Stein Schalkwijk

Placental transfer of the HIV integrase inhibitor dolutegravir in an ex vivo human cotyledon perfusion model

OBJECTIVES Data on fetal exposure to antiretroviral agents during pregnancy are important to estimate their potential for prevention of mother-to-child transmission (PMTCT) and possible toxicity. For the recently developed HIV integrase inhibitor dolutegravir, clinical data on fetal disposition are not yet available. Dual perfusion of a single placental lobule (cotyledon) provides a useful ex vivo model to predict the in vivo maternal-to-fetal transfer of this drug. The aim of this study was to estimate the transfer of dolutegravir across the human term placenta, using a dual-perfusion cotyledon model. METHODS After cannulation of the cotyledons (n = 6), a fetal circulation of 6 mL/min and maternal circulation of 12 mL/min were initiated. The perfusion medium consisted of Krebs-Henseleit buffer (pH = 7.2-7.4) supplemented with 10.1 mM glucose, 30 g/L human serum albumin and 0.5 mL/L heparin 5000IE. Dolutegravir was administered to the maternal circulation (∼ 4.2 mg/L) and analysed by UPLC-MS/MS. RESULTS After 3 h of perfusion, the mean ± SD fetal-to-maternal (FTM) concentration ratio of dolutegravir was 0.6 ± 0.2 and the mean ± SD concentrations in the maternal and fetal compartments were 2.3 ± 0.4 and 1.3 ± 0.3 mg/L, respectively. CONCLUSIONS Dolutegravir crosses the blood-placental barrier with a mean FTM concentration ratio of 0.6. Compared with other antiretroviral agents, placental transfer of dolutegravir is moderate to high. These data suggest that dolutegravir holds clinical potential for pre-exposure prophylaxis and consequently PMTCT, but also risk of fetal toxicity.

Etravirine pharmacokinetics in HIV-infected pregnant women

Background: The study goal was to describe etravirine pharmacokinetics during pregnancy and postpartum in HIV-infected women. Methods: IMPAACT P1026s and PANNA are on-going, non-randomized, open-label, parallel-group, multi-center phase-IV prospective studies in HIV-infected pregnant women. Intensive steady-state 12-h pharmacokinetic profiles were performed from 2nd trimester through postpartum. Etravirine was measured at two labs using validated ultra performance liquid chromatography (detection limits: 0.020 and 0.026 mcg/mL). Results: Fifteen women took etravirine 200 mg twice-daily. Etravirine AUC0–12 was higher in the 3rd trimester compared to paired postpartum data by 34% (median 8.3 vs. 5.3 mcg*h/mL, p = 0.068). Etravirine apparent oral clearance was significantly lower in the 3rd trimester of pregnancy compared to paired postpartum data by 52% (median 24 vs. 38 L/h, p = 0.025). The median ratio of cord blood to maternal plasma concentration at delivery was 0.52 (range: 0.19–4.25) and no perinatal transmission occurred. Conclusion: Etravirine apparent oral clearance is reduced and exposure increased during the third trimester of pregnancy. Based on prior dose-ranging and safety data, no dose adjustment is necessary for maternal health but the effects of etravirine in utero are unknown. Maternal health and infant outcomes should be closely monitored until further infant safety data are available. Clinical Trial registration: The IMPAACT protocol P1026s and PANNA study are registered at ClinicalTrials.gov under NCT00042289 and NCT00825929.

Free dug concentrations in pregnancy: Bound to measure unbound?

With this statement Marzolini et al. [1] underline a phenomenon of major importance when interpreting drug exposure during pregnancy. In the case presented, the authors find subtherapeutic total and free (unbound) elvitegravir concentrations during pregnancy. This is an important finding because subtherapeutic exposure of this antiretroviral drug puts women at an increased risk of virological failure and/or development of antiretroviral resistance, as well as an increased risk of perinatal HIV transmission during pregnancy [2, 3]. Unexpectedly, the authors also observe an increased protein binding during pregnancy. The statement above, combined with the findings of this case report, highlight that we cannot always rely on total concentrations for examining exposure during pregnancy. Here, we will first elaborate on the pharmacological mechanisms and physiology underlying the alterations in free and total concentrations during pregnancy. Next, we will present an overview of total and free concentrations for several other antiretroviral drugs during pregnancy. Finally, we will make some inferences based on the theory and the examples presented, and propose a rule of thumb for conducting clinical pharmacokinetic studies in pregnancy. As mentioned in the opening statement, an important and well-described pharmacological process that changes during pregnancy is drug protein binding [4, 5]. The main binding proteins in plasma are albumin and α1-acid glycoprotein (AAG) [6]. The concentrations of both are known to decrease during pregnancy [7]. When a drug binds to plasma proteins, changes in the protein concentrations may affect the fraction of the drug bound to proteins. The drug fraction that is not bound to protein is referred to as the fraction unbound (fu). The fu is defined as the free concentration (Cfree) divided by the total concentration (Ctot = Cfree + Cbound), equation (1).

Lowered Rilpivirine Exposure During the Third Trimester of Pregnancy in Human Immunodeficiency Virus Type 1-Infected Women

Background The use of antiretroviral therapy during pregnancy is important for control of maternal human immunodeficiency virus (HIV) disease and the prevention of perinatal HIV transmission. Physiological changes during pregnancy can reduce antiretroviral exposure. We studied the pharmacokinetics of rilpivirine 25 mg once daily in HIV-1-infected women during late pregnancy. Methods We conducted a nonrandomized, open-label, multicenter, phase 4 study. HIV-infected pregnant women receiving rilpivirine 25 mg once daily were included. Intensive 24-hour pharmacokinetic sampling was performed in the third trimester and at least 2 weeks postpartum. Pharmacokinetic parameters were calculated by noncompartmental analysis. Results Sixteen subjects were included. Geometric mean ratios of third trimester vs postpartum were 0.55 (90% confidence interval [CI], .46-.66) for the 24-hour area under the concentration-time curve (AUC0-24h); 0.65 (90% CI, .55-.76) for the maximum concentration; and 0.51 (90% CI, .41-.63) for the minimum observed concentration (Cmin). Four of 16 (25%) subjects had Cmin below the target concentration (0.04 mg/L) in the third trimester of pregnancy. No subtherapeutic levels were observed postpartum. No detectable viral loads were observed in this study. All newborns tested negative for HIV. No birth defects were reported. The median (range, n = 5) rilpivirine cord-to-maternal plasma concentration ratio was 0.50 (range, .35-.81). Conclusions Rilpivirine exposure is substantially lowered during late pregnancy. Despite lower exposure, virologic suppression was maintained and no perinatal transmission was observed. Overall, these results suggest that rilpivirine 25 mg once daily may be an alternative treatment option for HIV-1-infected pregnant women who are virologically suppressed, in settings where therapeutic drug monitoring and/or close viral load monitoring are feasible to detect suboptimal antiretroviral therapy. Clinical Trials Registration NCT00825929.

The pharmacokinetics of abacavir 600 mg once daily in HIV-1-positive pregnant women

Objective:To describe the pharmacokinetics of abacavir 600 mg once daily (q.d.) in HIV-1-positive women during pregnancy and postpartum. Design:A nonrandomized, open-label, multicentre, phase-IV study. Methods:HIV-positive pregnant women receiving abacavir 600 mg q.d. as part of clinical care were included. Intensive 24-h pharmacokinetic sampling was performed during the third trimester and at least 2 weeks after delivery. Pharmacokinetic parameters were calculated by noncompartmental analysis. Paired cord blood and maternal blood samples were taken at delivery when feasible. Results:A total of 14 women were included in the analysis. Geometric mean ratios (90% confidence intervals) of third trimester versus postpartum were 1.05 (0.92–1.19) for AUC0–24h and 1.00 (0.83–1.21) for Cmax. The median (range) ratio of abacavir cord plasma to maternal plasma was 1.0 (0.7–1.0, n = 3). Viral load at the third trimester visit was less than 50 copies/ml in 13 participants (93%; one unknown). In total, 13 (93%; one unknown) children were tested HIV-negative. Conclusion:The pharmacokinetics of abacavir 600 mg q.d. during pregnancy are equivalent to postpartum. No dose adjustments are required during pregnancy and similar antiviral activity is expected.

Maraviroc Pharmacokinetics in HIV-1–Infected Pregnant Women

OBJECTIVE To describe the pharmacokinetics of maraviroc in human immunodeficiency virus (HIV)-infected women during pregnancy and post partum. METHODS HIV-infected pregnant women receiving maraviroc as part of clinical care had intensive steady-state 12-hour pharmacokinetic profiles performed during the third trimester and ≥2 weeks after delivery. Cord blood samples and matching maternal blood samples were taken at delivery. The data were collected in 2 studies: P1026 (United States) and PANNA (Europe). Pharmacokinetic parameters were calculated. RESULTS Eighteen women were included in the analysis. Most women (12; 67%) received 150 mg of maraviroc twice daily with a protease inhibitor, 2 (11%) received 300 mg twice daily without a protease inhibitor, and 4 (22%) had an alternative regimen. The geometric mean ratios for third-trimester versus postpartum maraviroc were 0.72 (90% confidence interval, .60-.88) for the area under the curve over a dosing interval (AUCtau) and 0.70 (0.58-0.85) for the maximum maraviroc concentration. Only 1 patient showed a trough concentration (Ctrough) below the suggested target of 50 ng/mL, both during pregnancy and post partum. The median ratio of maraviroc cord blood to maternal blood was 0.33 (range, 0.03-0.56). The viral load close to delivery was <50 copies/mL in 13 women (76%). All children were HIV negative at testing. CONCLUSIONS Overall maraviroc exposure during pregnancy was decreased, with a reduction in AUCtau and maximum concentration of about 30%. Ctrough was reduced by 15% but exceeded the minimum Ctrough target concentration. Therefore, the standard adult dose seems sufficient in pregnancy. CLINICAL TRIALS REGISTRATION NCT00825929 and NCT000422890.