Lidocaine patch 5% and its positive impact on pain qualities in osteoarthritis: results of a pilot 2-week, open-label study using the Neuropathic Pain Scale.

OBJECTIVE: To determine the impact of the lidocaine patch 5% on distinct pain qualities associated with osteoarthritis (OA) through use of the Neuropathic Pain Scale (NPS), an assessment tool designed to assess intensity of various pain qualities (i.e.sharp, dull).

PATIENTS AND METHODS: Patients were enrolled in a prospective, open-label, non-randomized, parallel-group, 2-week study involving 8 clinical trial sites in the United States. Eligible patients had radiographic evidence of OA involving one or both knees and reported moderate-to-severe pain (despite prn or stable doses of analgesics) on the NPS at study enrollment. Patients on prn analgesics were discontinued from all analgesic regimens prior to study entry and received lidocaine patch 5% as monotherapy. Those on stable doses of analgesics were continued on their other analgesic regimens with no additions or dose alterations allowed other than the lidocaine patch 5% as add-on therapy. The lidocaine patch 5% was applied to the area of maximal pain, using no more than a total of 4 patches changed every 24 h. Effectiveness was measured by change from baseline to Week 2 in 4 composite measures of the NPS: NPS-10, NPS-4, NPS-8, and NPS-nonallodynia. Safety was assessed by adverse events (AEs), dermal assessment of application site(s), and skin sensory testing.

RESULTS: In the combined patient population (n = 100), 2 weeks of treatment with lidocaine patch 5% significantly improved all 4 NPS composite measures (p < 0.001). Separate analyses by subgroups revealed significant improvements in all 4 composite measures for both the monotherapy group (n = 12; p < 0.01) and add-on therapy group (n = 88; p < 0.001). No treatment-related AEs were reported for the monotherapy group. In the add-on therapy group, 5 patients experienced mild-to-moderate treatment-related AEs.

CONCLUSIONS: In patients with moderate-to-severe OA of the knee, 2 weeks of treatment with the lidocaine patch 5% significantly reduces the intensity of pain qualities as measured by all 4 NPS composite measures. Our results coincide with previously reported improvements in pain and physical function in the same patient population, as measured by the Western Ontario and McMaster Universities OA Index. Measuring the various qualities of pain appears to be a valid approach for assessing clinical outcomes in the treatment of OA pain. Pain measures such as the NPS can capture the multi-dimensional properties of a patient's pain experience and may offer clinicians the possibility to identify differential effects of analgesic treatments on various pain qualities associated with OA.