Absorption and Distribution of Oral Minoxidil
After oral intake of minoxidil tablet, about 90% of minoxidil is absorbed through the intestine. It enters portal vein and flows through the liver.
About 85% of oral minoxidil is metabolized in the liver. It changes primarily to glucuronide conjugate by metabolic pathways. The compounds are less effective and doesn’t exert significant pharmacological action on hair follicular cells. Finally, all the metabolites are excreted in the urine.
The other 15% of oral minoxidil is not metabolized in the liver, and it enters systemic circulation. Minoxidil in the blood is distributed to the whole body, and it works on hair follicles. Finally, minoxidil is excreted in the urine.
The half-life of minoxidil in the serum is 4.2 hours.
Minoxidil is not an antiandrogen drug, but there is an interesting study reporting that minoxidil slightly inhibited the activity of 5 alpha-reductase in the cultured human hair follicular cells.