A Study of Islatravir (MK-8591) in Anti-Retroviral Therapy-Naive, Human Immunodeficiency Virus-1 Infected Participants (MK-8591-003)

Inclusion Criteria: * Non-pregnant, non-breast feeding, postmenopausal or surgically sterile female * Female with reproductive potential agrees to use (or have male partner use) two acceptable methods of birth control * Male agrees to use acceptable method of contraception during study and for 90 days after last dose of trial drug * Has stable baseline health, other than HIV infection * Has no significantly abnormal electrocardiogram * Is HIV-1 positive * Have a screening plasma HIV-1 RNA ≥ 10,000 copies/mL within 30 days prior to the treatment phase of this study. For inclusion in Panel Islatravir Extended Observation, participants must also have a screening plasma HIV-1 RNA ≤ 25,000 copies/mL within 30 days prior to the treatment phase. * Is ART naive * Has not received any investigational agent or marketed ART within 30 days of trial drug administration * Is diagnosed with HIV-1 infection \>= 3 months prior to screening * Is willing to receive no other ART during treatment phase of study * Has no evidence of mutations conferring resistance to nucleoside reverse transcriptase inhibitors (NRTIs) Exclusion Criteria: * Is mentally or legally institutionalized/incapacitated, or has significant emotional problems, or has a history of clinically significant psychiatric disorder of the last 5 years * Has a history of clinically significant endocrine, gastrointestinal, cardiovascular, hematological, hepatic, immunological (outside of HIV-1 infection), renal, respiratory, genitourinary, major neurological abnormalities or diseases * Has a history of cancer (malignancy) * Has a history of significant multiple and/or severe allergies, or had an anaphylactic reaction to drugs or food * Is positive for hepatitis B surface antigen * Has a history of chronic Hepatitis C * Had major surgery or lost 500 mL of blood with 4 weeks prior to screening visit * Has participated in another investigational trial within 4 weeks prior to dosing visit * Will use any medications, prescribed drugs, or herbal remedies 4 weeks prior to dosing of trial drug, up to the post-trial visit * Consumes excessive amounts of alcohol, caffeinated beverages, or tobacco products * Uses illicit drugs or has a history of drug abuse within the prior 2 years