Therapeutic drug monitoring of darunavir/ritonavir in pregnancy

Guideline No. 450: Care of Pregnant Women Living with HIV and Interventions to Reduce Perinatal Transmission

OBJECTIVE

This guideline provides an update on the care of pregnant women living with HIV and the prevention of perinatal HIV transmission. This guideline is a revision of the previous guideline, No. 310 Guidelines for the Care of Pregnant Women Living With HIV and Interventions to Reduce Perinatal Transmission, and includes an updated review of the literature with contemporary recommendations.

TARGET POPULATION

Pregnant women newly diagnosed with HIV during antenatal screening and women living with HIV who become pregnant. This guideline does not include specific guidance for girls/women of reproductive age living with HIV who are not pregnant.

OUTCOMES

Prevention of perinatal HIV transmission is a key indicator of the success of a health care system and requires multidisciplinary care of pregnant women living with HIV. Intended outcomes include guidance on best practice in perinatal management for Canadian health care providers for pregnant women living with HIV; reduction of perinatal transmission of HIV toward a target of eradication of perinatal transmission; provision of optimal antenatal care for pregnant women to ensure the best maternal health outcomes and HIV suppression; and evidence-based support and recommendations for pregnant women living with HIV, maintaining awareness and consideration of the complex psychosocial impacts of living with HIV.

BENEFITS, HARMS, AND COSTS

The perinatal transmission of HIV has significant morbidity and mortality implications for the child, with associated lifelong health care costs. Pregnancy presents an emotionally and physically vulnerable time for pregnant women as well as an opportunity to engage them in health promotion. This guidance does not include recommendations with additional costs to health care facilities compared with the previous guideline. Application of the recommendations is aimed at health benefits to both mother and child by optimizing maternal health and preventing perinatal HIV transmission.

EVIDENCE

Published and unpublished literature was reviewed with a focus on publications post-2013. OVID-Medline, Embase, PubMed and the Cochrane Library databases were searched for relevant publications available in English or French for each section of this guideline. Results included systematic reviews, randomized controlled trials, and observational studies published from 2012 to 2022. Searches were updated on a regular basis and incorporated in the guideline until May 2023. Unpublished literature, protocols, and international guidelines were identified by accessing the websites of health-related agencies, clinical practice guideline collections, and national and international medical specialty societies.

VALIDATION METHODS

The authors rated the quality of evidence and strength of recommendations using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. See Appendix A (Tables A1 for definitions and A2 for interpretations of strong and conditional recommendations).

INTENDED AUDIENCE

The intended users of this guideline include obstetric care providers and infectious disease clinicians who provide care for pregnant women living with HIV.

SOCIAL MEDIA SUMMARY

Updated Canadian HIV in pregnancy guideline informed by global research and tailored to Canadian healthcare needs and goals for pregnant women living with HIV and their families.

SUMMARY STATEMENTS

RECOMMENDATIONS.

Simultaneous pharmacokinetic modeling of unbound and total darunavir with ritonavir in adolescents: a substudy of the SMILE trial

Darunavir (DRV) is an HIV protease inhibitor commonly used as part of antiretroviral treatment regimens globally for children and adolescents. It requires a pharmacological booster, such as ritonavir (RTV) or cobicistat. To better understand the pharmacokinetics (PK) of DRV in this younger population and the importance of the RTV boosting effect, a population PK substudy was conducted within SMILE trial, where the maintenance of HIV suppression with once daily integrate inhibitor + darunavir/ritonavir in children and adolescents is evaluated. A joint population PK model that simultaneously used total DRV, unbound DRV, and total RTV concentrations was developed. Competitive and non-competitive models were examined to define RTV's influence on DRV pharmacokinetics. Linear and non-linear equations were tested to assess DRV protein binding. A total of 443 plasma samples from 152 adolescents were included in this analysis. Darunavir PK was best described by a one-compartment model first-order absorption and elimination. The influence of RTV on DRV pharmacokinetics was best characterized by ritonavir area under the curve on DRV clearance using a power function. The association of non-linear and linear equations was used to describe DRV protein binding to alpha-1 glycoprotein and albumin, respectively. In our population, simulations indicate that 86.8% of total and unbound DRV trough concentrations were above 0.55 mg/L [10 times protein binding-adjusted EC50 for wild-type (WT) HIV-1] and 0.0243 mg/L (10 times EC90 for WT HIV-1) targets, respectively. Predictions were also in agreement with observed outcomes from adults receiving 800/100 mg DRV/r once a day. Administration of 800/100 mg of DRV/r once daily provides satisfactory concentrations and exposures for adolescents aged 12 years and older.

Daily ritonavir-boosted darunavir for viral suppression in pregnancy (DRV-P)

BACKGROUND

Ritonavir-boosted darunavir (DRV/r) is a preferred protease inhibitor in pregnant women living with HIV. Current practice at British Columbia's referral centre (the Oak Tree Clinic) is to dose DRV/r as 800/100 mg daily throughout pregnancy, although some guidelines recommend DRV/r 600/100 mg twice daily due to altered pharmacokinetics with once-daily dosing.

OBJECTIVES

We describe the effect of once-daily DRV/r on viral suppression, vertical transmission, adverse drug effects and adherence in pregnant women living with HIV.

METHODS

This was a retrospective analysis of pregnant women living with HIV in British Columbia. Eligible women gave birth between January 2015 and August 2021, and took DRV/r 800/100 mg daily at any time during pregnancy.

RESULTS

Thirty-four women were included in this study. The mean (SD) age was 33 (5) years. Thirty (88%) women were diagnosed with HIV prior to pregnancy, with 22 (73%) having viral suppression at baseline. Four (12%) were diagnosed in pregnancy, with a median baseline viral load of 9616 copies/mL (range 8370-165 000). Viral suppression was achieved by 16 (100%), 24 (75%) and 26 (74%) women in the first, second and third trimesters, respectively. No vertical transmission occurred. This combination was well tolerated, with adverse drug effects that did not result in discontinuation or change in therapy. Most women maintained >75% adherence to once-daily DRV/r at all times during pregnancy.

CONCLUSIONS

Ritonavir-boosted darunavir 800/100 mg daily appears to be an appropriate dosing strategy for pregnant women living with HIV who are able to maintain optimal adherence.

Magnitude of Drug–Drug Interactions in Special Populations

Drug–drug interactions (DDIs) are one of the most frequent causes of adverse drug reactions or loss of treatment efficacy. The risk of DDIs increases with polypharmacy and is therefore of particular concern in individuals likely to present comorbidities (i.e., elderly or obese individuals). These special populations, and the population of pregnant women, are characterized by physiological changes that can impact drug pharmacokinetics and consequently the magnitude of DDIs. This review compiles existing DDI studies in elderly, obese, and pregnant populations that include a control group without the condition of interest. The impact of physiological changes on the magnitude of DDIs was then analyzed by comparing the exposure of a medication in presence and absence of an interacting drug for the special population relative to the control population. Aging does not alter the magnitude of DDIs as the related physiological changes impact the victim and perpetrator drugs to a similar extent, regardless of their elimination pathway. Conversely, the magnitude of DDIs can be changed in obese individuals or pregnant women, as these conditions impact drugs to different extents depending on their metabolic pathway.

Successful Prediction of Human Fetal Exposure to P-Glycoprotein Substrate Drugs Using the Proteomics-Informed Relative Expression Factor Approach and PBPK Modeling and Simulation

Many women take drugs during their pregnancy to treat a variety of clinical conditions. To optimize drug efficacy and reduce fetal toxicity, it is important to determine or predict fetal drug exposure throughout pregnancy. Previously, we developed and verified a maternal-fetal physiologically based pharmacokinetic (m-f PBPK) model to predict fetal K_p,uu (unbound fetal plasma AUC/unbound maternal plasma AUC) of drugs that passively cross the placenta. Here, we used in vitro transport studies in Transwell, in combination with our m-f PBPK model, to predict fetal K_p,uu of drugs that are effluxed by placental P-glycoprotein (P-gp)-namely, dexamethasone, betamethasone, darunavir, and lopinavir. Using Transwell, we determined the efflux ratio of these drugs in hMDR1-MDCK^cP-gpKO cells, in which human P-gp was overexpressed and the endogenous P-gp was knocked out. Then, using the proteomics-informed efflux ratio-relative expressive factor approach, we predicted the fetal K_p,uu of these drugs at term. Finally, to verify our predictions, we compared them with the observed in vivo fetal K_p,uu at term. The latter was estimated using our m-f PBPK model and published fetal [umbilical vein (UV)]/maternal plasma drug concentrations obtained at term (UV/maternal plasma). Fetal K_p,uu predictions for dexamethasone (0.63), betamethasone (0.59), darunavir (0.17), and lopinavir (0.08) were successful, as they fell within the 90% confidence interval of the corresponding in vivo fetal K_p,uu (0.30-0.66, 0.29-0.71, 0.11-0.22, 0.04-0.19, respectively). This is the first demonstration of successful prediction of fetal K_p,uu of P-gp drug substrates from in vitro studies. SIGNIFICANCE STATEMENT: For the first time, using in vitro studies in cells, this study successfully predicted human fetal K_p,uu of P-gp substrate drugs. This success confirms that the m-f PBPK model, combined with the ER-REF approach, can successfully predict fetal drug exposure to P-gp substrates. This success provides increased confidence in the use of the ER-REF approach, combined with the m-f PBPK model, to predict fetal K_p,uu of drugs (transported by P-gp or other transporters), both at term and at earlier gestational ages.

Drug-Drug Interactions with Antiretroviral Drugs in Pregnant Women Living with HIV: Are They Different from Non-Pregnant Individuals?

Background and Objective

Although the separate effects of drug–drug interactions and pregnancy on antiretroviral drug pharmacokinetics have been widely studied and described, their combined effect is largely unknown. Physiological changes during pregnancy may change the extent or clinical relevance of a drug–drug interaction in a pregnant woman. This review aims to provide a detailed overview of the mechanisms, magnitude, and clinical significance of antiretroviral drug–drug interactions in pregnant women.

Methods

We performed a literature search and selected studies that compared the magnitude of drug–drug interactions with antiretroviral drugs in pregnant vs non-pregnant women.

Results

Forty-eight papers examining drug–drug interactions during pregnancy were selected, of which the majority focused on pharmacokinetic boosting. Other selected studies examined the drug–drug interactions between efavirenz and lumefantrine, efavirenz and tuberculosis drugs, etravirine and tenofovir disoproxil fumarate, atazanavir and tenofovir disoproxil, and mefloquine and nevirapine in pregnant compared to non-pregnant women. The clinical significance of antiretroviral drug–drug interactions changed during pregnancy from a minimal effect to a contra-indication. In almost all cases, the clinical significance of a drug–drug interaction was more relevant in pregnant women, owing to the combined effects of pregnancy-induced physiological changes and drug–drug interactions leading to a lower absolute drug exposure.

Conclusions

Multiple studies show that the clinical relevance of a drug–drug interaction can change during pregnancy. Unfortunately, many potential interactions have not been studied in pregnancy, which may place pregnant women living with human immunodeficiency virus and their newborns at risk.