Tilmicosin is a broad-spectrum bactericidal semisynthetic macrolide antibiotic synthesized from tylosin. It has an antibacterial spectrum predominantly effective against the genera Mycoplasma spp., Pasteurella spp. and Haemophilus spp. and various gram-positive organisms such as the genus Corynebacterium spp. It is believed to affect bacterial protein synthesis by binding to 50S ribosomal subunits. Cross-resistance phenomena have been observed between tilmicosin and other macrolide antibiotics. Following oral administration, tilmicosin is mainly excreted in the faeces via bile, with a small proportion being excreted via urine.