MOA-728, an investigational drug, is currently being studied for the relief of constipation associated with postoperative ileus and treatment of opioid induced constipation in patients receiving palliative care. This study will further investigate the IV formulation of MOA-728 comparing PK/PD time points for a 20-minute versus a 4-hour infusion.

Inclusion Criteria:

• Generally healthy men and nonlactating, nonpregnant women age 18 to 65 years with BMI of 18.0 to 35.0 kg/m2
• Must have been receiving methadone treatment of greater than or equal to 30 mg/day for at least one month and a positive drug screen for methadone
• High probability for compliance with and completion of the study

Exclusion Criteria:

• Significant cardiovascular, hepatic, renal , respiratory, gastrointestinal, endocrine, immunologic, dermatologic, hematologic, neurologic, or psychiatric disease. Presence or history of any disorder that may prevent the successful completion of the study. Any surgical or medical condition that my interfere with the distribution, metabolism or excretion of the test article.
• Acute disease state, family history of long QT syndrome and/or sudden cardiac death, allergy to opioids or drugs. Use of any investigational or prescription drugs within 30 days, any OTC drugs including herbal supplements within 14 days and drugs required to maintain regulation of bowel movements 48 hours before study day 1.
• History of alcoholism within 1 month before study day 1, admitted alcohol abuse, or consumption of more than 2 standard units of alcohol per day.