Буторфанол

Mixed opioid agonist-antagonist. Analgesic (narcotic); antitussive. Controlled substance.

ChEBI: Levorphanol in which a hydrogen at position 14 of the morphinan skeleton is substituted by hydroxy and one of the hydrogens of the N-methyl group is substituted by cyclopropyl. A semi-synthetic opioid agonist-antagonist analgesic, it is sed as its (S,S)-tartaric acid salt for relief or moderate to severe pain.

Butorphanol (Stadol) is chemically related to levorphanol but pharmacologically similar in action to pentazocine. As an opioid antagonist it is nearly 30 times as potent as pentazocine and has one-fortieth the potency of naloxone. It is a potent opioid analgesic indicated for the relief of moderate to severe pain. Its potency is 7 times that of morphine and 20 times that of pentazocine as an analgesic. Its onset of action is similar to that of morphine.The side effects and signs of toxicity are similar to those produced by pentazocine. It produces excitatory effects and sedation and precipitates withdrawal in opioid-dependent patients. Although generally administered parenterally because of its low bioavailability following oral administration, it is also unique in that a nasal spray formulation is available.The nasal spray is indicated for the relief of postoperative pain and migraine headache. The low molecular weight of butorphanol, its high lipophilicity, and its lack of vasoconstrictor effects make it particularly suitable for nasal administration.
Nasal administration of butorphanol decreases the onset of action to 15 minutes and decreases the firstpass effect of the drug, which increases bioavailability. Generally the patient sprays a set dose of 1 mg per hour for 2 hours. The duration of action is 4 to 5 hours. The convenience of such administration is a major advantage to patients requiring repeat dosing. The abuse potential following such administration has not been extensively studied, although it is thought to be small. Butorphanol is not a federally controlled (“scheduled”) drug, so physicians are not required to obtain the licenses and security safeguards required for other opioid analgesics.
Adverse effects, contraindications, and drug interactions are similar to those for pentazocine and morphine.

Structurally, butorphanol is a morphinan and shares the samecyclobutyl methyl group on the nitrogen as nalbuphine. Likenalbuphine, butorphanol is an agonist at the κ-receptor but atthe μ-receptor butorphanol is both a partial agonist and anantagonist. The affinity for opioid receptors in vitro is1:4:25 for the μ-, δ-, and κ-receptors respectively. Thehigh affinity for the κ-receptors is proposed to give butorphanolits analgesic properties and is also responsible for theCNS adverse effects such as hallucinations, psychosis, andparanoid reactions. Butorphanol binds with μ-receptors as apartial agonist, and administration to humans maintained onhigh-potency μ-agonists such as morphine may precipitatewithdrawal. Butorphanol was found to produce convulsionsin morphine-deprived, morphine-dependent monkeys.