Abstract
Studies on the percutaneous absorption, metabolism and excretion of paeonol (2-hydroxy-4-methoxyacetophenone, I) were carried out by using the stable isotope (SI) method, which is applicable to man. Radioactive tracer experiments in rats were also performed in order to evaluate the SI tracer technique. Hydrophilic ointment or absorptive ointment containing 5% I was topically applied under an occlusive dressing to man and rat for 6, 12 and 24 h. The amounts of metabolites (2, 5-dihydroxy-4-methoxyacetophenone II, resacetophenone III, and unchanged substrate I) excreted in the urine were determined by selected ion monitoring assay using I [methoxy-d3], II [methoxy-d3] and III [acetyl-13C2] as internal standards. After topical application of hydrophilic ointment for 6 h in man, the amounts of I, II and III in 0-24-h urine were 3.35, 16.28 and 5.17% of the applied dose, respectively. Urinary excretion of I metabolites continued for 6 d from the time of application, but the total amount of metabolites excreted in 0-24 h was as much as 89% of that excreted in 0-144 h. The results indicate that the SI tracer technique described here has sufficient sensitivity and repeatability. Paeonol is easily absorbed through the skin, and the metabolites are excreted rapidly in urine.
