Onset of Response with Duloxetine Treatment in Patients with Osteoarthritis Knee Pain and Chronic Low Back Pain: A Post Hoc Analysis of Placebo-Controlled Trials
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BACKGROUND: Knowing when to change pain-medication strategy is not well researched and remains a gap in treating chronic pain. OBJECTIVE: Our aim was to determine how long to treat osteoarthritis (OA) knee pain and chronic low back pain (CLBP) with duloxetine before considering a change in medication strategy. METHODS: We employed a post hoc analysis of changes in pain-severity data from placebo-controlled studies of duloxetine treatment in nondepressed patients with OA knee pain and CLBP. The studies were selected for inclusion in the analyses based on similarity of study design. Pain severity was recorded daily in patient diaries using an ordinal 11-point numerical rating scale (0 = no pain to 10 = most severe pain). The weekly means of the daily 24-hour average pain severity ratings from these diaries were pooled within disease states. Moderate response was defined as at least a 30% reduction from baseline in pain severity, and minimal improvement was defined as <10% reduction from baseline. The probability of achieving at least moderate pain reduction during 3 months treatment with duloxetine was estimated by Kaplan-Meier methods in patients with no or minimal improvement after 2, 4, and 6 weeks of treatment, as well as in all patients who had not yet achieved a moderate response (<30% reduction in pain severity). RESULTS: There were 239 OA patients and 541 CLBP patients who were randomly assigned to treatment with duloxetine 60/120 mg/d. OA and CLBP patients with minimal improvement at 2 weeks of treatment had <40% probability of achieving a moderate response, and at 4 weeks of treatment their chances were reduced to <30% in OA patients and <25% in CLBP patients. In patients showing <30% improvement at week 2 of treatment, OA patients had a 62% probability of achieving a moderate response, and CLBP patients had a 52% probability for a moderate response, and at 4 weeks of treatment, their chances were reduced to <50% in OA patients and <40% in CLBP patients. CONCLUSIONS: Patients taking duloxetine for OA or CLBP who have <10% reduction in pain after 4 weeks of treatment have limited possibility for eventually achieving even moderate pain reduction by the end of 12 weeks. ClinicalTrials.gov identifier: NCT00433290, NCT00408421, NCT00424593, NCT00408876, NCT00767806.
