Effect of UV light exposure on hydrophilic polymers used as drug release modulators in solid dosage forms

The effects of UV light on hydrophilic polymers used as drug release modulators in matrix-tablets are evaluated. Three different polymers were chosen for this study: hydroxypropylmethyl cellulose (HPMC), polyethylene oxide (PEO) and polyvinyl alcohol (PVA). Diltiazem hydrocloride, a well-known photostable molecule, was chosen as model drug. When matrix tablets prepared with PEO or with HPMC of higher viscosity grade were exposed to UV irradiation, displacements of the drug release profiles were observed compared to the dissolution profile of the non-irradiated samples. In the case of PVA tablets, the exposure to UV light did not modify the dissolution profile of the matrices. The polymers that showed to be affected by UV irradiation, were then subjected to viscosity measurements. The rheological analysis indicates that viscosities of solutions prepared with irradiated PEO were much lower compared to the solution prepared with non-irradiated polymer. The same results, but less evident, were found for HPMC.