Effect of Nalbuphine and Naloxone on Experimentally Induced Skin Sensitivity

In previous clinical studies of post-surgical pain the investigators found that nalbuphine
(Nubain), a narcotic pain killer, relieves pain more effectively when combined with low-dose
naloxone (Narcan), a drug that is used to treat narcotic overdose. This finding was
particularly true in men. The purpose of this study is to find out if nalbuphine combined
with naloxone is more effective in relieving experimentally produced pain than either drug
alone. A second reason for this study is to find out if study medications work more
effectively in women or in men. Subjects will come to the University of California at San
Francisco (UCSF) Clinical Research Center (CRC) for 4 study visits. The first visit will be
a 2-hour screening to assess the subject for study eligibility. During the other three
visits, the investigators will use a thermal stimulating device to produce temporary,
non-injurious skin sensitivity that subjects will feel as painful. Changes in pain will be
measured following the intravenous (i.v.) administration of study drugs. Three drug
combinations will be administered, a different one each visit: 1) nalbuphine 5 mg and
naloxone 0.4 mg , 2) naloxone 0.4 mg and saline (an inactive solution), nalbuphine 5 mg and
saline. These drug combinations will be administered in random order; all subjects will
receive all three combinations.