Cefoxitin Sodium: Solution and Solid-State Chemical Stability Studies

Studies were undertaken to provide the basic physicochemical information necessary for preparing a suitable parenteral formulation of cefoxitin sodium. Emphasis was placed on the physicochemical properties of the compound in solution and in the solid state. Cefoxitin sodium is very soluble in water and exhibits apparent first-order decomposition in this medium at pH 3-9. Maximum stability in water is at pH 5-7. Under these pH conditions, cefoxitin sodium loses about 10% of its activity in 2 days at 25°. Thermal decomposition rates for amorphous and crystalline cefoxitin sodium samples were determined. Amorphous cefoxitin sodium was considerably less stable than its corresponding crystalline form. Solid-state decomposition plots are biphasic, displaying initial rapid losses followed by a slower decay period. The extent of loss in the crystalline solid at the end of the more rapid initial phase can be correlated with the water content of the solid.