Effect of Renal and Hepatic Impairment on the Pharmacokinetics of Temsavir, the Active Moiety of Fostemsavir

Therapeutic drug monitoring of antiretroviral therapy: current progresses and future directions

INTRODUCTION

The treatment of HIV infection has been revolutionized in recent years thanks to the advent of dual antiretroviral regimens, administered orally or as long-acting injectable formulations. Here, we provide an update on the usefulness of therapeutic drug monitoring (TDM) of antiretroviral drugs to optimize the management of people with HIV (PWH) in the current scenario.

AREAS COVERED

A MEDLINE PubMed search for articles published between January 2014 and January 2024 was completed matching the terms HIV, antiretrovirals and TDM. Moreover, additional studies were identified from the reference list of retrieved articles.

EXPERT OPINION

Available antiretroviral treatments achieve a response rate of 90%-95%, making the routine TDM of antiretroviral drugs of limited clinical value. However, there are still some important applications of TDM in selected clinical conditions, such as assessing patient compliance or suspected drug-drug interactions (DDIs). Indeed, we are increasingly having to deal with polypharmacy and DDIs in the context of an aging patient with comorbidities that may potentially alter the pharmacokinetics of antiretroviral drugs. Finally, the role of pharmacogenetics, which is closely related to TDM, in influencing both the disposition of antiretrovirals and the course of DDIs should also be considered.

Long-term safety and impact of immune recovery in heavily treatment-experienced adults receiving fostemsavir for up to 5 years in the phase 3 BRIGHTE study

Introduction

Fostemsavir is a gp120-directed attachment inhibitor approved for heavily treatment-experienced (HTE) adults with multidrug-resistant HIV-1. We provide detailed week 240 safety results from the BRIGHTE study and evaluate the impact of immune recovery on safety outcomes.

Methods

The phase 3 BRIGHTE trial is ongoing; data for this analysis were collected from the first participant's first visit (February 23, 2015) through the last participant's last visit for week 240 (March 22, 2021). Safety endpoints were assessed in participants who received fostemsavir + optimized background therapy. In participants with baseline CD4+ T-cell count <200 cells/mm3, exposure-adjusted adverse event (AE) rates were assessed among subgroups with or without CD4+ T-cell count ≥200 cells/mm3 at any time during 48-week analysis periods through week 192.

Results

Through a median of 258 weeks (range, 0.14-319) of treatment, discontinuations due to AEs occurred in 30/371 (8%) participants. Serious AEs were reported in 177/371 (48%) participants, including 16 drug-related events in 13 (4%) participants. Thirty-five (9%) deaths occurred, primarily related to AIDS or acute infections. COVID-19-related events occurred in 25 (7%) participants; all resolved without sequelae. Among participants with baseline CD4+ T-cell count <200 cells/mm3, 122/162 (75%) achieved CD4+ T-cell count ≥200 cells/mm3 at week 192. Exposure-adjusted AE rates were markedly lower among participants achieving CD4+ T-cell count ≥200 cells/mm3 at any time vs those sustaining <200 cells/mm3. No new AIDS-defining events were reported after week 48 in participants with CD4+ T-cell count ≥200 cells/mm3.

Conclusions

Cumulative safety findings through the BRIGHTE 240-week interim analysis are consistent with other trials in HTE participants with advanced HIV-1 and comorbid disease. Reduced rates of AIDS-defining events and AEs were observed in participants with immunologic recovery on fostemsavir-based treatment.

Clinical trial number

NCT02362503, https://clinicaltrials.gov/study/NCT02362503.

Consensus recommendations for the use of novel antiretrovirals in persons with HIV who are heavily treatment-experienced and/or have multidrug-resistant HIV-1: Endorsed by the American Academy of HIV Medicine, American College of Clinical Pharmacy

Treatment options are currently limited for persons with HIV-1 (PWH) who are heavily treatment-experienced and/or have multidrug-resistant HIV-1. Three agents have been approved by the U.S. Food and Drug Administration (FDA) since 2018, representing a significant advancement for this population: ibalizumab, fostemsavir, and lenacapavir. However, there is a paucity of recommendations endorsed by national and international guidelines describing the optimal use (e.g., selection and monitoring after initiation) of these novel antiretrovirals in this population. To address this gap, a modified Delphi technique was used to develop these consensus recommendations that establish a framework for initiating and managing ibalizumab, fostemsavir, or lenacapavir in PWH who are heavily treatment-experienced and/or have multidrug-resistant HIV-1. In addition, future areas of research are also identified and discussed.

Development of a physiologically based pharmacokinetic model of fostemsavir and its pivotal application to support dosing in pregnancy

It is critical to understand the impact of significant physiological changes during pregnancy on the extent of maternal and fetal drug exposure. Fostemsavir (FTR) is a prodrug of temsavir (TMR) and is approved in combination with other antiretrovirals for multi-drug-resistant human immunodeficiency virus (HIV) infections. This physiologically based pharmacokinetic model (PBPK) study was used to estimate TMR PK in pregnant populations during each trimester of pregnancy to inform FTR dosing. A PBPK model was developed and validated for TMR using PK data collected following intravenous TMR and oral FTR dosing (immediate-release and extended-release tablets) in healthy volunteers. Predicted TMR concentration-time profiles accurately predicted the reported clinical data and variability in healthy (dense data) and pregnant (sparse data) populations. Predicted versus observed TMR geometric mean (CV%) clearance following intravenous administration was 18.01 (29) versus 17 (21) (L/h). Predicted versus observed TMR AUC0-inf (ng.h/mL) in healthy volunteers following FTR administration of the extended-release tablet were 9542 (66) versus 7339 (33). The validated TMR PBPK model was then applied to predict TMR PK in a population of pregnant individuals during each trimester. Simulations showed TMR AUC in pregnant individuals receiving FTR 600 mg twice daily was decreased by 25% and 38% in the second and third trimesters, respectively. However, TMR exposure remained within the range observed in nonpregnant adults with no need for dose adjustment. The current PBPK model can also be applied for the prediction of local tissue concentrations and drug-drug interactions in pregnancy.

Mechanism of action, resistance, interaction, pharmacokinetics, pharmacodynamics, and safety of fostemsavir

The Food and Drug Administration (FDA) has licensed many antiretroviral medications to treat human immunodeficiency virus type 1 (HIV-1), however, treatment options for people with multi-drug resistant HIV remain limited. Medication resistance, undesirable effects, prior tolerance, and previous interlacement incapacity to deliver new drug classes all lead to the requirement for new medication classes and drug combination therapy. Fostemsavir (FTR) is a new CD-4 attachment inhibitor medicine that was recently authorized by the United States FDA to treat HIV-1. In individuals with multidrug-resistant (MDR) HIV-1, FTR is well tolerated and virologically active. According to recent investigations, drug combination therapy can positively affect MDR-HIV. The mechanism of action, resistance, interaction, pharmacokinetics, pharmacodynamics, and safety of FTR has been highlighted in this review.

Model-Based Dose Selection of Fostemsavir for Pediatric Populations With Multidrug-Resistant HIV-1 and Relative Bioavailability Assessment in Healthy Adults

Fostemsavir, a prodrug of the first-in-class HIV-1 attachment inhibitor temsavir, is approved for the treatment of multidrug-resistant HIV-1 in adults; its use in pediatric populations is currently being studied. Population pharmacokinetic modeling across pediatric weight bands was used to guide pediatric fostemsavir dose selection. Dosing simulations demonstrated that twice-daily fostemsavir 600-mg (adult dose) and 400-mg doses met safety and efficacy criteria for 35 kg or greater and 20 or greater to less than 35 kg pediatric weight bands, respectively. Temsavir relative bioavailability of 2 low-dose fostemsavir extended-release formulations (3 × 200 mg; formulations A and B) and reference formulation (600 mg extended release) was assessed in a 2-part, open-label, randomized, crossover study in healthy adults. Part 1 (N = 32) compared single-dose temsavir relative bioavailability, and Part 2 (N = 16) evaluated the impact of fed versus fasted conditions using the selected low-dose formulation. Temsavir geometric mean ratios for the area under the plasma concentration-time curve from time zero to infinity and maximum concentration for formulation B were bioequivalent to the reference formulation. Temsavir maximum concentration for formulation B was similar in fed and fasted states, but area under the plasma concentration-time curve from time zero to infinity geometric mean ratio was increased under fed conditions, consistent with previous results in adults. These analyses demonstrated efficient pediatric dose selection using a model-based approach.

Fostemsavir and ethinyl estradiol drug interaction: Clinical recommendations for co‐administration

OBJECTIVES

Fostemsavir, a prodrug of temsavir, is indicated for heavily treatment-experienced adults with multidrug-resistant HIV-1 infection, antiretroviral (ARV) intolerance, or safety considerations. Understanding drug-drug interactions (DDIs) is important in individuals taking fostemsavir with hormonal contraceptives or menopausal or gender-affirming hormonal therapies.

METHODS

Effect of temsavir (active moiety) on the pharmacokinetics of ethinyl estradiol (EE) and norethindrone (NET) was evaluated in an open-label, single-sequence, four-cycle, four-treatment study in 26 healthy female participants (study 206279, NCT02480881). Relevant ARV-contraceptive interaction studies and guideline recommendations were reviewed; that information was then applied to other contraceptive methods and hormone-based therapies to predict the impact of fostemsavir co-administration.

RESULTS

Temsavir increased EE concentrations by 40% and had no effect on NET concentrations. Fostemsavir co-administration with hormone therapy is not expected to impact hormone treatment efficacy. Fostemsavir did not impact progestin; therefore, progestin-only and non-hormonal contraceptives will not be impacted by fostemsavir. Recommendations for co-administration of fostemsavir and hormonal contraceptives or menopausal or gender-affirming hormone therapies are based upon known and predicted DDIs, ensuring adequate hormonal concentrations to maintain the target effect.

CONCLUSIONS

Applying the results of Study 206279 and other relevant ARV-contraceptive studies, we recommend that when co-administering fostemsavir with combined oral contraceptives (COCs) and other oestrogen-based therapies, EE dose should not exceed 30 μg or equivalent, and caution is advised in the case of individuals with risk factors for thromboembolic events. Other oestrogen-based therapies may be co-administered with fostemsavir, with monitoring of oestrogen concentrations and appropriate dose adjustments. No impact of fostemsavir on COC efficacy is expected.

The impact of age on antiretroviral drug pharmacokinetics in the treatment of adults living with HIV

INTRODUCTION

People living with HIV (PLWH) are aging and will receive life-long treatment: despite substantial improvement in drug efficacy and tolerability, side effects still occur and they can blunt antiretroviral treatment effectiveness. Since age may affect drug exposure and may be associated with side-effects we aimed at reviewing available data on the effect of age on antiretrovirals' pharmacokinetics in adult patients.

AREAS COVERED

We searched public databases and major conference proceedings for data on age and pharmacokinetics/pharmacodynamics in PLWH. We limited our review to currently used drugs and focused on population pharmacokinetics and physiologically-based pharmacokinetic modeling studies.

EXPERT OPINION

Available evidence of a potential detrimental effect in elderly PLWH is limited by study design and small sample sizes. Careful consideration of undoubtful benefits and potential harms is advised when prescribing ARVs to geriatric patients and the knowledge of pharmacokinetics changes need to be included in the process. With the 'greying' of the pandemic we need studies with a specific focus on geriatric patients living with HIV that will consider specific phenotypes and associated changes (including sarcopenia).