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Pharmacological particulars
Pharmacotherapeutic group: Other alimentary tract and metabolism products: drugs for prevention and/or treatment of acetonemia. ATC vet code: QA16QA06
Monensin is a member of the pharmacotherapeutic group of polyether ionophores, specifically the carboxylic subgroup. They are the product of natural fermentation products produced by Streptomyces cinnamonensis.
Pharmacodynamic properties
Monensin binds to bacterial cell membranes and interferes with the maintenance of important ion gradients in the cell which are needed for the transport of nutrients and to generate proton-motive force. Monensin is mainly active against Gram-positive bacteria. Gram-negative bacteria have complex outer cell membranes, resulting in inherent resistance to the action of ionophores. Thus, the ultimate effect of monensin within the rumen is to shift the microbial population resulting in a decrease of the bacteria that produce acetate and butyrate and increasing the bacteria that produce propionate, the gluconeogenic precursor. As a result of the change in population of bacteria within the rumen, efficiency of energy metabolism is improved. In the peri-parturient dairy cow, the positive effects of monensin include reduced blood ketones, increased serum glucose and reduced incidence of ketosis.
Pharmacokinetic particulars
The site of action for intraruminal administered monensin is the gastrointestinal tract. Intraruminal administration of monensin is followed by extensive first pass metabolism which results in low concentrations of monensin in the systemic circulation. Metabolites and parent drug are excreted in the bile.
When the tablet-subunits inside the intraruminal device are in contact with rumen fluid at the orifice of the device, a gel is formed and is slowly released from the intraruminal device. Monensin is released from the intraruminal device at an approximate average dose of 335 mg/day.