and was associated with reduced in-ICU mortality. But amikacin overexposure (i.e. C max > 80 mg/L) was frequent and potentially associated with increased mortality.

Implementation of a Prolonged Infusion Guideline for Time-Dependent Antimicrobial Agents at a Tertiary Academic Medical Center.

Administration of time-dependent beta-lactam antibiotic as a prolonged infusion may maximize the pharmacodynamic target of time above the minimum inhibitory concentration. We describe the implementation of a prolonged infusion at a tertiary academic medical center, and a 1-year compliance analysis with the guideline. After performing a thorough literature search, a guideline was developed by members of the Department of Infectious Diseases and Department of Pharmacy. Approval and endorsement of the guideline was obtained by the Antimicrobial Subcommittee and Pharmacy and Therapeutics Committee. Physical champions were instrumental in the implementation of the guideline institution-wide. We then performed a 1-year retrospective analysis of guideline compliance from January 1, 2011 to December 31, 2011. Noncompliant administrations were obtained from smart infusion pumps. The total number of doses administered was taken from pharmacy information resources. In total, nearly 85,000 time-dependent doses were administered. Compliance with the prolonged infusion guideline was 89%. Rates of compliance did not significantly differ between medications (P = 0.555). Obtaining support from key stakeholders in collateral services and institutional leadership was vital for the success of this guideline. Compliance with the guideline 1 year after implementation was high. Implementation of a prolonged infusion guideline is feasible with institutional support and motivation.

A Combination Regimen Design Program Based on Pharmacodynamic Target Setting for Childhood Tuberculosis: Design Rules for the Playground.

Children with tuberculosis are treated with drug regimens copied from adults despite significant differences in antibiotic pharmacokinetics, pathology, and the microbial burden between childhood and adult tuberculosis. We sought to develop a new and effective oral treatment regimen specific to children of different ages. We investigated and validated the concept that target drug concentrations associated with therapy failure and death in children are different from those of adults. On that basis, we proposed a 4-step program to rapidly develop treatment regimens for children. First, target drug concentrations for optimal efficacy are derived from preclinical models of disseminated tuberculosis that recapitulate pediatric pharmacokinetics, starting with monotherapy. Second, 2-drug combinations were examined for zones of synergy, antagonism, and additivity based on a whole exposure–response surface. Exposures associated with additivity or synergy were then combined and the regimen was compared to standard therapy. Third, several exposures of the third drug were added, and a 3-drug regimen was identified based on kill slopes in comparison to standard therapy. Fourth, computer-aided clinical trial simulations are used to identify clinical doses that achieve these kill rates in children in different age groups. The proposed program led to the development of a 3-drug combination regimen for children from scratch, independent of adult regimens, in <2 years. The regimens and doses can be tested in animal models and in clinical trials.

New Oral Anticoagulants in Nonvalvular Atrial Fibrillation.

The choice of an oral anticoagulant (OAC) for patients with nonvalvular atrial fibrillation (NVAF) is a major and complex clinical decision taking into account the individual risk-benefit ratio and bearing in mind the chronicity of therapy. This review focuses on the safety and efficacy of new oral anticoagulants (NOACs) compared with conventional vitamin K antagonists (VKA) in patients with NVAF. Current data suggest that NOACs are at least as effective and safe as VKAs for most NVAF subjects. The NOACs do not mandate dietary restrictions and regular pharmacodynamic monitoring, and they seem to have lesser incidence of intracranial or fatal bleeding when compared with VKAs. However, both dabigatran 150 twice daily and rivaroxaban have a slightly higher incidence of gastrointestinal bleeding when compared with VKAs. The article will delineate the current knowledge as well as scientific gaps related to the choice and dosage of anticoagulation regimens for various NVAF subsets and will address certain common clinical scenarios requiring special considerations. The article also addresses the shortcomings of NOACs: lack of therapeutic pharmacokinetic and pharmacodynamic targets, absence of tools to assess compliance and efficacy, rigid and limited dosage options, and absence of effective and inexpensive reversal agents.