Investigations were carried out on the pharmacological effects of cyclocarbothiamine (CCT), a thiamine derivative newly developed in our laboratory. When orally administered in rat and mouse, LD_<50> were 7.6 g/kg and 6.2 g/kg, respectively, and when injected intravenously, they were 0.58 g/kg and 0.36 g/kg. On the cardio-vascular system, the blood pressure, respiration and EKG of rabbit, isolated heart of guinea-pig, and vascular preparation of rabbit ear, CCT acted similiarly to thiamine. CCT had little effect on the isolated intestine of rabbit. The motility of atrium preparation of guinea-pig was enhanced by CCT, but not by thiamine. On the nerve-muscular preparation of rat and on the EEG of rabbit, its effect resembled that of thiamine.
