The degradation profile of an antibiotic compound, panipenem (CAS No. 87726-17-8), in aqueous solution was investigated, and the influences of pH and initial concentration on the degradation profile were clarified. As for the effect of pH, panipenem in aqueous solution was most stable in neutral pH, but was unstable under acidic and alkaline conditions. Under acidic conditions, the dimer-type degradation products were typically formed, and other degradation products observed were β-lactam-ring-cleaved-type degradation products. Moreover, as the initial panipenem concentration increased, the acceleration of the degradation and the increased formation of the dimer-type degradation products were observed. Under alkaline conditions, on the other hand, dimer-type degradation products were not formed, and β-lactam-ring-cleaved-type degradation products were observed as the main degradation product. The experimental results were in agreement with the degradation scheme and the differential equations, based on the chemical structure of the degradation products.

We defined the lactose/corn starch in a 7/3 mixture with 20 w/w% binder as the standard formulation for the dry compression method and investigated the adaptation of this formulation for the direct compression method. Powdered crystalline lactose monohydrate, which is generally used as an additive for solid dosage forms, and three kinds of direct compression lactose with differing physicochemical properties were used as lactose. Microcrystalline cellulose (PH-101) or low-substituted hydroxypropylcellulose (LH-21) were used as binder. Consequently, tablets that had sufficient hardness of 40 N or higher as well as disintegration ability within one minute were obtained using this formulation without using direct compression lactose. Moreover, these tablets had excellent characteristics compared with tablets obtained by the standard formulation for the wet granulation method. As for the binder, the hardness of tablets containing the microcrystalline cellulose was higher than that of the tablets containing the low-substitute hydroxypropylcellulose. However, the difference was not significant, and there were no differences in the disintegration time between those two tablets.