The safety and tolerability of MK-8591A, a 2-drug fixed dose combination (FDC) of doravirine (100mg) and islatravir (0.75mg) \[DOR/ISL 100 mg/0.75 mg) will be evaluated in participants with Human Immunodeficiency Virus -1 (HIV-1) who were treated with DOR and ISL in earlier clinical studies.