Drug Groups

illicit; approved

Description

A synthetic morphinan analgesic with narcotic antagonist action. It is used in the management of severe pain. [PubChem]

Indication

For the relief of moderate to severe pain.

Pharmacology

Butorphanol is a synthetic opioid agonist-antagonist analgesic with a pharmacological and therapeutic profile that has been well established since its launch as a parenteral formulation in 1978. The introduction of a transnasal formulation of butorphanol represents a new and noninvasive presentation of an analgesic for moderate to severe pain. This route of administration bypasses the gastrointestinal tract, and this is an advantage for a drug such as butorphanol that undergoes significant first-pass metabolism after oral administration. The onset of action and systemic bioavailability of butorphanol following transnasal delivery are similar to those after parenteral administration. Butorphanol blocks pain impulses at specific sites in the brain and spinal cord.

Toxicity

The clinical manifestations of butorphanol overdose are those of opioid drugs in general. The most serious symptoms are hypoventilation, cardiovascular insufficiency, coma, and death.

Affected Organisms

Biotransformation

Extensively metabolized in the liver. The pharmacological activity of butorphanol metabolites has not been studied in humans; in animal studies, butorphanol metabolites have demonstrated some analgesic activity.

Absorption

Rapidly absorbed after intramuscular injection and peak plasma levels are reached in 20-40 minutes. The absolute bioavailability is 60-70% and is unchanged in patients with allergic rhinitis. In patients using a nasal vasoconstrictor (oxymetazoline) the fraction of the dose absorbed was unchanged, but the rate of absorption was slowed. Oral bioavailability is only 5-17% because of extensive first-pass metabolism.

Half Life

The elimination half-life of butorphanol is about 18 hours. In renally impaired patients with creatinine clearances <30 mL/min the elimination half-life is approximately doubled. After intravenous administration to patients with hepatic impairment, the elimination half-life of butorphanol was approximately tripled.

Protein Binding

Serum protein binding is approximately 80%.

Elimination

Butorphanol is extensively metabolized in the liver. Elimination occurs by urine and fecal excretion.

Distribution

* 305 to 901 L

Clearance

* 99 +/- 23 L/h [Young with IV 2 mg]
* 82 +/- 21 [Eldery with IV 2 mg]

References

External Links