A Comparative Study of the Effectiveness of Preservatives in Twelve Antacid Suspensions

Abstract

In this study the effectiveness of preservatives in twelve currently used antacid suspensions was evaluated. In eight of the twelve formulations, hydroxybenzoates were used as preservative. Only four of these products met the existing USP XXI requirements. One of the discarded products systematically contained a contaminant belonging to the Pseudomonas group. Of the remaining four products with other preservatives, two failed the USP XXI challenge tests. The main cause of all failures was the incompatibility of pH with the preservatives choosen. Especially the challenge test with the Ps. aeruginosa strain posed the greatest difficulties. However the Pseudomonas results were not always easy to interprete, partially due to the lack of interpretation criteria at the seventh and the twenty first day. Therefore we propose a three percent bacterial concentration level as an additional pass-fail criterion for the seventh and twenty first day.