Dextromethorphan

Absorption

A 30mg oral dose of dextromethorphan reaches a Cmax of 2.9 ng/mL, with a Tmax of 2.86 h, and an AUC of 17.8 ng*h/mL.

Toxicity

A dextromethorphan overdose may present as nausea, vomiting, stupor, coma, respiratory depression, seizures, tachycardia, hyperexcitability, toxic psychosis, ataxia, nystagmus, dystonia, blurred vision, changes in muscle reflexes, and serotonin syndrome. Overdose should be managed through symptomatic and supportive measures.

Description

Dextromethorphan is an over-the-counter drug that is sold alone and in combination with other products as a cough suppressant for children and adults. We have previously recommended dextromethorphan as a safe and effective cough suppressant for both children and adults. However, the weight of the evidence now suggests that dextromethorphan is no more effective than an inactive placebo syrup in suppressing a nighttime cough in children. It is the disomer of the potent opiate analgesic 3-methoxyN-methylmorphine (levorphanol). Although dextromethorphan is structurally related to opioids, it is devoid of analgesic or sedative effects at therapeutic doses. Dextromethorphan is metabolized by CYP2D6 to a more potent metabolite, dextrorphan. Dextrorphan is a stronger noncompetitive antagonist than dextromethorphan for the N-methyl-D-aspartate (NMDA) glutamate receptor.These properties promote its use in treatment of neuropathic and postoperative pain management.

Description

Dextromethorphan is a commonly used cough suppressant. It is the dextrorotatory form of the racemic racemethorphan, which was patented by Hoffmann-La Roche in 1954. O. H?fliger and co-workers prepared the chiral form in 1956. Dextromethorphan is an over-the-counter drug formulated most often as the hydrobromide monohydrate.
At high doses, dextromethorphan is a dissociative hallucinogen. Its effects are similar to those of phencyclidine (“angel dust”).
Recently, the combination of dextromethorphan and quinidine was shown to alleviate the symptoms of pseudobulbar affect: laughing and crying in patients with multiple sclerosis, amyotrophic lateral sclerosis, and other neurologic diseases. The combination drug was approved for this use by the US Food and Drug Administration in 2010. It is marketed by Avanir under the trade name Nuedexta.

The Uses of Dextromethorphan

Dextromethorphan is used therapeutically as an over-thecounter cough suppressant and antitussive. It is also commonly abused particularly by adolescents because of its relative ease of availability.

Indications

Dextromethorphan is indicated in combination with brompheniramine and pseudoephedrine in the treatment of coughs and upper respiratory symptoms associated with allergies or the common cold. Dextromethorphan is also used in combination with guaifenesin as an over-the-counter product to relieve a cough. Dextromethorphan in combination with quinidine is indicated in the treatment of pseudobulbar affect.

Background

Dextromethorphan is a levorphanol derivative and codeine analog commonly used as a cough suppressant and also a drug of abuse. Although similar in structure to other opioids, it has minimal interaction with opioid receptors.
Dextromethorphan was granted FDA approval before 3 December 1957.

Pharmacokinetics

Dextromethorphan is an opioid-like molecule indicated in combination with other medication in the treatment of coughs and pseudobulbar affect. It has a moderate therapeutic window, as intoxication can occur at higher doses. Dextromethorphan has a moderate duration of action. Patients should be counselled regarding the risk of intoxication.

Metabolism

Dextromethorphan can be N-demethylated to 3-methoxymorphinan by CYP3A4, CYP2D6, and CYP2C9 or O-demethylated to dextrorphan by CYP2D6 and CYP2C9. Dextrorphan is N-demethylated by CYP3A4 and CYP2D6, while 3-methoxymorphinan is O-demethylated by CYP2D6. Both are metabolized to form 3-hydroxymorphinan. Dextrorphan and 3-hydroxymorphinan are both O-glucuronidated or O-sulfated.