Study to Determine How BCX4161 is Metabolized and Eliminated by the Body

Inclusion Criteria: 1. Healthy males 2. Age 30 to 65 years of age (inclusive) 3. Body mass index of 18.0 to 32.0 kg/m2 4. Must be willing and able to communicate and participate in the whole study 5. Must provide written informed consent 6. A history of regular bowel movements 7. Must agree to use an adequate method of contraception Key Exclusion Criteria: 1. Participation in a clinical research study within the previous 3 months 2. Current or history of any drug or alcohol abuse in the past 2 years or positive drugs of abuse screen 3. Current smokers 4. Radiation exposure, including that from the present study, exceeding 5 mSv in the last 12 months or 10 mSv in the last 5 years 5. Clinically significant medical history, current medical or psychiatric condition, ECG finding, or laboratory/urinalysis abnormality 6. Activated partial thromboplastin time or PT outside of normal laboratory limits