A Comparative Study of the Quality of OTC Transdermal Patches for Pain Relief

Tharunkumar J, Padmapriya E, Selvamuthukumar R, Saminathan C

Transdermal drug delivery systems provide a convenient and non-invasive approach for delivering therapeutic agents through the skin and may offer advantages over conventional routes of administration. The present study was undertaken to comparatively evaluate the quality and physicochemical characteristics of commercially available over-the-counter (OTC) transdermal patches used for pain relief. Three commercially available patches containing different active pharmaceutical ingredients, namely diclofenac, lidocaine, and ketoprofen, were selected for evaluation. The patches were assessed for important physicochemical and mechanical parameters, including thickness, weight uniformity, folding endurance, moisture content, surface pH, and tensile strength. The results demonstrated that all three patches showed acceptable thickness and weight uniformity. The thickness values ranged from 0.22 to 0.28 mm, while percentage weight variation remained below 5%, indicating satisfactory formulation consistency. Ketoprofen patches exhibited the highest folding endurance (245 folds) and tensile strength (1.38), indicating superior flexibility and mechanical strength. Diclofenac patches demonstrated good uniformity and a surface pH of 6.2, while lidocaine patches showed a surface pH of 6.6 and comparatively lower folding endurance and tensile strength. Moisture content was below 5% for all tested patches, indicating acceptable moisture characteristics. Comparative evaluation indicated that ketoprofen patches demonstrated the most favorable mechanical properties, followed by diclofenac, whereas lidocaine patches showed comparatively lower mechanical strength and folding endurance. One-way ANOVA revealed statistically significant differences among the tested patches for tensile strength and folding endurance (p < 0.05), while differences in thickness and weight were not statistically significant. Overall, the study demonstrated that all three OTC transdermal patches possessed acceptable physicochemical characteristics; however, ketoprofen patches showed superior mechanical strength and flexibility, making them comparatively more robust for prolonged or active use. Diclofenac patches showed satisfactory uniformity and surface pH, whereas improvement in the mechanical properties of lidocaine patches may enhance their durability and user experience.

Keywords – Comparative study, Diclofenac, Ketoprofen, Lidocaine, Transdermal patches.