Intramuscular Administration of Diphenylhydantoin

Thirteen cats were given intramuscular injections of diphenylhydantoin. Eight cats were killed 24 hours following injection, and five at intervals up to four weeks. Hemorrhage and necrosis of muscle tissue were found in five of eight specimens taken at 24 hours, and microscopic crystallization of diphenylhydantoin was seen only in association with necrotic muscle. Crystal morphology was dependent on intracellular or extracellular localization. Chromatographic analysis showed retention of diphenylhydantoin in injection sites at 24 hours.