Butorphanol, sold for horses under the tradenames Torbugesic® and Delorex®, is a opiate sedative and pain reliever. Butorphanol tartrate is indicated for the relief of pain associated with colic in adult horses and yearlings. Clinical studies in the horse have shown that butorphanol tartrate alleviates abdominal pain associated with torsion, impaction, intussusception, spasmodic and tympanic colic, and postpartum pain. Though not labeled for this use it has been used in combination with some sedatives to potentiate sedation. This article is about the contraindications, toxic effects, dosages, and association drug rules that apply to this medication.

Following intravenous injection in horses, butorphanol is largely eliminated from the blood within 3 to 4 hours. This drug is extensively metabolized in the liver and excreted in the urine. Butorphanol tartrate is a totally synthetic, centrally acting, narcotagonist-antagonist analgesic with potent antitussive activity. It is a member of the phenanthrene series.

In animals, butorphanol has been demonstrated to be 4 to 30 times more potent than morphine and pentazocine respectively. In humans, butorphanol has been shown to have 5 to 7 times the analgesic activity of morphine and 20 times that of pentazocine. Butorphanol has 15 to 20 times the oral antitussive activity of codeine or dextromethorphan in dogs and guinea pigs. As an antagonist, butorphanol is approximately equivalent to nalorphine and 30 times more potent than pentazocine.

In ponies, butorphanol given intramuscularly at a dosage of 0.22 mg/kg was shown to alleviate experimentally induced visceral pain for about 4 hours. In horses, intravenous dosages of butorphanol ranging from 0.005 to 0.4 mg/kg were shown to be effective in alleviating visceral and superficial pain for at least 4 hours. A definite dosage-response relationship was detected in that butorphanol dosage of 0.1 mg/kg was more effective than 0.05 mg/kg, but not differ from 0.2 mg/kg, in alleviating deep abdominal pain.