Déborah Hirt

Retention of Plasmodium falciparum ring-infected erythrocytes in the slow, open microcirculation of the human spleen

The current paradigm in Plasmodium falciparum malaria pathogenesis states that young, ring-infected erythrocytes (rings) circulate in peripheral blood and that mature stages are sequestered in the vasculature, avoiding clearance by the spleen. Through ex vivo perfusion of human spleens, we examined the interaction of this unique blood-filtering organ with P falciparum-infected erythrocytes. As predicted, mature stages were retained. However, more than 50% of rings were also retained and accumulated upstream from endothelial sinus wall slits of the open, slow red pulp microcirculation. Ten percent of rings were retained at each spleen passage, a rate matching the proportion of blood flowing through the slow circulatory compartment established in parallel using spleen contrast-enhanced ultrasonography in healthy volunteers. Rings displayed a mildly but significantly reduced elongation index, consistent with a retention process, due to their altered mechanical properties. This raises the new paradigm of a heterogeneous ring population, the less deformable subset being retained in the spleen, thereby reducing the parasite biomass that will sequester in vital organs, influencing the risk of severe complications, such as cerebral malaria or severe anemia. Cryptic ring retention uncovers a new role for the spleen in the control of parasite density, opening novel intervention opportunities.

An optimized ibuprofen dosing scheme for preterm neonates with patent ductus arteriosus, based on a population pharmacokinetic and pharmacodynamic study

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT Ibuprofen is a nonsteroidal anti-inflammatory agent that induces closure of the patent ductus arteriosus in neonates. Few studies of ibuprofen pharmacokinetics have been performed and were limited to small groups of preterm infants, showing a large intersubject variability and an increase in clearance with either postnatal or gestational age. WHAT THIS STUDY ADDS A population pharmacokinetic study was performed on 66 neonates to characterize the concentration-time courses of ibuprofen. Ibuprofen clearance significantly increased from postnatal age day 1 to day 8, but not with gestational age. A relationship was shown between ibuprofen area under the curve (AUC) and patent ductus arteriosus closure rate, and an effective threshold AUC was evidenced. Dosing schemes were proposed as a function of postnatal age, to achieve this AUC and to improve the efficacy of treatment for patent ductus arteriosus in neonates. AIMS To describe ibuprofen pharmacokinetics in preterm neonates with patent ductus arteriosus (PDA) and to establish relationships between doses, plasma concentrations and ibuprofen efficacy and safety. METHODS Sixty-six neonates were treated with median daily doses of 10, 5 and 5 mg kg(-1) of ibuprofen-lysine by intravenous infusion on 3 consecutive days. A population pharmacokinetic model was developed with NONMEM. Bayesian individual pharmacokinetic estimates were used to calculate areas under the curve (AUC) and to simulate doses. A logistic regression was performed on PDA closure. RESULTS Ibuprofen pharmacokinetics were described by a one-compartment model with linear elimination. Mean population pharmacokinetic estimates with corresponding intersubject variabilities (%) were: elimination clearance CL = 9.49 ml h(-1) (62%) and volume of distribution V = 375 ml (72%). Ibuprofen CL significantly increased with postnatal age (PNA): CL = 9.49*(PNA/96.3)(1.49). AUC after the first dose (AUC1D), the sum of AUC after the three doses (AUC3D) and gestational age were significantly higher in 57 neonates with closing PDA than in nine neonates without PDA closure (P = 0.02). PDA closure was observed in 50% of the neonates when AUC1D < 600 mg l(-1) h (or AUC3D < 900 mg l(-1) h) and in 91% when AUC1D > 600 mg l(-1) h (or AUC3D > 900 mg l(-1) h) (P = 0.006). No correlation between AUC and side-effects could be demonstrated. CONCLUSIONS To achieve these optimal AUCs, irrespective of gestational age, three administrations at 24 h intervals are recommended of 10, 5, 5 mg kg(-1) for neonates younger than 70 h, 14, 7, 7 mg kg(-1) for neonates between 70 and 108 h and 18, 9, 9 mg kg(-1) for neonates between 108 and 180 h.

Population Pharmacokinetics of Tenofovir in HIV-1-Infected Pregnant Women and Their Neonates (ANRS 12109)

Thirty‐eight human immunodeficiency virus‐1 (HIV‐1)‐infected pregnant women were administered tenofovir disoproxil fumarate (TDF; 300 mg)–emtricitabine (FTC; 200 mg) tablets: two at labor initiation and one daily for 7 days postpartum. Maternal, umbilical, and neonatal plasma tenofovir concentrations were measured by high‐performance liquid chromatography and analyzed using a population approach. Data were described using a two‐compartment model for the mother, an effect compartment linked to maternal circulation for cord, and a neonatal compartment disconnected after delivery. Absorption was greater for women delivering by caesarian section than for those delivering vaginally. The maternal 600 mg TDF administration before delivery produces the same concentrations as 300 mg administration in other adults. If the time elapsed between maternal administration and delivery is ≥12 h, two tablets of TDF–FTC should be readministered. Tenofovir showed good placental transfer (60%). Administering 13 mg/kg of TDF as soon as possible after birth should produce neonatal concentrations comparable with those observed in adults.

Population analysis of weight-, age-, and sex-related differences in the pharmacokinetics of lopinavir in children from birth to 18 years

ABSTRACT The pharmacokinetics of lopinavir were investigated by the use of a population approach performed with the nonlinear mixed effect modeling program NONMEM and 157 children ranging in age from 3 days to 18 years. The pharmacokinetics of lopinavir were well described by a one-compartment model in which the absorption and the elimination rate constants were equal. Typical population estimates of the apparent volume of distribution (V/F) and plasma clearance (CL/F) were 24.6 liters and 2.58 liters/h, respectively. The lopinavir V/F and CL/F were both related to body weight (BW), with an important increase in weight-normalized CL/F for the lowest BW. Combined treatment with lopinavir and nevirapine was found to increase the CL/F. The lopinavir CL/F was also age and sex related, as a 39% increase was observed after the age of 12 years for boys compared to the CL/F for girls. The consequences of these pharmacokinetic discrepancies and the necessity to modify the currently recommended dosage regimen should be further investigated.

Is the Recommended Dose of Efavirenz Optimal in Young West African Human Immunodeficiency Virus-Infected Children?

ABSTRACT We aimed in this study to describe efavirenz concentration-time courses in treatment-naïve children after once-daily administration to study the effects of age and body weight on efavirenz pharmacokinetics and to test relationships between doses, plasma concentrations, and efficacy. For this purpose, efavirenz concentrations in 48 children were measured after 2 weeks of didanosine-lamivudine-efavirenz treatment, and samples were available for 9/48 children between months 2 and 5 of treatment. Efavirenz concentrations in 200 plasma specimens were measured using a validated high-performance liquid chromatography method. A population pharmacokinetic model was developed with NONMEM. The influence of individual characteristics was tested using a likelihood ratio test. The estimated minimal and maximal concentrations of efavirenz in plasma (Cmin and Cmax, respectively) and the area under the concentration-time curve (AUC) were correlated to the decrease in human immunodeficiency virus type 1 RNA levels after 3 months of treatment. The threshold Cmin (and AUC) that improved efficacy was determined. The target minimal concentration of 4 mg/liter was considered for toxicity. An optimized dosing schedule that would place the highest percentage of children in the interval of effective and nontoxic concentrations was simulated. The pharmacokinetics of efavirenz was best described by a one-compartment model with first-order absorption and elimination. The mean apparent clearance and volume of distribution for efavirenz were 0.211 liter/h/kg and 4.48 liters/kg, respectively. Clearance decreased significantly with age. When the recommended doses were given to 46 of the 48 children, 19% (44% of children weighing less than 15 kg) had Cmins below 1 mg/liter. A significantly higher percentage of children with Cmins of >1.1 mg/liter or AUCs of >51 mg/liter·h than of children with lower values had viral load decreases greater than 2 log10 copies/ml after 3 months of treatment. Therefore, to optimize the percentage of children with Cmins between 1.1 and 4 mg/liter, children should receive the following once-daily efavirenz doses: 25 mg/kg of body weight from 2 to 6 years, 15 mg/kg from 6 to 10 years, and 10 mg/kg from 10 to 15 years. These assumptions should be prospectively confirmed.

Population Pharmacokinetics of Emtricitabine in Human Immunodeficiency Virus Type 1-Infected Pregnant Women and Their Neonates

ABSTRACT The objectives of this study were to evaluate emtricitabine (FTC) pharmacokinetics in pregnant women and their neonates and to determine the optimal prophylactic dose for neonates after birth to prevent mother-to-child transmission of human immunodeficiency virus (HIV). A total of 38 HIV-infected pregnant women were administered tenofovir disoproxyl fumarate (300 mg)-FTC (200 mg) tablets—two tablets at the initiation of labor and one daily for 7 days postpartum. By pair, 11 maternal, one cord blood, and two neonatal FTC concentrations were measured using a high-performance liquid chromatography-tandem mass spectrometry validated method and analyzed by a population approach. Model and mean estimates (interpatient variability) were a two-compartment model for mothers, with an absorption rate constant of 0.54 h−1 (61%), apparent elimination and intercompartmental clearances of 23.2 (17%) and 6.04 liters·h−1, and apparent central and peripheral volumes of 127 and 237 liters, respectively; an effect compartment linked to maternal circulation for cord blood and a neonatal compartment disconnected, after delivery, with a 10.6-h half-life (30%). After the 400-mg FTC administration, the median population area under the concentration-time curve and the minimal and maximal plasma FTC concentrations in pregnant women were 14.3 mg·liter−1·h and 1.68 and 0.076 mg/liter, respectively. At delivery, median (range) predicted maternal and cord blood FTC concentrations were, respectively, 1.16 (0.14 to 1.99) and 0.72 (0.05 to 1.19) mg·liter−1. We concluded that the 400-mg FTC administration in pregnant women produces higher exposition than does the 200-mg administration in other adults, at steady state. FTC was shown to have good placental transfer (80%). Administering 1 mg FTC/kg as soon as possible after birth or 2 mg/kg 12 h after birth should produce neonatal concentrations comparable to the concentrations observed in adults.

Pregnancy-Related Effects on Nelfinavir-M8 Pharmacokinetics: a Population Study with 133 Women

ABSTRACT A relationship between nelfinavir antiretroviral efficacy and plasma concentrations has been previously established. As physiological changes associated with pregnancy have a large impact on the pharmacokinetics of many drugs, a nelfinavir population study with women was developed, and the large intersubject variability was analyzed in order to optimize individual treatment schedules for this drug during pregnancy. A population pharmacokinetic model was developed in order to describe the concentration time course of nelfinavir and its metabolite M8 in pregnant and nonpregnant women. Individual characteristics, such as age, body weight, and weeks of gestation or delivery, which may influence nelfinavir-M8 pharmacokinetics were investigated. Data from therapeutic drug monitoring in 133 women treated with nelfinavir were retrospectively analyzed with NONMEM. Nelfinavir pharmacokinetics was described by a one-compartment model with linear absorption and elimination and M8 produced from the nelfinavir central compartment. Mean pharmacokinetic estimates and the corresponding intersubject percent variabilities for a nonpregnant woman were the following: absorption rate, 0.83 h−1; absorption lag time, 0.85 h; apparent nelfinavir elimination clearance (CL10/F), 35.5 liters/h (50%); apparent volume of distribution (V/F), 596 liters (118%); apparent formation clearance to M8 (CL1M/F), 0.65 liters/h (69%); and M8 elimination rate constant (kM0), 3.3 h−1 (59%). During pregnancy, we observed significant increases in nelfinavir (44.4 liters/h) and M8 (5 h−1) elimination but unchanged nelfinavir transformation clearance to M8, suggesting an induction of CYP3A4 but no effect on CYP2C19. Apparent nelfinavir clearance and volume showed a twofold increase on the day of delivery, suggesting a decrease in bioavailability on this day. The M8 elimination rate was increased by concomitant administration of nonnucleoside reverse transcriptase inhibitors. A trough nelfinavir plasma concentration above 1 mg/liter was previously shown to improve the antiretroviral response. The Bayesian individual pharmacokinetic estimates suggested that the dosage should not be changed in pregnant women but may be doubled on the day of delivery.

Population pharmacokinetics of nevirapine in HIV-1-infected pregnant women and their neonates.

ABSTRACT The aim of the present study was to describe the nevirapine (NVP) pharmacokinetics (PK) in pregnant women and their neonates and to evaluate the transplacental drug transfer and administration scheme for the prevention of mother-to-child transmission. Thirty-eight HIV-1-infected pregnant women were administered one tablet of NVP (200 mg) and two tablets of tenofovir-emtricitabine (Truvada) at the initiation of labor. Children were given NVP syrup (2 mg/kg of body weight) as a single dose (sdNVP) on the first day of life. By pair, NVP concentrations were measured in 11 maternal, 1 cord blood, and 2 neonatal plasma samples and analyzed by a population approach. A one-compartment model was used for mothers and neonates; the absorption rate constants for mothers and neonates were 0.95 h−1 (intersubject variability, 111%) and 0.39 h−1, respectively; the apparent elimination clearances were 1.42 liter·h−1 (intersubject variability, 22%) and 0.035 liter·h−1, respectively; and apparent volumes of distribution were 87.3 liters (intersubject variability, 25%) and 5.65 liters, respectively. An effect compartment was linked to maternal circulation by mother-to-cord and cord-to-mother rate constants of 1.10 h−1 and 1.43 h−1, respectively. Placental transfer, expressed as the fetal-to-maternal area under the curve ratio, was 75%. Neonates had a very long half-lives (110 h) compared to adults. In the 38 mothers, the simulated median individual predicted time during which the NVP concentration remained above the half-maximal inhibitory concentration (IC50) was 13.2 days (range, 12 to 19.2 days). Thus, the administration of tenofovir-emtricitabine for at least 3 weeks after delivery should be considered to prevent the emergence of resistant viruses. The neonate must receive sdNVP immediately after birth when the infant is born less than 30 min after maternal drug intake to keep NVP concentrations above the IC50.

Population Pharmacokinetics of Emtricitabine in HIV-1-Infected Adult Patients

ABSTRACT The aims of this study were to describe emtricitabine concentration-time courses in a large population of HIV-1-infected adults, to evaluate the influence of renal function on emtricitabine disposition, and to assess current dosing adjustment recommendations. Emtricitabine blood plasma concentrations were determined from samples collected from 161 adult patients during therapeutic drug monitoring and measured by liquid chromatography coupled to tandem mass spectrometry. The data were analyzed by a population approach. Emtricitabine pharmacokinetics was best described by a two-compartment model in which the absorption and distribution rate constants were assumed to be equal. Typical population parameter estimates (interindividual variability) were apparent elimination and intercompartmental clearances of 15.1 liters/h (17.4%) and 5.75 liters/h, respectively, and apparent central and peripheral volumes of distribution of 42.3 liters and 55.4 liters, respectively. The apparent elimination clearance was significantly related to creatinine clearance (CLCR), reflecting renal function. For 200 mg once a day (QD), the median area under the concentration-time curve over 24 h (AUC0-24) was 12.5 mg · h/liter for patients with normal renal function (CLCR, >80 ml/min), 14.7 mg · h/liter for patients with mild renal impairment (CLCR, 79 to 50 ml/min), and 17.9 mg · h/liter for patients with moderate renal impairment (CLCR, 49 to 30 ml/min). Simulations of the recommended dosing schemes for the oral solid form of emtricitabine (i.e., 200 mg per 48 h according to renal function) led to lower emtricitabine exposures for patients with moderate renal impairment (median AUC0-48, 17.2 mg · h/liter) than for patients with normal renal function (median AUC0-48, 25.6 mg · h/liter). Administering 18 ml of emtricitabine oral solution (10 mg/ml) QD to patients with moderate renal impairment should yield emtricitabine exposures similar to those in patients with normal renal function.

Population pharmacokinetics of tenofovir in HIV-1-infected pediatric patients.

ObjectivesTo evaluate the pharmacokinetics of tenofovir in children and the influence of covariates [body weight (BW), age, cotreatments]. The main goal was then to suggest for the first time the dose of tenofovir disoproxil fumarate (TDF) to give in children. Design/MethodsTenofovir concentrations were monitored on a routine basis and measured in 93 children aged 5 to 18 years; 283 tenofovir plasma concentrations were used to perform a population pharmacokinetic analysis. ResultsA 2-compartment model adequately described the data. A BW allometric scaling was used; and the typical population estimates (interindividual variability), standardized for 70 kg, for apparent clearance, central and peripheral volume of distribution, intercompartmental clearance, and absorption rate constant, were 59.8 L·h-1 (0.48), 386 L (1.39), 666 L, 92.8 L·h-1 and 0.43 h-1, respectively. TDF clearance increased significantly with BW and decreased with lopinavir/ritonavir (LPV/r) coadministration, thus these factors were used to propose doses for children. Dosing scheme, according BW and LPV/r coadministration were simulated to produce the same 24-hr exposure as adults after 300-mg TDF dose. ConclusionsChildren without LPV/r should receive: 150 mg TDF from 20 to 30 kg, 225 mg TDF from 30 to 40 kg, and the adult dosage of 300 mg TDF over 40 kg. To avoid risk of renal toxicity, TDF dose should be decreased when coadministrated with LPV/r, children should receive 150 mg TDF from 20 to 40 kg, 225 mg TDF from 40 to 55 kg, and the adult dosage of 300 mg TDF over 55 kg.