Epidural Methadone in Healthy Volunteers

Acute postoperative pain control remains a major challenge in healthcare, with a need to
balance analgesic effectiveness, patient safety, and cost. Excellent analgesia is a universal
clinical imperative, but our current approaches are often inadequate. Epidural opioids can be
useful tools, but each carries its own strengths and limitations. Bolus morphine is long
lasting but exhibits rostral spread in the cerebrospinal fluid, which raises risks of adverse
effects, particularly late-onset respiratory depression. Lipophilic opioids such as fentanyl
and sufentanil exhibit selective segmental analgesia but are of short duration due to
systemic absorption. As such, they require continuous epidural administration via an
indwelling epidural catheter and a pump (patient-controlled or continuous infusion), which
has implications for nursing, pain management services, and hospital cost. Methadone's
physico-chemical properties suggest that epidural methadone administration would be ideal in
providing long-duration analgesia with fewer of the adverse effects seen with medications
like morphine.

The aim of this study is to compare the effects of two medications given epidurally: morphine
and methadone. We will do so using a randomized, double-blinded, crossover design study.
During each of two study visits, participants will receive a single epidural bolus of either
morphine or methadone. We will examine the ability of the medication to blunt pain from heat
or pressure using quantitative sensory testing at both the dermatome of injection (leg) and a
distant dermatome (face); in doing so, we will demonstrate relative segmental versus
supraspinal or systemic opioid activity. Additionally, we will assess signs and symptoms of
supraspinal opioid activity, which may predispose to adverse effects, and blood
concentrations of each medication. Each of the aforementioned measurements will be conducted
at multiple points over a 24 hour period. Following a washout period, patients will return
for a second visit, at which time the protocol will be repeated using the other medication.

Inclusion Criteria:

1. Age ≥18;

2. Body mass index between 18.5 and 30

3. Good general health with no remarkable medical conditions;

4. Able and willing to provide informed consent.

Exclusion Criteria:

1. Known history of hepatic, renal, and cardiac disease;

2. Known history of diabetes mellitus;

3. Chronic pain;

4. A skin or spine condition preventing safe epidural catheter placement;

5. Current pregnancy or lactation;

6. Known coagulopathy or ongoing anticoagulant use which contraindicates epidural
catheter placement;

7. Known allergic reactions to opioids or local anesthetics;

8. History of current or prior substance use disorder or positive screen using the
4-question Simple Screening Instrument for Substance Abuse (SSI-SA).