Dextrorphan

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Dextrorphan (DXO) is a psychoactive drug of the morphinan class which acts as an antitussive or cough suppressant and in high doses a dissociative hallucinogen. It is the dextrorotatory enantiomer of racemorphan; the levorotatory enantiomer is levorphanol. Dextrorphan is produced by O-demethylation of dextromethorphan by CYP2D6. Dextrorphan is an NMDA antagonist and contributes to the psychoactive effects of dextromethorphan.

Pharmacology

Pharmacodynamics

Dextrorphan

Site	Ki (nM)	Species	Ref
NMDAR (MK-801)	486–906	Rat
σ1	118–481	Rat
σ2	11,325–15,582	Rat
Template:Abbrlink	420 >1,000	Rat Human
Template:Abbrlink	34,700	Rat
Template:Abbrlink	5,950	Rat
Template:Abbrlink	401–484	Rat
Template:Abbrlink	≥340	Rat
Template:Abbrlink	>1,000	Rat
5-HT1A	>1,000	Rat
5-HT1B/1D	54% at 1 μM	Rat
5-HT2A	>1,000	Rat
α1	>1,000	Rat
α2	>1,000	Rat
β	35% at 1 μM	Rat
D2	>1,000	Rat
H1	95% at 1 μM	Rat
Template:Abbrlink	100% at 1 μM	Rat
Template:Abbrlink	1,300–29,600 (IC50)	Rat
Template:Abbrlink	ND	ND	ND
Values are Ki (nM), unless otherwise noted. The smaller the value, the more strongly the drug binds to the site.

The pharmacology of dextrorphan is similar to that of dextromethorphan (DXM). However, dextrorphan is much more potent as an NMDA receptor antagonist and much less active as a serotonin reuptake inhibitor, but retains DXM's activity as a norepinephrine reuptake inhibitor. It also has more affinity for the opioid receptors than dextromethorphan, significantly so at high doses.

Pharmacokinetics

Dextrorphan has a notably longer elimination half-life than its parent compound, and therefore has a tendency to accumulate in the blood after repeated administration of normally dosed dextromethorphan formulations. It is further converted to 3-HM by CYP3A4 or glucuronidated.

Society and culture

Legal status

Dextrorphan was formerly a Schedule I controlled substance in the United States, but was unscheduled on October 1, 1976.

Research

Dextrorphan was under development for the treatment of stroke, and reached phase II clinical trials for this indication, but development was discontinued.

Environmental presence

In 2021, dextrorphan was identified in >75% of sludge samples taken from 12 wastewater treatment plants in California. The same study associated dextrorphan with estrogenic activity by using predictive modelling, before observing it in in vitro.

See also

• Cough syrup
• Racemorphan; Levorphanol
• Noscapine
• Codeine; Pholcodine
• Dextromethorphan; Dimemorfan
• Butamirate
• Pentoxyverine
• Tipepidine
• Cloperastine
• Levocloperastine