The purpose of this study is to evaluate the photostability of nifedipine (NIF) in solid monolaurin (ML)-based matrix and the micellar solutions thereof. NIF loaded-ML matrices at concentrations of 1:1, 1:4 and 1:9 w/w were prepared using a fusion-high shear homogenization method and characterized using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The absence of an endothermic melting peak at 173° C in the 1:4 and 1:9 w/w NIF-ML matrices indicates that NIF is in an amorphous state. The 1:1 w/w NIF-ML matrix showed an endothermic peak at 154° C indicating the transformation of NIF into polymorph III. Stability-indicating HPLC method was developed and validated to quantify NIF and its degradation product. Photoexposed 1:1, 1:4 and 1:9 w/w NIF-ML matrices exhibited 2.1, 4.6 and 17 fold slower first-order degradation rates as compared to the NIF powder. After 24 days of exposure, the percent drug remaining in the 1:9 w/w NIF-ML matrix was 85% as compared to only 5% in pure NIF powder. The micellar solutions exhibited 7-fold slower degradation kinetics than the aqueous solution. The results of this study indicate that the stability of nifedipine can be improved by formulation into monoglycerides matrix.
Key words: photostability; nifedipine; monoglycerides; monolaurin; solid-lipid matrix; micellar solution
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