Reduction of residual topical diclofenac in waste water by a wiping procedure before hand washing

Diclofenac is non-steroidal anti-inflammatory drug (NSAID) with widespread usage as a topical treatment for relief of pain and inflammation in soft-tissue injuries. While the permeation mechanisms of topically applied diclofenac are well documented, the fate of residual diclofenac not retained at the site of pain following subsequent hand-washing is still not well characterized. The aim of this study quantifies the amount of diclofenac present in rinse water after the application of a topical pain gel containing 23.2 mg/g diclofenac diethylamine, and subsequent washing of the hands. A comparison of two different hand washing techniques was completed with and without wiping hands directly after product application and before washing. A pilot study was completed to optimize the analytical procedures used in the quantification of diclofenac in the rinse water, followed by a main study with 24 test subjects. The data were first analyzed separately and subsequently pooled for statistical analysis. To determine the amount of diclofenac in the rinse water samples, we used reverse phase-liquid chromatography-mass spectrometry (RP-LC-MS/MS). It was determined that a hand washing procedure with a pre-wash wipe of the hands with a paper towel resulted in a 66% reduction in diclofenac released into the waste water system (7.43 ± 3.02 mg/L). This study shows for the first time that a wiping procedure before hand washing will have a significant impact on the amount of diclofenac in the rinse water. Thus, it is possible to significantly impact the release of non-absorbed residual diclofenac after product application.