Butorphanol (INN) is a morphinan-type synthetic opioid analgesic marketed in the US under the trade name Stadol. It is most closely structurally related to dextromethorphan. Butorphanol is available only as butorphanol tartrate in injectable and intranasal spray formulations.

Mechanism of Action

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Butorphanol exhibits partial agonist and antagonist activity at the μ opioid receptor and agonist activity at the κ opioid receptor. Stimulation of these receptors on central nervous system neurons causes an intracellular inhibition of adenylate cyclase, closing of influx membrane calcium channels, and opening of membrane potassium channels. This leads to hyperpolarization of the cell membrane potential and suppression of action potential transmission of ascending pain pathways. Because of its κ-agonist activity, at analgesic doses butorphanol increases pulmonary arterial pressure and cardiac work. Additionally, κ-agonism can cause dysphoria at therapeutic or supertherapeutic doses; this gives butorphanol a lower potential for abuse than other opioid drugs, and narcotic addicts do not like it.

Place in therapy

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The most common indication for butorphanol is management of migraine using the intranasal spray formulation. It may also be used parenterally for management of moderate-to-severe pain, as a supplement for balanced general anesthesia, and management of pain during labor.

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