Estimated reading time: 4 minutes
Subedited by Dr Phil Tucak
Pergolide mesylate is an ergot derivative that is a potent dopamine agonist. It is used to control signs associated with equine Cushing’s disease or pituitary pars intermedia dysfunction (PPID). Due to an increased potential for heart valve damage associated with pergolide use in humans, all dosage forms were withdrawn from the market in 2007. Pergolide is available from compounding pharmacies for veterinary use.
Quattro is an eight-year-old male neutered black labrador. The owner had a compounded tablet of pergolide wrapped in bread in her jacket pocket ready to administer to her horse for treatment of PPID. Quattro, in true labrador form, managed to remove and eat the pergolide tablet and the bread. The dose of pergolide ingested was 500ug (0.5mg).
About 90 minutes after ingestion of the pergolide, Quattro vomited, bringing up all of his meal from the morning. There was no apparent evidence of the pergolide tablet or bread in the vomit. About 60 minutes after vomiting (2.5 hours after initial ingestion), Quattro was becoming lethargic and was presented to Dandenong Ranges Veterinary Centre for examination and assessment.
Quattro was quiet, alert and responsive at presentation which was a stark contrast to his usual boisterous self. His physical examination was mostly unremarkable with the exception of some periodontal disease, slight tachycardia, lethargy, weakness and slightly prolonged capillary refill time (two seconds). His pupils were mid dilated, lungs clear and abdominal palpation was normal with normal borborygmi. His body temperature was normal and his skin tent hydration status was normal.
There is limited information available about pergolide overdose in animals. Assistance for information was sought from various sources including a compounding pharmacy, the Australian Animal Poisons Centre, Plumbs Veterinary Drug Handbook, the Lort Smith Animal Hospital (Melbourne) and an equine veterinary practice.
No information for horses or dogs is readily available about the pharmacokinetics of pergolide. In humans, the drug is absorbed orally (estimated 60% available) and is 90% bound to plasma proteins. The principal route of elimination is the kidneys. Peak onset of effects is generally noted within three to four hours.
Pergolide is well tolerated in horses but information is lacking about tolerance in dogs. The presumed clinical signs for overdose in dogs would be consistent with the effects of excess dopamine. Potential side effects could include gastrointestinal disturbances, central nervous system effects, seizures, pale gums, collapse and postural hypotension.
Common findings in dogs from limited reported clinical cases in decreasing frequency included vomiting, lethargy, depression, hyperactivity and hypotension. Treatment is supportive but dopamine agonists (phenothiazines) may decrease the central nervous system stimulation and metoclopramide may decrease other effects.
In dogs, no adverse effects at a dose of 0.1mg/kg/day were noted in a one-year study, however clinical signs of vomiting and lethargy have been noted with doses as low as 0.01-0.07mg/kg. The lethal dose is stated to be 25mg/kg in dogs.
Since ingestion of the pergolide by Quattro was at least two and a half hours prior to presentation, emesis was not considered. Apomorphine could theoretically potentiate any subsequent dopaminergic effects from pergolide. Anti-dopamine sedatives such as acepromazine may be beneficial as well as intravenous fluids to assist with postural hypotensive effects. The dose of pergolide ingested by Quattro who weighed 40kg, was 0.0125mg/kg.
Quattro was admitted for blood pressure measurement, intravenous fluid administration, activated charcoal and regular monitoring. His serial blood pressure measurements averaged 125/76 (normal). He was administered activated charcoal 250mg x 10 tablets which he promptly vomited back up.
Quattro was then given 12mg metoclopramide subcutaneously. He was still quite lethargic. One hour later his heart rate had normalised and he was much brighter. His capillary refill time was now one second and he was starting to vocalise (much more alert) and was a lot stronger (back to normal).
He was given activated charcoal tablets once again which he didn’t vomit this time around. He had rank flatulence. Quattro was discharged home for monitoring overnight by the owner. Reports from the owner over the subsequent two days were that he had returned to his normal self.
Plumb’s Veterinary Drug Handbook (6th Edition).
Australian Animal Poisons Centre – case studies and previous calls.
Lort Smith Animal Hospital – previous treatment experience.
Telephone advice from BOVA Compounding Pharmacy, Sydney.
Dr Moss Siddle BVSc,
Dandenong Ranges Veterinary Centre,
MedeChat and VetCheck 24/7
Dr Moss Siddle established Dandenong Ranges Veterinary Centre in 1999 after working in various veterinary practices in Australia and throughout the UK. He also has a telemedicine business, Medechat, and an after-hours referral service for vet clinics, VetCheck 24/7.
In 2012 Dr Siddle produced the VetCheck app—a free pet care diary and reminder app.
Dr Siddle is currently the chair of the AVA Veterinary Business Group (VBG) and the president of the Wheelchair Sports for Kids charity.