| t Hydrophilic matrix systems are currently some of
the most widely used drug delivery systems for controlledrelease
oral dosage forms. Amongst a variety of polymers,
polyethylene oxide (PEO) is considered an important material
used in pharmaceutical formulations. As PEO is sensitive to
thermal oxidation, it is susceptible to free radical oxidative
attack. The aim of this study was to investigate the stability
of PEO based formulations containing different model drugs
with different water solubility, namely propranolol HCl, theophylline
and zonisamide. Both polyox matrices 750 and 303
grade were used as model carriers for the manufacture of
tablets stored at 40 °C. The results of the present study suggest
that the drug release from the matrix was affected by the
length of storage conditions, solubility of drugs and the molecular
weight of the polymers. Generally, increased drug release
rates were prevalent in soluble drug formulations
(propranolol) when stored at the elevated temperature
(40 °C). In contrast, it was not observed with semi soluble
(theophylline) and poorly soluble (zonisamide) drugs especially
when formulated with PEO 303 polymer. This indicates
that the main parameters controlling the drug release from
fresh polyox matrices are the solubility of the drug in the
dissolution medium and the molecular weight of the polymer.
DSC traces indicated that that there was a big difference in the
enthalpy and melting points of fresh and aged PEO samples
containing propranolol, whereas the melting point of the aged
polyox samples containing theophylline and zonisamide was
unaffected. |