A Healthy Volunteer Study Evaluating the the Safety, Tolerability, and Pharmacokinetics of RT234

Inclusion Criteria: 1. Healthy male or female, 18 to 45 years of age (inclusive at time of informed consent) 2. Normal heart, lung, kidney, and liver function based on physical examination 3. Systolic blood pressure of 100-145 mmHg, diastolic blood pressure of 50-90 mmHg, and a resting heart rate of 40-100 bpm at Screening 4. A body mass index (BMI) of ≤18 to ≥30 kg/m2 at Screening 5. Must be a non-smoker or ex-smoker with less than a 5-pack year history of smoking (including the use of electronic cigarettes) and have ceased smoking ≥1 year prior to Screening; or a social smoker (defined as less than 10 cigarettes in the previous 12 months) Exclusion Criteria: 1. Has serum transaminase (i.e., alanine aminotransferase \[ALT\], aspartate aminotransferase \[AST\], or gamma-glutamyl transferase \[GGT\]) levels greater than three times the upper level of normal 2. Abnormal orthostatic vital signs (at screening) defined as a decrease of ≥20 mmHg in systolic blood pressure and/or a decrease of ≥10 mmHg in diastolic blood pressure and/or \>25 bpm increase in heart rate within 3 minutes of standing, or with symptoms of light-headedness, dizziness, or fainting upon standing. 3. History of hypotension including fainting, syncope, orthostatic hypotension, and/or vasovagal reactions 4. History of retinitis pigmentosa 5. Vision loss due to non-arteritic anterior ischemic optic neuropathy (NAION) or other optic perfusion impairment 6. History of priapism or anatomical deformation of the penis 7. History of sudden sensorineural hearing loss (SSHL), need for hearing aids, and/or other documented hearing loss 8. A corrected QT interval using Fridericia's formula (QTcF) \>450 msec 9. Has evidence of significant obstructive lung disease on spirometry. Subjects with any of the following criteria will be excluded: 1. FEV1 \<60% (predicted) (pre-bronchodilators); or 2. FEV1/FVC \<65% (pre-bronchodilators)