Distribution of Aminoglycoside Antibiotics in Blood and Milk

Summary Serum and milk concentrations of gentamicin, kananiycin, neomycin and paro-momycin were determined in lactating ewes after intravenous treatment (20 mg/kg) and duringequilibrium, and following intramuscular injection (10 mg/kg) to cows and ewes. After a singleintravenous injection, the half-life values in serum ranged from 1.85 h for gentamicin to 4.65 h for paromomycin. The drugs were calculated to occupy less than 20% of total body volume and onlya very small traction oj the dose was recovered in milk secreted from normal or irritated glandsduring the 12 h after treatment. At equilibrium the milk to serum ultrafiltrate concentration ratios were less titan the calculatedtheoretical ratios expected had penetration into milk been by passive diffusion. It is suggested thatthe limited penetration of these drugs into milk was mainly due to their poor lipid solubilitycharacteristics, which would curtail their potential usefulness in the parenteral treatment of mastitis.