[Stability study of an aqueous formulation of captopril at 1 mg/ml]

The stability of captopril was studied in several extemporaneously prepared oral liquid formulations for pediatric use. Solutions were prepared at a concentration of 1 mg/ml from the pure chemical product.

Captopril 1 mg/ml oral liquid formulations were prepared from powder in three types of water (tap water, mineral water, distilled chemically pure water), in syrup and different chelating and antioxidants agents, and the pH was modified with sodium citrate. The liquids were stored at 4 and 25 degrees C in PVC plastic containers. Samples were removed at regular intervals of less than thirty days. Captopril and captopril disulfide concentrations were analyzed by high-performance liquid chromatography. Captopril in formulations in which the only vehicle was distilled chemically pure water were more stable than in formulations made either with tap water or with mineral water.

The formulations containing edetate disodium, syrup, ascorbic acid, sodium ascorbate, sodium metabisulphite were less stable than those in which the only vehicle was distilled chemically pure water. The change of pH did not improve the formulation stability. The samples stored at 4 degrees C were much more stable than those stored at 25 degrees C, and the microbiological quality was much better.

Captopril, at a concentration of 1 mg/ml, made with distilled chemically pure water stored in PVC plastic container and protected from light, was stable for 30 days at 4 degrees C.