Population Pharmacokinetics of Fluconazole in Critically Ill Patients Receiving Continuous Venovenous Hemodiafiltration: Using Monte Carlo Simulations To Predict Doses for Specified Pharmacodynamic Targets

ABSTRACTFluconazole is a widely used antifungal agent that is extensively reabsorbed in patients with normal renal function. However, its reabsorption can be compromised in patients with acute kidney injury, thereby leading to altered fluconazole clearance and total systemic exposure. Here, we explore the pharmacokinetics of fluconazole in 10 critically ill anuric patients receiving continuous venovenous hemodiafiltration (CVVHDF). We performed Monte Carlo simulations to optimize dosing to appropriate pharmacodynamic endpoints for this population. Pharmacokinetic profiles of initial and steady-state doses of 200 mg intravenous fluconazole twice daily were obtained from plasma and CVVHDF effluent. Nonlinear mixed-effects modeling (NONMEM) was used for data analysis and to perform Monte Carlo simulations. For each dosing regimen, the free drug area under the concentration-time curve (fAUC)/MIC ratio was calculated. The percentage of patients achieving an AUC/MIC ratio greater than 25 was then compared for a range of MIC values. A two-compartment model adequately described the disposition of fluconazole in plasma. The estimate for total fluconazole clearance was 2.67 liters/h and was notably 2.3 times faster than previously reported in healthy volunteers. Of this, fluconazole clearance by the CVVHDF route (CLCVVHDF) represented 62% of its total systemic clearance. Furthermore, the predicted efficiency of CLCVVHDFdecreased to 36.8% when filters were in use >48 h. Monte Carlo simulations demonstrated that a dose of 400 mg twice daily maximizes empirical treatment against fungal organisms with MIC up to 16 mg/liter. This is the first study we are aware of that uses Monte Carlo simulations to inform dosing requirements in patients where tubular reabsorption of fluconazole is probably nonexistent.

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Using Population Pharmacokinetics To Determine Gentamicin Dosing during Extended Daily Diafiltration in Critically Ill Patients with Acute Kidney Injury

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00222-10 ◽

2010 ◽

Vol 54 (9) ◽

pp. 3635-3640 ◽

Cited By ~ 34

Author(s):

Jason A. Roberts ◽

Jonathan Field ◽

Adam Visser ◽

Rosemary Whitbread ◽

Mandy Tallot ◽

...

Keyword(s):

Acute Kidney Injury ◽

Monte Carlo ◽

Monte Carlo Simulations ◽

Critically Ill ◽

Critically Ill Patients ◽

Population Pharmacokinetic Model ◽

Pharmacokinetic Model ◽

Kidney Injury ◽

Therapeutic Drug ◽

Population Pharmacokinetic

ABSTRACT The objective of the present prospective pharmacokinetic study was to describe the variability of plasma gentamicin concentrations in critically ill patients with acute kidney injury (AKI) necessitating extended daily diafiltration (EDD-f) using a population pharmacokinetic model and to subsequently perform Monte Carlo dosing simulations to determine which dose regimen achieves the pharmacodynamic targets the most consistently. We collected data from 28 gentamicin doses in 14 critically ill adult patients with AKI requiring EDD-f and therapeutic gentamicin. Serial plasma samples were collected. A population pharmacokinetic model was used to describe the pharmacokinetics of gentamicin and perform Monte Carlo simulations with doses of between 3 mg/kg of body weight and 7 mg/kg and at various time points before commencement of EDD-f to evaluate the optimal dosing regimen for achieving pharmacodynamic targets. A two-compartment pharmacokinetic model adequately described the gentamicin clearance while patients were on and off EDD-f. The plasma half-life of gentamicin during EDD-f was 13.8 h, whereas it was 153.4 h without EDD-f. Monte Carlo simulations suggest that dosing with 6 mg/kg every 48 h either 30 min or 1 h before the commencement of EDD-f results in 100% attainment of the target maximum concentration drug in plasma (<10 mg/liter) and sufficient attainment of the target area under the concentration-time curve from 0 to 24 h (AUC0-24; 70 to 120 mg·h/liter). None of the simulated dosing regimens satisfactorily achieved the targets of the minimum concentrations of drug in plasma (<1.0 mg/liter) at 24 h. In conclusion, dosing of gentamicin 30 min to 1 h before the commencement of an EDD-f treatment enables attainment of target peak concentrations for maximal therapeutic effect while enhancing drug clearance to minimize toxicity. Redosing in many patients should occur after 48 h, and we recommend the use of therapeutic drug monitoring to guide dosing to optimize achievement of the AUC0-24 targets.

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Population Pharmacokinetic Study of the Suitability of Standard Dosing Regimens of Amikacin in Critically Ill Patients with Open-Abdomen and Negative-Pressure Wound Therapy

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.02098-19 ◽

2020 ◽

Vol 64 (4) ◽

Author(s):

Cédric Carrié ◽

Faustine Delzor ◽

Stéphanie Roure ◽

Vincent Dubuisson ◽

Laurent Petit ◽

...

Keyword(s):

Monte Carlo ◽

Body Weight ◽

Monte Carlo Simulations ◽

Critically Ill ◽

Negative Pressure ◽

Critically Ill Patients ◽

Open Abdomen ◽

Population Pharmacokinetic ◽

Pressure Therapy ◽

Dosing Regimens

ABSTRACT The aim was to assess the appropriateness of recommended regimens for empirical MIC coverage in critically ill patients with open-abdomen and negative-pressure therapy (OA/NPT). Over a 5-year period, every critically ill patient who received amikacin and who underwent therapeutic drug monitoring (TDM) while being treated by OA/NPT was retrospectively included. A population pharmacokinetic (PK) modeling was performed considering the effect of 10 covariates (age, sex, total body weight [TBW], adapted body weight [ABW], body surface area [BSA], modified sepsis-related organ failure assessment [SOFA] score, vasopressor use, creatinine clearance [CLCR], fluid balance, and amount of fluids collected by the NPT over the sampling day) in patients who underwent continuous renal replacement therapy (CRRT) or did not receive CRRT. Monte Carlo simulations were employed to determine the fractional target attainment (FTA) for the PK/pharmacodynamic [PD] targets (maximum concentration of drug [Cmax]/MIC ratio of ≥8 and a ratio of the area under the concentration-time curve from 0 to 24 h [AUC0–24]/MIC of ≥75). Seventy critically ill patients treated by OA/NPT (contributing 179 concentration values) were included. Amikacin PK concentrations were best described by a two-compartment model with linear elimination and proportional residual error, with CLCR and ABW as significant covariates for volume of distribution (V) and CLCR for CL. The reported V) in non-CRRT and CRRT patients was 35.8 and 40.2 liters, respectively. In Monte Carlo simulations, ABW-adjusted doses between 25 and 35 mg/kg were needed to reach an FTA of >85% for various renal functions. Despite an increased V and a wide interindividual variability, desirable PK/PD targets may be achieved using an ABW-based loading dose of 25 to 30 mg/kg. When less susceptible pathogens are targeted, higher dosing regimens are probably needed in patients with augmented renal clearance (ARC). Further studies are needed to assess the effect of OA/NPT on the PK parameters of antimicrobial agents.

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Amikacin Initial Dose in Critically Ill Patients: a Nonparametric Approach To Optimize A Priori Pharmacokinetic/Pharmacodynamic Target Attainments in Individual Patients

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00993-19 ◽

2019 ◽

Vol 63 (11) ◽

Cited By ~ 3

Author(s):

Clément Boidin ◽

Laurent Bourguignon ◽

Sabine Cohen ◽

Claire Roger ◽

Jean-Yves Lefrant ◽

...

Keyword(s):

Critically Ill ◽

Critically Ill Patients ◽

A Priori ◽

Predictive Performance ◽

Compartment Model ◽

Population Pharmacokinetic ◽

Time Curve ◽

Data Set ◽

Nonparametric Approach ◽

The Right

ABSTRACT Amikacin is commonly used for probabilistic antimicrobial therapy in critically ill patients with sepsis. Its narrow therapeutic margin makes it challenging to determine the right individual dose that ensures the highest efficacy target attainment rate (TAR) in this setting. This study aims to develop a new initial dosing approach for amikacin by optimizing the a priori TAR in this population. A population pharmacokinetic model was built with a learning data set from critically ill patients who received amikacin. It was then used to design an initial dosing approach maximizing a priori TAR for a target ratio of ≥8 for the peak concentration to the MIC (Cmax/MIC) or of ≥75 for the ratio of the area under the concentration-time curve from 0 to 24 h to the MIC (AUC0–24/MIC). In the 166 patients included, 53% had amikacin Cmax of ≥64 mg/liter with a median dose of 23.4 mg/kg. A two-compartment model with creatinine clearance and body surface area as covariates best described the data and showed good predictive performance. Our dosing approach was successful in optimizing TAR for Cmax/MIC, with a rate of 92.9% versus 67.9% using a 30-mg/kg regimen, based on an external subset of data and assuming a MIC of 8 mg/liter. Mean optimal doses were higher (3.5 ± 0.5 g) than with the 30-mg/kg regimen (2.1 ± 0.3 g). Suggested doses varied with the MIC, the target index, and desired TAR threshold. A dosing algorithm based on the method is proposed for a large range of patient covariates. Clinical studies are necessary to confirm efficacy and safety of this optimized dosing approach.

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Association between Vancomycin Trough Concentration and Area under the Concentration-Time Curve in Neonates

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.03620-14 ◽

2014 ◽

Vol 58 (11) ◽

pp. 6454-6461 ◽

Cited By ~ 53

Author(s):

Adam Frymoyer ◽

Adam L. Hersh ◽

Mohammed H. El-Komy ◽

Shabnam Gaskari ◽

Felice Su ◽

...

Keyword(s):

Monte Carlo ◽

Serum Creatinine ◽

Monte Carlo Simulations ◽

Serum Creatinine Level ◽

Creatinine Level ◽

Population Pharmacokinetic ◽

Time Curve ◽

Concentration Time ◽

Vancomycin Trough ◽

Trough Concentrations

ABSTRACTNational treatment guidelines for invasive methicillin-resistantStaphylococcus aureus(MRSA) infections recommend targeting a vancomycin 24-h area under the concentration-time curve (AUC0–24)-to-MIC ratio of >400. The range of vancomycin trough concentrations that best predicts an AUC0–24of >400 in neonates is not known. This understanding would help clarify target trough concentrations in neonates when treating MRSA. A retrospective chart review from a level III neonatal intensive care unit was performed to identify neonates treated with vancomycin over a 5-year period. Vancomycin concentrations and clinical covariates were utilized to develop a one-compartment population pharmacokinetic model and examine the relationships between trough and AUC0–24in the study neonates. Monte Carlo simulations were performed to examine the effect of dose, postmenstrual age (PMA), and serum creatinine level on trough and AUC0–24achievement. A total of 1,702 vancomycin concentrations from 249 neonates were available for analysis. The median (interquartile range) PMA was 39 weeks (32 to 42 weeks) and weight was 2.9 kg (1.6 to 3.7 kg). Vancomycin clearance was predicted by weight, PMA, and serum creatinine level. At a trough of 10 mg/liter, 89% of the study neonates had an AUC0–24of >400. Monte Carlo simulations demonstrated that troughs ranging from 7 to 11 mg/liter were highly predictive of an AUC0–24of >400 across a range of PMA, serum creatinine levels, and vancomycin doses. However, a trough of ≥10 mg/liter was not readily achieved in most simulated subgroups using routine starting doses. Higher starting doses frequently resulted in troughs of >20 mg/liter. A vancomycin trough of ∼10 mg/liter is likely adequate for most neonates with invasive MRSA infections based on considerations of the AUC0–24. Due to pharmacokinetic and clinical heterogeneity in neonates, consistently achieving this target vancomycin exposure with routine starting doses is difficult. More robust clinical dosing support tools are needed to help clinicians with dose individualization.

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Evaluation of Initial and Steady-State Gatifloxacin Pharmacokinetics and Dose in Pulmonary Tuberculosis Patients by Using Monte Carlo Simulations

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00479-13 ◽

2013 ◽

Vol 57 (9) ◽

pp. 4164-4171 ◽

Cited By ~ 13

Author(s):

Wynand Smythe ◽

Corinne S. Merle ◽

Roxana Rustomjee ◽

Martin Gninafon ◽

Mame Bocar Lo ◽

...

Keyword(s):

Monte Carlo ◽

Steady State ◽

Pulmonary Tuberculosis ◽

Monte Carlo Simulations ◽

Controlled Trial ◽

Systemic Exposure ◽

Initial Increase ◽

Combination Regimen ◽

Time Curve ◽

Single Dose Study

ABSTRACTA 4-month regimen of gatifloxacin with rifampin, isoniazid, and pyrazinamide is being evaluated for the treatment of tuberculosis in a phase 3 randomized controlled trial (OFLOTUB). A prior single-dose study found that gatifloxacin exposure increased by 14% in the combination. The aims of the study are to evaluate the initial and steady-state pharmacokinetics of gatifloxacin when daily doses are given to patients with newly diagnosed drug-sensitive pulmonary tuberculosis as part of a combination regimen and to evaluate the gatifloxacin dose with respect to the probability of attaining a pharmacokinetic/pharmacodynamic target. We describe the population pharmacokinetics of gatifloxacin from the first dose to a median of 28 days in 169 adults enrolled in the OFLOTUB trial in Benin, Guinea, Senegal, and South Africa. The probability of achieving a ratio of ≥125 for the area under the concentration time curve to infinity (AUC0–∞) for the free fraction of gatifloxacin over the MIC (fAUC/MIC) was investigated using Monte Carlo simulations. The median AUC0–∞of 41.2 μg · h/ml decreased on average by 14.3% (90% confidence interval [CI], −90.5% to +61.5%) following multiple 400-mg daily doses. At steady state, 90% of patients achieved anfAUC/MIC of ≥125 only when the MIC was <0.125 μg/ml. We conclude that systemic exposure to gatifloxacin declines with repeated daily 400-mg doses when used together with rifampin, isoniazid, and pyrazinamide, thus compensating for any initial increase in gatifloxacin levels due to a drug interaction. (The OFLOTUB study has been registered at ClinicalTrials.gov under registration no. NCT00216385.)

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Population Pharmacokinetic Modeling of Total and Free Ceftriaxone in Critically Ill Children and Young Adults and Monte Carlo Simulations Support Twice Daily Dosing for Target Attainment

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01427-21 ◽

2021 ◽

Author(s):

Sonya Tang Girdwood ◽

Min Dong ◽

Peter Tang ◽

Erin Stoneman ◽

Rhonda Jones ◽

...

Keyword(s):

Monte Carlo ◽

Monte Carlo Simulations ◽

Pediatric Intensive Care ◽

Compartment Model ◽

The United States ◽

Volume Of Distribution ◽

Critically Ill Children ◽

Population Pharmacokinetic ◽

Population Pharmacokinetic Modeling ◽

Dosing Regimens

Critical illness, including sepsis, causes significant pathophysiologic changes that alter the pharmacokinetics (PK) of antibiotics. Ceftriaxone is one of the most prescribed antibiotics in patients admitted to the pediatric intensive care unit (PICU). We sought to develop population PK models of both total ceftriaxone and free ceftriaxone in children admitted to a single-center PICU using a scavenged opportunistic sampling approach. We tested if the presence of sepsis and phase of illness (before or after 48 hours of antibiotic treatment) altered ceftriaxone PK parameters. We performed Monte Carlo simulations to evaluate whether dosing regimens commonly used in PICUs in the United States (50 mg/kg every 12 hours vs. 24 hours) resulted in adequate antimicrobial coverage. We found that a two-compartment model best described both total and free ceftriaxone concentrations. For free concentrations, the population clearance value is 6.54 L/h/70 kg, central volume is 25.4 L/70 kg and the peripheral volume is 19.6 L/70kg. For both models, we found that allometric weight scaling, post-menstrual age, creatinine clearance and daily highest temperature had significant effects on clearance. Presence of sepsis or phase of illness did not have a significant effect on clearance or volume of distribution. Monte Carlo simulations demonstrated that to achieve free concentrations above 1 μg/mL for 100% of the dosing intervals, a dosing regimen of 50 mg/kg every 12 hours is recommended for most patients. A continuous infusion could be considered if the target is to maintain free concentrations four times above the minimum inhibitory concentrations (4 μg/mL).

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Pharmacokinetic Modeling of Voriconazole To Develop an Alternative Dosing Regimen in Children

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01194-17 ◽

2017 ◽

Vol 62 (1) ◽

Cited By ~ 6

Author(s):

Silke Gastine ◽

Thomas Lehrnbecher ◽

Carsten Müller ◽

Fedja Farowski ◽

Peter Bader ◽

...

Keyword(s):

Monte Carlo ◽

Monte Carlo Simulations ◽

Compartment Model ◽

Volume Of Distribution ◽

Pharmacokinetic Modeling ◽

Population Pharmacokinetic ◽

Dosing Regimen ◽

Concentration Data ◽

Days Of Therapy ◽

Dosing Regimens

ABSTRACT The pharmacokinetic variability of voriconazole (VCZ) in immunocompromised children is high, and adequate exposure, particularly in the first days of therapy, is uncertain. A population pharmacokinetic model was developed to explore VCZ exposure in plasma after alternative dosing regimens. Concentration data were obtained from a pediatric phase II study. Nonlinear mixed effects modeling was used to develop the model. Monte Carlo simulations were performed to test an array of three-times-daily (TID) intravenous dosing regimens in children 2 to 12 years of age. A two-compartment model with first-order absorption, nonlinear Michaelis-Menten elimination, and allometric scaling best described the data (maximal kinetic velocity for nonlinear Michaelis-Menten clearance [V max] = 51.5 mg/h/70 kg, central volume of distribution [V 1] = 228 liters/70 kg, intercompartmental clearance [Q] = 21.9 liters/h/70 kg, peripheral volume of distribution [V 2] = 1,430 liters/70 kg, bioavailability [F] = 59.4%, Km = fixed value of 1.15 mg/liter, absorption rate constant = fixed value of 1.19 h−1). Interindividual variabilities for V max, V 1, Q, and F were 63.6%, 45.4%, 67%, and 1.34% on a logit scale, respectively, and residual variability was 37.8% (proportional error) and 0.0049 mg/liter (additive error). Monte Carlo simulations of a regimen of 9 mg/kg of body weight TID simulated for 24, 48, and 72 h followed by 8 mg/kg two times daily (BID) resulted in improved early target attainment relative to that with the currently recommended BID dosing regimen but no increased rate of accumulation thereafter. Pharmacokinetic modeling suggests that intravenous TID dosing at 9 mg/kg per dose for up to 3 days may result in a substantially higher percentage of children 2 to 12 years of age with adequate exposure to VCZ early during treatment. Before implementation of this regimen in patients, however, validation of exposure, safety, and tolerability in a carefully designed clinical trial would be needed.

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Novel Population Pharmacokinetic Model for Linezolid in Critically Ill Patients and Evaluation of the Adequacy of the Current Dosing Recommendation

Pharmaceutics ◽

10.3390/pharmaceutics12010054 ◽

2020 ◽

Vol 12 (1) ◽

pp. 54 ◽

Cited By ~ 2

Author(s):

Amaia Soraluce ◽

Helena Barrasa ◽

Eduardo Asín-Prieto ◽

Jose Ángel Sánchez-Izquierdo ◽

Javier Maynar ◽

...

Keyword(s):

Critically Ill ◽

Critically Ill Patients ◽

Population Pharmacokinetic Model ◽

Pharmacokinetic Model ◽

Standard Dose ◽

Compartment Model ◽

Antimicrobial Treatment ◽

Population Pharmacokinetic ◽

Renal Replacement Therapies ◽

Continuous Renal Replacement Therapies

Antimicrobial treatment in critically ill patients remains challenging. The aim of this study was to develop a population pharmacokinetic model for linezolid in critically ill patients and to evaluate the adequacy of current dosing recommendation (600 mg/12 h). Forty inpatients were included, 23 of whom were subjected to continuous renal replacement therapies (CRRT). Blood and effluent samples were drawn after linezolid administration at defined time points, and linezolid levels were measured. A population pharmacokinetic model was developed, using NONMEM 7.3. The percentage of patients that achieved the pharmacokinetic/pharmacodynamic (PK/PD) targets was calculated (AUC24/MIC > 80 and 100% T>MIC). A two-compartment model best described the pharmacokinetics of linezolid. Elimination was conditioned by the creatinine clearance and by the extra-corporeal clearance if the patient was subjected to CRRT. For most patients, the standard dose of linezolid did not cover infections caused by pathogens with MIC ≥ 2 mg/L. Continuous infusion may be an alternative, especially when renal function is preserved.

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1319. Pharmacokinetics of Ceftolozane/Tazobactam in Patients with Burns

Open Forum Infectious Diseases ◽

10.1093/ofid/ofaa439.1501 ◽

2020 ◽

Vol 7 (Supplement_1) ◽

pp. S670-S671

Author(s):

Ronald G Hall ◽

Jotam Pasipanodya ◽

William C Putnam ◽

John Griswold ◽

Sharmila Dissanaike ◽

...

Keyword(s):

Human Plasma ◽

Kidney Injury ◽

Compartment Model ◽

Pharmacokinetic Parameters ◽

Therapeutic Drug ◽

Population Pharmacokinetic ◽

Parameter Estimates ◽

Population Parameter ◽

Full Thickness ◽

Severe Burns

Abstract Background Antimicrobial dosing in moderate/severe burns patients is complicated due to the potential unpredictable hyperdynamic pathophysiologic states including 1) hypoproteinemia, 2) acute kidney injury and 3) onset of septicemia. Therefore, distribution assumptions about the population pharmacokinetic (PopPK) profiles of either endogenous or xenobiotic pharmacophores in this patient population can lead to biased parameter estimates. In order to prevent potential bias an agnostic nonparametric adaptive grid approach to describe ceftolozane/tazobactam (C/T) PopPK profiles in patients with partial- and full-thickness burns was employed. Methods A human clinical PK study in burn patients was conducted using the standard approved dose of C/T (2 grams/1 gram). A single intravenous dose was administered over 60 minutes. Whole blood was obtained pre-dose and at 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, 12, 16, and 24 hours following the start of infusion. LC-MS/MS bioanalytical methods were developed, validated and employed to determine C/T concentrations in human plasma. PopPK were modeled using Pmetrics package for R. One-, two- and three-compartment models were examined and compared. The influence of several parameters, including %body surface area burns, creatinine clearance (CrCL), weight, albumin and age were tested. Results The bioanalytical method for determination of C/T in human plasma met all recommended criteria of the LC-MS/MS. Five males and one female (ages 24 to 66 years), contributed 148 plasma PK samples. The female had 35% partial-thickness burns. The males had full-thickness burns ranging from 27 to 66%. The median CrCL was 104 mL/min (range 73-148 mL/min). Two-compartment model with absorption (Ka) from compartment 1 to 2 and elimination from compartment 2 (Ke), with nonlinear interactions between C/T elimination and CrCL best described the data. Figure A show that bias was minimal. Importantly, both drugs exhibited marked variability for both volume and elimination (Table), since volume was bimodally distributed (Figure B). A) Observation-versus-Prediction; B) Estimated Ke, V and Ka population parameter densities Summary of pharmacokinetic parameters Conclusion C/T exhibited high variability surpassing that observed with severe infections, suggesting that dose adjustment and/or may be therapeutic drug monitoring may be needed to balance target attainment from dose-related toxicities. Disclosures Ronald G. Hall, II, PharmD, MSCS, Medical Titan Group (Grant/Research Support)Merck (Research Grant or Support)

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Population Pharmacokinetics of Intravenous Amoxicillin Combined With Clavulanic Acid in Healthy and Critically Ill Dogs

Frontiers in Veterinary Science ◽

10.3389/fvets.2021.770202 ◽

2021 ◽

Vol 8 ◽

Author(s):

Maria D. Vegas Cómitre ◽

Stefano Cortellini ◽

Marc Cherlet ◽

Mathias Devreese ◽

Beatrice B. Roques ◽

...

Keyword(s):

Monte Carlo ◽

Monte Carlo Simulations ◽

Clavulanic Acid ◽

Critically Ill ◽

Drug Exposure ◽

De Novo ◽

Clinical Failure ◽

Clinical Covariates ◽

Amoxicillin Clavulanic Acid ◽

Healthy Dogs

Background: Data regarding antimicrobial pharmacokinetics (PK) in critically ill dogs are lacking and likely differ from those of healthy dogs. The aim of this work is to describe a population PK model for intravenous (IV) amoxicillin–clavulanic acid (AMC) in both healthy and sick dogs and to simulate a range of clinical dosing scenarios to compute PK/PD cutoffs for both populations.Methods: This study used a prospective clinical trial in normal and critically ill dogs. Twelve client-owned dogs hospitalized in the intensive care unit (ICU) received IV AMC 20 mg/kg every 8 h (0.5-h infusion) during at least 48 h. Eight blood samples were collected at predetermined times, including four trough samples before the next administration. Clinical covariates and outcome were recorded, including survival to discharge and bacteriologic clinical failure. Satellite PK data were obtained de novo from a group of 12 healthy research dogs that were dosed with a single AMC 20 mg/kg IV. Non-linear mixed-effects model was used to estimate the PK parameters (and the effect of health upon them) together with variability within and between subjects. Monte Carlo simulations were performed with seven dosage regimens (standard and increased doses). The correlation between model-derived drug exposure and clinical covariates was tested with Spearman's non-parametric correlation analysis. Outcome was recorded including survival to discharge and bacteriologic clinical failure.Results: A total of 218 amoxicillin concentrations in plasma were available for healthy and sick dogs. A tricompartmental model best described the data. Amoxicillin clearance was reduced by 56% in sick dogs (0.147 L/kg/h) compared with healthy dogs (0.336 L/kg/h); intercompartmental clearance was also decreased (p <0.01). None of the clinical data covariates were significantly correlated with individual exposure. Monte Carlo simulations showed that higher PK/PD cutoff values of 8 mg/L could be reached in sick dogs by extending the infusion to 3 h or doubling the dose.Conclusions: The PK of AMC is profoundly different in critically ill dogs compared with normal dogs, with much higher interindividual variability and a lower systemic clearance. Our study allows to generate hypotheses with regard to higher AMC exposure in clinical dogs and provides supporting data to revise current AMC clinical breakpoint for IV administration.

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