The intravenous ketamine test predicts subsequent response to an oral dextromethorphan treatment regimen in fibromyalgia patients.

Pain Management Division, Department of Anesthesiology & Critical Care Medicine, Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA.
Journal of Pain (Impact Factor: 4.22). 06/2006; 7(6):391-8. DOI: 10.1016/j.jpain.2005.12.010
Source: PubMed

ABSTRACT Fibromyalgia (FM) is a challenging pain syndrome for which no reliable pharmacologic treatment exists. Recent clinical studies suggest that N-methyl-D-aspartate receptors might play a role in the pathogenesis of this disorder. To determine whether an intravenous (IV) ketamine test predicts the response to a therapeutic trial with an oral N-methyl-D-aspartate receptor antagonist, we performed a low-dose (0.1 mg/kg) IV ketamine infusion on 34 consecutive patients with FM, which was subsequently followed by an oral dextromethorphan (DX) treatment regimen. As per previous guidelines, the cutoff value for a positive response to the IV ketamine test was designated to be 67% pain relief, and a positive response to DX treatment was 50% pain reduction at 4- to 6-week follow-up visits. The degree of correlation between pain relief with ketamine and DX was highly significant (Pearson correlation coefficient, 0.66; P < .001). Ten patients responded positively to both ketamine and DX, 19 responded to neither drug, 3 had a positive response to ketamine but not DX, and 2 obtained good pain relief with DX but not ketamine. The sensitivity of the IV ketamine test was 83%, the specificity was 86%, the positive predictive value was 77%, and the negative predictive value was 91%. An association was also found between the development of side effects to the two treatments. PERSPECTIVE: The response to an IV ketamine infusion was found to predict the subsequent response to an oral dextromethorphan treatment regimen in fibromyalgia patients, with an observed agreement of 83%. Considering the refractory nature of fibromyalgia to conventional pain treatments, the IV ketamine test might enhance patient care by saving time and reducing unnecessary treatment trials.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Objectives The present study challenges chronic Whiplash Associated Disorders (WAD)-subjects to a pharmacological intravenous (i.v.) test with morphine, ketamine, and active placebo (midazolam). The aim was to describe the short-term responses to drugs and the assumed heterogeneity in the patterns of responses. We related the different responder groups to the results from psychometric tests.Methods The study includes 95 patients, all with chronic WAD and referred to our departments. They answered a questionnaire including the following psychometric instruments relevant for chronic pain: Beck Depression Inventory, Coping Strategies Questionnaire, Multidimensional Pain Inventory, Life Satisfaction Checklist, SF36 and EuroQol. The subjects also went through sessions with separate infusions of morphine (0.3 mg/kg), ketamine (0.3 mg/kg) and midazolam (0.05 mg/kg). Infusion time was 30 min followed by a 2-h post-infusion assessment. Assessments were made using a Visual Analogue Scale (VAS) for pain intensity and unpleasantness and by statements of per cent pain relieved. A categorical pain rating scale was also used. A positive response was defined as ≥50% decrease of the VAS-level on two consecutive assessment points during the test sessions, anything less was a non response. The placebo responders were defined as those with a positive response to the active placebo infusion.ResultsThe tests were completed by 94 subjects and 26% of these were placebo responders. Among the placebo non responders, 47% responded to morphine, 41% to ketamine, 25% to both drugs and 37% to neither morphine nor ketamine (pain intensity assessments). Similar proportions were found in the assessments of pain unpleasantness and per cent pain relieved. Approximately one in four subjects (27%, pain intensity assessment) did not respond to any of the drugs tested. This relatively high proportion of non responders seemed to be worst cases in some aspects of the psychometric tests. Generally, this non responder group had a trend to score worse for most items in the psychometric tests with some reaching significance in a univariate analysis. This result was confirmed in a multivariate context, although the results indicated only small differences between the groups. All three substances showed significant pain relief compared to baseline on all assessment points. On most variables, morphine and ketamine were significantly more effective compared to the active placebo.Conclusions There are different subgroups among subjects with chronic WAD with variations in responses to i.v. morphine, ketamine, and midazolam (active placebo). Subjects with chronic WAD who did not respond to any of the drugs tested scored badly in some aspects of the psychometric instruments.ImplicationsThe present study confirms one aspect of the heterogeneity in the population with chronic WAD. The study does not elucidate precise pain mechanisms but taken together with other studies exploring other aspects, it stresses the importance of individualizing the assessment and treatment of subjects with chronic WAD. A common clinical experience is that depression, anxiety and maladaptive coping strategies often are obstacles for successful medical treatment of chronic pain. The present study supports this experience and emphasizes the need for assessment of psychometric variables when planning the treatment of chronic WAD.
    Scandinavian Journal of Pain 07/2012; 3(3):151–163. DOI:10.1016/j.sjpain.2012.01.003
  • [Show abstract] [Hide abstract]
    ABSTRACT: Fibromyalgia is a chronic pathology and its main symptom is pain which usually does not respond to traditional analgesia. Its clinical characteristics and the diverse neurophysiologic findings in these patients point to a central sensitization process of the nociceptive system as the central physiopathologic axis in this disease. The knowledge of the nociceptive system functioning and its behavior in this disease has led, in the past few years, to new possibilities for the therapeutic approach. In that way, drugs with a differential mechanism of action, allowing a modulation of the nociceptive system capable of producing analgesia where other medications have failed are being developed. Different drugs with the capacity increasing the activity of biologically active amines implicated in the nociceptive inhibition process and others which are destined to reduce the excitability of the system through ion channels, are being tested with some benefit in Fibromyalgia patients and may constitute a more rational neuromodulating drug profile for this disease.This article reviews the different pharmacological strategies supported by scientific evidence and points to some future research lines that fortifies the therapeutic change taking place in the treatment approach of these patients.
    Reumatología Clínica 08/2009; 5. DOI:10.1016/j.reuma.2009.04.003
  • La Lettre de médecine physique et de réadaptation 06/2007; 23(2).