Fluphenazine-induced extrapyramidal side effects in a horse.

This study outlines the case of a horse that suffered from side effects induced by the drug fluphenazine, a powerful phenothiazine derivative neuroleptic. The horse experienced abnormal seizing behavior due to the drug, which was originally administered to reduce rambunctious behavior that could potentially harm a surgical site on the horse. On arrival to the veterinary hospital, the horse was sedated heavily with different drugs, like xylazine, phenobarbital, and pentobarbital in an attempt to control the outburst but to no avail. However, after five days, the horse’s symptoms subsided.

Case Background and History

• The subject is a 4-year-old, male Thoroughbred horse who underwent surgery for removal of a bone exostosis from a forelimb.
• The horse was administered a 25 mg dose of fluphenazine decanoate due to its rambunctious behavior posing danger to the surgery site.
• Following this, the horse exhibited progressively worsening episodes of seizure-like activity which could be temporarily controlled through the administration of xylazine.

Examination and Assessment

• On arrival at the hospital, the horse was in physical distress and had to be assisted out of its entrapment.
• Initial physical examination seemed normal except for heart conditions attributed to the sedative effects of xylazine.
• The observations led to a primary diagnosis considering fluphenazine-induced extrapyramidal side effects among other possibilities such as rabies, fumonisin toxicity, equine protozoal myeloencephalitis (EPM), and equine herpes virus (EHV)-1.

Diagnostic Procedures and Results

• Blood samples were taken for a complete blood count, serum chemistry analysis, EPM and EHV-1 titers, and fluphenazine quantification. A CSF was also collected from the lumbosacral site.
• Results showed evidence of a stress leukogram, a hyperglycemia, and a slight increase in serum creatinine. However, most other results were within normal limits. Fluphenazine serum levels were considerably high.

Case Management and Recovery

• Management of the case involved sedation and fluid administration for the horse. The horse was also placed under a continuous pentobarbital drip and given fluid maintenance levels due to the lack of response to initial therapy. Anticholinergic drug diphenhydramine reportedly successful in controlling fluphenazine toxicity, was also administered but it yielded no effect.
• Despite the sustained violent activity, the horse started to appear normal on day 5 and the pentobarbital, and other medications were discontinued.
• On day 14, the horse was discharged without any recurrence of the extrapyramidal side effects.

Discussion of Findings

• Fluphenazine, typically used for behavior modification in humans and other animals, incites certain unwanted side effects – tardive dyskinesia, akathisia, and hyperreflexia, that likely caused the horse’s abnormal activities.
• It is proposed that horses have a more extensive extrapyramidal system than people, making them more susceptible to the drug’s undesirable side effects.
• The lack of conclusive research on fluphenazine’s effect on horses made it challenging to confirm the diagnosis. Factors like negative findings from alternative diagnoses, high serum levels in the horse as compared to humans, and a complete recovery from these side-effects led the team to a tentative fluphenazine-induced extrapyramidal side effects diagnosis.