Milk secretion of nitrofurantoin,as a specific BCRP/ABCG2 substrate,in assaf sheep: modulation by isoflavones1

Studies on residues in milk used for human consumption have increased due to health concerns and priority interest in the control of potentially risky drugs. The protein BCRP/ABCG2, present in the mammary epithelia, actively extrudes drugs into milk and can be modulated by isoflavones. Nitrofurantoin is a specific BCRP substrate which is actively excreted into milk by this transporter. In this research, we studied nitrofurantoin transport into milk in four experimental groups: G1‐calves fed forage with isoflavones; G2‐calves fed forage with isoflavones and administered exogenous genistein and daidzein; G3‐calves fed forage without isoflavones; G4‐calves fed forage without isoflavones and administered exogenous genistein and daidzein. Results show increased levels of nitrofurantoin in milk from calves without isoflavones (G3) and decreased nitrofurantoin residues in milk when isoflavones were present, either by forage (G1 and G2) or by exogenous administration (G4). The values of C_max in milk were significantly lower in those groups with isoflavones in forage (G1, G2). Plasma levels were low and unmodified among the groups. Inter‐individual variation was high. All these results seem to point to a feasible control of drug secretion into milk through isoflavones in the diet when the drug is a good BCRP/ABCG2 substrate.