Inclusion Criteria

Inclusion Criteria

1. Age 18 and greater

2. Clinical diagnosis of constipation

3. Any patients that report taking an opioid analgesic for greater than two (2) weeks
(eg known oncology patients and chronic pain syndrome patients, including those with
low back pain or sciatica)

4. Patients must have previously tried a stable laxative regiment for at least three (3)
days prior to study entry.

5. All patients will have a flat and upright abdominal x-ray, and chest x-ray to exclude
gastrointestinal (GI) obstruction. Any patients who have radiographic evidence of GI
obstruction will need a CT scan of the abdomen to exclude GI obstruction prior to
study enrollment.

6. Females of childbearing potential must have a negative pregnancy test and must be
encouraged to use appropriate birth control for a period after the study.

7. Willing to comply with study instructions and sign an informed consent

Exclusion Criteria:

1. Pregnancy or lactation

2. Recent surgery within six (6) weeks of the emergency department visit

3. Opioid withdrawal syndrome as determined by clinical judgment.

4. Patients with previous history of diabetic gastroparesis.

5. Any patient who has known or suspected gastrointestinal obstruction

6. Any patients with creatinine clearance ≤ 30 mL/min

7. Constipation for which other medical causes cannot be excluded such as
anticholinergic medications, botulinum toxin, or botulism.

8. Any patient with SBP ≤ 80 mmHg or DBP ≤ 45 mmHg or unstable vital signs.

9. Inability to understand or follow the instructions associated with the clinical study
as determined by clinical judgment.

10. A known history of substance abuse on methadone maintenance therapy > 12 months

11. Allergy or contraindication to use of methylnaltrexone

12. Prior enrollment in study