A Study of Doravirine/Islatravir (DOR/ISL, MK-8591A) for the Treatment of Human Immunodeficiency Virus 1 (HIV-1) Infection in Participants Who Previously Received DOR/ISL (MK-8591A-054)

The purpose of this study is to evaluate the safety and tolerability of DOR/ISL in adult participants with HIV-1 who had been previously treated with DOR/ISL in earlier clinical studies. There are no formal hypotheses to be tested in this study.

Inclusion Criteria: * Is currently receiving doravirine/islatravir (DOR/ISL) adult fixed dose combination (FDC) tablet in Merck Sharp \& Dohme (MSD)-sponsored clinical studies (MK-8591A-018, -020, and -033 \[except for heavily treatment-experienced (HTE) participants\]). Exclusion Criteria: * Has confirmed HIV-1 RNA ≥200 copies/mL in MSD DOR/ISL (100 mg/0.75 mg) MK-8591A-018 /-020, or at screening for participants entering from DOR/ISL (100 mg/0.75 mg) MK-8591A-033. * Has confirmatory laboratory findings for cluster of differentiation 4+ (CD4+) T-cell counts or lymphocyte counts in the prior DOR/ISL study that meet criteria for discontinuation of DOR/ISL. * Is a HTE participant receiving treatment in MK-8591A-019 or -033.