|Systematic (IUPAC) name|
|Trade names||Robitussin, Delsym, DM, DexAlone, Duract|
|Pregnancy cat.||A (AU) C (US)|
|Legal status||Pharmacy Only (S2) (AU) OTC (CA) OTC (UK) OTC (US)|
|Metabolism||Hepatic (liver) enzymes: major CYP2D6, minor CYP3A4, and minor CYP3A5|
|Half-life||2-4 hours (extensive metabolisers); 24 hours (poor metabolisers)|
|Mol. mass||271.40 g/mol|
|Melt. point||111 °C (232 °F)|
|(what is this?)|
Dextromethorphan (DXM or DM) is an antitussive (cough suppressant) drug. It is one of the active ingredients in many over-the-counter cold and cough medicines, including generic labels and store brands, Benylin DM, Mucinex DM, Robitussin, NyQuil, Dimetapp, Vicks, Coricidin, Delsym, TheraFlu, and others. Dextromethorphan has also found other uses in medicine, ranging from pain relief to psychological applications. It is sold in syrup, tablet, spray, and lozenge forms. In its pure form, dextromethorphan occurs as a white powder.
DXM is also used recreationally. When exceeding label-specified maximum dosages, dextromethorphan acts as a dissociative hallucinogen. Its mechanism of action is via multiple effects, including actions as a nonselective serotonin reuptake inhibitor and a sigma-1 receptor agonist. The major metabolite of DXM, dextrorphan, also acts as an NMDA receptor antagonist. In high doses this produces effects similar to, yet distinct from, the dissociative states created by other dissociative anaesthetics such as ketamine and phencyclidine. As well, the metabolite 3-methoxymorphinan of dextrorphan (thus a second-level metabolite of DXM) produces local anesthetic effects in rats with potency above dextrorphan, but below that of DXM.
The primary use of dextromethorphan is as a cough suppressant, for the temporary relief of cough caused by minor throat and bronchial irritation (such as commonly accompanies the flu and common cold), as well as those resulting from inhaled particle irritants.
A 2004 study showed that dextromethorphan was no more effective for children than a placebo. Studies conducted by the American Academy of Pediatrics show that dextromethorphan is not superior to a placebo in providing nocturnal symptom relief for children with cough and sleep difficulty due to upper respiratory infections.
A combination of dextromethorphan and quinidine, a CYP2D6 inhibitor, has been shown to alleviate symptoms of easy laughing and crying (pseudobulbar affect) in patients with amyotrophic lateral sclerosis and multiple sclerosis. Dextromethorphan is also being investigated as a possible treatment for neuropathic pain and pain associated with fibromyalgia. In 2010, the FDA approved the combination product dextromethorphan/quinidine (Nuedexta) for the treatment of pseudobulbar affect (PBA).
Over-the-counter preparations containing dextromethorphan have been used in manners inconsistent with their labeling, often as a recreational drug. At doses much higher than medically recommended, dextromethorphan is classified as a dissociative hallucinogen, possessing certain effects that are somewhat similar to the dissociative agents ketamine and phencyclidine. It may produce distortions of the visual field - feelings of dissociation, distorted bodily perception, and excitement, as well as a loss of sense of time. Some users report stimulant-like euphoria, particularly in response to music. Dextromethorphan usually provides its recreational effects in a non-linear fashion, so that they are experienced in significantly varied stages. These stages are commonly referred to as "plateaus".
At normal doses:
- body rash/itching (see below)
- Closed-eye hallucination
At dosages 3 to 10 times the recommended therapeutic dose:
- Increased energy
- Increased confidence
- Slight Nauseousness
- "speeding"/talking fast
- Feelings of increased strength
- Enlargened pupils/glazed eyes (but not red)
At dosages 15 to 75 times the recommended therapeutic dose:
- blurred vision and/or double vision
- bloodshot eyes
- dilated pupils
- shallow respiration
- urinary retention
- muscle spasms
- sight loss
- inability to focus eyes
- skin rash
Dextromethorphan can also cause other gastrointestinal disturbances. Dextromethorphan had been thought to cause Olney's Lesions when administered intravenously; however, this was later proven inconclusive, due to lack of research on humans. Tests were performed on rats, giving them 50 mg and up every day up to a month. Neurotoxic changes, including vacuolation, have been observed in posterior cingulate and retrosplenial cortices of rats administered other NMDA antagonists such as PCP, but not with dextromethorphan. In many documented cases, dextromethorphan has produced psychological dependence in people who used it recreationally. However, it does not produce physical addiction, according to the WHO Committee on Drug Dependence.
Because dextromethorphan can trigger a histamine release (allergic reaction), atopic children, who are especially susceptible to allergic reactions, should be administered dextromethorphan only if absolutely necessary, and only under the strict supervision of a healthcare professional.
Dextromethorphan should not be taken with monoamine oxidase inhibitors (MAOIs) due to the potential for serotonin syndrome, which is a potentially life-threatening condition that can occur rapidly, due to a buildup of an excessive amount of serotonin in the body. Dextromethorphan can also cause serotonin syndrome when used with SSRI medicines, an interaction which has been documented in clinical cases where dextromethorphan is taken at recreational doses. It has been suggested that the link between therapeutic dosages of dextromethorphan and serotonin syndrome is less conclusive.
Caution should be exercised when taking dextromethorphan when drinking grapefruit juice or eating grapefruits, as compounds in grapefruit affect a number of drugs, including dextromethorphan, through the inhibition of the cytochrome p450 system in the liver and can lead to excessive accumulation and prolonged effects. It is generally recommended that grapefruits and grapefruit juices (especially white grapefruit juice, but also including other citrus fruits such as bergamot and lime, as well as a number of non-citrus fruits) be avoided while using dextromethorphan and numerous other medications.
Testing for this drug is done either by blood or by urine. Blood can be either serum or plasma, serum in a plain red top 2mL preferred. Urine requires only 2mL minimum.
Dextromethorphan is the dextrorotatory enantiomer of levomethorphan, which is the methyl ether of levorphanol, both opioid analgesics. It is named according to IUPAC rules as (+)-3-methoxy-17-methyl-9α,13α,14α-morphinan. As the pure free base, dextromethorphan occurs as an odorless, white to slightly yellow crystalline powder. It is freely soluble in chloroform and insoluble in water. Dextromethorphan is commonly available as the monohydrated hydrobromide salt, however some newer extended-release formulations contain dextromethorphan bound to an ion exchange resin based on polystyrene sulfonic acid. Dextromethorphan's specific rotation in water is +27.6° (20 °C, Sodium D-line).
Dextromethorphan has been shown to possess the following properties, mainly in binding assays to various receptors of animal tissues. Low Ki values mean strong binding or high affinity; high Ki values mean weak binding to the target or low affinity:
- Uncompetitive NMDA receptor (PCP site) antagonist (Ki = 7,253 nM).
- σ1 and σ2 sigma receptor agonist (Ki = 205 nM and 11,060 nM, respectively). In a comparative investigation of dimemorfan, dextromethorphan and dextrorphan in mouse cells, dextromethorpan binds with relatively high affinity to Sigma-1 receptors and with very low affinity to Sigma-2 receptors.
- α3β4-, α4β2-, and α7-nACh receptor (Ki = in the μM range) antagonist. Dextromethorphan binds to nicotinic receptors in frog eggs (Xenopus oocytes), human embryonic kidney cells and mouse tissue. It inhibits the antinociceptive (pain killing) action of nicotine in the tail-flick test in mice, where mouse tails are exposed to heat, which makes the mouse flick its tail if it feels pain.
- μ-, δ-, and κ-opioid receptor agonist (Ki = 1,280 nM, 11,500 nM, and 7,000 nM, respectively).
- SERT and NET inhibitor (Ki = 23 nM and 240 nM, respectively).
- NADPH oxidase inhibitor.
Its affinities for some of the sites listed are relatively very low and are probably insignificant, such as binding to NMDA receptors and opioid receptors, even at high recreational doses. Instead of acting as a direct antagonist of the NMDA receptor itself, it is likely that dextromethorphan functions as a prodrug to its nearly 10-fold more potent metabolite dextrorphan, and this is the true mediator of its dissociative effects. It is not entirely clear what role, if any, (+)-3-Methoxymorphinan, dextromethorphan's other major metabolite, plays in its effects.
At therapeutic doses, dextromethorphan acts centrally (meaning that it acts on the brain) as opposed to locally (on the respiratory tract). It elevates the threshold for coughing, without inhibiting ciliary activity. Dextromethorphan is rapidly absorbed from the gastrointestinal tract and converted into the active metabolite dextrorphan in the liver by the cytochrome P450 enzyme CYP2D6. The average dosage necessary for effective antitussive therapy is between 10 mg and 45 mg, depending on the individual. The International Society for the Study of Cough recommend "an adequate first dose of medication is 60 mg in the adult and repeat dosing should be infrequent rather than the qds recommended."
The duration of action after oral administration is approximately three to eight hours for dextromethorphan-hydrobromide, and ten to twelve hours for dextromethorphan-polistirex. Approximately 1 in 10 of the caucasian population has little or no CYP2D6 enzyme activity leading to long lived high drug levels.
The first-pass through the hepatic portal vein results in some of the drug's being metabolized by O-demethylation into an active metabolite of dextromethorphan called dextrorphan (DXO). DXO is the 3-hydroxy derivative of dextromethorphan. The therapeutic activity of dextromethorphan is believed to be caused by both the drug and this metabolite. Dextromethorphan also undergoes N-demethylation (to 3-methoxymorphinan or MEM), and partial conjugation with glucuronic acid and sulfate ions. Hours after dextromethorphan therapy, (in humans) the metabolites (+)-3-hydroxy-N-methylmorphinan, (+)-3-morphinan, and traces of the unchanged drug are detectable in the urine.
A major metabolic catalyst involved is the cytochrome P450 enzyme known as 2D6, or CYP2D6. A significant portion of the population has a functional deficiency in this enzyme and are known as poor CYP2D6 metabolizers. O-demethylation of DXM to DXO contributes to at least 80% of the DXO formed during DXM metabolism. As CYP2D6 is a major metabolic pathway in the inactivation of dextromethorphan, the duration of action and effects of dextromethorphan can be increased by as much as three times in such poor metabolizers. In one study on 252 Americans, 84.3% were found to be "fast" (extensive) metabolizers, 6.8% to be "intermediate" metabolizers, and 8.8% were "slow" metabolizers of DXM. There are a number of known alleles for CYP2D6, including several completely inactive variants. The distribution of alleles is uneven amongst ethnic groups; see also CYP2D6 - Ethnic factors in variability.
A large number of medications are potent inhibitors of CYP2D6. Some types of medications known to inhibit CYP2D6 include certain SSRI and tricyclic antidepressants, some antipsychotics, and the commonly-available antihistamine diphenhydramine. There exists, therefore, the potential of interactions between dextromethorphan and medications that inhibit this enzyme, particularly in slow metabolizers. See also CYP2D6 - Ligands.
A number of other CYP enzymes are implicated as minor pathways of DXM metabolism. CYP2B6 is actually more effective than CYP3A4 at N-demethylation of DXM, but, since the average individual has a much lower CYP2B6 content in his/her liver relative to CYP3A4, most N-demethylation of DXM is catalyzed by CYP3A4.
The racemic parent compound racemorphan was first described in a Swiss and US patent application from Hoffmann-La Roche in 1946 and 1947 respectively, a patent was granted in 1950. A resolution of the two isomers of racemorphan with tartaric acid was published in 1952, and DXM was successfully tested in 1954 as part of US Navy and CIA-funded research on nonaddictive substitutes for codeine. DXM was approved by the FDA in 1958 as an over-the-counter antitussive. As had been initially hoped, DXM was a solution for some of the problems associated with the use of codeine phosphate as a cough suppressant, such as sedation and opiate dependence, but like the dissociative anesthetics phencyclidine and ketamine, DXM later became associated with non-medical use.
During the 1960s and 1970s, dextromethorphan became available in an over-the-counter tablet form by the brand name Romilar. In 1973, Romilar was taken off the shelves after a burst in sales because of frequent misuse, and was replaced by cough syrup in an attempt to cut down on abuse. The advent of widespread internet access in the 1990s allowed users to rapidly disseminate information about DXM, and online discussion groups formed around use and acquisition of the drug. As early as 1996 DXM HBr powder could be purchased in bulk from online retailers, allowing users to avoid consuming DXM in syrup preparations. As of January 1, 2012, dextromethorphan is prohibited for sale to minors in the state of California, except with a doctor's prescription.
|Wikimedia Commons has media related to Dextromethorphan.|
- Cough syrup
- (+)-Naloxone - another dextrorotatory enantiomer of an opioid drug with useful non-opioid effects
- Kukanich B, Papich MG (2004). "Plasma profile and pharmacokinetics of dextromethorphan after intravenous and oral administration in healthy dogs". J. Vet. Pharmacol. Ther. 27 (5): 337–41. doi:10.1111/j.1365-2885.2004.00608.x. PMID 15500572.
- "Balminil DM, Benylin DM (dextromethorphan) dosing, indications, interactions, adverse effects, and more". Medscape Reference. WebMD. Retrieved 15 April 2014.
- "Reference Tables: Description and Solubility - D". Retrieved 2011-05-06.
- Schwartz AR, Pizon AF, Brooks DE (September 2008). "Dextromethorphan-induced serotonin syndrome". Clinical Toxicology (Philadelphia, Pa.) 46 (8): 771–3. doi:10.1080/15563650701668625. PMID 19238739.
- Shin EJ, Nah SY, Chae JS, Bing G, Shin SW, Yen TP, Baek IH, Kim WK, Maurice T, Nabeshima T, Kim HC (May 2007). "Dextromethorphan attenuates trimethyltin-induced neurotoxicity via sigma1 receptor activation in rats". Neurochemistry International 50 (6): 791–9. doi:10.1016/j.neuint.2007.01.008. PMID 17386960.
- Shin EJ, Nah SY, Kim WK, Ko KH, Jhoo WK, Lim YK, Cha JY, Chen CF, Kim HC (April 2005). "The dextromethorphan analog dimemorfan attenuates kainate-induced seizures via sigma1 receptor activation: comparison with the effects of dextromethorphan". British Journal of Pharmacology 144 (7): 908–18. doi:10.1038/sj.bjp.0705998. PMC 1576070. PMID 15723099. Retrieved 2011-05-06.
- "Dextromethorphan". Drugs and Chemicals of Concern. Drug Enforcement Administration. August 2010.
- Hou CH, Tzeng JI, Chen YW, Lin CN, Lin MT, Tu CH, Wang JJ (2006). "Dextromethorphan, 3-methoxymorphinan, and dextrorphan have local anesthetic effect on sciatic nerve blockade in rats". European Journal of Pharmacology 544 (1-3): 10–6. doi:10.1016/j.ejphar.2006.06.013. PMID 16844109.
- Rossi, S, ed. (2013). Australian Medicines Handbook (2013 ed.). Adelaide: The Australian Medicines Handbook Unit Trust. ISBN 978-0-9805790-9-3.
- Davidson K (July 8, 2004). "Kids' cough medicine no better than placebo / Study of OTC meds shows syrup is just as effective". SFGate.
- Paul IM, Yoder KE, Crowell KR, Shaffer ML, McMillan HS, Carlson LC, Dilworth DA, Berlin CM (2004). "Effect of Dextromethorphan, Diphenhydramine, and Placebo on Nocturnal Cough and Sleep Quality for Coughing Children and Their Parents". Pediatrics 114 (1): e85–90. doi:10.1542/peds.114.1.e85. PMID 15231978.
- Brooks BR, Thisted RA, Appel SH, Bradley WG, Olney RK, Berg JE, Pope LE, Smith RA (2004). "Treatment of pseudobulbar affect in ALS with dextromethorphan/quinidine: a randomized trial". Neurology 63 (8): 1364–70. doi:10.1212/01.wnl.0000142042.50528.2f. PMID 15505150.
- "Cough Drug May Help Fibromyalgia Pain". WebMD.
- Koyuncuoğlu H, Güngör M, Sağduyu H, Aricioğlu F (Apr 1990). "Suppression by ketamine and dextromethorphan of precipitated abstinence syndrome in rats". Pharmacol Biochem Behav. 35 (4): 829–32. doi:10.1016/0091-3057(90)90366-P. PMID 2345761.
- "Dextromethorphan (DXM)". Cesar.umd.edu. Retrieved 2013-07-28.
- White W. "The DXM Experience". Erowid.org. Retrieved December 21, 2010.
- Giannini AJ (1997). Drugs of abuse (2nd ed.). Los Angeles, Calif.: Practice Management Information Corp. ISBN 1570660530.[page needed]
- Erowid DXM (Dextromethorphan, DM) Vault, Erowid.org
- "Dextromethorphan". NHTSA.
- "Teen Drug Abuse: Cough Medicine and DXM (Dextromethorphan)". webmd.
- Olney JW, Labruyere J, Price MT (1989). "Pathological changes induced in cerebrocortical neurons by phencyclidine and related drugs". Science 244 (4910): 1360–2. doi:10.1126/science.2660263. PMID 2660263.
- Carliss RD, Radovsky A, Chengelis CP, O'Neill TP, Shuey DL (2007). "Oral administration of dextromethorphan does not produce neuronal vacuolation in the rat brain". NeuroToxicology 28 (4): 813–8. doi:10.1016/j.neuro.2007.03.009. PMID 17573115.
- WHO Expert Committee on Drug Dependence (1970). Seventeenth Report (PDF). World Health Organization. Retrieved 2008-12-29.
- "Inhibitors of CYP3A4". ganfyd.org. Retrieved 23 August 2013.
- Chou YC, Liao JF, Chang WY, Lin MF, Chen CF (1999). "Binding of dimemorfan to sigma-1 receptor and its anticonvulsant and locomotor effects in mice, compared with dextromethorphan and dextrorphan". Brain Research 821 (2): 516–9. doi:10.1016/S0006-8993(99)01125-7. PMID 10064839.
- Wong BY, Coulter DA, Choi DW, Prince DA (1988). "Dextrorphan and dextromethorphan, common antitussives, are antiepileptic and antagonize N-methyl-d-aspartate in brain slices". Neuroscience Letters 85 (2): 261–6. doi:10.1016/0304-3940(88)90362-X. PMID 2897648.
- Church J, Jones MG, Davies SN, Lodge D (1989). "Antitussive agents as N-methylaspartate antagonists: further studies". Canadian journal of physiology and pharmacology 67 (6): 561–7. doi:10.1139/y89-090. PMID 2673498.
- Kamel IR, Wendling WW, Chen D, Wendling KS, Harakal C, Carlsson C (2008). "N-Methyl-D-Aspartate (NMDA) Antagonists—S(+)-ketamine, Dextrorphan, and Dextromethorphan—Act as Calcium Antagonists on Bovine Cerebral Arteries". Journal of Neurosurgical Anesthesiology 20 (4): 241–8. doi:10.1097/ANA.0b013e31817f523f. PMID 18812887.
- Damaj MI, Flood P, Ho KK, May EL, Martin BR (2004). "Effect of Dextrometorphan and Dextrorphan on Nicotine and Neuronal Nicotinic Receptors: In Vitro and in Vivo Selectivity". Journal of Pharmacology and Experimental Therapeutics 312 (2): 780–5. doi:10.1124/jpet.104.075093. PMID 15356218.
- Lee JH, Shin EJ, Jeong SM, Kim JH, Lee BH, Yoon IS, Lee JH, Choi SH, Lee SM, Lee PH, Kim HC, Nah SY (2006). "Effects of dextrorotatory morphinans on α3β4 nicotinic acetylcholine receptors expressed in Xenopus oocytes". European Journal of Pharmacology 536 (1-2): 85–92. doi:10.1016/j.ejphar.2006.02.034. PMID 16563374.
- Hernandez SC, Bertolino M, Xiao Y, Pringle KE, Caruso FS, Kellar KJ (2000). "Dextromethorphan and its metabolite dextrorphan block alpha3beta4 neuronal nicotinic receptors". The Journal of Pharmacology and Experimental Therapeutics 293 (3): 962–7. PMID 10869398.
- Codd EE, Shank RP, Schupsky JJ, Raffa RB (1995). "Serotonin and norepinephrine uptake inhibiting activity of centrally acting analgesics: structural determinants and role in antinociception". The Journal of Pharmacology and Experimental Therapeutics 274 (3): 1263–70. PMID 7562497.
- Schwartz AR, Pizon AF, Brooks DE (2008). "Dextromethorphan-induced serotonin syndrome". Clinical toxicology (Philadelphia, Pa.) 46 (8): 771–3. doi:10.1080/15563650701668625. PMID 19238739.
- Henderson MG, Fuller RW (1992). "Dextromethorphan antagonizes the acute depletion of brain serotonin by p-chloroamphetamine and H75/12 in rats". Brain Research 594 (2): 323–6. doi:10.1016/0006-8993(92)91144-4. PMID 1280529.
- Gillman PK (2005). "Monoamine oxidase inhibitors, opioid analgesics and serotonin toxicity". British Journal of Anaesthesia 95 (4): 434–41. doi:10.1093/bja/aei210. PMID 16051647.
- Zhang W, Wang T, Qin L, Gao HM, Wilson B, Ali SF, Zhang W, Hong JS, Liu B (2004). "Neuroprotective effect of dextromethorphan in the MPTP Parkinson's disease model: role of NADPH oxidase". FASEB J. 18 (3): 589–91. doi:10.1096/fj.03-0983fje. PMID 14734632.
- Schmider J, Greenblatt DJ, Fogelman SM, von Moltke LL, Shader RI (1997). "Metabolism of Dextromethorphan in vitro: Involvement of Cytochromes P450 2D6 and 3A3/4, with a Possible Role of 2E1". Biopharmaceutics & Drug Disposition 18 (3): 227–240. doi:10.1002/(SICI)1099-081X(199704)18:3<227::AID-BDD18>3.0.CO;2-L. PMID 9113345.
- Professor Alyn H Morice paper titled 'Cough' par. 'Dextromethorphan' http://www.issc.info/cough.html
- Morice AH. "Cough". International Society for the Study of Cough.
- Yu A, Haining RL (2001). "Comparative contribution to dextromethorphan metabolism by cytochrome P450 isoforms in vitro: can dextromethorphan be used as a dual probe for both CTP2D6 and CYP3A activities?". Drug metabolism and disposition: the biological fate of chemicals 29 (11): 1514–20. PMID 11602530.
- Capon DA, Bochner F, Kerry N, Mikus G, Danz C, Somogyi AA (1996). "The influence of CYP2D6 polymorphism and quinidine on the disposition and antitussive effect of dextromethorphan in humans". Clin. Pharmacol. Ther. 60 (3): 295–307. doi:10.1016/S0009-9236(96)90056-9. PMID 8841152.
- Woodworth JR, Dennis SR, Moore L, Rotenberg KS (1987). "The polymorphic metabolism of dextromethorphan". Journal of clinical pharmacology 27 (2): 139–43. doi:10.1002/j.1552-4604.1987.tb02174.x. PMID 3680565.
- Morris, H.; Wallach, J. (2014). "From PCP to MXE: a comprehensive review of the non-medical use of dissociative drugs". Drug Testing and Analysis.
- "Memorandum for the Secretary of Defense" (PDF). Retrieved 2013-07-28.
- "Senate Bill No. 514". An act to add Sections 11110 and 11111 to the Health and Safety Code, relating to nonprescription drugs. State of California, Legislative Counsel.
- U.S. National Library of Medicine: Drug Information Portal - Dextromethorphan
- Nuedexta (dextromethorphan hydrobromide and quinidine sulfate): Prescribing Information (Original Approval Date FDA: October 29, 2010)
- DXM at Erowid