Metabolic Fate following a Dermal Application of Tulobuterol Tape (3): Absorption, Distribution and Excretion in Infant Rats after a Single Application

The absorption, distribution and excretion of 14C-tulobuterol or unlabeled tulobuterol following a single application was examined in infant rats. 1. After a single dermal application of a tape containing 14C-tulobuterol at 10 mg/kg, blood radioactivity reached maximum at 4 hr in male and female infant rats, respectively. Radioactivity disappeared with T1/2 of 17.0 and 17.3 hr in male and female infant rats, respectively. 2. After a single dermal application of unlabeled tulobuter ol at 5, 10 and 20 mg/kg to male infant rats, blood levels of unchanged tulobuterol reached maximum at 4.0 hr and then disappeared with T1/2 of 2.8-2.9 hr. Cmax and AUC increased dose-dependently within a dose range of 5-20 mg/kg. 3. After a single dermal application of 14C-tulobuterol to male infant rats, the radioactivity in nearly all tissues reached maximum at 4 hr. Radioactivity was distributed well in target organs such as the lung and trachea, and was particularly high in the skin at the site of application followed by the liver and kidney. 4. After a single dermal application of 14C-tulobuterol at 10 mg/kg, the urinary and fecal excretion of radioactivity within 168 hr was 50.1 and 30.5% in male infant rats and, 52.5 and 32.2% in female infant rats, respectively. Recoveries in urine and feces and from residue in the removed tape was almost complete in male (99.4%) and female (98.5%) rats.