The species differences in the metabolism and excretion of tulobuterol (I) were investigated in rat, dog, guinea pig and rabbit after oral administration of 14C-tulobuterol. The urinary metabolites were analyzed by thin-layer chromatography. The urinary excretion of radioactivity within 72 hr. was estimated and about 50% of the administered dose were excreted in the urine of rat, dog and guinea pig, whereas relatively a small amount (24.6% of dose) in the urine of rabbit. The excretion of 14CO2 into expired air within 48 hr. was 19.6% and 35.8% of dose in guinea pig and rabbit, respectively, and these values were larger than 0.8% in rat. Major metabolites excreted in the urine were 3-hydroxy-(III) and 4-hydroxy-5-methoxytulobuterol (IV) in rat, IV and o-chloromandelic acid (VI) in dog, an unchanged drug, 1-(o-chlorophenyl)-1, 2-ethandiol (V) and IV in guinea pig, and VI in rabbit. On the basis of these results it was clarified that there were marked species differences in the metabolism and excretion of I.
