Around one in 10 of the Caucasian population has little or no CYP2D6 enzyme activity, leading to long-lived high drug levels. 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 , [30] and partial conjugation with glucuronic acid and sulfate ions. A significant portion of the population has a functional deficiency in this enzyme and are known as poor CYP2D6 metabolizers. The distribution of alleles is uneven amongst ethnic groups. A large number of medications are potent inhibitors of CYP2D6. Some types of medications known to inhibit CYP2D6 include certain SSRIs and tricyclic antidepressants , some antipsychotics , and the commonly available antihistamine diphenhydramine.
Therefore, the potential of interactions exists between dextromethorphan and medications that inhibit this enzyme, particularly in slow metabolizers. As its pure form, dextromethorphan occurs as an odorless, opalescent white powder.
It is freely soluble in chloroform and insoluble in water ; the hydrobromide salt is water-soluble up to 1. A resolution of the two isomers of racemorphan with tartaric acid was published in , [34] and DXM was successfully tested in as part of US Navy and CIA -funded research on nonaddictive substitutes for codeine.
Neither dextromethorphan nor codeine in the dosages used was significantly more effective than placebo in reduction of acute cough. Studies using larger dosages have not been performed. Other studies focusing exclusively on children with cough have not been placebo-controlled trials. Demonstration of the efficacy of antitussive preparations in children is lacking, and these medications may be potentially harmful.
Codeine In adults, codeine and dextromethorphan have been shown to suppress both artificially induced and disease-related cough, mainly through central nervous system mechanisms. Dosage Pharmacokinetic studies of codeine therapy in children are lacking.
Adverse Reactions and Overdosage The principal clinical manifestations of codeine toxicity are respiratory depression and obtundation. Furthermore, alteration of hepatic enzyme pathways by illness or concurrent drug therapy such as acetaminophen may further alter metabolism of this drug and increase the risk of drug toxicity.
Dextromethorphan The addictive potential of codeine encouraged the marketing of dextromethorphan in a variety of cough and cold preparations. Although dextromethorphan is chemically derived from the opiates, it has no analgesic or addictive properties. The cough suppression potency of dextromethorphan in adults is nearly equal to that of codeine.
Dosages of dextromethorphan of equal antitussive potency to codeine produce comparable levels of central nervous system depression in adults. Indications for their use in children have not been established. Suppression of cough in many pulmonary airway diseases may be hazardous and contraindicated. Cough due to acute viral airway infections is short-lived and may be treated with fluids and humidity. Dosage guidelines for cough and cold mixtures are extrapolated from adult data and clinical experience, and thus are imprecise for children.
Adverse effects and overdosage associated with administration of cough and cold preparations in children are reported.
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