The invention provides a combination comprising at feast one compound selected from metergoline, proglurnide, sertraline, hydroflumethiazide, perphenazine, fiuphenazine and pimethtxene, or a pharmaceutically acceptable derivative thereof, and a polymyxin selected from polymyxin. B and coiistin, or a pharmaceutically acceptable derivative thereof. This combination is particularly useful for the treatment of microbial infections.