Abstract
In order to estimate the extent of gastrointestinal absorption of methylene blue (MB) in dogs and to search for more contributory route of excretion than urine, elimination of MB was investigated after oral and intravenous administration at a dose of 15 mg/kg in mongrel dogs. After oral administration, total MB, which was the sum of unchanged MB and leucomethylene blue (LMB), was recovered from urine and feces with averages of 3.9 and 44.3% of the dose, respectively. When MB was intravenously injected at the same dose, total urinary and fecal recoveries were 6.6 and 19.9%, respectively. Therefore, it was assumed that about 60-70% of orally administered MB should have been absorbed from the gastrointestinal tracts of dogs. In anesthetized dogs, total biliary recovery was about 7 times greater than that from urine after intravenous administration of MB to dogs. On the basis of these results, it was concluded that total urinary recovery should not be taken as an index of gastrointestinal absorption after oral administration of MB to dogs, and that there would not be a great species difference in gastrointestinal absorption of MB between man and the dog. A few metabolites other than LMB were found in urine and feces of dogs, though quantitative analysis was not carried out.
