Inclusion Criteria:

- The subject enrolled in this study must have been previously randomized and dosed in
the double-blind treatment period of study EN3202-016 or EN3202-019 and completed the
exit visits for these studies.

- Males or females, age 18 and 75 years, inclusively.

- The subject continues to have chronic moderate to severe back or cancer pain that
requires opioid medication. Women must continue to be of non-childbearing potential.

Exclusion Criteria:

- The subject experienced any serious drug related adverse events in studies EN3202-016
or EN3202-019.

- The subject withdrew from EN3202-016 or EN3202-019 for a reason other than lack of
efficacy.

- Subjects with known allergies to opiate-class narcotic agents (morphine, codeine,
hydrocodone, propoxyphene, meperidine, oxycodone, etc.) or naproxen, or subjects who
have any medical condition in which opiates are medically contraindicated.