Clinical Neuropharmacology of Pain in Spinal Cord Injury- Dextromethorphan Dose Response Clinical Trial
Condition: Central Neuropathic Pain; Allodynia; Spinal Cord Injury
MeSH terms: Spinal Cord Injuries; Neuralgia; Hyperalgesia; Wounds and Injuries
Intervention: Dextromethorphan
Intervention description: 0, 25, 50 and 100% of maximum tolerated dose, each administered over a 4 week period
Intervention MeSH terms: Dextromethorphan
Phase: Phase 2
Study type: Interventional
Primary purpose: Treatment
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Enrollment: 26.0
Sex: All
Minimum age: 18 Years
Maximum age: 70 Years
Healthy volunteers: No
Keywords: chronic pain; central neuropathic pain; spinal cord injury; dextromethorphan; lidocaine; combination therapy; analgesia

Summary:

      This randomized, placebo-controlled, double-blind 4x4 crossover clinical trial was part of a
      larger NIH-funded study to evaluate the analgesic efficacy of three doses of chronic oral
      (PO) dextromethorphan compared to placebo in central neuropathic pain following spinal cord
      injury. Subjects' maximally tolerated doses (MTD) were first determined to establish
      individual dose-analgesic response relationships in a run-in period; following a washout
      period, subjects were then randomized to receive an order of four doses of dextromethorphan
      (including placebo) in a 4x4 Latin square cross-over design.
    

Eligibility criteria:

        Inclusion Criteria:

          1. Healthy male or female adults, age 18 to 70 with central neuropathic pain for a
             minimum of 3 months following SCI as confirmed by neurologic evaluation, with an
             average pain intensity score of at least moderate over at least 50% of the day for the
             7 days prior to the screening visit and over the 7 days prior to starting study
             medication.

          2. Subjects used no medication or a stabilized medication regimen for chronic and
             well-controlled medical conditions

          3. Serum laboratory examination obtained at study entry:

               -  Liver function tests (albumin within 20% of normal, SGOT/SGPT within 50% of
                  normal).

               -  For women of childbearing age: negative serum beta HCG.

          4. Postmenopausal women, or be physically incapable of childbearing, or be practicing an
             acceptable method of birth control.

          5. Normal cognitive function.

          6. Normal communicative ability (English).

          7. Ability to demonstrate competence in recording five times daily in pain diary for 1
             week (with 100% compliance), and in completing required questionnaires.

          8. Signed informed consent.

        Exclusion Criteria:

          1. Pregnancy or breast-feeding.

          2. Renal or hepatic dysfunction.

          3. Significant cardiac disease (e.g. MI within 1 year).

          4. Signs or symptoms of central neurological disorder, excluding SCI.

          5. Severe psychological disorder requiring treatment.

          6. Concurrent use of monoamine oxidase inhibitors within 2 weeks prior to study entry.

          7. Use of known CYP2D6 (but not CYP3A4) inhibitors or inducers.

          8. History of hypersensitivity or intolerance to dextromethorphan or lidocaine.

          9. Chronic substance abuse, including alcohol.

         10. Participation in a study of an investigational drug or device within 30 days prior to
             screening for this study.

         11. Poor metabolizer of P450 2D6 substrates.