Fluphenazine decanoate (Modecate, Prolixin) is potent long-acting sedative that is used in horses to facilitate handling and early training in difficult and dangerous animals, and is also used to treat some vices, such as self-mutilation syndrome. It is in the phenothiazine group of medications. In people it is used to treat a number of psychoses, such as schizophrenia.
The drug is effective in horses, although rare reactions can occur including severe progressive hyperexcitability, dementia and muscular rigidity. These are described as an extrapyramidal syndrome, describing uncontrolled involuntary movements. These are not an uncommon side effect of anti-psychotic medication in people. Interestingly, in horses a frequent sign is rubbing the face on the ground.
The syndrome can also occur in horses receiving the human anti-psychotic drug, sulpiride. Sulpiride is part of a protocol in mares to induce lactation.
Treatment and outcome
Although the syndrome looks a bit like seizure activity it is very poorly responsive to routine anti-convulsive therapy. It is usually well controlled with the anti-histamine diphenhydramine (Benadryl), 0.5 to 1.0 mg/kg IV as necessary (usually 2 or 3 doses, but up to 10 doses over 48 to 96 hours) or benztropine, a drug that inhibits dopamine receptors, as well as histamine and muscarine (acetylcholine) receptors.
The prognosis is generally good, unless the horse self-injures or is euthanised.
As of the time of writing (June 2022) Modecate was no longer available in Australia due to an apparent shortage of ingredients.
Tags: Neurology; Toxicities