Species differences and toxicity

SPECIES DIFFERENCES WITH OPIATES

  • Equine, Bovine, Caprine, Ovine, Porcine, and Feline patients may show CNS stimulation rather than CNS depression. Canine patients may initially defecate with the opioids. This is frequently followed by decreased GI motility, leading to constipation that is more commonly associated with this class of drugs.
  • Dogs may also respond to opiates with initial respiratory stimulation, which is then followed by typical respiratory depression. The opiates are cough suppressants in dogs. Additionally, dogs will exhibit coronary vasoconstriction, the opposite effect of that observed in humans.
  • Rabbits, Canines (and primates) exhibit miosis (pupillary constriction) while feline and other species exhibit mydriasis (pupillary dilatation). Canine and feline patients will exhibit emesis at very high doses, while other species (especially ruminants and swine) do not exhibit emesis.
  • Dogs and rabbits will typically exhibit hypothermia in response to the opiates while cattle, goats, horses, and cats typically exhibit hyperthermia.
  • The opiates are used primarily as analgesics in veterinary practice, often administered with an ataractic (such as acepromazine), especially in excitable species.

Absorption, fate and excretion

  • Opioids are readily absorbed from the small intestine and some from the stomach.
  • Absorbed well after subcutaneous administration. Not absorbed through intact skin.
  • Glucuronide conjugation is the primary metabolic pathway.

Toxicity

  • Toxicity decreases with maturity of the animal. In dogs convulsions similar to strychnine are noticed.
  • In cattle CNS stimulation and gastrointestinal disturbances without fatality. Addiction is rarely encountered in animals.

Precautions and contraindications

  • Tolerance develops to morphine usage. High degree of tolerance is exhibited in analgesia, euphoria, sedation, respiratory depression, antidiuresis, emesis and anti tussive, moderate tolerance is exhibited in bradycardia and no tolerance is exhibited in miosis and constipation.
  • Used with caution in uremic and toxemic dogs. Should not be used to control strychnine poisoning, tetanus and epilepsy. Should not be administered in shock and in animals with head injury.
Last modified: Friday, 6 May 2011, 5:52 PM