Some studies of the stability of compounded cefazolin ophthalmic solution

The chemical stability of three compounded batches of cefazolin ophthalmic solution was monitored by a stability-indicating high-performance liquid chromatography assay. The degradation was governed by first-order kinetics, and the effect of temperature on reaction rate was in accordance with the Arrhenius equation at and above 17 deg C. Although the stability of all three batches was essentially the same, buffering the formulations may be useful. Even using a most cautious and conservative approach to the assignment of a beyond-use date for this type of product, it appears that, if the product is stored at controlled room temperature, a beyond-use date of six days would be fully justifiable. If the product is stored in a refrigerator, then a beyond-use date of 14 days could be assigned.