Tiamulin hydrogen fumarate is a semisynthetic derivative of pleuromutilin. Tiamulin is active against gram-positive bacteria, mycoplasmas, and anaerobes, including Brachyspira hyodysenteriae. Tiamulin is well absorbed when administered PO. It is labeled for use as an oral medicated feed or water in swine in the US to treat swine dysentery and Actinobacillus pleuropneumoniae. In poultry, tiamulin interferes with monensin and salinomycin metabolism, and if the drugs are administered together, they become toxic. Generally, however, tiamulin has few adverse effects.