EFFECT OF THE BINDING OF WATER TO EXCIPIENTS AS MEASURED BY H-2-NMR RELAXATION-TIME ON CEPHALOTHIN DECOMPOSITION RATE

H-2-NMR spectra and the relaxation time of deuterium oxide adsorbed on some pharmaceutical excipients were measured using a high resolution NMR spectrometer in order to clarify the effect of the binding of water to some pharmaceutical excipients on drug decomposition. The decomposition rate of cephalothin was determined in the presence of corn starch and MCC as model excipients under various humidity conditions. The decomposition rate increased with the increasing water content of the excipients. The spin-lattice relaxation time increased with increasing water content similarly to the decomposition rate. This suggests that the H-2-MMR spin-lattice relaxation time can be used as a measure of the water mobility which affects the decomposition rate of drugs in the solid state.