This is a multicenter, non-randomized, single-dose, parallel-group study. Each subject will receive a subcutaneous dose of MNTX. Eight subjects with normal hepatic function and eight subjects from each classification of hepatic impairment will be enrolled. Plasma samples will be collected before and at specified intervals after dosing and the concentration of MNTX will be analyzed.

Inclusion Criteria:

1. Males and females between the ages of 18-80 years
2. Body weight greater than 100 lbs and BMI between 18-38
3. Liver values that are abnormal must not be clinically relevant as judged by the investigator. Liver enzyme and bilirubin must be less than 5 times the upper normal of reference range and may be repeated under fed conditions if abnormal. Stable hepatitis patients as well as cirrhosis patients of either etiology.

Exclusion Criteria:

1. History of current alcohol abuse with less than 1 year abstinence
2. Conditions possibly affecting drug absorption, e.g. gastrectomy or clinically significant diabetic gastroenteropathy.
3. Currently pregnant or nursing
4. Methadone use.