Reversible binding of polymyxin B and neomycin to the solid part of faeces

Previous studies have shown that polymyxin B and neomycin were bound to the solid part of human faeces. In the present study, the faecal binding of polymyxin B and neomycin was studied, using a wide range of concentrations of drugs and faecal dilutions. Up to 25 mg of polymyxin B and 15 mg of neomycin could bind to 1 g of faeces but the binding was found to be reversible. With faeces of rats it was found that polymyxin B was mainly bound to the non-bacterial part of faeces, whereas neomycin was bound to the bacterial as well as the non-bacterial part. The implications of the reversible binding of antibiotics to intestinal contents for selective decontamination are discussed.