This study is to evaluate the relative bioavailability of nalbuphine after single IM injection of Sebacoyl Dinalbuphine Ester (SDE) injection and Bain®, Nalbuphine HCl IM injection in healthy volunteers.

Inclusion Criteria:

1. Subjects must be male or female adults in good health on the basis of medical history, physical examination, electrocardiogram, chest X-ray, and routine laboratory evaluations.

2. Vital signs (after 3 minutes resting in a upright position) which are within the following ranges:

   Ear body temperature between 35.0-37.5°C. Systolic blood pressure, 90-140 mm Hg. Diastolic blood pressure, 50-90 mm Hg. Pulse rate, 50-90 bpm. Fasting blood glucose, < 110 mg/dL.

3. Within -20% to +20% of the ideal body weight. For male subjects, body weight must be above 50 kg and for female subjects, body weight must be above 45 kg.

4. Able to sign informed consent prior to study.

5. Able to communicate well with the investigator and comply with the requirements of the study.

Exclusion Criteria:

1. Use of any alcohol-containing products, prescription medications or over-the-counter, non-prescription preparations (including herbal preparations) within 2 weeks prior to study entry unless deemed acceptable by the Investigator (except up to 5 doses of ≤ 1000 mg of acetaminophen or ≤ 400 mg ibuprofen within this 2 week period).
2. Alcohol or caffeine ingested within 48 hours prior to dosing.
3. Significant illness within 2 weeks prior to dosing.
4. Participation in any clinical investigation within 2 months prior to dosing or longer as required by local regulation.
5. Donation or loss of more than 500 mL of blood within 3 months prior to dosing. Donation or loss of more than 250 mL of blood within 2 months prior to dosing.
6. Presence of cardiovascular disease.
7. Presence of gastrointestinal disease.
8. Presence of asthma or lung disease.
9. Presence of liver disease or liver injury as indicated by an abnormal liver function profile such as AST, ALT, gamma-GT, Alkaline Phosphatase, or Total Bilirubin. (value of AST or ALT above 3 times of the upper limit of the normal range; other items clinically significant abnormality judged by investigator).
10. Presence of impaired renal function as indicated by abnormal creatinine or BUN values or abnormal urinary constituents. (value of creatinine or BUN beyond the range from -20% of the lower limit of the normal range to +20% of the upper limit of the normal range; other items clinically significant abnormality judged by investigator)
11. Presence of neurological disease.
12. Presence of psychiatric disease.
13. Subject is positive for HIV immunology test.
14. A known hypersensitivity to nalbuphine or its analogs.
15. History of drug or alcohol abuse within 12 months prior to dosing.
16. Permanent confinement to an institution.
17. Pregnant or lactating women.
18. Individuals are judged by the investigator or pharmacokineticist to be undesirable as subjects for other reasons