RESUMEN
Background: The chemical stability of a pharmaceutical product depends, among other factors, on environmental factors during transport, storage and manipulation of the product. Aim: To study the chemical stability of acetylsalicylic acid (AAS) tablets during ten months of storage in five pharmacies of Concepci-n, Chile. Material and methods: Tablets were randomly collected at the beginning of the study and at the third, sixth and tenth month. Quantitative analyses of AAS tablets was carried out by instrumental thin layer chromatography (HPTLC). Results: AAS in tablets was between 99 and 109 percent at the beginning of the study, between 76 and 110 percent at three months, between 71 percent and 112 percent at six months and between 86 and 110 percent at ten months of storage. Conclusions: There was a progressive decrease in the content of acetylsalicylic acid in tables during storage, but it remained between the limits accepted by the United States Pharmacopoeia (USP) (90-110 percent)