Equivalent amounts to 20 mg of thiamine-HCl per kg body weight of S-carbethoxythiamine, S-carbobutoxythiamine, O, S-dicarbethoxythiamine and thiamine-HCl were daily administered to respective groups of mongrel dogs together with the diet for 100 days. No toxic signs were seen in various liver and kidney functions tests throughout the whole experimental period. However, serum choline esterase activity of the dogs of all groups decreased very gradually week by week, although they were within the normal range. Minimum thiamine levels of the dog blood increased week by week remarkably arriving at peak levels after 8 to 11 weeks and showing a plateau afterwards. Most of thiamine in the blood was of the conjugated form in the blood cells. These dogs were sacrificed after the 100 days administration. No pathological findings thought to be significant to the drug administration was found both by gross and microscopic examinations of the organs of the dogs.
