Deceleration of light-induced changes of selected pharmacons by means of light screening films

Abstract Photo-induced changes in three pharmacons (Promethazine HCl, Carbidopa and Niphedipine), under exposure to light rich in UV component, could be characterised with the rate constants of the occurring processes. Partial rate constants could be determined after exposure to selected wavelenght regions emitted by the light source. The most effective wavelength regions characteristics for the single pharmacons could be derived from the calculated partial rate constants. Six composite plastic films were applied for the desired light protection. A matrix LDPE film was particle filled — keeping the transparency of the extruded films — with colloidal titanium dioxide. By using three particle filled films of three different TiO 2 concentrations together with two commercial products, the photoactive ranges of wavelength could be cut off from the illuminating light. Satisfactory light stability of the pharmacons could be established with the help of the most appropriate single light screening films or with their best binary combination.