Safety and efficacy of duloxetine treatment in older and younger patients with osteoarthritis knee pain: a post hoc, subgroup analysis of two randomized, placebo-controlled trials

BACKGROUND Osteoarthritis (OA) knee pain is common in older patients and contributes to decreased quality of life. Older patients are generally at higher risk of adverse drug reactions due to age-related changes in physiology that affect drug disposition, metabolism, and response. These analyses examined efficacy and safety outcomes of older (≥65 years) versus younger patients from clinical trials of duloxetine in the management of OA knee pain. METHODS This is a post hoc analysis of two 13-week studies, in which patients were randomized to duloxetine 60 mg/day or placebo. Both studies allowed potential dose changes after 7 weeks of dosing, with Study I re-randomizing duloxetine treated patients to either stay on 60 mg/day or increase to 120 mg/day; while Study II more closely mimicked clinical practice by escalating only non-responding patients to 120 mg/day. For all analyses patients were subgrouped by age: older (≥65 years) and younger (40-64 years). Overall efficacy and safety age-group comparisons of duloxetine versus placebo were performed using pooled data from both studies with all duloxetine dose levels combined. Safety analyses included discontinuation rates, treatment-emergent adverse events, and serious adverse events. To evaluate the effects of increasing the dose in non-responding patients, only Study II data were evaluated. Treatment arms were defined post hoc as placebo, duloxetine 60 mg/day, and duloxetine 60/120 mg/day. RESULTS At study end, patients in each age group who were treated with duloxetine versus placebo had significantly greater improvement in pain (both, p<.05), and there was no significant effect of age on treatment (p=.72). Increasing the dose to 120 mg in non-responding patients was not found to have a significant advantage. Among treatment-emergent adverse events with duloxetine treatment, only dizziness had a significantly differential treatment effect (p=.02) with greater incidence over placebo in younger patients (6.6% versus 0.6%, p=.02), but not in older patients (1.0% versus 3.2%, p=.29). CONCLUSIONS Duloxetine was efficacious and generally well tolerated for management of symptomatic knee OA in both older and younger patients, but increasing the dose to 120 mg in non-responding patients did not provide additional benefit.