Evaluating the Pharmacokinetics, Safety, and Tolerability of Doravirine (MK-1439) and Doravirine/Lamivudine/Tenofovir Disoproxil Fumarate (MK-1439A) in HIV-1-Infected Children and Adolescents

This study will evaluate the pharmacokinetics (PK), safety, and tolerability of DOR and
DOR/3TC/TDF in HIV-1-infected children and adolescents.

This study will be conducted in two sequential cohorts: Cohort 1 and Cohort 2. At study entry
(Day 0), participants in Cohort 1 will receive a single dose of DOR added to their current
HIV regimens. (The antiretroviral drugs in their current HIV regimens will not be provided by
the study.) Participants in Cohort 1 will undergo intensive PK evaluations, and they will
have an additional study visit at Week 2.

The study team in consultation with a Study Monitoring Committee will evaluate data from
Cohort 1 before enrolling participants in Cohort 2. Participants in Cohort 2 will receive
DOR/3TC/TDF once daily from Day 0 through Week 96. They will attend study visits at Weeks 1,
2, 4, 8, 12, 16, 24, 36, 48, 64, 80, and 96. Study visits will include physical examinations,
PK evaluations, and blood and urine collection.

Inclusion Criteria:

- Age 12 years to less than 18 years at entry

- Weight greater than or equal 35 kg at entry

- If not of legal age to provide independent informed consent: Parent or guardian is
willing and able to provide written informed consent for study participation; in
addition, when applicable per local Institutional Review Board / Ethics Committee
(IRB/EC) policies and procedures, potential participant is willing and able to provide
written informed assent for study participation. If of legal age to provide
independent informed consent as determined by site Standard Operating Procedures
(SOPs) and consistent with site IRB/EC policies and procedures: Potential participant
is willing and able to provide written informed consent for study participation

- Confirmed HIV-1-infection based on documented testing of two samples collected at
different time points. More information on this criterion can be found in the
protocol.

- Antiretroviral therapy (ART) exposure, virologic suppression, and resistance
requirements, as follows:

- Cohort 1

- ART exposure requirements, based on individual or parent/guardian's report and,
if available, confirmed by medical records:

- At entry, receiving combination ART with raltegravir (RAL) or dolutegravir (DTG)
plus 2 nucleoside reverse transcriptase inhibitors (NRTIs); AND

- At entry, has not received non-nucleoside reverse transcriptase inhibitors
(NNRTIs), protease inhibitor (PIs), or cobicistat within the previous 30 days;

- AND

- Virologic suppression, as documented in medical records and as defined by:

- One or more HIV RNA polymerase chain reaction (PCR) result below the level of
quantification (BLLQ) within 15 months prior to enrollment, AND

- If any HIV RNA PCR tests have been done within 3 months prior to enrollment, all
results are below the level of quantification, AND

- HIV RNA PCR result less than 40 copies/mL at screening, performed as per the
protocol. Note: A single, unconfirmed HIV-1 RNA result greater than or equal to
the level of quantification but less than 500 copies/mL, between 3 and 15 months,
prior to enrollment is not exclusionary as long as the other criteria for
documentation of virologic suppression are met.

- Cohort 2 ART-naive

- ART exposure requirements, based on individual or parent/guardian's report and,
if available, confirmed by medical records:

- At entry, received no antiretrovirals (ARVs) for treatment of HIV infection
including investigational agents (prior receipt of ARVs for prevention of
perinatal transmission is permitted);

- AND

- Screening genotypic resistance test results indicate susceptibility to doravirine
(DOR), tenofovir disoproxil fumarate (TDF), and lamivudine (3TC) (see the
protocol for more information; result must be available prior to enrollment),
performed as per the protocol;

- AND

- If available, as documented in medical records, any prior genotypic resistance
test result indicates susceptibility to DOR, TDF, and 3TC (see the protocol for
more information). Note: For individuals that are re-screened, the genotypic
resistance test does not need to be repeated.

- Cohort 2 ART-experienced

- ART exposure requirements, based on individual or parent/guardian's report and,
if available, confirmed by medical records:

- No previous history of change in ARVs due to clinical or virologic failure, in
the opinion of the site investigator or designee;

- AND

- Virologic suppression, as documented in medical record and as defined by:

- One or more HIV RNA PCR result BLLQ within 15 months prior to enrollment, AND

- If any HIV RNA PCR tests have been done within 3 months prior to enrollment, all
results are below the level of quantification, AND

- HIV RNA PCR result less than 40 copies/mL at screening (see the protocol for more
information);

- AND

- If available, as documented in medical records, any prior genotypic resistance
test result indicates susceptibility to DOR, TDF, and 3TC (see the protocol for
more information). Note: This group of ARV-experienced, virologically suppressed
participants will only enroll once there are data from the adult switch studies
indicating virologic efficacy and safety (see the protocol for more information).
Sites will be informed via a Clarification Memorandum when ART-experienced
participants can be enrolled. Note: A single, unconfirmed HIV-1 RNA result
greater than or equal to the level of quantification but less than 500 copies/mL,
between 3 and 15 months, prior to enrollment is not exclusionary as long as the
other criteria for documentation of virologic suppression are met.

- Grade 2 or lower hemoglobin, aspartate aminotransferase (AST), alanine transaminase
(ALT), alkaline phosphatase, and lipase on specimens obtained at screening

- For Cohort 2 only, grade 2 or lower creatinine, proteinuria, and glycosuria on
specimens obtained at screening

- Estimated glomerular filtration rate (eGFR) greater than or equal to 60 mL/min/1.73
m^2, on specimens obtained at screening, based on the Schwartz equation. More
information on this criterion can be found in the protocol.

- For females who have reached menarche or who are engaging in sexual activity
(self-reported), negative pregnancy test at entry

- For females engaging in sexual activity that could lead to pregnancy (self-reported),
agrees to use two effective, medically accepted birth control methods while on study
and for two weeks after permanently discontinuing study drug

- For males engaging in sexual activity that could lead to pregnancy (self-reported),
agrees to use condoms while on study and for two weeks after permanently discontinuing
study drug

- Able and willing to swallow available formulation(s) (tablet or, as available, oral
granules). Note: The study is expected open to accrual with only the tablet
formulation available. Sites will be informed when the oral granule formulation is
available for participant use. Once the granule formulation is available, participants
in Cohort 2 will be asked to choose which formulation they would like to take at
Entry. Formulation switches during the study may be allowed, as described in the
protocol.

Exclusion Criteria:

- Evidence of decompensated liver disease manifested by the presence of or a history of
ascites, esophageal or gastric variceal bleeding, hepatic encephalopathy, or other
signs or symptoms of advanced liver diseases. Note: Individuals with chronic hepatitis
B who have grade 2 or lower ALT and AST and have no significant impairment of hepatic
synthetic function (significant impairment of hepatic synthetic function is defined as
a serum albumin less than 2.8 mg/dL or an international normalized ratio (INR) greater
than 1.7 in the absence of another explanation for the abnormal laboratory value) are
eligible.

- For Cohort 2 only, detectable hepatitis C virus (HCV) by RNA PCR or current or planned
treatment with direct antiviral agent for HCV. Note: HCV antibody positivity but
undetectable by HCV RNA PCR results are permitted.

- Presence of any active AIDS-defining opportunistic infection

- History of malignancy (ever), with the exception of localized malignancies such as
squamous cell or basal cell carcinoma of the skin

- Clinical evidence of pancreatitis, as determined by the clinician (at entry)

- Use of nafcillin, dicloxacillin, or any of the prohibited medications, within 30 days
prior to study entry (see the protocol for a complete list of prohibited medications)

- For females, currently breastfeeding an infant at entry

- Enrolled in another clinical trial of an investigational agent, device, or vaccine

- Unlikely to adhere to the study procedures or keep appointments, in the opinion of the
site investigator or designee

- Used, or anticipates using, chronic systemic immunosuppressive agents or systemic
interferon (e.g., for treatment of HCV infection) within 30 days prior to study entry.
Note: Systemic corticosteroids (e.g., prednisone or equivalent up to 2 mg/kg/day) for
replacement therapy or short courses (less than or equal to 30 days) are permitted.
See the protocol for a complete list of prohibited medications.

- Diagnosed with current active tuberculosis and/or is currently being treated with a
rifampicin-containing regimen

- Individual has any other condition, that in the opinion of the site investigator or
designee, would make participation in the study unsafe, complicate interpretation of
study outcome data, or otherwise interfere with achieving study objectives