The role of fillers and sodium metabisulfite on drug release from aged polyox tablets.

Polyethylene oxides (PEOs) are extensively used to control the release rate of drugs from matrices. Unfortunately, polyox polymers are prone to oxidation under high temperature and relative humidity. The aim of this study was to investigate the effect of sodium metabisulfite as an antioxidant to overcome the drug release changes from polyox matrices (PEO 301 and 303) when stored at 40 °C. The effect of different types of fillers (lactose, mannitol and dicalcium phosphate dihydrate) on stability of diltiazem HCl release profiles was also investigated. Generally, the presence of sodium metabisulfite stabilized the release of drug from PEO matrices stored at 40 °C for 8 weeks. Whilst the absence of metabisulfite caused an increase in drug release from polyox matrices when stored at 40 °C. The results indicate that all three concentrations (0.25, 0.5 and 1% w/w) of sodium metabisulfite were able to overcome structural changes of polyox samples hence stabilizing the drug release. The results also showed that the incorporation of fillers in polyox matrices reduced the sensitivity of drug release when stored at elevated temperature. This indicates that when these excipients were used there was no need to incorporate additional antioxidant. DSC results showed that there was no difference in the melting points of fresh polyox samples and aged polyox samples containing sodium metabisulfite, whereas the melting point of aged polyox samples without sodium metabisulfite were lower than fresh polyox samples. This indicates that the presence of metabisulfite is essential to stabilize polyox samples.