Permeability of the blood-milk barrier to methylene blue in cows and goats.
A 2% aqueous solution of methylene blue was administered as a single intravenous (i.v.) bolus injection (10 mg/kg) to six lactating cows and seven lactating goats and a continuous i.v. drip to five lactating goats. The same dose was administered as a 10% solution by intramammary infusion to five lactating goats. Blood and milk samples collected at various times after these treatments were assayed for the drug by a colorimetric method. Methylene blue, a highly charged molecule (pKa less than or equal to 1), passed readily from blood into milk; drug concentrations in milk 4-36 h after the single i.v. bolus injection were higher than those in blood. When examined at constant methylene blue levels in blood, a milk--blood ratio of 5:1 was observed. After intramammary infusion, the drug passed quickly into systemic circulation, peaked at 3 h and was still detectable in blood 12 h after infusion. The drug appeared in the urine within 15 min after intramammary infusion. The rapid movement of the drug across the blood--milk barrier cannot be explained on the basis of its known physicochemical properties or according to the pH--pKa passive diffusion concept.
D000818:Animals; D002199:Capillary Permeability; D002417:Cattle / Q000378:metabolism*; D005260:Female; D006041:Goats / Q000378:metabolism*; D007275:Injections, Intravenous / Q000662:veterinary; D007774:Lactation; D008297:Male; D008751:Methylene Blue / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*; D008892:Milk / Q000378:metabolism*; D011247:Pregnancy; D013997:Time Factors
D008751:Methylene Blue