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Levallorphan (Lorfan, Naloxiphan) is a drug of the morphinan family used as an opioid modulator and antidote. It acts as an antagonist on μ-opioid receptor and agonist on kappa receptor, and as a result, blocks the effects of stronger agents with greater intrinsic activity such as morphine or endogenous β-endorphin.
Levallorphan was formerly widely used in general anaesthesia, mainly to reverse the respiratory depression produced by the opioid analgesics and barbiturates used for induction of surgical anaesthesia while maintaining a degree of analgesia (via kappa opioid receptor agonization) although it is now less common as the newer drug naloxone tends to be used, instead.
It was also used in combination with opioids to reduce their side effects, mainly in obstetrics, and a very small dose of levallorphan used alongside an opioid full agonist can produce greater analgesia than when the agonist is used by itself. The combination of levallorphan with pethidine (meperidine) was indeed used so frequently, a standardized formulation was made available, known as Pethilorfan.
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- Bullough, J. (1959). "Use of premixed pethidine and antagonists in obstetrical analgesia; with special reference to cases in which levallorphan was used" (PDF). British Medical Journal 2 (5156): 859–862. doi:10.1136/bmj.2.5156.859. PMC 1990381. PMID 13805887.
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