Pharmacokinetics of highly ionized drugs. II. Methylene blue--absorption, metabolism, and excretion in man and dog after oral administration.

Methylene blue was administered orally to seven normal human subjects at a dose of 10 mg. in capsule form. Total urinary recovery ranged from 53 to 97% of the dose, with an average of 74%. Of the material recovered, an average of 78% was excreted as Ieucomethylene blue (stabilized in some salt, complex, or combination form) and the remainder as methylene blue. Some excretion rate-time plots of both methylene blue and leucomethylene blue showed evidence of a circadian rhythm. In a male dog and a female dog, administered 15 mg./kg. methylene blue orally, no drug was detected in blood. The female dog was catheterized and urine was collected for 10 hr. postdosing; recovery was 2.4% of the dose. The female dog was also administered a 10-mg. dose of methylene blue orally, and urine was collected by catheter over 14 hr. Recovery was 3.8% of the dose. It was concluded that methylene blue is well absorbed in man and poorly absorbed in the dog after oral administration.