Area under the concentration–time curve to minimum inhibitory concentration ratio as a predictor of vancomycin treatment outcome in methicillin-resistant Staphylococcus aureus bacteraemia

There have been few clinical studies on the association between the 24-h area under the concentration–time curve (AUC₂₄) to minimum inhibitory concentration (MIC) ratio and vancomycin treatment outcomes in methicillin-resistant Staphylococcus aureus (MRSA) infections. Patients with MRSA bacteraemia between July 2009 and January 2012 were analysed retrospectively. All adult patients treated with vancomycin for ≥72 h without dialysis were included. The MIC was determined by Etest and broth microdilution (BMD). Initial steady-state AUC₂₄ was estimated using a Bayesian model, and the AUC₂₄/MIC cut-off value for differentiating treatment success and failure was calculated by classification and regression tree (CART) analysis. In total, 76 patients were enrolled; vancomycin treatment failure occurred in 20 patients (26.3%). Catheter-related infection was the most frequent (35.5%), followed by surgical site infection (26.3%), whilst 25 (32.9%) had complicated infections. In univariate analysis, decreased MRSA vancomycin susceptibility (MIC ≥ 1.5 mg/L) and vancomycin trough levels (15–20 mg/L) were not associated with treatment outcomes. In the CART analysis, low initial vancomycin AUC₂₄/MIC (<430 by Etest; <398.5 by BMD) was associated with a higher treatment failure rate (50.0% vs. 25.0%, P = 0.039 by Etest; 45.0% vs. 23.2%; P = 0.065 by BMD). In multivariate analysis, low initial vancomycin AUC₂₄/MIC was a significant risk factor for treatment failure [adjusted odds ratio (aOR) = 4.39, 95% confidence interval (CI), 1.26–15.35 by Etest; aOR = 3.73, 95% CI 1.10–12.61 by BMD]. In MRSA bacteraemia, a low initial vancomycin AUC₂₄/MIC is an independent risk factor for vancomycin treatment failure.     

Determination of vancomycin exposure target and individualised dosing recommendations for neonates: model-informed precision dosing

IntroductionFew studies incorporating population pharmacokinetic/pharmacodynamic (Pop-PK/PD) modelling have been conducted to quantify the exposure target of vancomycin in neonates. A retrospective observational cohort study was undertaken in neonates to determine this target and dosing recommendations (chictr.org.cn, ChiCTR1900027919).MethodsA Pop-PK model was developed to estimate PK parameters. Causalities between acute kidney injury (AKI) occurrence and vancomycin use were verified using Naranjo criteria. Thresholds of vancomycin exposure in predicting AKI or efficacy were identified via classification and regression tree analysis. Associations between exposure thresholds and clinical outcomes, including AKI and efficacy, were analysed by logistic regression. Dosing recommendations were designed using Monte Carlo simulations based on the optimised exposure target.ResultsPop-PK modelling included 182 neonates with 411 observations. On covariate analysis, neonatal physiological maturation, renal function and concomitant use of vasoactive agents (VAS) significantly affected vancomycin PK. Seven cases of vancomycin-induced AKI were detected. Area under the concentration-time curve from 0–24 hours (AUC_0–24) ≥ 485 mg?h/L was an independent risk factor for AKI after adjusting for VAS co-administration. The clinical efficacy of vancomycin was analysed in 42 patients with blood culture-proven staphylococcal sepsis. AUC_0–24 to minimum inhibitory concentration (AUC_0–24/MIC) ≥ 234 was the only significant predictor of clinical effectiveness. Monte Carlo simulations indicated that regimens in Neonatal Formulary 7 and Red Book (2018) were unsuitable for all neonates.ConclusionAn AUC_0–24 of 240–480 (assuming MIC = 1 mg/L) is a recommended exposure target of vancomycin in neonates. Model-informed dosing regimens are valuable in clinical practice.     

A 10‐Year Experience of Therapeutic Drug Monitoring (TDM) of Linezolid in a Hospital‐wide Population of Patients Receiving Conventional Dosing: Is there Enough Evidence for Suggesting TDM in the Majority of Patients?

A retrospective study was conducted to assess our 10‐year experience of therapeutic drug monitoring (TDM) of linezolid in a large patient population to establish whether conventional dosing may result in adequate drug exposure in the majority of patients. Patients included in this study underwent TDM of linezolid trough concentration (C_min) during treatment with conventional doses of 600 mg every 12 hr in the period between January 2007 and June 2016. The desired range of C_min was set between 2 and 7 mg/L (underexposure, C_min < 2 mg/L; overexposure, C_min > 7 mg/L). Multivariate logistic regression analysis investigated variables potentially correlated with linezolid C_min. One thousand and forty‐nine patients had 2484 linezolid C_min assessed during treatment with conventional doses. Median (IQR) linezolid C_min was 5.08 mg/L (2.78–8.52 mg/L). Linezolid C_min was within the desired range in 50.8% of cases (1262/2484). Overexposure (n = 821; 33%) occurred much more frequently than underexposure (n = 401; 16.2%) and was severe (>20 mg/L) in 3.9% of cases (98/2484). Linezolid overexposure was significantly associated with CrCL_C‐G estimates ≤40 mL/min. (OR 1.463; 95% CI 1.124–1.904, p = 0.005). Linezolid underexposure was significantly associated with CrCL_C‐G estimates >100 mL/min. (OR 3.046; 95% CI 2.234–4.152, p < 0.001). Linezolid C_min was not correlated linearly with CrCL_C‐G (R² = 0.061). Variability in renal function explained only partially the very wide interindividual linezolid C_min variability. Our study suggests that TDM could represent a valuable approach in optimizing linezolid exposure in the majority of patients.     

The dosing and monitoring of vancomycin: what is the best way forward?

We have evaluated the literature to review optimal dosing and monitoring of intravenous vancomycin in adults, in response to evolving understanding of targets associated with efficacy and toxicity. The area under the total concentration–time curve (0–24 h) divided by the minimum inhibitory concentration (AUC₂₄/MIC) is the most commonly accepted index to guide vancomycin dosing for the treatment of Staphylococcus aureus infections, with a value of 400 h a widely recommended target for efficacy. Upper limits of AUC₂₄ exposure of around 700 (mg/L).h have been proposed, based on the hypothesis that higher exposures of vancomycin are associated with an unacceptable risk of nephrotoxicity. If AUC₂₄/MIC targets are used, sources of variability in the assessment of both AUC₂₄ and MIC need to be considered. Current consensus guidelines recommend measuring trough vancomycin concentrations during intermittent dosing as a surrogate for the AUC₂₄. Trough concentrations are a misleading surrogate for AUC₂₄ and a poor end-point in themselves. AUC₂₄ estimation using log-linear pharmacokinetic methods based on two plasma concentrations, or Bayesian methods are superior. Alternatively, a single concentration measured during continuous infusion allows simple AUC₂₄ estimation and dose-adjustment. All of these methods have logistical challenges which must be overcome if they are to be adopted successfully.     

Bactericidal activity of daptomycin versus vancomycin in the presence of human albumin against vancomycin-susceptible but tolerant methicillin-resistant Staphylococcus aureus (MRSA) with daptomycin minimum inhibitory concentrations of 1–2 μg/mL

This study explored the influence of vancomycin tolerance and protein binding on the bactericidal activity of vancomycin versus daptomycin (protein binding 36.9% vs. 91.7%, respectively) against four vancomycin-tolerant methicillin-resistant Staphylococcus aureus (MRSA) [minimum inhibitory concentration/minimum bactericidal concentration (MIC/MBC) = 0.5/16, 1/32, 2/32 and 1/32 μg/mL for vancomycin and 1/1, 1/2, 2/2 and 2/4 μg/mL for daptomycin]. Killing curves were performed with vancomycin/daptomycin concentrations equal to serum peak concentrations (C_max) (65.70/98.60 μg/mL) and trough concentrations (C_min) (7.90/9.13 μg/mL) in the presence and absence of a physiological human albumin concentration (4 g/dL), controlled with curves with the theoretical free drug fraction of vancomycin/daptomycin C_max (41.45/8.18 μg/mL) and C_min (4.98/0.76 μg/mL). Vancomycin C_max and C_min concentrations, regardless of the media, showed a bacteriostatic profile not reaching a reduction of 99% or 99.9% of the initial inocula during the 24-h experimental time period. Daptomycin antibacterial profiles significantly differed when testing C_max and C_min. C_max was rapidly bactericidal (≤4 h) with >5 log₁₀ reduction in the initial inocula for all strains, regardless of the presence or not of albumin or the use of concentrations similar to free C_max. C_min exhibited similar final colony counts at 0 h and 24 h in curves with albumin, but with >3 log colony-forming units (CFU)/mL reduction at ≤4 h for strains with an MIC of 1 μg/mL and ca. 2 log CFU/mL reduction at ≤6 h for strains with an MIC of 2 μg/mL. This activity was significantly higher than the activity of the free C_min fraction. The results of this study reinforce the idea that pharmacodynamics using concentrations calculated using reported protein binding are unreliable. Daptomycin exhibited rapid antibacterial activity against vancomycin-tolerant MRSA isolates even against those with high daptomycin MICs in the presence of physiological albumin concentrations.     

Optimal teicoplanin loading regimen to rapidly achieve target trough plasma concentration in critically ill patients

Teicoplanin is used for the treatment of Methicillin‐resistant Staphylococcus aureus infection. It has been demonstrated that conventional loading regimen was insufficient for teicoplanin to achieve target trough plasma concentration (C_min > 10 mg/L). Therefore, a Chinese expert group recommended an optimal loading dose regimen of teicoplanin to treat severe Gram‐positive infection. However, there was no report about the teicoplanin concentration, and the safety and efficacy of teicoplanin therapy in Chinese patients since the consensus was published. The objective of this study was to compare the teicoplanin C_min and clinical response in critically ill Chinese patients after the administration of conventional or optimal loading regimen, and to reveal the potential factors that may affect teicoplanin C_min in addition to loading regimen. Fifty‐five patients were retrospectively divided into two groups based on teicoplanin loading regimen: (a) CD group (conventional loading dose group, n = 18, loading dose was 400 mg); (b) OD group (optimal loading dose group, n = 37, loading dose was 800 mg). Initially, three loading doses were administered every 12 hours, while the fourth loading dose was injected 24 hours after the third dose. The maintenance dose was 400 mg (CD group) or 800 mg (OD group), respectively. The mean teicoplanin C_min on day 2 and day 4 in the OD group was significantly higher than those in the CD group, which were 14.75 ± 5.93 mg/L vs 8.26 ± 4.87 mg/L (P < .001) and 14.90 ± 5.20 mg/L vs 9.13 ± 4.75 mg/L (P = .019), respectively. The percentages of patients in the OD group achieving the target teicoplanin C_min on day 2 and day 4 were also significantly higher than those in the CD group, which were 83.7% vs 33.3% (P < .001) and 82.4% vs 28.6% (P = .0013), respectively. Furthermore, multivariate linear regression analysis showed that body‐weight exerted significant effect on teicoplanin C_min in the OD group. The percentage of favourable clinical response in the OD group was significantly higher than that in the CD group (83.8% vs 55.6%, P = .025). There was no difference between teicoplanin adverse effects in the two groups. The study demonstrated that the optimal loading dose regimen of teicoplanin can rapidly reach target C_min, and result in a good clinical efficacy and low adverse effect in critically ill Chinese patients.     

Pharmacokinetics of extended-release and immediate-release formulations of galantamine at steady state in healthy volunteers

ABSTRACT

Objective: To assess the steady-state galantamine (GAL) bioavailability of the extended-release 24‐mg qd capsule (GAL‐ER) with and without food and to evaluate the relative bioavailability of GAL‐ER with the immediate-release 12‐mg bid tablet (GAL‐IR) at steady state.

Methods: This was a single-center, open-label, randomized, 3-way crossover study in 24 healthy volunteers (12 males and 12 females) aged 18 to 45 years. After 7 days of GAL‐ER 8?mg qd each morning and 7 days of GAL‐ER 16?mg qd each morning, subjects received the following treatments in randomized, crossover order (7 days each): GAL‐ER 24?mg qd each morning (fasted before Day 7 morning dose), GAL‐ER 24?mg qd each morning (fed before Day 7 morning dose), and GAL‐IR 12?mg bid (fasted before Day 7). Pharmacokinetic parameters of GAL at steady state were determined after morning intake on Day 7 of each treatment week. Safety evaluations included adverse event (AE) reporting, physical examination, clinical laboratory tests, vital signs, and electrocardiography.

Results: The treatment ratios of area under the plasma concentration-time curve of GAL from time 0–24?h post-dosing (AUC_{24 h}), peak plasma concentration (C_max), and pre-dose plasma concentration (C_min) for GAL‐ER fed/fasting were 105%, 112%, and 103%, respectively. The treatment ratios and 90% confidence intervals for all above mentioned pharmacokinetic parameters demonstrated bioequivalence (with the range of 80-125%), indicating that food had no effect on GAL‐ER bioavailability. As anticipated, GAL‐ER (fasting) had mean AUC_{24 h} similar to GAL‐IR (fasting), with lower C_max (63 ng/mL vs 84 ng/mL) and longer time to reach C_max (4.4?h vs 1.2?h). The treatment ratios and 90% confidence intervals for both AUC_{24 h} and C_min demonstrated bioequivalence (within the range of 80-125%). The treatment ratio for C_max was 75.7%, indicating a 24% lower C_max for GAL‐ER than for GAL‐IR. In this study, GAL‐ER was safe and well tolerated with or without food and was comparable to the GAL‐IR formulation.

Conclusion: Food had no effect on the GAL bioavailability of GAL‐ER at steady state. GAL‐ER was bioequivalent to GAL‐IR with respect to AUC_{24 h} and C_min.     

Evaluation of super-boosted lopinavir/ritonavir in combination with rifampicin in HIV-1-infected patients with tuberculosis

Rifampicin induces the metabolism of many drugs. To overcome the reduction in serum concentrations of lopinavir/ritonavir (LPV/r) when used in combination with rifampicin, 800/200 mg or 400/400 mg doses are used. This study evaluated super-boosted LPV/r (400/400 mg) in HIV/TB co-infected patients for adequate concentrations as well as short-term safety, tolerability and clinical response to therapy. This was an open-label, non-randomised pharmacokinetic (PK) study in HIV/TB patients. The primary objective was to determine the PK profile of super-boosted LPV/r when given with a rifampicin-based TB regimen. Secondary objectives were short-term safety, tolerability and clinical response. Primary endpoints were a lopinavir trough concentration (C_min) >1.0 µg/mL and a rifampicin maximum concentration (C_max) of 8–24 µg/mL. Secondary PK endpoints were a rifampicin area under the concentration–time curve from 0–24 h (AUC_0–24) of 44–70 µg·h/mL, a lopinavir C_max of 6–14 µg/mL and a lopinavir AUC_0–12 of 56–130 µg·h/mL. Eleven patients (10 male, age 25–43 years) were enrolled. Two patients were discontinued due to non-compliance. A lopinavir C_min of >1.0 µg/mL was achieved in a least one of the PK samplings in all nine subjects who completed treatment. All patients met lopinavir C_max and AUC_0–12 targets. Five patients achieved the primary endpoint of rifampicin C_max (≥8 µg/mL) in at least one of the PK samplings, and five achieved the minimum rifampicin AUC_0–24 (≥44 µg·h/mL). One grade 3 adverse event was reported. Super-boosted LPV/r was safe and effective in HIV/TB patients. [ClinicalTrials.gov ID NCT01700790.]     

The association between trough blood concentration and systemic exposure of tacrolimus: Comparison between once-daily (Advagraf®) and twice-daily (Prograf®) formulation in de novo kidney transplant recipients

Available data of early conversion from twice-daily tacrolimus (TAC-BID) to once-daily tacrolimus (TAC-OD) in de novo kidney transplant (KT) recipients are limited. We conducted a prospective study of early conversion to TAC-OD in de novo KT recipients. Eligible patients were enrolled to receive TAC-BID (Prograf®) and then converted to TAC-OD (Advagraf®) by 1:1 ratio, approximately 14 days after KT (range 9–22). Blood samples were investigated for pharmacokinetic parameters before and 7–14 days after the conversion. Fifteen patients were included and provided AUC_0-24 of 202.9 ± 44.4 ng h/mL for TAC-BID (pre-conversion) and 193.0 ± 63.4 ng h/mL for TAC-OD (post-conversion) (p = 0.41). Mean trough blood concentration (C_min) of TAC-BID and TAC-OD was 6.4 ± 1.4 ng/mL and 4.9 ± 1.6 ng/mL (p = 0.01). Correlation coefficient (r) between C_min and AUC_0-24 of TAC-BID and TAC-OD were 0.620 and 0.875. Additional analysis found that patients with a drop of C_min > 30% had a significant lower AUC_0-24 after conversion. Renal function remains stable. We conclude that early conversion to TAC-OD is safe and well tolerated with an indifferent systemic exposure. However, patients with a drop of C_min > 30% after conversion to TAC-OD will require additional dose adjustment.     

Pharmacokinetics and safety of single and multiple doses of rasagiline in healthy Japanese and caucasian subjects

As of March 2018, rasagiline is approved for the treatment of Parkinson disease in 55 countries including Japan. The present study evaluated the pharmacokinetics (PK) and safety of rasagiline in healthy Japanese and Caucasian subjects following single and multiple administrations of three rasagiline doses. In this double‐blind, placebo‐controlled study, 64 healthy subjects (32 Japanese and 32 Caucasian) received either rasagiline (0.5, 1.0, or 2.0 mg) or placebo for 10 days with PK sampling for single‐dose administration on day 1 and for multiple administration on day 10. Regardless of administration schedule, rasagiline plasma concentrations and dose‐related increases in exposure parameters were similar between Japanese and Caucasians. Rasagiline accumulation (2‐fold for 0.5 mg and 3‐fold for 1.0 mg and 2.0 mg doses) following multiple administration was similar across the ethnic groups. Geometric mean ratios (GMR) comparing Japanese to Caucasians for AUC_0‐24, C_max and AUC_inf following single administration were 1.38, 1.17 and 1.38 for 0.5 mg; 1.22, 1.20 and 1.22 at 1.0 mg; and 1.02, 1.00 and 1.02 at for 2.0 mg. GMR for AUC_tau and C_max,ss following multiple administration were 1.43 and 1.06 at 0.5 mg, 1.06 and 1.00 at 1.0 mg, and 1.09 and 1.07 at 2.0 mg. Safety measures were unremarkable and similar between Caucasian and Japanese subjects. Comparable systemic exposure and safety parameters were demonstrated for rasagiline administered to healthy Japanese and Caucasian subjects.     

Efavirenz does not meaningfully affect the single dose pharmacokinetics of 1200 mg raltegravir

Raltegravir is a human immunodeficiency virus (HIV)‐1 integrase strand transfer inhibitor currently marketed at a dose of 400 mg twice daily (BID). Raltegravir for once daily regimen (QD) at a dose of 1200 mg (2 x 600 mg) is under development and offers a new treatment option for HIV‐1 infected treatment‐naive subjects. Since raltegravir is eliminated mainly by metabolism via an UDP‐glucuronosyltransferase (UGT) 1 A1‐mediated glucuronidation pathway, co‐administration of UGT1A1 inducers may alter plasma levels of raltegravir. Efavirenz, an UGT1A1 inducer, was used to assess the impact of altered UGT activity on a 1200 mg QD dose of raltegravir. An open label, randomized, 2‐period fixed‐sequence Phase 1 study was performed in adult healthy male and female subjects (non‐childbearing potential) ≥ 19 and ≤55 years of age, with a body mass index (BMI) ≥ 18.5 and ≤32.0 kg/m². Subjects (n = 21) received a single oral dose of 1200 mg raltegravir at bedtime on an empty stomach on Day 1 in Period 1. After a washout period of at least 7 days, subjects received oral doses of 600 mg efavirenz QD at bedtime for 14 consecutive days in Period 2. Subjects received a single oral dose of 1200 mg raltegravir co‐administered with 600 mg efavirenz on Day 12 of Period 2. Pharmacokinetic (PK) samples were collected for 72 hours following raltegravir dosing and analyzed using a validated bioanalytical method to quantify raltegravir plasma concentrations. PK parameters were estimated using non‐compartmental analysis. Administration of single 1200 mg oral doses of raltegravir alone and co‐administered with multiple oral doses of efavirenz were generally well tolerated in healthy subjects. Co‐administration with efavirenz yielded geometric mean ratios (GMRs) and their associated 90% confidence intervals (90% CIs) for raltegravir AUC_0‐∞, C_max, and C₂₄ of 0.86 (0.73, 1.01), 0.91 (0.70, 1.17), and 0.94 (0.76, 1.17), respectively. The results show that efavirenz modestly reduced the exposure of raltegravir. The reduction in raltegravir exposure is not considered clinically meaningful. Copyright © 2016 John Wiley & Sons, Ltd.     

Randomized,controlled study of bleselumab (ASKP1240) pharmacokinetics and safety in patients with moderate‐to‐severe plaque psoriasis

This study evaluated the pharmacokinetics (PK), efficacy, safety, and tolerability of bleselumab – a fully‐human anti‐CD40 monoclonal recombinant IgG4. Patients with moderate‐to‐severe psoriasis were randomized on day 1 to receive bleselumab or placebo on days 1, 15 and 29 in a dose‐escalation of bleselumab at 0.1, 0.3, 1.0 or 3.0 mg/kg. The safety‐analysis set (SAF) and full‐analysis set (FAS) included all patients who received bleselumab or placebo, and the PK‐analysis set (PKAS) included patients in the SAF with ≥1 quantifiable serum bleselumab concentration. Serial blood samples were collected after each dose, and the bleselumab serum concentration was measured. After each dose, the area‐under‐the‐concentration–time curve over 336 hours (AUC₃₃₆) and the maximum serum concentration (C_max), and dose proportionality of AUC₃₃₆ and C_max were determined. The psoriasis area and severity index (PASI) score, the physician static global assessment (PSGA) score, the percentage body surface area (%BSA) affected with psoriasis, adverse events and laboratory parameters were assessed. Sixty patients were randomized and included in the SAF/FAS (bleselumab, n = 49; placebo, n = 11); 48 formed the PKAS. Bleselumab C_max and AUC₃₃₆ were more than dose proportional in the range 0.1–3.0 mg/kg, suggesting nonlinear PK after single/multiple doses. No clinically significant infusion reactions, cytokine‐release syndrome, or thromboembolic events were reported. Bleselumab did not improve the PASI scores, PSGA scores, or %BSA versus placebo. Transient elevation of alanine aminotransferase and aspartate aminotransferase levels by >3 × upper limit of normal were observed in four (8.2%) and two (4.1%) patients, respectively, in the 1.0 or 3.0 mg/kg groups. Patients with liver function test increases had no concurrent changes in bilirubin. Bleselumab demonstrated nonlinear PK after single and multiple doses, with few adverse reactions.     

Atazanavir increases the plasma concentrations of 1200 mg raltegravir dose

Raltegravir is a human immunodeficiency virus (HIV)‐1 integrase strand transfer inhibitor currently marketed at a dose of 400 mg twice‐daily (b.i.d.). Raltegravir 1200 mg once‐daily (q.d.) (investigational q.d. formulation of 2 × 600 mg tablets; q.d. RAL) was found to be generally well tolerated and non‐inferior to the marketed 400 mg b.i.d. dose at 48 weeks in a phase 3 trial. Since raltegravir is eliminated mainly by metabolism via a uridine diphosphate glucuronosyltransferase (UGT) 1A1‐mediated glucuronidation pathway, co‐administration of UGT1A1 inhibitors may increase the plasma levels of q.d. RAL. To assess this potential, the drug interaction of 1200 mg raltegravir using atazanavir, a known UGT1A1 inhibitor, was studied. An open‐label, randomized, 2‐period, fixed‐sequence phase 1 study was performed in adult healthy male and female (non‐childbearing potential) subjects ≥ 19 and ≤ 55 years of age, with a body mass index (BMI) ≥ 18.5 and ≤ 32.0 kg/m². Subjects (n = 14) received a single oral dose of 1200 mg raltegravir in period 1. After a washout period of at least 7 days, the subjects received oral doses of 400 mg atazanavir q.d. for 9 consecutive days, with a single oral dose of 1200 mg raltegravir co‐administered on day 7 of period 2. Serial blood samples were collected for 72 h following raltegravir dosing and analysed using a validated bioanalytical method to quantify raltegravir plasma concentrations. Co‐administration with atazanavir yielded GMRs (90% CIs) for raltegravir AUC_0‐∞, C_max and C₂₄ of 1.67 (1.34, 2.10), 1.16 (1.01, 1.33) and 1.26 (1.08, 1.46), respectively. There was no effect of raltegravir on serum total bilirubin. In contrast, atazanavir increased the mean bilirubin by up to 200%, an effect that was preserved in the atazanavir/raltegravir treatment group. Administration of single q.d. RAL alone and co‐administered with multiple oral doses of atazanavir were generally well tolerated in healthy subjects. The results show that atazanavir increased the PK exposure of raltegravir; therefore, co‐administration of atazanavir with raltegravir q.d. is not recommended. Copyright © 2016 John Wiley & Sons, Ltd.     

Pharmacokinetics of caffeine in plasma and saliva, and the influence of caffeine abstinence on CYP1A2 metrics

Objectives To investigate the utility of metrics of CYP1A2 activity using caffeine as a probe, and saliva and plasma sampling with or without a 24‐h caffeine abstinence. Methods This was a cross‐over pharmacokinetic study in 30 healthy male subjects who received a single oral 100 mg caffeine dose after 24‐h caffeine abstinence or after maintaining their regular caffeine intake (no caffeine abstinence). Serial blood and saliva samples were collected simultaneously over 24 h. Caffeine and paraxanthine concentrations were measured using a validated HPLC assay. Key findings There was a strong correlation between the paraxanthine/caffeine AUC_0–24 ratio (reference metric) and the paraxanthine/caffeine concentration (C_t) ratio at 4 h (C₄) in both saliva and plasma (r ≥ 0.75). The paraxanthine/caffeine AUC_0–24 ratio in plasma and saliva did not differ between the 24‐h caffeine abstinence and the no abstinence period (P > 0.05). The optimal paraxanthine/caffeine C_t that correlated with the plasma paraxanthine/caffeine AUC_0–24 ratio in the 24‐h abstinence period was 2 and 4 h (r = 0.88) in plasma, and 4 and 6 h in saliva (r = 0.70), while it was the saliva 4 h time‐point in the no abstinence period (r = 0.78). Conclusions The saliva paraxanthine/caffeine concentration ratio at 4 h was a suitable metric to assess CYP1A2 activity after oral administration of caffeine without the need for 24‐h caffeine abstinence.     

Effect of Truncating AUC at 12, 24 and 48 hr When Evaluating the Bioequivalence of Drugs with a Long Half‐Life

Bioequivalence studies of drugs with a long half‐life require long periods of time for pharmacokinetic sampling. The latest update of the European guideline allows the area under the curve (AUC) truncated at 72 hr to be used as an alternative to AUC_0–t as the primary parameter. The objective of this study was to evaluate the effect of truncating the AUC at 48, 24 and 12 hr on the acceptance of the bioequivalence criterion as compared with truncation at 72 hr in bioequivalence trials. The effect of truncated AUC on the within‐individual coefficient of variation (CV_w) and on the ratio of the formulations was also analysed. Twenty‐eight drugs were selected from bioequivalence trials. Pharmacokinetic data were analysed using WinNonLin 2.0 based on the trapezoidal method. Analysis of variance (anova ) was performed to obtain the ratios and 90% confidence intervals for AUC at different time‐points. The degree of agreement of AUC_0–72 in relation to AUC_0–48 and AUC_0–24, according to the Landis and Koch classification, was ‘almost perfect’. Statistically significant differences were observed when the CV_w of AUC truncated at 72, 48 and 24 hr was compared with the CV_w of AUC_0–12. There were no statistically significant differences in the AUC ratio at any time‐point. Compared to AUC_0–72, Pearson's correlation coefficient for mean AUC, AUC ratio and AUC CV_w was worse for AUC_0–12 than AUC_0–24 or AUC_0–48. These preliminary results could suggest that AUC truncation at 24 or 48 hr is adequate to determine whether two formulations are bioequivalent.     

Safety,Pharmacokinetics and Pharmacodynamics of Hetrombopag Olamine,a Novel TPO‐R Agonist,in Healthy Individuals

Hetrombopag olamine (hetrombopag) is a novel small‐molecule, orally bioavailable, non‐peptide thrombopoietin (TPO) receptor agonist that is being developed as the treatment for thrombocytopenia. Two randomized, placebo‐controlled phase I studies were conducted in 72 healthy individuals to assess the safety, tolerability, pharmacokinetics and pharmacodynamics of hetrombopag. Hetrombopag was orally administered with a single dose in five dose cohorts (5 mg, 10 mg, 20 mg, 30 mg or 40 mg) in the first study, and given once daily for 10 days in three dose cohorts (2.5 mg, 5.0 mg or 7.5 mg) in the second study, respectively. Hetrombopag was well tolerated, and the majority of adverse events associated with medicine were platelet elevations significantly above the normal range in healthy individuals. The single dose‐escalation study revealed a T_max of approximate 8 hr, and a t_1/2 of 11.9 hr to 40.1 hr in a dose‐prolonged manner. A dose‐proportional increase in maximum concentration (C_max) of hetrombopag was observed, with area under the curve (AUC) increasing in a greater than dose‐proportional manner. The plasma concentration of hetrombopag reached the steady‐state after 7 days. The steady‐state AUC_0–24 hr and C_max were dose‐proportionally elevated from the 5.0 mg to 7.5 mg dose level. The potent pharmacological effect of the hetrombopag‐induced platelet elevation was observed in a time‐ and dose‐dependent manner. Furthermore, the thrombopoietic response was significantly (p < 0.0001) correlated to the plasma exposure level of hetrombopag in single and multiple administration studies. Taken together, results of this study support further clinical development of hetrombopag in patients with thrombocytopenia.     

Individualized vancomycin dosing in infants: prospective evaluation of an online dose calculator

BackgroundEmpiric vancomycin dosing regimens fail to achieve recommended target trough concentrations of 10-20 mg/L in the majority of infants. This study assessed the performance of a model-based dosing calculator (Vanc App) in achieving target vancomycin concentrations at first steady-state level.MethodsThis was a multicenter prospective study in four tertiary pediatric hospitals over an 18-month period. Infants aged 0-90 days with suspected Gram-positive sepsis requiring empiric vancomycin treatment were included if they did not meet any of the exclusion criteria: post-menstrual age (PMA) <25 weeks, weight <500 g, glycopeptide allergy, receiving extracorporeal membrane oxygenation, vancomycin use within the previous 72 h, and renal impairment. The Vanc App used a published population pharmacokinetic model to generate a dose based on the infant's PMA, weight, creatinine, and target vancomycin concentration.ResultsA total of 40 infants were included; 40% were female, median (range) weight was 2505 (700-4460) g and median (range) PMA was 37.4 (25.7-49.0) weeks. The median (range) vancomycin dose was 45 (24-79) mg/kg/day. All infants had trough vancomycin concentrations measured at steady-state (24-<48 hours) and 30 (75%) infants achieved target concentrations. Five infants had supratherapeutic (median 25, range 21-38 mg/L) and five had subtherapeutic (median 6, range <5-9 mg/L) concentrations. An area under the concentration-time curve (AUC_0-24) of 400-650 mg/L.h was achieved in 33 (83%) infants. There were no infusion-related reactions or nephrotoxicity.ConclusionIndividualized intermittent vancomycin dosing using a model-based online calculator resulted in 75% and 83% of infants achieving target trough and AUC_0-24, respectively, at first steady-state level. There were no vancomycin-related nephrotoxicity or infusion-related reactions.     

Comparable Lumefantrine Oral Bioavailability when Co‐administered With Oil‐Fortified Maize Porridge or Milk in Healthy Volunteers

Co‐administration of artemether–lumefantrine with milk is recommended to improve lumefantrine (L) absorption but milk may not be available in resource‐limited settings. This study explored the effects of cheap local food in Uganda on oral bioavailability of lumefantrine relative to milk. In an open‐label, four‐period crossover study, 13 healthy adult volunteers were randomized to receive a single oral dose of artemether–lumefantrine (80 mg artemether/480 mg lumefantrine) with water, milk, maize porridge or maize porridge with oil on separate occasions. Plasma lumefantrine was assayed using high‐performance liquid chromatography with ultraviolet detection. Pharmacokinetic exposure parameters were determined by non‐compartmental methods using WinNonlin. Peak concentrations (C_max) and area under concentration–time curve restricted to 48 hr after single dosing (AUC_(0–48)) were selected for relative bioavailability evaluations using confidence interval approach for average bioequivalence. Lumefantrine exposure was comparable in milk and maize porridge plus oil study groups. When artemether–lumefantrine was administered with maize porridge plus oil, average bioequivalence ranges (means ratios 90% CI, 0.84–1.88 and 0.85–1.69 for C_max and AUC_(0–48), respectively) were within and exceeded acceptance ranges relative to milk (90% CI, 0.80–1.25). Both fasted and maize porridge groups demonstrated similarly much lower ranges of lumefantrine exposures (bioinequivalence) relative to milk. If milk is not available, it is thus possible to recommend fortification of carbohydrate‐rich food with little fat (maize porridge plus vegetable oil) to achieve similarly optimal absorption of lumefantrine after artemether–lumefantrine administration.     

In-vitro pharmacokinetic/pharmacodynamic model data suggest a potential role of new formulations of posaconazole against Candida krusei but not Candida glabrata infections

Posaconazole exhibits in-vitro activity against Candida glabrata and Candida krusei. Epidemiological cut-off values set by the European Committee on Antimicrobial Susceptibility Testing (EUCAST) and the Clinical and Laboratory Standards Institute (CLSI) are 1/1 and 0.5/0.5 mg/L, respectively, but clinical breakpoints have not been established to date. This study explored the pharmacodynamics (PD) of posaconazole in a validated one-compartment in-vitro pharmacokinetic (PK)/PD model, and determined the probability of PK/PD target attainment (PTA) for the available formulations. Five C. glabrata and three C. krusei isolates with posaconazole minimum inhibitory concentrations (MICs) of 0.06–2 and 0.03–0.25 mg/L, respectively, were tested in the PK/PD model simulating different time–concentration profiles of posaconazole. The exposure–effect relationship fAUC_0–24/MIC was described for EUCAST/CLSI methods, and PTA was calculated in order to determine PK/PD susceptibility breakpoints for oral solution (400 mg q12h), and intravenous (i.v.)/tablet formulations (300 mg q24h). Fungicidal activity (~2log kill) was found against the most susceptible C. glabrata isolate alone, and against all three C. krusei isolates. The corresponding EUCAST/CLSI PK/PD targets (fAUC_0–24/MIC) were 102/79 for C. glabrata and 12/8 for C. krusei. Mean PTA was high (>95%) for C. glabrata isolates with EUCAST/CLSI MICs ≤0.03/≤0.03 mg/L for oral solution and ≤0.125/≤0.125 mg/L for i.v. and tablet formulations for the wild-type population. For C. krusei isolates, mean PTA was high (>95%) for EUCAST/CLSI MICs ≤0.25/≤0.5 mg/L for oral solution and ≤1/≤2 mg/L for i.v. and tablet formulations for the wild-type population. The use of posaconazole to treat C. glabrata infections is questionable. Intravenous and tablet formulations may be therapeutic options for the treatment of C. krusei infections, and oral exposure can be optimized with therapeutic drug monitoring (trough levels >0.6–0.9 mg/L).