Permeability of the blood-milk barrier to methylene blue in cows and goats |
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| Authors: | G ZIV J E HEAVNER |
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| Institution: | Ministry of Agriculture, Kimron Veterinary Institute, Bet Dagan, Israel;*Division of Veterinary Medical Research, Bureau of Veterinary Medicine, Food and Drug Administration, Beltsville, Maryland, U.S.A. |
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| Abstract: | 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 as 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<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 1 5 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. |
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