The purpose of this study is to determine the safety, tolerability and pharmacokinetics of TAK-648 when administered as a single oral dose of TAK-648 solution at escalating dose levels in healthy participants.

This was a phase 1, randomized, double-blind, placebo-controlled, single-center, single-dose study in healthy participants. The study is the first TAK-648 study in humans and is designed to evaluate the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of a single dose of TAK-648 to healthy participants.

The compound being tested in this study is TAK-648. TAK-648 is being tested to find a safe and well-tolerated single dose.

This study measured how much of the study drug got into the blood stream and how long it took the body to get rid of it. Information about any side effects that may have occurred was also collected. This study was a randomized dose-rising study which means that the first group of research participants was assigned by chance to receive either the study drug or placebo. Placebo is a solution that looks like the study drug but has no active ingredient. The lowest dose of the study drug or placebo was given to the 1st group of participants (1st cohort) and a higher dose was given to the next group until all the doses of the study drug were tested. TAK-648 was dosed in 5 sequential cohorts with escalating doses from the lowest dose given in Cohort 1 to higher doses given in the subsequent cohort. Doses could be adjusted based on available safety, tolerability, and pharmacokinetic (PK) data.

Approximately 40 healthy male and female participants were planned for enrollment with 8 subjects planned (6 randomized to TAK-648 and 2 randomized to placebo) for each cohort. The study included 5 cohorts.

This single-center trial was conducted in the United States. The overall time to participate in this study was up to 45 days. Participants made multiple visits to the clinic, including one 5-day period of confinement to the clinic. All participants were contacted by telephone 14 days after the last dose of study drug and on Day 84 (+/-2 days) for a follow-up assessment.

Inclusion Criteria:

1. Is a healthy adult male or non-pregnant, non-lactating female.
2. Is aged 18 to 55 years, inclusive.
3. Weighs at least 55 kg (121 lbs) and has a body mass index (BMI) between 18.0 and 30.0 kg/m^2, inclusive.
4. Has a systolic blood pressure >90 and ≤150 mm Hg and a diastolic blood pressure of >60 and ≤90 mm Hg at Screening and at Check-in (Day -2).
5. Has a calculated creatinine clearance >60 mL/min at Screening and Check-in (Day -2).

Exclusion Criteria:

1. Has a known hypersensitivity to any component of the formulation of TAK-648, phosphodiesterase inhibitors or Listerine strips.
2. Has significant medical histories or currently uncontrolled clinical conditions, which may not be safe for participant to participate in the study, may impact the participant's ability to participate in the study; may influence absorption of the study drug, or may potentially confound the study results.
3. Has a history of persistent, chronic or intermittent nausea, vomiting, or diarrhea or had a current or recent (within 6 months) gastrointestinal disease that would influence the absorption of drugs
4. Has a diagnosis of major depression, bipolar disorder, or anxiety disorders or received any medication to treat any psychological disorders within 1 year prior to Screening.
5. Has abnormal laboratory values that suggest a clinically significant underlying disease or has the following laboratory abnormalities: alanine aminotransferase (ALT) and/or aspartate aminotransferase (AST) >2.5 times the upper limits of normal.
6. Use of any excluded medications, supplement, or food product outlined in the protocol.
7. Use of new medications during the course of the study including through the Follow-up period.

All randomized participants.

14 Days

At each visit the investigator had to document any occurrence of adverse events irrespective of the relation to study treatment.