Prospective Pharmacokinetic Study Research Articles

Influence of the clindamycin administration route on the magnitude of clindamycin–rifampicin interaction: a prospective pharmacokinetic study

ObjectivesAn important clindamycin–rifampicin pharmacokinetic (PK) interaction has been reported, but the potential influence of the clindamycin administration route on that interaction is unknown. This prospective, observational, comparative PK study was undertaken to characterize and analyse the impact of the route, comparing the rifampicin enzyme-inductor effects on clindamycin clearance (CLclin) for oral versus intravenous (IV) administration. MethodsPatients with bone-and-joint infections (BJIs) were treated with clindamycin monotherapy (n = 20) or clindamycin–rifampicin combination therapy (n = 19). Patients received continuous IV clindamycin infusion for 2–6 weeks, followed by an oral regimen. Liquid chromatography–mass spectrometry was used to measure plasma clindamycin concentrations at the end of IV and after 2 weeks of oral treatment. The ratios of the mean CLclin for the combination and monotherapy groups were calculated for IV (Riv) and oral (Rpo) routes, with the final ratio, Rf = Rpo/Riv, representing the fold change of the rifampicin-inducing effect from the IV to the oral route. ResultsComparing monotherapy with combination-therapy groups, the former's median steady-state concentration was two-fold higher after IV administration (8.49 versus 3.82 mg/L, p < 0.001) and its median AUC0–8h was 12 times higher after oral intake (37.7 versus 3.1 mg.h/L, p < 0.001). Riv, Rpo and Rf were 2.68, 18.8 and 7.0 respectively. ConclusionThe magnitude of this interaction was markedly increased by oral intake, questioning the use of oral treatment for difficult-to-treat infections like BJIs. Nevertheless, the clindamycin–rifampicin combination seems possible provided that clindamycin is administered by continuous IV infusion.

Once-daily 1 g ceftriaxone optimizes exposure in patients with septic shock and hypoalbuminemia receiving continuous veno-venous hemodiafiltration.

Ceftriaxone total and unbound pharmacokinetics (PK) can be altered in critically ill patients with septic shock and hypoalbuminemia receiving continuous veno-venous hemodiafiltration (CVVHDF). The objective of this study was to determine the dosing strategy of ceftriaxone that maximizes the probability of maintaining the concentration above the MIC of the susceptible bacteria (≤2 mg/L by the EUCAST) for a 100% of the dosing interval (100% ƒuT>MIC). In a prospective PK study in the intensive care units of two tertiary Spanish hospitals, six timed blood samples were collected per patient; for each sample, ceftriaxone total and unbound concentrations were measured using a liquid chromatography coupled to tandem mass spectrometry method. Population PK analysis and Monte-Carlo simulations were performed using NONMEMv.7.3®. We enrolled 8 critically ill patients that met the inclusion criteria (47 blood samples). Median age (range) was 70 years (47-85), weight 72.5 kg (40-95), albumin concentration 24.2 g/L (22-34), APACHE II score at admission 26 (17-36), and SOFA score on the day of study 12 (9-15). The unbound fraction (ƒu) of ceftriaxone was 44%, and total CL was 1.27 L/h, 25-30% higher than the CL reported in septic critically ill patients not receiving renal replacement therapies, and dependent on albumin concentration and weight. Despite this increment in ƒu and CL, Monte-Carlo simulations showed that a dose of 1 g once-daily ceftriaxone is sufficient to achieve a 100% ƒuT>MIC for MICs ≤2 mg/L for any range of weight and albumin concentration. Once-daily 1 g ceftriaxone provides optimal exposure in critically ill patients with septic shock and hypoalbuminemia receiving CVVHDF.

Pharmacokinetics of Tobramycin Administered at the Beginning of Intermittent Hemodialysis Session (ESRD Study).

Background and Objectives:There is a renewed interest in the successful use of aminoglycosides due to increasing resistance in gram-negative infections. Few studies to date have examined the pharmacokinetics (PK) of intradialytic infusions of tobramycin. This study sought to characterize the pharmacokinetic profile of intradialytically administered tobramycin in infected patients receiving chronic intermittent hemodialysis and to determine whether it is possible to achieve favorable PK targets.Design, Setting, Participants, and Measurements:In this prospective pharmacokinetic study, a single dose (5 mg/kg) of tobramycin was administered intradialytically to 11 noncritically ill patients undergoing chronic intermittent hemodialysis. Blood samples were collected at selected time to determine tobramycin serum concentrations. The PK analysis was performed using Phoenix™ NLME. The efficacy exposure outcome for nonsevere gram-negative infections sensitive to tobramycin with a minimum inhibitory concentration ≤1 were maximum concentration (Cmax ≥ 10 mg/L) and area under the curve (AUC24 h > 30 mg⋅h/L). For toxicity, the goal was to identify plasma trough concentrations <2 mg/L.Results:Tobramycin disposition was best described by a one-compartment model using a total clearance composed of the systemic clearance and a transitory hemodialysis clearance. Tobramycin mean (SD) Cmax, trough levels, and AUC24h were 13.1 (1.3) mg/L, 1.32 (0.47) mg/L, and 61 (23) mg⋅h/L, respectively. Monte Carlo simulation run with 1000 virtual patients showed that a 5 mg/kg dose of tobramycin administered intradialytically can outperformed the usual low-dose postdialysis dosing (80% meeting all targets versus <1%, respectively).Conclusions:A single high dose of tobramycin can achieve favorable PK outcome when administered using intradialytic infusions in hemodialysis patients. This practical dosing regimen may represent an effective and safer alternative to the usual dosing in the treatment of nonsevere gram-negative infections.

Low initial trough concentration of rituximab is associated with unsatisfactory response of first-line R-CHOP treatment in patients with follicular lymphoma with grade 1/2.

For follicular lymphoma (FL) with grade 1/2, the complete response (CR) rate of the first-line R-CHOP treatment was significantly low. In this study, we assessed the rationality of the administration of rituximab for FL patients with grade 1/2 based on concentration-response relationship analyses. Thus, we conducted a prospective pharmacokinetic (PK) study in 68 FL patients with grades 1-3 treated with R-CHOP at 21-day intervals. Plasma rituximab concentrations were quantified using ELISA and the population PK modeling was established with Phoenix® NLMETM. The first cycle trough concentration (C1-trough) of rituximab was a significant independent risk factor for achieving CR in matched-pair logistic regression analysis, rather than the concentrations in later cycles; the recommendatory minimum optimal C1-trough was 13.60 μg/mL. Patients with grade 1/2 had significantly lower C1-trough compared with grade 3 (12.21 μg/mL vs. 23.45 μg/mL, P < 0.001), only 30% patients with grade 1/2 could reach 13.60 μg/mL, compared with 91.67% in patients with grade 3, which was in accord with its unsatisfactory CR rates (43.33% vs. 76.32%). The stage indicating the tumor burden (the target) was a crucial influence factor for C1-trough, accounting for 40.70% of its variability, 70% patients with grade 1/2 were stage IV in this study, since the systemic therapy only started at the disseminated disease stage. The initial dose of 1800 mg was recommended by Monte Carlo simulation for patients with grade 1/2. In summary, low C1-trough accounted for low-grade FL's unsatisfactory CR rate, designing the first dosage of rituximab should be a very important component of individualized therapy for FL.

Inhibition of CYP2D6 with low dose (5 mg) paroxetine in patients with high 10-hydroxynortriptyline serum levels-A prospective pharmacokinetic study.

The antidepressant nortriptyline is metabolized by cytochrome P450 2D6 (CYP2D6) to the less active and more cardiotoxic drug metabolite, 10-hydroxynortriptyline. High serum levels of this metabolite (>200 μg/L) may lead to withdrawal of nortriptyline therapy. Adding CYP2D6 inhibitors reduce the metabolic activity of CYP2D6 (phenoconversion) and so decrease the forming of hydroxynortriptyline. In this study, 5 mg paroxetine is administered to patients with high hydroxynortriptyline concentrations (>200 μg/L). The shift in number of patients to therapeutic nortriptyline (50-150 μg/L) and safe hydroxynortriptyline (<200 μg/L) concentrations, and the degree of phenoconversion, expressed as the change in ratio nortriptyline/hydroxynortriptyline concentrations before and after paroxetine addition, are prospectively observed and described. After paroxetine addition, 12 patients (80%) had therapeutic nortriptyline and safe hydroxynortriptyline concentrations. Hydroxynortriptyline concentrations decreased in all patients. The average nortriptyline/hydroxynortriptyline concentrations ratio increased from 0.32 to 0.59. This study shows that 5 mg paroxetine addition is able to lower high hydroxynortriptyline serum levels to safe ranges.

Insufficient plasma concentrations of empiric anti‐pseudomonal beta‐lactam antibiotics in critically ill patients with suspected sepsis

AbstractAimTo determine if empirical anti‐pseudomonal beta‐lactam antibiotic (BLA) dosing achieves adequate drug exposure in septic patients.MethodA single‐centre, prospective pharmacokinetic study was conducted in Intensive Care Unit (ICU) patients with sepsis, receiving empirical therapy with piperacillin/tazobactam or meropenem. The pharmacokinetic/pharmacodynamic (PK/PD) targets were free BLA concentrations above the MIC at the mid‐point (Concentration A, 50%f T &gt; MIC) and end of the dosing interval (Concentration B, 100% fT &gt; MIC). Sub‐therapeutic concentrations were defined as concentration A &lt; MIC, and sub‐optimal as concentration B &lt; MIC. The MIC breakpoint for Pseudomonas aeruginosa, as defined by The European Committee on Antimicrobial Susceptibility Testing (EUCAST) (available from &lt;http://www.eucast.org/clinical_breakpoints&gt;) was used.ResultsOf the 37 eligible patients, 20 were receiving piperacillin/tazobactam (TZP), and 17 meropenem (MEM). PK data were available for 36 patients (concentration A) and 34 patients (concentration B). The median measured plasma concentrations (mg/L) were: piperacillin for doses 4 g 8‐hourly and 4 g 6‐hourly – concentration A 53.9 [14.38–123.71] and 36.44 [13.38–107.45], concentration B 8.01 [2.57–71.08] and 27.31 [3.32–59.76], MEM for doses 1 g 8‐hourly and 2 g 8‐hourly – concentration A 12.49 [7.35–23.63] and 30.5, concentration B 7.47 [2.97–11.33] and 9.31. 27.8% (10 of 36) of patients had sub‐therapeutic concentrations (concentration A) and 50% (17 of 34) had sub‐optimal concentrations (concentration B).ConclusionOur study confirms that sub‐therapeutic unbound plasma anti‐pseudomonal BLA concentrations are common in critically ill septic patients and underscores the urgent need for future trials exploring the efficacy of BLA therapeutic drug monitoring in these patients.

P156 Standard doses of intravenous colistin do not achieve therapeutic plasma target levels in adult cystic fibrosis patients: preliminary results from a multicentre, prospective pharmacokinetic study

P156 Standard doses of intravenous colistin do not achieve therapeutic plasma target levels in adult cystic fibrosis patients: preliminary results from a multicentre, prospective pharmacokinetic study

Tacrolimus Area Under the Concentration Versus Time Curve Monitoring, Using Home-Based Volumetric Absorptive Capillary Microsampling.

Therapeutic drug monitoring (TDM) of tacrolimus (Tac) is mandatory in renal transplant recipients (RTxR). Area under the concentration versus time curve (AUC) is the preferred measure for Tac exposure; however, for practical purposes, most centers use trough concentrations as a clinical surrogate. Limited sampling strategies in combination with population pharmacokinetic model-derived Bayesian estimators (popPK-BE) may accurately predict individual AUC. The use of self-collected capillary microsamples could simplify this strategy. This study aimed to investigate the potential of AUC-targeted Tac TDM using capillary microsamples in combination with popPK-BE. A single-center prospective pharmacokinetic study was conducted in standard-risk RTxR (n = 27) receiving Tac twice daily. Both venous and capillary microsamples (Mitra; Neoteryx, Torrance, CA) were obtained across 2 separate 12-hour Tac dosing intervals (n = 13 samples/AUC). Using popPK-BE, reference AUC (AUCref) was determined for each patient using all venous samples. Different limited sampling strategies were tested for AUC predictions: (1) the empiric sampling scheme; 0, 1, and 3 hours after dose and (2) 3 sampling times determined by the multiple model optimal sampling time function in Pmetrics. Agreement between the predicted AUCs and AUCref were evaluated using C-statistics. Accepted agreement was defined as a total deviation index ≤±15%. The AUC from capillary microsamples revealed high accuracy and precision compared with venous AUCref, and 85% of the AUCs had an error within ±11.9%. Applying microsamples at 0, 1, and 3 hours after dose predicted venous AUCref with acceptable agreement. Patients performed self-sampling with acceptable accuracy. Capillary microsampling is patient-centered, making AUC-targeted TDM of Tac feasible without extended hospital stays. Samples obtained 0, 1, and 3 hours after dose, combined with popPK-BE, accurately predict venous Tac AUC.

Development of a method for clinical pharmacokinetic testing to allow for targeted Melphalan dosing in multiple myeloma patients undergoing autologous transplant.

High dose melphalan (HDM) and autologous stem cell transplant (ASCT) is standard of care for multiple myeloma (MM), but there is significant variability in melphalan exposure (area under the plasma drug concentration-time curve, AUC) when using body surface area-based dosing. Our aim was to establish a method of pharmacokinetic (PK) testing for real-time melphalan dose adjustments. We performed a prospective PK study of melphalan 140 or 200 mg/m2 in MM patients undergoing ASCT. Twenty MM patients were administered HDM on days -2 and - 1, with PK sampling at 8-10 time points. PK testing was performed on day -2 in all patients, and on day -1 in 5 patients. Less than 20% interpatient variation in the day -2 and - 1 AUC was observed. The day -2 range in AUC (4.95-11.28 mg h/L) confirmed significant interpatient variability. The hypothetical total dose ranged from 133-302 mg/m2 to achieve the total median AUC. A 4-time point AUC (0, 30, 150 and 240 min) highly correlated with the AUC from the 8-time point schedule. A higher AUC correlated with increased risk of febrile neutropenia (P = .05). Here we outline the methods to establish novel melphalan dosing using PK testing in MM patients undergoing ASCT to target a desired melphalan AUC.

Correlation Between the Metabolic Conversion of a Capecitabine Metabolite, 5'-Deoxy-5-fluorocytidine, and Creatinine Clearance.

Capecitabine is a prodrug that is metabolized to its active form, 5-fluorouracil (5-FU), in three enzymatic steps. This prospective pharmacokinetic study evaluated cytidine deaminase (CDA) activity, the second drug-metabolizing enzyme that generates 5'-deoxy-5-fluorouridine (5'-DFUR) from 5'-deoxy-5-fluorocytidine (5'-DFCR), as well as creatinine clearance (CLcr). Patients with colorectal cancer who received capecitabine plus oxaliplatin were selected. Pharmacokinetics of capecitabine and its metabolites, and CDA activity in plasma were analyzed. Eighteen patients were examined. The area under the plasma concentration-time curve (AUC) of 5'-DFUR showed a significant inverse correlation with CLcr (p=0.003). The metabolic ratio, i.e. the ratios of the AUC of 5'-DFUR plus that of 5-FU to the AUC of 5'-DFCR, significantly increased when CLcr decreased (p=0.001) but did not depend on plasma CDA activity. Metabolism of 5'-DFCR to form 5'-DFUR increased as CLcr decreased but the mechanism remains unknown.

Imported malaria and artemisinin-based combination therapy failure in travellers returning to Belgium: A retrospective study.

Malaria (Plasmodium spp) remains a top cause of travel-associated morbidity among European residents. Here, we describe recent trends of imported malaria to Belgium and characterize the first cases of P.falciparum failure to artemisinin-based combination therapy (ACT). National surveillance data and registers from national reference laboratory were used to investigate malaria cases and ACT failures in the past 20 years. Recurrent infections were confirmed by pfmsp genotyping and polymorphisms in drug resistance-associated genes pfk13, pfcrt, pfmdr1, pfpm2, pfap2mu and pfubp1 were determined by sequencing or quantitative PCR. Annual malaria cases steadily increased in the last decade, reaching 428 in 2017 (all species). An estimated 15% of P.falciparum cases were severe. Between 2014 and 2017, 727 P.falciparum cases were reported and six non-immune travellers presented late recurrence. Five had hyperparasitaemia and/or signs of severe malaria at initial consultation. No mutations in ACT drug resistance markers were detected, although pfcrt-pfmdr1 haplotypes associated with lumefantrine tolerance were common. The upward trend in imported malaria, the substantial proportion of severe cases and the emergence of ACT failures are sources of concern, although late failures were infrequent. Genetic analysis did not support parasitological resistance to ACT, suggesting prospective pharmacokinetic studies should assess adequacy of partner drug dosage and duration of treatment in non-immune populations.

Population pharmacokinetics of total and unbound concentrations of intravenous posaconazole in adult critically ill patients

BackgroundThe population pharmacokinetics of total and unbound posaconazole following intravenous administration has not yet been described for the critically ill patient population. The aim of this work was, therefore, to describe the total and unbound population pharmacokinetics of intravenous posaconazole in critically ill patients and identify optimal dosing regimens.MethodsThis was a prospective observational population pharmacokinetic study in critically ill adult patients with presumed/confirmed invasive fungal infection. A single dose of 300 mg posaconazole was administered intravenously as an add-on to standard antifungal therapy, and serial plasma samples were collected over 48 h. Total and unbound posaconazole concentrations, measured by chromatographic method, were used to develop a population pharmacokinetic model and perform dosing simulations in R using Pmetrics.ResultsFrom eight patients, 93 pairs of total and unbound concentrations were measured. A two-compartment linear model with capacity-limited plasma protein binding best described the concentration-time data. Albumin and body mass index (BMI) were included as covariates in the final model. Mean (SD) parameter estimates for the volume of the central compartment (V) and the elimination rate constant were 72 (43) L and 42.1 (23.7) h−1, respectively. Dosing simulations showed that high BMI was associated with a reduced probability of achieving target total and unbound posaconazole concentrations. Low serum albumin concentration was associated with a reduced probability of attaining target total but not unbound posaconazole concentrations.ConclusionsAn important clinical message of this study is that critically ill patients with increased BMI may require larger than approved loading doses of intravenous posaconazole when considering currently recommended dosing targets. Variability in plasma albumin concentration appears unlikely to affect dosing requirements when the assessment is based on unbound concentrations. Where available, therapeutic drug monitoring of unbound concentrations may be useful.

Tobramycin Clearance Is Best Described by Renal Function Estimates in Obese and Non-obese Individuals: Results of a Prospective Rich Sampling Pharmacokinetic Study

PurposeTobramycin is an aminoglycoside antibiotic of which the 24 h exposure correlates with efficacy. Recently, we found that clearance of the aminoglycoside gentamicin correlates with total body weight (TBW). In this study, we investigate the full pharmacokinetic profile of tobramycin in obese and non-obese individuals with normal renal function.MethodsMorbidly obese individuals (n = 20) undergoing bariatric surgery and non-obese healthy volunteers (n = 8), with TBW ranging 57–194 kg, received an IV dose of tobramycin with plasma concentrations measured over 24 h (n = 10 per individual). Statistical analysis, modelling and simulations were performed using NONMEM.ResultsIn a two-compartment model, TBW was the best predictor for central volume of distribution (p < 0.001). For clearance, MDRD (de-indexed for body surface area) was identified as best covariate (p < 0.001), and was superior over TBW ((p < 0.05). Other renal function estimates (24 h urine GFR and de-indexed CKD-EPI) led to similar results as MDRD (all p < 0.001)).ConclusionsIn obese and non-obese individuals with normal renal function, renal function estimates such as MDRD were identified as best predictors for tobramycin clearance, which may imply that other processes are involved in clearance of tobramycin versus gentamicin. To ensure similar exposure across body weights, we propose a MDRD-based dosing nomogram for obese patients.

Boosting pazopanib exposure by splitting intake moments: A prospective pharmacokinetic study in cancer patients.

3119 Background: Pazopanib is approved for the treatment of renal cell carcinoma (RCC) and soft tissue sarcoma (STS). Due to high (40-70%) interpatient variability in pharmacokinetic (PK) exposure, 16-20% of patients do not reach the 20 mg/L exposure threshold related to prolonged progression free survival (20 weeks versus 52 weeks, respectively) with the currently used fixed dose of 800 mg QD (Suttle, 2014; Verheijen, 2017). PK simulations showed that, due to non-linear absorption of pazopanib, splitting the intake (400 mg BID) leads to an increase in Cmin and AUC0-24h of 75% and 59%, respectively (Yu, 2017). This study aimed to show whether switching patients from an 800 mg QD to a 400 mg BID dose schedule will lead to a significant increase in PK exposure. Methods: We performed a prospective PK trial (NL6137) in which PK sampling at the 800 mg QD dose schedule occurred at day 1, after which the intake moments were split into 400 mg BID during one week, followed by PK sampling at day 8. Paired samples t-tests were used to assess differences in Cmin, Cmax and AUC0-24h between these two dose schedules. To detect an increase in PK exposure of 50% (2-sided α = 0.05 and β = 0.20), 10 evaluable patients were needed. Results: Eleven patients (6 RCC and 5 STS) have been included, of whom ten were evaluable for PK analyses. Using the 800 mg QD dose schedule mean Cmin, Cmax and AUC0-24h were 26.7 mg/L (coefficient of variation (CV%) 44.7), 46.1 mg/L (CV% 37.1) and 809 mg h/L (CV% 42.1), respectively. Switching to 400 mg BID resulted in an increase of both Cmin and AUC0-24h to 40.7 mg/L (CV% 37.0, p = 0.013) and 1059 mg h/L (CV% 33.1, p = 0.068), respectively, while Cmax did not significantly change (56.5 mg/L, CV% 33.2, p = 0.185). One patient (9%) experienced grade 3 diarrhea after splitting intake moments, leading to treatment interruption. This strategy could potentially save up to 2000 USD/patient/month compared to conventional dose increments. Conclusions: This study demonstrates that boosting pazopanib exposure by splitting intake moments leads to a significant increase in Cmin, of 52%, with acceptable tolerability. Therefore, this new dose schedule offers a safe and cost-neutral opportunity to optimize treatment for patients with low PK exposure. Clinical trial information: NL6137.

Accumulation of active metabolite M-2 predicts overall survival (OS) of chemorefractory metastatic colorectal cancer patients treated with regorafenib (REGO).

3121 Background: TEXCAN, a prospective phase II GERCOR study of treatment with REGO in chemorefractory metastatic colorectal cancer (mCRC) patients (NCT02699073) included a prospective pharmacokinetic (PK) ancillary study aiming to investigate correlations between OS and concentrations (C) of REGO and its active metabolites M-2 and M-5. Methods: 55 patients were included, with the same inclusion/exclusion criteria as CORRECT (NCT01103323), and treated orally with 160 mg REGO daily for 3 weeks on and 1 week off. 34 patients had PK samples at C1D15 and 26 at C2D15 for Cmin. REGO, M-2 and M-5 Cmin were measured by LC-MS/MS. PK analyses studied the link between OS and PK parameters: Cmin of REGO, M-2 and M-5 at C1 and accumulation of pharmacological active metabolites between C1 and C2, assessed by the C2/C1 ratio of M-2 or M-5 Cmin concentrations. Results: REGO, M-2 and M-5 Cmin [median (Q1-Q3)] were respectively 1.99 (1.03-2.73), 1.44 (0.89-2.49) and 1.61 (0.79-2.37) mg/L at C1D15 and 1.90 (1.10-2.76), 1.29 (0.77-2.24) and 1.17 (0.45-2.42) mg/L at C2D15. C2/C1 M-2 ratio and M-5 ratio medians were 0.82 (0.50-1.78) and 0.75 (0.41-1.93), respectively. Univariate analyses showed a major OS benefit in patients with C2/C1 M-2 ratio ≥median vs &lt; median (12.6 vs 4.0 months respectively, hazard ratio = 0.35, 95% confidence interval 0.14-0.86, p-value = 0.023) but not for C2/C1 M-5 ratio ≥median. Multivariate analyses, including the CORRECT REGOSCORE groups, showedan independent 66% reduction in death risk in the group of patients with C2/C1 M-2 ratio ≥median. The C2/C1 M-2 ratio correlated with C1 REGO+M-2+M-5 (Csum) (0.53, p-value = 0.006). Restricted Cubic spline analysis showed an increased OS benefit as the C2/C1 M-2 ratio rises and when C1 Csum ranged between 2.5 and 5.5 mg/L. PK parameters were not associated with toxicities. Conclusions: M-2 accumulation between C1 and C2 is independently associated with improved OS in mCRC patients treated by REGO. M-2 accumulates and OS is favorable when C1 REGO+M-2+M-5 sum ranged between 2.5 and 5.5 mg/L. These results may lead to develop individual REGO dosage modification strategies based on PK monitoring. Clinical trial information: NCT02699073.

Pharmacokinetics of adjusted-dose 8-hourly lopinavir/ritonavir in HIV-infected children co-treated with rifampicin.

To evaluate the proportion of children with lopinavir Cmin ≥1 mg/L when receiving a novel 8-hourly lopinavir/ritonavir dosing strategy during rifampicin co-treatment. HIV-infected children on lopinavir/ritonavir and rifampicin were enrolled in a prospective pharmacokinetic study. Children were switched from standard-of-care lopinavir/ritonavir-4:1 with additional ritonavir (1:1 ratio) twice daily to 8-hourly lopinavir/ritonavir-4:1 using weight-banded dosing. Rifampicin was dosed at 10-20 mg/kg/day. After 2 weeks, plasma samples were collected ∼2, 4, 6, 8 and 10 h after the morning lopinavir/ritonavir-4:1 dose, ALT was obtained to assess safety and treatment was switched back to standard of care. ClinicalTrials.gov registration number: NCT01637558. We recruited 11 children in two weight bands: 5 (45%) were 10-13.9 kg and received 20-24 mg/kg/dose of lopinavir and 6 (55%) children weighed 6-9.9 kg and received 20-23 mg/kg/dose of lopinavir. The median age was 15 months (IQR = 12.6-28.8 months). The median (IQR) lopinavir Cmin was 3.0 (0.1-5.5) mg/L. Seven (63.6%) of the 11 children had Cmin values ≥1 mg/L. Children with a lopinavir mg/kg dose below the median 21.5 were more likely to have Cmin <1 mg/L (P = 0.02). There was a strong positive correlation between lopinavir and ritonavir concentrations. No associations were found between lopinavir AUC2-10 and age, sex, weight, nutritional status or mg/kg/dose of lopinavir. These data do not support the use of 8-hourly lopinavir/ritonavir at studied doses. Evaluation of higher doses is needed to optimize treatment outcomes of TB and HIV in young children.

Population Pharmacokinetics and Dosing Optimization of Linezolid in Pediatric Patients.

Linezolid is a synthetic antibiotic very effective in the treatment of infections caused by Gram-positive pathogens. Although the clinical application of linezolid in children has increased progressively, data on linezolid pharmacokinetics in pediatric patients are very limited. The aim of this study was to develop a population pharmacokinetic model for linezolid in children and optimize the dosing strategy in order to improve therapeutic efficacy. We performed a prospective pharmacokinetic study of pediatric patients aged 0 to 12 years. The population pharmacokinetic model was developed using the NONMEM program. Goodness-of-fit plots, nonparametric bootstrap analysis, normalized prediction distribution errors, and a visual predictive check were employed to evaluate the final model. The dosing regimen was optimized based on the final model. The pharmacokinetic data from 112 pediatric patients ages 0.03 to 11.9 years were analyzed. The pharmacokinetics could best be described by a one-compartment model with first-order elimination along with body weight and the estimated glomerular filtration rate as significant covariates. Simulations demonstrated that the currently approved dosage of 10 mg/kg of body weight every 8 h (q8h) would lead to a high risk of underdosing for children in the presence of bacteria with MICs of ≥2 mg/liter. To reach the pharmacokinetic target, an elevated dosage of 15 or 20 mg/kg q8h may be required for them. The population pharmacokinetics of linezolid were characterized in pediatric patients, and simulations provide an evidence-based approach for linezolid dosage individualization.

Piperacillin pharmacokinetics and target attainment in children with cancer and fever: Can we optimize our dosing strategy?

Data on piperacillin-tazobactam pharmacokinetics and optimal dosing in children with cancer and fever are limited. Our objective was to investigate piperacillin pharmacokinetics and the probability of target attainment (PTA) with standard intermittent administration (IA), and to simulate PTA in other dosing regimens. This prospective pharmacokinetic study was conducted from April 2016 to January 2018. Children with cancer receiving empiric piperacillin-tazobactam to treat infections were included. Piperacillin-tazobactam 100mg/kg was infused over 5min every 8hours (IA). An optimized sample schedule provided six blood samples per subject for piperacillin concentration determination. The evaluated targets included: (1) 100% time of free piperacillin concentration above the minimum inhibitory concentration (fT>MIC) and (2) 50% fT>4× MIC. MIC50 and MIC90 were defined based on an intrainstitutional MIC range. A total of 482 piperacillin concentrations were obtained from 43 children (aged 1-18 years) during 89 fever episodes. Standard IA resulted in insufficient target attainment, with significant differences in piperacillin pharmacokinetics for different body weights. Median fT>MIC was 61.2%, 53.5%, and 36.3% for MIC50 (2.0mg/L), MIC90 (4.0mg/L), and breakpoint for Pseudomonas aeruginosa (16.0mg/L), respectively. Correspondingly, the median fT>4× MIC was 43%, 36.3%, and 20.1%. Simulations showed that only continuous infusion reached a PTA of 95% for MIC=16.0mg/L, while extended infusion lasting half of the dosing interval reached a PTA of 95% for MIC≤8mg/L. Our data revealed insufficient PTA with standard IA of piperacillin-tazobactam in children with cancer and fever. Alternative dosing strategies, preferably continuous infusion, are required to ensure adequate PTA.

Conversion from Twice-Daily Prograf® to Once-Daily Advagraf® in Multi-ethnic Asian Adult Renal Transplant Recipients With or Without Concomitant Use of Diltiazem: Impact of CYP3A5 and MDR1 Genetic Polymorphisms on Tacrolimus Exposure

Tacrolimus is the mainstay of immunosuppression in renal transplantation. Given that once-daily administration improves patient compliance, 1:1 dose conversion from twice-daily Prograf® to once-daily Advagraf® is recommended. Although cytochrome P450 (CYP) 3A5 and multi-drug resistance 1 (MDR1) polymorphisms influence tacrolimus concentrations, it is unknown if these impact on conversion. This study investigated the change in the pharmacokinetics of tacrolimus after conversion from Prograf® to Advagraf® and examined the impact of CYP3A5 and MDR1 C3435T polymorphisms on those pharmacokinetics. A prospective open-label pharmacokinetic study of 1:1 conversion from Prograf® to Advagraf® with or without diltiazem was conducted on 26 stable renal transplant recipients. Blood samples were collected over 24h during each phase, tacrolimus concentrations were assayed, and noncompartmental pharmacokinetic analysis was performed. All participants were genotyped for CYP3A5*3 and MDR1 C3435T. After conversion, without diltiazem, the area under the concentration-time curve at steady state from 0 to 24 h after dose administration (AUCss, 0-24) was significantly reduced [median224 (range172-366) vs. 184 (104-347) ng·h/mL, p = 0.006, n = 26]. A decrease in tacrolimus exposure (median 21%) was only evident among CYP3A5 expressors [227 (172-366) vs. 180 (104-347) ng·h/mL, p = 0.014, n = 18], not among non-expressors [215 (197-290) vs. 217 (129-281) ng·h/mL, p = 0.263, n = 8]. In contrast, among CYP3A5 expressors receiving diltiazem, AUCss, 0-24 did not change significantly upon conversion [229 (170-296) vs. 221 (123-342) ng·h/mL, p = 0.575, n = 10]. An independent effect was not evident for MDR1 C3435T polymorphism. The high prevalence of CYP3A5 polymorphism among Asians may lead to a significant reduction in tacrolimus exposure with 1:1 dose conversion of Prograf® to Advagraf®. These results advocate for CYP3A5 determination prior to conversion, and suggest that 1:1.25 conversion should be used for CYP3A5 expressors and 1:1 conversion for other patients.

Pharmacokinetics of 2,000 Milligram Ertapenem in Tuberculosis Patients.

Ertapenem is a carbapenem antibiotic with activity against Mycobacterium tuberculosis Dose simulations in a hollow-fiber infection model showed that 2,000 mg once daily is an appropriate dose to be tested in clinical studies. Before using this dose in a phase II study, the aim of this prospective pharmacokinetic study was to confirm the pharmacokinetics of 2,000 mg once daily in tuberculosis (TB) patients. Twelve TB patients received a single intravenous dose of 2,000 mg ertapenem as a 30-min infusion. Blood samples were collected at 0, 0.5, 1, 2, 3, 4, 8, 12, and 24 h postadministration. Drug concentrations were measured using a validated liquid chromatography-tandem mass spectrometry assay. A large interindividual variation in the pharmacokinetics of ertapenem was observed. The median (interquartile range) area under the plasma concentration-time curve to infinity (AUC0-∞) was 2,032 (1,751 to 2,346) mg · h/liter, the intercompartmental clearance (CL12) was 1.941 (0.979 to 2.817) liters/h, and the volume of distribution in the central compartment (V1) was 1.514 (1.064 to 2.210) liters. A more than dose-proportional increase in AUC was observed compared to results reported for 1,000 mg ertapenem in multidrug-resistant TB patients. Based on a MIC of 1.0 mg/liter, 11 out of 12 patients would have reached the target value of unbound drug exceeding the MIC over 40% of the time (f40% T>MIC). In conclusion, this study shows that 2,000 mg ertapenem once daily in TB patients reached the expected f40% T>MIC for most of the patients, and exploration in a phase 2 study can be advocated.