An in vitro study of the interaction between diazepam and some antacid or excipients

The adsorption of diazepam on magnesium trisilicate, magnesium oxide, aluminium hydroxide, calcium carbonate, magnesium carbonate, bismuth oxycarbonate bismuth subsalicylate, talc, dibasic calcium phosphate, magnesium stearate, kaolin and charcoal was studied at 37 degrees C. With the exception of charcoal, magnesium trisilicate exhibited the highest adsorptive capacity for the drug. Talc and dibasic calcium phosphate had the lowest adsorptive power while the other materials tested had intermediate adsorption properties. In general, low elution values were obtained with both acidic and alkaline solutions. The presence of a specific interaction between diazepam and surface sites of the adsorbing materials was suggested. The Langmuir relationship was obeyed in case of bismuth oxycarbonate. The dissolution of the drug in absence and presence of magnesium trisilicate, which had a very high retention ability, was also studied. The antacid decreased obviously the dissolution of the tranquilizer. The implication of diazepam interaction with antacids and excipients on its bioavailability is to be further confirmed by in vivo testing.