Antacids containing aluminium/magnesium hydroxide or magnesium trisilicate can reduce the urinary excretion of
chlorpromazine by up to 45%. Similarly, an aluminium/magnesium hydroxide antacid reduced the absorption of sulpiride.
In vitro studies suggest that this interaction may possibly also occur with other
antacids and phenothiazines.
The
clinical importance of these interactions are not established, but it would seem reasonable to give
chlorpromazine or sulpiride 2 to 3 hours after alum- inium/magnesium hydroxide
antacids to minimise any interaction.