Tolerability of diclofenac sodium 1% gel with concomitant medications known to interact with diclofenac

John H Peniston,1 Morris S Gold,2 Matthew S Wieman,3 Lawrence K Alwine4 1Feasterville Family Health Care Center, Feasterville, PA, 2Novartis Consumer Health, Inc, Parsippany, NJ, 3Endo Pharmaceuticals Inc, Malvern, PA, 4Downingtown Family Medicine, Downingtown, PA, USA Background: Topical diclofenac sodium 1% gel (DSG) has demonstrated efficacy and tolerability in patients with osteoarthritis (OA) of the knees or hands, including elderly patients and those with an increased risk of gastrointestinal, cardiovascular, and renal adverse events (AEs). Medications known to interact with diclofenac were disallowed in a clinical trial of DSG for knee OA; however, patients were not to be discontinued for intake of disallowed treatment, unless there was a safety issue. This post hoc analysis examined the frequency and type of AEs in patients who received DSG concomitantly with drugs known to have potential interactions with diclofenac. Materials and methods: This was a post hoc analysis of a randomized controlled trial of DSG for knee OA pain. Patients (n = 254) aged ≥ 35 years with OA in one or both knees, but with clinical OA symptoms in only one knee, administered DSG topically to the target knee four times daily (total dose, 16 g/d) for 12 weeks. Drugs with the potential for major or moderate drug–drug interactions (DDIs) were identified via Drugs.com. AE rates were compared in patients with versus those without ≥1 potential DDI. Results: At least one AE was experienced by 62.6% (107/171) of patients with ≥1 DDI and by 55.4% (46/83) of patients with no DDIs. Gastrointestinal AEs (upper and lower) were reported in 5.3% (9/171) and 7.2% (6/83), cardiovascular AEs in 4.7% (8/171) and 1.2% (1/83), renal AEs in 1.2% (2/171) and 0%, and hepatic AEs in 0% and 1.2% (1/83) of patients with ≥1 DDI compared with patients with no DDIs, respectively. Conclusion: Concurrent use of DSG with medications that had potential for major to moderate DDIs had little impact on the frequency of AEs in this population. Further research is needed to consider how factors such as dose, duration, and timing of concomitant drug administration may affect the likelihood of clinically evident AEs resulting from a potential DDI. Keywords: drug interactions, nonsteroidal anti-inflammatory drugs, topical administration, knee osteoarthritis