Dextromethorphan dosage

Three double-blind, crossover, randomized, placebo-controUed studies of the role of dextromethorphan in neurological pain conditions in 40 adults with diabetic neuropathy, postherpetic neuralgia, and non-specific neuropathic pain sjmdromes have been reviewed (5). Dextromethorphan dosages varied from 13.5 mg tds on alternate days to 120 mg qds. High-dose dextromethorphan significantly reduced pain in diabetic neuropathy with no effect in postherpetic neuralgia. Sedation (58%) and dizziness (25%) were the most commonly reported adverse effects. 

Information seems to be limited to this study. The elinieal implieations are that amiodarone may interfere with the results of phenotyping if dextromethorphan is used to determine CYP2D6 aetivity, and that dextromethorphan toxieity (exeitation, eonfusion) may possibly develop in patients taking amiodarone. Be alert for any signs of toxieity if both are used. As yet, too little is known about this interaetion to say by how mueh the dextromethorphan dosage should be reduced. Remember that dextromethorphan oeeurs in a eonsiderable number of proprietary eough preparations. 

A few infants have been treated with antagonists of the NMDA receptor, an excitatory glutamatergic receptor for which glycine is a co-agonist (see Ch. 15) [29], Ketamine and dextromethorphan have been used with inconclusive results. Some infants may have had an improvement of their irritability and electroencephalogram. One infant, treated with both benzoate and dextromethorphan, was seizure-free by 12 months of age and had only moderately delayed development. However, this favorable experience has not always been duplicated. Treatment with dextromethorphan at the recommended dosage (maximum 5mg/kg/day) seems to be well-tolerated. 

J. E. Kountourellis, C. K. Markoupoulou, and P. E. Georgako-poulos, An HPLC method for the separation and simultaneous determination of antihistamines, sympathomimetic amines and dextromethorphan in bulk dry material and dosage forms, Anal. Lett., 23 883 (1990). 

In a double-blind, placebo-controlled, crossover pilot study in three patients with cancer-associated postamputation phantom limb pain, oral dextromethorphan 60-90 mg bd or placebo were given for 1 week each, followed by dextromethorphan or placebo again (10). Dextromethorphan satisfactorily improved phantom Umb pain at a dosage of 60 mg bd in two patients and 90 mg bd in the third. Even though a relatively high total dose of dextromethorphan was used, there were no adverse effects. 

The risk of serotonin syndrome may be increased shortly after dosage increases of SSRIs or when drug interactions increase serotonin activity. Concomitant or proximal use of SSRIs, tricyclic antidepressants, or monoamine oxidase inhibitors may cause serotonin syndrome. Further, the addition of certain drugs, such as tryptophan, dextromethorphan, cocaine, or sympathomimetics, to SSRI therapy may increase the risk of developing serotonin syndrome." ... 

Use it cautiously and in rednced dosage with alcohol, barbiturates, and other sedatives, narcotics, dextromethorphan, and tricyclic antidepressants. Cocaine and vasoconstrictors in local anesthetics may precipitate a hypertensive response (see also Figure 80). 

Other authors have reported this interaction, and suggest reducing the flecainide dosage by between one-third to one-half when amiodarone is added. " Another study found that amiodarone raised steady-state flecainide plasma levels by 37% in extensive metabolisers, and 55% in poor me-tabolisers of dextromethorphan (a probe drug for CYP2D6 activity). In a later report of this study the authors concluded that these differences were nof clinically imporfanf, and that CYP2D6 phenotype does not affect the extent of the flecainide-amiodarone interaction. An isolated report describes torsade de pointes in a patient on amiodarone when given flecainide. ... 

Psychiatric A 60-year-old woman developed a psychosis after taking dextromethorphan at more than the recommended over-the-counter dosage, propoxyphene, and hydrocodone [71 ]. She developed religious and paranoid delusions, olfactory and visual hallucinations, and agitation. Propoxyphene may have slowed the metabolism of dextromethorphan, resulting in intoxication. 

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