To assess the analgesic efficacy of the N-methyl-D-aspartate receptor antagonist S(+)-ketamine on fibromyalgia pain, the authors performed a randomized double blind, active placebo-controlled trial.
Twenty-four fibromyalgia patients were randomized to receive a 30-min intravenous infusion with S(+)-ketamine (total dose 0.5mg/kg, n=12) or the active placebo, midazolam (5mg, n=12).
Visual Analogue Pain Scores (VAS) and ketamine plasma samples were obtained for 2.5 hours following termination of treatment; pain scores derived from the fibromyalgia impact questionnaire (FIQ) were collected weekly during an 8-week follow-up.
• 15 minutes after termination of infusion the number of patients showing a reduction in pain scores greater than 50% was 8 in the ketamine group vs. 3 in the placebo group (P<0.05)
• At 180 minutes, 6 vs. 2 (ns),
• At the end of week-1, 2 vs. 0 (ns)
• And at end of week-8, 2 vs. 2.
Ketamine effect on VAS closely followed ketamine plasma concentrations. For VAS and FIQ scores no significant differences in treatment effects were observed in the 2.5 hours following infusion or during the 8-week follow-up.
Side effects as measured by the Bowdle questionnaire (which scores for 13 separate psychedelic symptoms) were mild to moderate in both study groups and declined rapidly, indicating adequate blinding of treatments.
Efficacy of ketamine was limited and restricted in duration to its pharmacokinetics [what the body does to the drug, vs pharmacodynamics, what the drug does to the body].
The authors argue that a short-term infusion of ketamine is insufficient to induce long-term analgesic effects in fibromyalgia patients.
Source: European Journal of Pain, Apr 9, 2011. PMID: 21482474, by Noppers I, Niesters M, Swartjes M, Bauer M, Aarts L, Geleijnse N, Mooren R, Dahan A, Sarton E. Department of Anesthesiology, Leiden University Medical Center, Leiden, The Netherlands.