To determine the effect of escalating doses of lidocaine infusion with or without added magnesium on pain levels and the duration of pain relief in patients with fibromyalgia (FM).
A retrospective chart review of 74 patients diagnosed with FM who underwent at least three escalating doses of intravenous (IV) lidocaine infusions (5 mg/kg of body weight, 7.5 mg/kg, and 7.5 mg/kg of lidocaine + 2.5 g of magnesium sulfate) was conducted. Each patient's subjective impression of change in pain intensity and duration of pain relief after each treatment was recorded, along with an 11-point numeric rating scale (NRS) for pain intensity, immediately before and after each infusion.
Short-term lidocaine analgesia was evaluated by the reduction in NRS pain score according to the patients reported pre- (immediately before treatment) and post-treatment (immediately after treatment) values. There was a statistical difference in the NRS score reduction between doses 5 mg/kg and 7.5 mg/kg of lidocaine (P = 0.009). Long-term analgesia was evaluated at follow-up visits by the patient's subjective impression of change in pain intensity and duration of pain relief. There was a statistical difference in the percentage of pain relief and the mean duration of pain relief between the treatments with 5 mg/kg and 7.5 mg/kg of lidocaine (P = 0.007 and P = 0.003). Although there was a trend of greater response to magnesium sulfate as a beneficial adjunct to the lidocaine infusion, we were unable to find a statistically significant difference for any of the variables studied.
This study demonstrated that escalating doses of IV lidocaine to 7.5 mg/kg safely and effectively reduced the pain with prolonged effect in a significant number of patients diagnosed with fibromyalgia. Larger, prospective clinical studies are required to confirm this finding.