Stability of diclofenac sodium and piroxicam in new transdermal "soft-patch" type gel systems

The authors examined the stability of the non-steroidal anti-inflammatory d rugs diclofenac sodium and piroxicam in new, semisolid gel systems suitable for topical "soft-patch" formulations. The decomposition of active substan ces in the stearate and lipophilic gels during storage at 4, 25 and 40 degr eesC was studied using high performance liquid chromatography (HPLC). The q uantifies of non-decomposed active substances wet-e selectively determined. The decomposition rates of active substances and the expiry dates for gel formulations were calculated. It was concluded that both the active ingredi ents tested were chemically more stable in the case of the stearate gel.