This study is evaluating the Pharmacokinetics of MNTX in healthy control subjects and in patients with mild, moderate, or severe renal impairment who do not require hemodialysis.

Inclusion Criteria:

1. Body weight >100 lbs. (> 45 kg), and body mass index (BMI) between 18-38 kg/m2, inclusive (BMI 18-30 for the matched reference group)
2. For patients/subjects requiring pharmacotherapy, a stable drug regimen, defined as not having started a new drug or changed dosage within three (3) days or five (5) half-lives (whichever was longer) prior to administration of MNTX concomitant medication must either have conformed to the list of approved drugs and dosage or have been approved by the sponsor.
3. Patients with normal renal function, demographically comparable to the patients with impaired renal function weights and ages were within the range of chronic kidney disease (CKD) group and the average for the matched reference group was within 10 years and 10 kg of the average for the CKD
4. Patients with impaired renal function, good general health except for those illnesses associated with CKD.

Exclusion Criteria:

1. Subjects/patients with any conditions possibly affecting drug absorption (eg. Gastrectomy or clinically significant diabetic gastroenteropathy)
2. Methadone use
3. Consumption of grapefruit or grapefruit juice within seven (7) days prior to administration of study medication.
4. Patients requiring hemodialysis.