Quality control of metoprolol extended-release formulations in the presence of ethanol.

: This paper presents in-vitro metoprolol release from four different extended-release (ER) formulations, i.e. Metoprolol GEA® Retard, Logimax® forte, Metoprolol Sandoz® and Seloken ZOC® in the presence of 10 to 40% (v/v%) ethanol at pH 1.2 and pH 6.8. The assay of metoprolol in the dissolution media was performed by reversed phase liquid chromatography (RP-LC) using a mixture of methanol and 100 mM phosphate buffer (pH 3.5) in 40:60 ratio as eluent. The dissolution data showed that the metoprolol contents of Metoprolol Sandoz® and Seloken ZOC® were released fast in the presence of 20% ethanol at the investigated conditions, while the other products demonstrated much more stability against ethanol. Unexpectedly it was discovered that the release of metoprolol from Metoprolol GEA® Retard and to some extent also from Logimax® forte decreased in the ethanol containing media.