Multivariate analysis of chronic pain patients undergoing lidocaine infusions: increasing pain severity and advancing age predict likelihood of clinically meaningful analgesia.

OBJECTIVES: The proportion of chronic pain patients with suspected neuropathic pain who will have clinically meaningful pain relief with intravenous (IV) lidocaine and the clinical characteristics that identify these patients have not been described previously.
METHODS: We conducted a cohort study of 99 patients who underwent IV lidocaine infusions for suspected neuropathic pain. An 11-point Numerical Rating Score (NRS) of pain intensity was recorded at the beginning and end of each infusion. A predefined literature-based criteria for "clinically meaningful" reductions in pain score was used to classify patients as responders or nonresponders. Multivariate logistic regression was used to determine clinical variables that predicted an increased likelihood of being a lidocaine responder.
RESULTS: The mean reduction in NRS during lidocaine infusions was 2.34 (95% confidence interval 2.83-1.85, P<0.001). Forty-two percent of patients (95% confidence interval 32.5%-52.8%) had NRS reductions of 30% or greater and met the predefined criteria as lidocaine responders. Univariate and multivariate analyses indicated that advancing age and pain severity significantly increased the odds of being a lidocaine responder. Controlled for all other factors, each decade of advancing age increased the odds of being a lidocaine responder by 36%. Each 1-point increase, on an 11-point scale of baseline pain severity, increased the odds of being a lidocaine responder by 29%. DISCUSSION: IV lidocaine effectively reduces pain in a minority of patients suspected of having neuropathic pain. Pain severity and patient age can be used to target therapy to those most likely to respond.