The improvement of aqueous chemical stability of a model basic drug by ion pairing with acid groups of polyelectrolytes

A. F. JIMENEZ-KAIRUZ, D. A. ALLEMANDI AND R. H. MANZO

INTERNATIONAL JOURNAL OF PHARMACEUTICS

Elsevier

Año: 2004 vol. 269 p. 149 - 149

0378-5173

p>Carbomer (C) and procaine (P) were selected respectively as models of polyelectrolyte (PE) and basic drug (B) of low stability in aqueous solution. The purpose of this investigation was to test if a (C?P) aqueous system provides a microenvironment in which P is less exposed to hydroxyl ion catalyzed degradation, its main degradation pathway over a wide pH range. It was determined that in (C?P) a high fraction of P was present in the form of ion pairs [RCOO−PH+] with the carboxylate groups of C. The [RCOO−PH+] fraction was above 97% for compositions containing higher than 50 mol% of P. The chemical stability of C?P was assayed at two selected pHs (7.5 and 8.5) in comparison with conventional reference solutions (RS) without C. Procaine in (C?P) was 4.2 and 6.2 times more stable than in its respective RS at the two conditions assayed. The stabilizing factor was calculated as the ratio of the rate constants kobs