The combination of amoxicillin and colistin has additive action. Amoxicillin is a semisynthetic broad-spectrum penicillin with a bactericidal action against both Gram-positive and Gram-negative bacteria. The spectrum of amoxicillin includes
Campylobacter spp.,
Clostridium spp.,
Corynebacterium spp.,
E. coli,
Erysipelothrix spp.,
Haemophilus spp.,
Pasteurella spp.,
Salmonella spp., penicillinase-negative
Staphylococcus spp. and
Streptococcus spp. The bactericidal action is due to inhibition of cell wall synthesis. Amoxicillin is mainly excreted in urine. A major part can also be excreted in bile. Colistin is an antibiotic from the group of polymyxins with a bactericidal action against Gram-negative bacteria, like
E. coli,
Haemophilus spp. and
Salmonella spp. Since colistin is absorbed for a very small part after oral administration, only gastrointestinal indications are relevant.