Ethanol effect on acid resistance of selected enteric polymers

The aim of this study was to investigate under in vitro conditions the influence of ethanol on acid resistance of four commercially-available enteric polymers (Acryl-EZE^®, AQOAT^®, Hypromellose phthalate, and Sureteric^®). For this purpose, custom-prepared paracetamol tablets were coated with the enteric polymers and tested for release using the buffer-addition method. Ten different hydro-ethanolic media were used in the acid stage corresponding to five levels of ethanol (0, 5, 10, 20, and 40% v/v) in two acidic solutions representing low and high gastric pH (0.1 N HCl pH 1.2, L_GpH, and phosphate buffer pH 4.0, H_GpH, respectively). The coats were found to resist both types of acidic solution with ethanol percentages up to 10% leading to release profiles that conformed with the pharmacopeial requirements (<10% release after 2 h in acid stage) except for Acryl-EZE^®, which showed a premature release in H_GpH media. At the higher ethanol levels (20 and 40%), premature release associated with increased acid uptake by coated tablets was noticed for all polymers and more remarkably in H_GpH media. ANOVA tests revealed significant effects of polymer type, acidic solution type, and ethanol level on the onset and extent of premature release.