A Study of the Safety and Efficacy of TRTL-913 in Healthy Volunteers (Part A) and in Adults With Tinnitus (Part B)

Inclusion criteria

Part A Inclusion Criteria:

• Healthy male or female adults aged 18 to 64 years (or 65 to 80 years for an elderly cohort, if enrolled), as determined by the investigator.
• Able and willing to provide written informed consent and comply with all study procedures.
• Body mass index (BMI) 18.0 to 35.0 kilograms per square meter (kg/m^2) and body weight greater than (>) 50 kilogram (kg).
• Clinically acceptable medical history, physical examination, vital signs, clinical laboratory tests, and 12-lead ECG, as determined by the investigator.
• QT interval corrected using the Fridericia method (QTcF) of less than or equal to (≤) 450 millisecond (msec) for males or ≤470 msec for females.
• Nonsmokers or light smokers (<10 cigarettes/week or equivalent vaping) for at least 3 months before dosing and willing to abstain during confinement.
• Women of childbearing potential must have a negative pregnancy test and agree to use highly effective contraception throughout the required study period.
• Male participants must agree to use appropriate contraception and refrain from sperm donation for the required study period.

Part B Inclusion Criteria:

• Male or female adults aged 18 to 64 years.
• Able and willing to provide written informed consent and comply with study procedures.
• Diagnosis of subjective, stable, chronic, non-pulsatile tinnitus.
• Generally healthy aside from tinnitus, with no clinically significant abnormalities on medical history, physical or neurologic examination, vital signs, laboratory tests, or ECG that would interfere with study participation.
• BMI 18.0 to 35.0 kg/m^2 and body weight >50 kg.
• Willing to discontinue prohibited medications and substances before study treatment and throughout study participation.
• Women of childbearing potential must have a negative pregnancy test and agree to use highly effective contraception throughout the required study period.
• Male participants must agree to use appropriate contraception and refrain from sperm donation for the required study period.

Exclusion criteria

Part A Exclusion Criteria:

• Any clinically significant acute or chronic medical condition that, in the investigator's opinion, could affect participant safety or study assessments.
• Use of prohibited medications, including moderate or strong cytochrome (CY)P450 inhibitors or inducers, or other prohibited foods or supplements before dosing.
• History of seizures, epilepsy, significant head injury associated with loss of consciousness, or other conditions or medications that increase seizure risk.
• Clinically significant cardiovascular disease, clinically significant ECG abnormalities, long QT syndrome, torsade de pointes, or a family history of long QT syndrome or sudden cardiac death.
• Active infection or clinically significant recent illness before screening or dosing.
• Positive test for human immunodeficiency virus (HIV), hepatitis B, or hepatitis C.
• Clinically significant hepatic or renal impairment or clinically significant laboratory abnormalities.
• History of malignancy within the past 10 years (except adequately treated nonmelanoma skin cancer or cervical carcinoma in situ).
• Current or recent substance or alcohol use disorder or positive drug or alcohol screening.
• Current or history of clinically significant psychiatric illness or suicidal ideation or behavior that would increase study risk.
• Pregnant, breastfeeding, or planning pregnancy during the study.

Part B Exclusion Criteria:

• Current use of, or plans to initiate, pharmacologic or non-pharmacologic treatment for tinnitus during the study.
• Regular night-shift work that could interfere with study assessments.
• Use of prohibited medications, including moderate or strong CYP450 inhibitors or inducers, or other prohibited foods or supplements before dosing.
• History of seizures, epilepsy, significant head injury associated with loss of consciousness, or other conditions or medications that increase seizure risk.
• Clinically significant acute or chronic medical condition that, in the investigator's opinion, could affect participant safety or study assessments.
• Positive test for HIV, hepatitis B, or hepatitis C.
• History of malignancy within the past 10 years (except adequately treated nonmelanoma skin cancer or cervical carcinoma in situ).
• Current or recent substance or alcohol use disorder or positive drug or alcohol screening.
• Current or history of clinically significant psychiatric illness or suicidal ideation or behavior that would increase study risk.
• Pregnant, breastfeeding, or planning pregnancy during the study.