Epidurally administered opioid pain medications are important tools for postoperative pain
control, but each agent has its own limitations. Methadone's properties suggest that it may
provide a long duration of pain control with minimal side effects related to spread to the
brain or absorption into the blood stream. In this study, the investigators aim to compare
the relative pain relieving effects, markers of side effects, and concentrations in the blood
of epidurally administered methadone as compared to another long-acting opioid which is
commonly administered epidurally, morphine.