Prednisolone pharmacokinetics after oral prednisone administration in paediatric patients with kidney transplant.

AIMS: Glucocorticoids are 1 of the primary treatments in paediatric kidney transplantation. The aims of this study were: (i) to build a population pharmacokinetics (PPK) model of free prednisolone, which is the active form of prednisone, in paediatric kidney transplant recipients; (ii) to identify covariates accounting for interindividual variability (IIV) of pharmacokinetics (PK) parameters; and (iii) to investigate drug exposure-safety relationships. METHODS: Ninety-seven samples were obtained from 39 paediatric kidney transplant recipients (aged 3.4-17.2 years) in order to investigate prednisone PPK. We selected children receiving oral prednisone as part of their immunosuppressive regimen. A PPK analysis was performed using Monolix. RESULTS: A 1-compartment model best described prednisolone concentrations. Large IIV was observed as prednisolone was undetectable at H12 in some patients but could still be detected at H24 in others. Both bodyweight and ciclosporin cotreatment influenced the PK. The clearance (CLU ) and volume of distribution of free prednisolone allometrically scaled to 70 kg were 27.6 L/h and 101 L. Ciclosporin cotreatment decreased CLU by 67%. High blood pressure and new onset diabetes after transplantation were associated with daily free prednisolone exposure. CONCLUSION: This study is the first analysis of prednisolone PPK in kidney-transplanted children. Some of the IIV in the PK parameters was explained by bodyweight and ciclosporin cotreatment. These data suggest that dose adjustment is required after identifying variability factors to optimize efficacy and limit side effects. The use of therapeutic drug monitoring in kidney-transplanted children may be useful, especially with respect to safety issues.

Effect of Pregnancy on Unbound Raltegravir Concentrations in the ANRS 160 RalFe Trial.

A population pharmacokinetic model was developed to explore the pharmacokinetics modification of unbound raltegravir during pregnancy. The RalFe ANRS160 study was a nonrandomized, open-label, multicenter trial enrolling HIV-infected pregnant women receiving a combined antiretroviral regimen containing 400 mg raltegravir twice daily. Biological samples were collected during the third trimester of pregnancy (between 30 and 37 weeks of gestational age) and at postpartum (4 to 6 weeks after delivery). A population pharmacokinetic model was developed with Monolix software. A total of 360 plasma samples were collected from 43 women during pregnancy and postpartum. The unbound raltegravir was described by a one-compartment model with a transit compartment with first-order absorption, evolving to bound raltegravir (by a linear binding to albumin) or metabolism to RAL-glucuronide or to a first-order elimination, with a circadian rhythm. During pregnancy, the absorption was decreased and delayed and the raltegravir elimination clearance and glucuronidation increased by 37%. Median total and unbound area under the curve from 0 to 12 h significantly decreased by 36% and 27% during pregnancy. Median total trough concentration (Ctrough) decreased significantly in the evening (28%); however, the median total Ctrough in the morning, unbound Ctrough in the morning, and unbound Ctrough in the evening showed a nonsignificant decrease of 16%, 1%, and 15%, respectively, during pregnancy compared to the postpartum period. This is the first study reporting the pharmacokinetics of unbound raltegravir during pregnancy. As unbound Ctrough did not significantly decrease during the third trimester, the pregnancy effect on raltegravir unbound concentrations was not considered clinically relevant. (This study has been registered at ClinicalTrials.gov under identifier NCT02099474.).

Simultaneous quantification of levofloxacin, pefloxacin, ciprofloxacin and moxifloxacin in microvolumes of human plasma using high-performance liquid chromatography with ultraviolet detection.

Levofloxacin, pefloxacin, ciprofloxacin and moxifloxacin are four fluoroquinolones used in the treatment of serious bacterial infections. The antibacterial activity of fluoroquinolones is concentration dependent. Therefore, therapeutic drug monitoring in daily clinical practice is warranted to ensure the therapy's efficacy and prevent bacterial resistance. The purpose of the present study was to develop a method using high-pressure liquid chromatography with an ultraviolet detector for simultaneous quantification of these four fluoroquinolones in human plasma. A 50 µL aliquot of plasma was precipitated by 200 µL of methanol using gatifloxacin as internal standard. The chromatographic separation was performed on a Kinetex XB-C18 column using a mobile phase composed of a mixture of orthophosphoric acid 0.4% (v/v), acetonitrile and methanol at a flow rate of 1.2 mL/min. Dual UV wavelength mode was used, with levofloxacin and moxifloxacin monitored at 293 nm, and pefloxacin and ciprofloxacin monitored at 280 nm. The calibration was linear over the ranges of 0.125-25 mg/L for levofloxacin, 0.1-20mg/L for moxifloxacin and 0.05-10 mg/L for both pefloxacin and ciprofloxacin. Inter- and intra-day trueness and precision were <13% for all the compounds under study. The proposed method was simple, reliable, cost-effective and suitable for therapeutic drug monitoring or pharmacokinetics studies.

Pharmacokinetics of Efavirenz at a High Dose of 25 Milligrams per Kilogram per Day in Children 2 to 3 Years Old.

The MONOD ANRS 12206 trial was designated to assess simplification of a successful lopinavir (LPV)-based antiretroviral treatment in HIV-infected children younger than 3 years of age using efavirenz (EFV; 25 mg/kg of body weight/day) to preserve the class of protease inhibitors for children in that age group. In this substudy, EFV concentrations were measured to check the consistency of an EFV dose of 25 mg/kg and to compare it with the 2016 FDA recommended dose. Fifty-two children underwent blood sampling for pharmacokinetic study at 6 months and 12 months after switching to EFV. We applied a Bayesian approach to derive EFV pharmacokinetic parameters using the nonlinear mixed-effect modeling (NONMEM) program. The proportion of midinterval concentrations 12 h after drug intake (C12 h) corresponding to the EFV therapeutic pharmacokinetic thresholds (1 to 4 mg/liter) was assessed according to different dose regimens (25 mg/kg in the MONOD study versus the 2016 FDA recommended dose). With both the 25 mg/kg/day dose and the 2016 FDA recommended EFV dose, simulations showed that the majority of C12 h values were within the therapeutic range (62.6% versus 62.8%). However, there were more children underexposed with the 2016 FDA recommended dose (11.6% versus 1.2%). Conversely, there were more concentrations above the threshold of toxicity with the 25 mg/kg dose (36.2% versus 25.6%), with C12 h values of up to 15 mg/liter. Only 1 of 52 children was switched back to LPV because of persistent sleeping disorders, but his C12 h value was within therapeutic ranges. A high EFV dose of 25 mg/kg per day in children under 3 years old achieved satisfactory therapeutic effective levels. However, the 2016 FDA recommended EFV dose appeared to provide more acceptable safe therapeutic profiles. (This study has been registered at ClinicalTrials.gov under identifier NCT01127204.).

Population Pharmacokinetic Modeling of Tenofovir in the Genital Tract of Male HIV-Infected Patients.

The aims of this study were to describe the blood plasma (BP) and seminal plasma (SP) pharmacokinetics of tenofovir (TFV) in HIV-1-infected men, to assess the role of genetic polymorphism in the variability of TFV transfer into the male genital tract, and to evaluate the impact of TFV SP exposure on seminal plasma HIV load (spVL). Men from the Evarist-ANRS EP 49 study treated with TFV as part of their antiretroviral therapy were included in the study. A total of 248 and 217 TFV BP and SP concentrations from 129 men were available for the analysis. For pharmacogenetic assessment, a total of 121 single nucleotide polymorphisms (SNP) were genotyped. Data were analyzed using a nonlinear mixed-effects modeling approach. TFV pharmacokinetics were best described by a two-compartment model for BP and by an effect compartment with different input and output constants for SP. TFV exposures (area under the concentration-time curve from 0 to 24 h [AUC0-24]) were higher in SP than in BP (median AUC0-24, 7.01 versus 2.97 mg · liter-1 · h, respectively). The median (range) SP-to-BP AUC0-24 ratio was 2.24 (0.53 to 34.13). After correction for multiple testing, none of the SNPs were significantly associated with the TFV transfer rate constant. The impact of the TFV SP AUC0-24 or TFV SP-to-BP AUC0-24 ratio on spVL was not significant (P = 0.808 and 0.768, respectively). This is the first population model describing TFV pharmacokinetics in the male genital tract. TFV SP concentrations were higher than BP concentrations. Despite TFV SP exposures being higher than BP exposures, an spVL was detectable for 12.2% of the men.

Suboptimal cotrimoxazole prophylactic concentrations in HIV-infected children according to the WHO guidelines.

AIMS: A clinical study was conduct in HIV-infected children to evaluate the prophylactic doses of cotrimoxazole [sulfamethoxazole (SMX) and trimethoprim (TMP)] advised by the WHO. METHODS: Children received lopinavir-based antiretroviral therapy with cotrimoxazole prophylaxis (200 mg of SMX/40 mg of TMP once daily). A nonlinear mixed effects modelling approach was used to analyse plasma concentrations. Factors that could impact the pharmacokinetic profile were investigated. The model was subsequently used to simulate individual exposure and evaluate different administration schemes. RESULTS: The cohort comprised 136 children [average age: 1.9 years (range: [0.7-4]), average weight: 9.5 kg (range: [6-16.3])]. A dose per kg was justified by the significant influence of implementing an allometrically scaled body size covariate on SMX and TMP pharmacokinetics. SMX and TPM clearance were estimated at 0.49 l h-1 /9.5 kg and 3.06 l h-1 /9.5 kg, respectively. The simulated exposures obtained after administration of oral dosing recommended by the WHO for children from 10 to 15 kg were significantly lower than in adults for SMX and TMP. This could induce a reduction of effectiveness of cotrimoxazole. Simulations show that regimens of 30 mg kg-1 of SMX and 6 mg kg-1 of TMP in the 5-10 kg group and 25 mg kg-1 of SMX and 5 mg kg-1 of TMP in the 10-15 kg group are more suitable doses. CONCLUSIONS: In this context of high prevalence of opportunistic infections, a lower exposure to cotrimoxazole in children than adults was noted. To achieve comparable exposure to adults, a dosing scheme per kg was proposed.

Prediction of human fetal pharmacokinetics using ex vivo human placenta perfusion studies and physiologically based models.

AIMS: Pregnant women can be exposed to numerous drugs during the gestational period. For obvious ethical reasons, in vivo studies of fetal exposure to drugs are limited. Information about the transplacental transfer of drugs prior to their administration to pregnant women would be highly useful. In the present study, a novel approach was developed quantitatively predict or to predict the fetal exposure to drugs administered to the mother quantitatively. METHODS: Transplacental parameters estimated from ex vivo human placenta perfusion experiments were implemented in pregnancy-physiologically based pharmacokinetic (p-PBPK) models in order to predict fetal PK. Thereafter, fetal PK profiles for two antiretroviral drugs, tenofovir (TFV) and emtricitabine (FTC) were simulated. These predictions were then compared to observed cord blood concentrations, to validate these models. RESULTS: Parameters obtained from the ex vivo experiments enabled a good prediction of observed cord blood concentrations without additional a scaling factor. Moreover, a sensitivity analysis showed that fetal predictions were sensitive to changes in transplacental parameters values obtained ex vivo. CONCLUSION: The integration of ex vivo human placental perfusion parameters in a p-PBPK model should be a promising new approach for predicting human fetal exposure to xenobiotics.

Emtricitabine seminal plasma and blood plasma population pharmacokinetics in HIV-infected men in the EVARIST ANRS-EP 49 study.

We aimed to describe blood plasma (BP) and seminal plasma (SP) pharmacokinetics of emtricitabine (FTC) in HIV-1-infected men, assess its penetration in the male genital tract, and evaluate its impact on seminal plasma HIV load (spVL) detection. Men from the EVARIST ANRS EP49 study receiving combined antiretroviral therapy with FTC and with suppressed BP viral load were included in the study. A total of 236 and 209 FTC BP and SP concentrations, respectively, were available. A population pharmacokinetic model was developed with Monolix 4.1.4. The impact of FTC seminal exposure on spVL detection was explored by receiver operating characteristic (ROC) curves and mixed-effects logistic regressions. FTC BP pharmacokinetics was described by a two-compartment model. The addition of an effect compartment with different input and output constants best described FTC SP pharmacokinetics. No covariates were found to explain the variability in SP. FTC exposures (area under the concentration-time curve from 0 to 24 h [AUC0-24]) were higher in SP than in BP (median AUC0-24, 38.04 and 12.95 mg · liter(-1) · h, respectively). The median (range) SP-to-BP AUC0-24 ratio was 2.91 (0.84 to 10.08). Less than 1% of FTC AUC0-24 ratios were lower than 1. The impact of FTC SP AUC0-24 or FTC SP-to-BP AUC0-24 ratio on spVL detection was not significant (P = 0.943 or 0.893, respectively). This is the first population model describing FTC pharmacokinetics simultaneously in both BP and SP. FTC distributes well in the male genital tract with higher FTC concentrations in SP than in BP. FTC seminal plasma exposures were considered efficient in the majority of men.

Population approach to analyze the pharmacokinetics of free and total lopinavir in HIV-infected pregnant women and consequences for dose adjustment.

The aims of this study were to describe the unbound and total lopinavir (LPV) pharmacokinetics in pregnant women in order to evaluate if a dosing adjustment is necessary during pregnancy. Lopinavir placental transfer is described, and several genetic covariates were tested to explain its variability. A total of 400 maternal, 79 cord blood, and 48 amniotic fluid samples were collected from 208 women for LPV concentration determinations and pharmacokinetics analysis. Among the maternal LPV concentrations, 79 samples were also used to measure the unbound LPV concentrations. Population pharmacokinetics models were developed by using NONMEM software. Two models were developed to describe (i) unbound and total LPV pharmacokinetics and (ii) LPV placental transfer. The pharmacokinetics was best described by a one-compartment model with first-order absorption and elimination. A pregnancy effect was found on maternal clearance (39% increase), whereas the treatment group (monotherapy versus triple therapy) or the genetic polymorphisms did not explain the pharmacokinetics or placental transfer of LPV. Efficient unbound LPV concentrations in nonpregnant women were similar to those measured during the third trimester of pregnancy. Our study showed a 39% increase of maternal total LPV clearance during pregnancy, whereas unbound LPV concentrations were similar to those simulated in nonpregnant women. The genetic polymorphisms selected did not influence the LPV pharmacokinetics or placental transfer. Thus, we suggest that the LPV dosage should not be increased during pregnancy.

Vaccine-induced Aß-specific CD8+ T cells do not trigger autoimmune neuroinflammation in a murine model of Alzheimer's disease.

BACKGROUND: Active immunization against Aß was reported to have a therapeutic effect in murine models of Alzheimer's disease. Clinical Aß vaccination trial AN1792 was interrupted due to the development in 6 % of the patients of meningoencephalitis likely involving pro-inflammatory CD4(+) T cells. However, the potential implication of auto-aggressive anti-Aß CD8(+) T cells has been poorly investigated. METHODS: Potential MHC-I-restricted Aß-derived epitopes were first analyzed for their capacity to recruit functional CD8(+) T cell responses in mouse models. Their impact on migration of CD8(+) T cells into the brain parenchyma and potential induction of meningoencephalitis and/or neuronal damage was investigated upon vaccination in the APPPS1 mouse model of AD. RESULTS: We identified one nonamer peptide, Aß33-41, which was naturally processed and presented in association with H-2-D(b) molecule on neurons and CD11b(+) microglia. Upon optimization of anchor residues for enhanced binding to H-2-D(b), immunization with the modified Aß33-41NP peptide elicited Aß-specific IFNγ-secreting CD8(+) T cells, which are cytotoxic towards Aß-expressing targets. Whereas T cell infiltration in the brain of APPPS1 mice is dominated by CD3(+)CD8(-) T cells and increases with disease evolution between 4 and 7 months of age, a predominance of CD3(+)CD8(+) over CD3(+)CD8(-) cells was observed in 6- to 7-month-old APPPS1 but not in WT animals, only after vaccination with Aß33-41NP. The number of CD11b(+) mononuclear phagocytes, which significantly increases with age in the brain of APPPS1 mice, was reduced following immunization with Aß33-41NP. Despite peripheral activation of Aß-specific CD8(+) cytotoxic effectors and enhanced infiltration of CD8(+) T cells in the brain of Aß33-41NP-immunized APPPS1 mice, no clinical signs of severe autoimmune neuroinflammation were observed. CONCLUSIONS: Altogether, these results suggest that Aß-specific CD8(+) T cells are not major contributors to meningoencephalitis in response to Aß vaccination.

A rapid LC-MS/MS method for the simultaneous quantification of ivacaftor, lumacaftor, elexacaftor, tezacaftor, hexyl-methyl ivacaftor and ivacaftor carboxylate in human plasma.

Cystic fibrosis is one of the most common genetic diseases among caucasian population. This disease is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene encoding for the CFTR protein. Lumacaftor, elexacaftor, tezacaftor, and ivacaftor were currently used as the treatment to Cystic fibrosis. In this study, we describe a new method for the simultaneous quantification of four molecules: lumacaftor, elexacaftor, tezacaftor, and ivacaftor, alongside two metabolites of ivacaftor, specifically hexyl-methyl ivacaftor and ivacaftor carboxylate by liquid chromatography-tandem mass spectrometry. This method holds significant utility for therapeutic drug monitoring and the optimization of treatments related to CFTR modulators. Molecules were extracted from 100 µL of plasma by a simple method of protein precipitation using acetonitrile. Following extraction, chromatographic separation was carried out by reverse chromatography on a C18 analytical column, using a gradient elution of water (0.05 % formic acid, V/V) and acetonitrile (0.05 % formic acid, V/V). The run time was 7 minutes at a flow rate of 0.5 mL/min. After separation, molecules were detected by electrospray ionization on a Xevo TQD triple-quadrupole-mass-spectrometer (Waters®, Milford, USA). The calibration range were: 0.053-20.000 mg/L for elexacaftor, tezacaftor and lumacaftor, 0.075-14.000 mg/L for ivacaftor, and 0.024-6.500 mg/L for hexyl-methyl ivacaftor and ivacaftor carboxylate. The proposed method underwent throughout validation demonstrating satisfactory precision (inter- and intra-day coefficients of variation less than 14.3 %) and a good accuracy (inter- and intra-day bias ranging between -13.7 % and 14.7 %) for all the analytes. The presented method for the simultaneous quantification of CFTR modulators and their metabolites in human plasma has undergone rigorous validation process yielding good results including strong precision and accuracy for all analytes. This method has been effectively used in routine analytical analysis and clinical investigations within our laboratory.

Prophylactic Intravenous Acetaminophen in Extremely Premature Infants: Minimum Effective Dose Research by Bayesian Approach.

BACKGROUND: Patent ductus arteriosus (PDA) in preterm infants is associated with increased morbidities and mortality. Prophylactic treatment with cyclooxygenase inhibitors, as indomethacin or ibuprofen, failed to demonstrate significant clinical benefits. Acetaminophen may represent an alternative treatment option. OBJECTIVE: This study evaluated the minimum effective dose of prophylactic acetaminophen to close the ductus and assessed the safety and tolerability profile in extremely preterm infants at 23-26 weeks of gestation. METHODS: A dose finding trial with Bayesian continual reassessment method was performed in a multicenter study with premature infants hospitalized in neonatal intensive care unit. Infants of 23-26 weeks of gestation and post-natal age ≤ 12 h were enrolled. Four intravenous acetaminophen dose levels were predefined. The primary outcome was the ductus arteriosus closing at two consecutive echocardiographies or at day 7. The main secondary objectives included the safety of acetaminophen on hemodynamics and biological hepatic function. RESULTS: A total of 29 patients were analyzed sequentially for the primary analysis with 20 infants assigned to the first dose level followed by 9 infants to the second dose level. No further dose level increase was necessary. The posterior probabilities of success, estimated from the Bayesian logistic model, were 46.1% [95% probability interval (PI), 24.9-63.9] and 67.6% (95% PI, 51.5-77.9) for dose level 1 and 2, respectively. A closing or closed pattern was observed among 19 patients at the end of treatment [65.5% (95% confidence interval (CI), 45.7-82.0)]. No change in alanine aminotransferase values was observed during treatment. A significant decrease in aspartate aminotransferase values was observed with postnatal age. No change in systolic and diastolic blood pressures was observed during treatment. CONCLUSIONS: Minimum effective dose to close the ductus was 25 mg/kg loading dose then 10 mg/kg/6 h for 5 days in extremely preterm infants. Acetaminophen was well tolerated in this study following these doses. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT04459117.

Lumacaftor/Ivacaftor Population Pharmacokinetics in Pediatric Patients with Cystic Fibrosis: A First Step Toward Personalized Therapy.

BACKGROUND: A major breakthrough in cystic fibrosis (CF) therapy was achievedAQ1 with CFTR modulators. The lumacaftor/ivacaftor combination is indicated for the treatment of CF in pediatric patients above 6 years old. Pharmacokinetic (PK) studies of lumacaftor/ivacaftor in these vulnerable pediatric populations are AQ2crucial to optimize treatment protocols. OBJECTIVES AND METHODS: The objectives of this study were to describe the population PK (PPK) of lumacaftor and ivacaftor in children with CF, and to identify factors associated with interindividual variability. The association between drug exposure and clinical response was also investigated. RESULTS: A total of 75 children were included in this PPK study, with 191 concentrations available for each compound and known metabolites (lumacaftor, ivacaftor, ivacaftor-M1, and ivacaftor-M6). PPK analysis was performed using Monolix software. A large interindividual variability was observed. The main sources of interpatient variability identified were patient bodyweight and hepatic function (aspartate aminotransferase). Forced expiratory volume in the first second (FEV1) was statistically associated with the level of exposure to ivacaftor after 48 weeks of treatment. CONCLUSIONS: This study is the first analysis of lumacaftor/ivacaftor PPK in children with CF. These data suggest that dose adjustment is required after identifying variability factors to optimize efficacy. The use of therapeutic drug monitoring as a basis for dose adjustment in children with CF may be useful.

MHC-independent genetic factors control the magnitude of CD4+ T cell responses to amyloid-ß peptide in mice through regulatory T cell-mediated inhibition.

Accumulation of amyloid-ß peptide (Aß) is considered the triggering factor of pathogenic lesions in Alzheimer's disease (AD), and vaccines targeting Aß are promising therapeutic options. However, the occurrence of meningoencephalitides attributed to T cell responses in 6% of Aß-immunized patients underscores the need for a better understanding of T cell responses to Aß. We characterized the parameters controlling the magnitude of Aß-specific CD4(+) T cell responses in mice. T cell responsiveness to Aß1-42 was highly heterogeneous between mouse strains of different H-2 haplotypes, with SJL/J (H-2(s)) mice displaying a strong response, mainly specific for Aß10-24, and C57BL/6 (H-2(b)) mice displaying a weak response to Aß16-30. Surprisingly, C57BL/6 mice congenic for the H-2(s) haplotype (B6.H-2(S)), which display a "permissive" MHC class II allele for presentation of the immunodominant Aß10-24 epitope, showed a very weak CD4(+) T cell response to Aß, suggesting that MHC-independent genes downmodulate Aß-specific CD4(+) T cell responses in C57BL/6 background. Vaccine-induced CD4(+) T cell responses to Aß were significantly enhanced in both C57BL/6 and B6.H-2(S) mice upon depletion of regulatory T cells (Tregs), whereas Treg-depleted SJL/J mice displayed unaltered Aß-specific T cell responses. Finally, Treg depletion in C57BL/6 transgenic APPPS1 mice, a mouse model of AD, results in enhanced vaccine-induced CD4(+) T cell responses in AD compared with wild-type animals. We concluded that the magnitude of Aß-specific CD4(+) T cell responses is critically controlled in both physiological and pathological settings by MHC-independent genetic factors that determine the overall potency of Aß-specific Treg responses.

Development of a simple and rapid method to determine the unbound fraction of dolutegravir, raltegravir and darunavir in human plasma using ultrafiltration and LC-MS/MS.

Dolutegravir, raltegravir and darunavir are three antiretroviral drugs widely used in combined antiretroviral therapies. These three drugs are highly bound to plasma proteins. Compared to the total concentration, the concentration of unbound drug which is considered as the only pharmacological active form should be more informative to improve therapeutic drug monitoring in patients to avoid virological failure or toxicity. The aim of the present study was to develop an ultrafiltration protocol and a LC-MS/MS method to simultaneously determine the concentrations of the unbound dolutegravir, raltegravir and darunavir in human plasma. Finally, 150 µL of plasma was ultrafiltrated using Centrifree® ultrafiltration devices with ultracel YM-T membrane (cutoff 30 KDa) during 5 min at 37 °C at 1500 g. Then, 20 µL of the ultrafiltrate were injected into the LC-MS/MS system. The chromatographic separation was carried out on a BEH C18 column using a mobile phase containing deionized water and acetonitrile, both with 0.05 % (v/v) of formic acid, with a gradient elution at a flow rate of 0.5 mL/min. The run time was only 4 min. The calibration curve ranged from 0.5-200 ng/mL for dolutegravir, 1 to 400 ng/mL for raltegravir and 10-4000 ng/mL for darunavir. This method was validated with a good precision (inter- and intra-day CV% lower than 14 %) and a good accuracy (inter- and intra-day bias between -5.6-8.8 %) for all the analytes. This method is simple, reliable and suitable for pharmacokinetic studies.

Predictive Performance of Population Pharmacokinetic Models of Levetiracetam in Children and Evaluation of Dosing Regimen.

Levetiracetam is a broad-spectrum antiepileptic drug that exhibits high interindividual variability in serum concentrations in children. A population pharmacokinetic approach can be used to explain this variability and optimize dosing schemes. The objectives are to identify the best predictive population pharmacokinetic model for children and to evaluate recommended doses using simulations and Bayesian forecasting. A validation cohort included children treated with levetiracetam who had a serum drug concentration assayed during therapeutic drug monitoring. We assessed the predictive performance of all the population pharmacokinetic models published in the literature using mean prediction errors, root mean squared errors, and visual predictive checks. A population model was finally constructed on the data, and dose simulations were performed to evaluate doses. We included 267 levetiracetam concentrations ranging from 2 to 69 mg/L from 194 children in the validation cohort. Six published models were externally evaluated. Most of the models underestimated the variability of our population. A 1-compartment model with first-order absorption and elimination with allometric scaling was finally fitted on our data. In our cohort, 57% of patients had a trough concentration <12 mg/L and 12% <5 mg/L. To reach a trough concentration >5 mg/L, doses ≥30 mg/kg/d for patients ≤50 kg and ≥2000 mg/d for patients >50 kg are required. In our population, a high percentage of children had low trough concentrations. Our population pharmacokinetic model could be used for therapeutic drug monitoring of levetiracetam in children.

HPLC-MS/MS method for the simultaneous quantification of dolutegravir, elvitegravir, rilpivirine, darunavir, ritonavir, raltegravir and raltegravir-ß-d-glucuronide in human plasma.

Therapeutic drug monitoring (TDM) is essential in the optimization of antiretroviral (ARV) treatments. In this work, we describe a new method for the simultaneous quantification of six molecules: the three novel ARV agents dolutegravir (DTG), elvitegravir (ELV) and rilpivirine (RPV), the first integrase inhibitor raltegravir (RAL) and its major metabolite the raltegravir-ß-d-glucuronide (RAL-GLU), an protease inhibitor darunavir (DRV) and its booster ritonavir (RTV) in human plasma. The drugs were extracted from 100 µL of plasma by a simple method of protein precipitation using acetonitrile. The separation was carried out on a Kinetex phehyl-hexyl column using a phase mobile composed of 55 % of water (0.05 % formic acid,v/v) and 45 % of methanol (0.05 % formic acid,v/v). The flow rate was set at 0.5 mL/min. The calibration ranged from 60 to 15000 ng/mL for DRV, from 20 to 5000 ng/mL for DTG and ELV, from 10 to 2500 ng/mL for RAL, RAL-GLU, RTV and RPV. The proposed method was validated with a good precision (inter- and intra-day CV% inferior to 12.3 %) and a good accuracy (inter- and intra-day bias between -9.9 % and 10 %) for all the analytes. The proposed method is simple, reliable and suitable for therapeutic drug monitoring (TDM) and for pharmacokinetics studies.

Free prednisolone pharmacokinetics predicted from total concentrations in patients with inflammatory - immunonologic conditions.

Prednisone is an anti-inflammatory drug widely used in internal medicine and rheumatology, but dosing remains empirical. The active metabolite of prednisone is free prednisolone. The aim of this work was to build a population pharmacokinetic (PK) model that can predict free prednisolone concentrations in patients with inflammatory/immunologic conditions.A total of 107 patients from the department of internal medicine of Cochin hospital provided 343 observations. Blood samples drawn for biological analyses were used for drug determination. Total plasma prednisolone concentrations were measured by liquid chromatography-mass spectrometry, and the data were modelled using Monolix. The pharmacokinetics was ascribed a one-compartment open model with three transit compartments standing for the absorption and metabolism process. The model used predicts free concentrations that served to derive total concentrations given published binding constants. Only size parameters influenced the pharmacokinetics. Free prednisolone CLU /F and VU /F, scaled allometrically on lean body weight, were, respectively, 26.7 L/h and 94.3 L for 50 kg LBW. CLU /F interindividual variability was 0.20. The additive and proportional residual variabilities were, respectively, 4.3 µg/L and 0.20. The results point out some dosing issues, that is the possibility of under- or over-dosage in thin or overweight patients respectively.

Maternal Betamethasone for Prevention of Respiratory Distress Syndrome in Neonates: Population Pharmacokinetic and Pharmacodynamic Approach.

Despite antenatal corticosteroids therapy, respiratory distress syndrome (RDS) is still a leading cause of neonatal morbidity and mortality in premature newborns. To date, the relationship between in utero fetal drug exposure and occurrence of RDS remains poorly evaluated. This study aims to describe the pharmacokinetics of betamethasone in pregnant women and to evaluate the transplacental drug transfer and administration scheme for the prevention of RDS. Pregnant women > 27 weeks' gestation and who received at least a single dose of betamethasone for prevention of RDS were enrolled. Maternal, cord blood, and amniotic fluid betamethasone time-courses were analyzed using the Monolix software. A total of 220 maternal blood, 56 cord blood, and 26 amniotic fluid samples were described by a two-compartment model with two effect compartments linked by rate transfer constants. Apparent clearances and volumes of distribution parameters were allometrically scaled for a 70 kg third trimester pregnant woman. The impact of a twin pregnancy was found to increase maternal clearance by 28%. Using a fetal-to-mother exposure ratio, the median (95% confidence interval (CI)) transplacental transfer of betamethasone was estimated to 35% (95% CI 0.11-0.67). After adjustment for gestational age and twin pregnancy, RDS was found to be associated to the time spent in utero below quantifiable concentrations (i.e., < 1 ng/mL): odds ratio of 1.10 (95% CI 1.01-1.19) per day increase (P < 0.05). Trying to take into account both efficacy and safety, we simulated different dosing schemes in order to maintain a maximum of fetuses above 1 ng/mL without exceeding the total standard dose.

Methodological Approaches to Evaluate Fetal Drug Exposure.

BACKGROUND: Drug prescriptions are usual during pregnancy, however, women and their fetuses still remain an orphan population with regard to drugs efficacy and safety. Most xenobiotics diffuse through the placenta and some of them can alter fetus development resulting in structural abnormalities, growth or functional deficiencies. METHODS: To summarize the different methodologies developed towards the prediction of fetal drug exposure. RESULTS: Neonatal cord blood concentration is the most specific measurement of the transplacental drug transfer at the end of pregnancy. Using the cord blood and mother drug concentrations altogether, drug exchanges between the mother and fetus can be modeled and quantified via a population pharmacokinetic analysis. Thereafter, it is possible to estimate the fetus exposure and the fetus-to-mother exposure ratio. However, the prediction of placental transfer before any administration to pregnant women is desirable. Animal studies remain difficult to interpret due to structural and functional inter-species placenta differences. The ex-vivo perfusion of the human placental cotyledon is the method of reference to study the human placental transfer of drugs because it is thought to mimic the functional placental tissue. However, extrapolation of data to in vivo situation remains difficult. Some research groups have extensively worked on physiologically based models (PBPK) to predict fetal drug exposure and showed very encouraging results. CONCLUSION: PBPK models appeared to be a very promising tool in order to predict fetal drug exposure in-silico. However, these models mainly picture the end of pregnancy and knowledge regarding both, development of the placental permeability and transporters is strongly needed.