Doravirine/Islatravir (DOR/ISL) in Pediatric Participants With Human Immunodeficiency Virus Type 1 (HIV-1) Who Are <18 Years of Age and Weigh ≥35 kg (MK-8591A-028)

This is a phase 2, single-group, multi-site, open-label study of an islatravir/doravirine (ISL/DOR, MK-8591A) fixed dose combination (FDC) for the treatment of human immunodeficiency virus type 1 (HIV-1) infection in pediatric participants who are virologically suppressed (VS) on antiretroviral therapy (ART) for ≥3 months or are treatment-naive (TN). The primary purposes of the study are 1) to examine the steady-state pharmacokinetics (PK) of ISL in plasma; 2) the steady-state PK of ISL-triphosphate (ISL-TP) in peripheral blood mononuclear cells (PBMCs); and 3) to examine the safety and tolerability of ISL/DOR.

As of protocol amendment 03 (approved 08-Feb-2022), all participants have been discontinued from study therapy and will be switched to non-study antiretroviral therapy and monitored for safety. The present results cover data obtained through the cut-off date of 30-Mar-2022, and will be updated once monitoring is completed.

Eligibility Criteria:
Inclusion Criteria:

* Is HIV-1 positive, is \<18 years of age, and weighs ≥35 kg at screening.
* VS Participants: Is HIV-1 positive at Screening with plasma HIV-1 RNA \<50 copies/mL and has been receiving continuous, stable oral 2-drug or 3-drug combination ART ± PK booster with documented viral suppression for ≥3 months prior to providing documented informed consent/assent and has no history of prior virologic treatment failure on any past or current regimen.
* TN Participants: Is HIV-1 positive at Screening with plasma HIV-1 RNA ≥500 copies/mL and is naive to ART defined as having received \<=10 days of prior therapy with any antiretrovirals following HIV-1 diagnosis other than pre-exposure prophylaxis (PrEP) or potentially exposed person (PEP).
* If female, is not pregnant or breastfeeding, and is either 1) not a woman of childbearing potential (WOCBP) or 2) is a WOCBP and is using acceptable contraception or is abstinent.

Exclusion Criteria:

* Has HIV-2 infection.
* Has hypersensitivity or other contraindication to any of the components of the study drugs as determined by the investigator.
* Has an active diagnosis of hepatitis due to any cause, including active hepatitis B virus (HBV) infection (defined as hepatitis B surface antigen \[HBsAg\]-positive or HBV deoxyribonucleic acid \[DNA\] positive).
* Has a history of malignancy ≤5 years prior to providing documented informed consent except for adequately treated basal cell or squamous cell skin cancer, in situ cervical cancer, or cutaneous Kaposi's sarcoma.
* Has a history or current evidence of any condition (including active tuberculosis infection), therapy, laboratory abnormality or other circumstance (including drug or alcohol use or dependence) that might, in the opinion of the investigator, confound the results of the study or interfere with the participant's participation for the full duration of the study, such that it is not in the best interest of the participant to participate.
* Is taking or is anticipated to require systemic immunosuppressive therapy, immune modulators, or any prohibited therapies from 45 days prior to Day 1 through the study treatment period.
* Is currently taking long-acting cabotegravir-rilpivirine.
* Is currently participating in or has participated in an interventional clinical study with an investigational compound or device from 45 days prior to Day 1 through the study treatment period.
* Has a documented or known virologic resistance to DOR/ISL (DOR resistance substitutions in reverse transcriptase: V106A/M, V108I, Y188L, H221Y, P225H, F227C/L, M230I/L, L234I, P236L, or Y318F; ISL resistance substitution in reverse transcriptase: M184V/I).
* Has exclusionary laboratory values.
* Is female and expecting to conceive or donate eggs at any time during the study.