Tiamulin is a semi-synthetic diterpene antibiotic. The mode of action is by inhibition of ribosomal protein synthesis in sensitive bacteria. It is a bacteriostatic antibiotic and the following organisms show sensitivity in vitro:

Brachyspira: Brachyspira hyodysenteriae

Mycoplasmas: Mycoplasma hyopneumoniae, M.hyorhinis, M. hyosynoviae, , Mycoplasma synoviae,.

Gram-positive: Staphylococcus spp., Streptococcus spp., Arcanobacterium pyogenes.

Gram-negative: Pasteurella spp., Klebsiella pneumoniae, Actinobacillus (Haemophilus) spp., Fusobacterium necrophorum, Bacteroides spp., Campylobacter coli.

The mechanism of resistance is chromosomal. Appearance of resistance is slow and progressive.

Following a single intramuscular administration at a dose rate of approximately 14 mg tiamulin per kg bodyweight, mean maximum tiamulin concentration (approximately 350ng/ml) was reached after approximately 3 hours. The mean terminal half-life is approximately 12 hours.