The impact of active substance on the adhesiveness of medicated patches containing liquid additives

Adhesiveness of dermal patches can be modified in the presence of active substances. The effect is more complex when liquid components are also present in the matrix. Commercial grade pressure sensitive adhesive (PSA) polyacrylates (three types) and silicones (two types) were used to prepare adhesive matrices and liquid additives were propylene glycol, polyoxyethylene glycol, isopropyl myristate, triacetin, triethyl citrate or low viscosity silicone oil. Drug-in-adhesive patches were prepared with model active substances (5% w/w): indomethacin or cytisine. The effect of the suspended or dissolved drug on adhesiveness was evaluated with probe tack test and 90° peel test. Most of the acrylate patches loaded with dissolved indomethacin showed acceptable level of adhesiveness. In case of cytisine, suspension type patches were often formed and only in some patches sufficient adhesiveness was retained. Adhesion of silicone based matrices was altered profoundly by the simultaneous drug and excipient addition. Only one matrix with indomethacin and silicone oil showed acceptable quality in both tack and peel tests (S1, Bio-PSA MD7-4502). In the course of the data analysis of the adhesiveness, the relevance of film formation mechanism was noted. It was observed, that if the film formation occurs by solvent evaporation in patches where drug particles are suspended, the impact of the particles on adhesion might be greater than in the case of patches with the dissolved drug. It was concluded, that a choice of a suitable polymer-liquid mixture for a particular active substance requires an experimental work in case of an adhesive properties adjustment. Due to complex physicochemical interaction between the components reliable theoretical predictions are considered as questionable.