Previous studies indicate that chronic pain, including fibromyalgia (FM), negatively impacts quality of life (QoL) for the reportedly affected 3%-6% of the world population. “There is supportive evidence for the use of intravenous (IV) lidocaine for FM; however, there is also a paucity of data regarding safety, effectiveness, and clear indications for IV lidocaine alone and in combination with magnesium,” explains Igor Wilderman, MD, CCFP, FCFP, DCAPM. “There is currently no established consensus for optimal infusion rates and doses, nor criteria for patient selection in the use of lidocaine infusion for chronic pain.”

Assessing Escalating Lidocaine Doses

For a study published in Pain Medicine, Dr. Wilderman and colleagues sought to determine the effect of escalating doses of IV lidocaine with or without magnesium on pain level and duration of relief in patients with FM. The study team conducted a retrospective chart review of patients with FM at a private clinic. Participants had received at least three treatments of IV lidocaine with doses progressing from 5 mg/kg of adjusted body weight (ABW) to 7.5 mg/kg of ABW, and to 7.5 mg/kg of ABW plus magnesium sulfate 2.5 g. Patients rated their pain on a 0-10 numeric rating scale (NRS) before and after every treatment, and responses to treatment were recorded after each visit.

Encouraging Results

From a pretreatment mean of 7.9, patients reported reduced NRS scores by 2.41 after the first treatment, 3.15 after second, and 3.62 after third). “The Figure demonstrates the distribution of absolute NRS pain score reductions (short-term analgesia) for all three treatments, as measured by pre- and post-treatment NRS scores,” adds Dr. Wilderman. “Data indicate the percentage of short-term pain relief was 30.51% to 46.71%. This is encouraging, as previous studies have reported that pain reduction from 20% to 50% has a clinically meaningful impact.” Patients reported an average 16 days of pain relief following all treatments, with mean durations of 8.68 days, 14.05 days, and 17.54 days, respectively, following each of the three doses.

The 7.5 mg/kg ABW dose of lidocaine was found to provide participants with a greater analgesic response than the 5 mg/kg ABW dose, in both the short and long term. “A higher dose of IV lidocaine was not associated with a higher frequency of adverse reactions when performed over 90 min with the maximum infusion rate not more than 9.73 mg/min,” notes Dr. Wilderman.

The study team defined patients with FM who responded to IV lidocaine as those who reported at least a 25% reduction in pain for at least 14 days. After the first, second, and third treatments, 25.8%, 45.5%, and 57.6% of patients, respectively, met the long-term responder criteria.

Important Implications

“More in-depth research into IV lidocaine for patients with FM is needed,” says Dr. Wilderman, “including a randomized, double-blind, placebo-controlled trial and properly designed IV lidocaine dose-response studies in patients with FM and neuropathic pain with frequently scheduled patient-reported outcomes. These reported outcomes should include pain relief diaries, analgesic medication consumption, and use of other concurrent treatments for a prolonged period following the infusion.”

In the meantime, according to Dr. Wilderman, the “research suggests that clinicians should, during the initial infusion, administer IV lidocaine at 5 mg/kg ABW. If the patient can tolerate the lidocaine treatment, but the pain relief is not significant, the dose can be increased to 7.5 mg/kg ABW for the subsequent infusions to reach a clinically meaningful effect. Adding 2.5 g of magnesium sulfate as an adjuvant to the infusion with lidocaine at 7.5 mg/kg ABW was also beneficial for some patients and can be recommended in order to increase or prolong pain relief. To avoid adverse reactions, we recommend 90 min duration of the infusion.”