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PubMed1992

Determination of dextromethorphan and its O-demethylated metabolite from urine.

A high-performance liquid chromatography (HPLC) assay for the simultaneous quantitation of dextromethorphan and its O-demethylated metabolite dextrorphan from urine is described. A cyano analytical column was used with a mobile phase consisting of MeOH 16%, acetonitrile 3%, and triethylamine 0.06% at pH 2.8 and a flow rate of 1.0 ml/min. Betaxolol was used as the internal standard. Standard curves from 50 ng/ml to 10,000 ng/ml (dextrorphan), and from 50 ng/ml to 8,000 ng/ml (dextromethorphan) were developed. The peaks eluted at 7.8 min (dextrorphan), 12.2 min (betaxolol), and 17.8 min (dextromethorphan). The coefficients of variance ranged from 1.3 to 4.5% at 250 ng/ml and 0.9 to 2.5% at 5,000 ng/ml. This assay was used to determine dextromethorphan/dextrorphan molar ratios in healthy male volunteers for the purpose of determining phenotype status for the P450IID6 isozyme.

Chromatography, High Pressure Liquid↗
PubMed1995

Dextromethorphan polymorphic hepatic oxidation (CYP2D6) in healthy black American adult subjects.

The objective of this study was to assign metabolizer phenotype to 107 healthy adult black Americans using dextromethorphan as the substrate probe. Eligible subjects were unrelated, healthy, nonsmoking, aged 18-50 years, and taking no medications. Fifteen milliliters of dextromethorphan syrup (85 mumol, 30 mg) was administered orally at bedtime, and 8-h overnight urine was collected. Dextromethorphan and dextrorphan urinary areas and molar ratios were determined using high-performance liquid chromatography with fluorescence detection. A molar metabolic ratio of < 0.3 was used to segregate poor metabolizers (PM) from extensive metabolizers (EM). Data were obtained in 99 subjects: 68 women, 31 men. (Five were lost to follow-up, three did not take the probe drug.) Six (6.1%) were PM (five women, one man), and 93 were EM. The prevalence of PM was 6.1% (95% confidence interval, 2.3-12.7%) in our sample. This compares to 5 to 10% reported in white unrelated subjects and 1.9% in 106 black children (64 healthy and 42 with cancer), and 0-8.6% in black African populations. The clinical implications of these findings warrant further investigation.

Administration, Oral↗
PubMed2004

Dextromethorphan abuse.

Dextromethorphan is an over-the-counter dissociative agent of increasing popularity as a drug of abuse among younger adolescents. The drug produces a range of toxicities depending upon either the dose or the components of the specific formulation that was ingested. Most cases improve with supportive care alone, but severely intoxicated patients may require significant attention. Because dextromethorphan is misused primarily by younger adolescents, the early identification and treatment of dextromethorphan abuse may be important in preventing broader substance abuse in these children. Consequently, it is important for clinicians to recognize, treat, and appropriately refer those who present with intoxication from this drug.

Adolescent↗
PubMed2005

A study of the effects of lorazepam and dextromethorphan on the response to cortical 1 Hz repetitive transcranial magnetic stimulation.

We studied the effects of lorazepam and dextromethorphan on the responses to 1 Hz repetitive transcranial magnetic stimulation applied to the left human motor cortex. Lorazepam, dextromethorphan or placebo was administered to 45 normal controls in a double-blind fashion 2.5 h before the repetitive transcranial magnetic stimulation procedure. Motor cortical excitability was measured with single transcranial magnetic stimulation pulses before and after 15 min of 1 Hz repetitive transcranial magnetic stimulation applied at supra-threshold intensity. 1 Hz repetitive transcranial magnetic stimulation resulted in a decrease in motor cortical excitability in the placebo group but not in the groups taking lorazepam or dextromethorphan. These results suggest that cortical responses to 1 Hz repetitive transcranial magnetic stimulation are dependent on activity at both gamma-aminobutyric acid and N-methyl-D-asparate receptor systems.

Adult↗
PubMed1997

Four years' treatment with ketamine and a trial of dextromethorphan in a patient with severe post-herpetic neuralgia.

N-methyl-D-aspartate (NMDA) receptors are involved in the development of neuropathic pain. Ketamine, a non-competitive NMDA receptor antagonist, has in several case reports given pain relief but efficacy in dosages tolerated in long-term ketamine treatment is unknown. Another substance with an antagonist action at NMDA receptors and which is approved for peroral administration is dextromethorphan. In a randomized study dextromethorphan was no better than placebo for neuropathic pain but this does not exclude efficacy in selected patients. We report a patient with severe post-herpetic pain resistant to conventional pain treatment which was treated with ketamine for 4 years with good pain relief. The practical application of long-term treatment in different administration forms of ketamine is described. The patient also responded with pain relief in a double-blind trial with oral dextromethorphan.

Aged↗
PubMed1990

The effects of vadocaine, dextromethorphan, diphenhydramine and hydroxyzine on the ciliary beat frequency in rats in vitro.

Mucociliary function is a major cleansing mechanism of the respiratory tract. Many drugs used in the treatment of respiratory diseases impair the ciliary beat frequency (CBF) of mucous membrane. Our aim was to study by means of a photoelectric technique, the effects of two antitussives--dextromethorphan and vadocaine--and two antihistamines--hydroxyzine and diphenhydramine--on the rat tracheal CBF in vitro. The CBF was measured from tracheal explants immersed in drug solutions. Dextromethorphan (1.0 mg/ml and 10.0 mg/ml) caused 16.9-20.8% decrease in the CBF during the 40 min. measurement period. Vadocaine (0.1 mg/ml and 0.5 mg/ml) decreased the CBF by 6.9%. Higher vadocaine concentrations caused a dose-dependent inhibitory effect so that mucociliary function stopped totally within 20 min. with 5.0 mg/ml vadocaine solution. Both diphenhydramine and hydroxyzine totally stopped the ciliary activity during 20 min. with concentrations of 2.5 mg/ml and 1.0 mg/ml. respectively. Locke-Ringer solution used as a control did not cause any change in the CBF. These results suggest that the antihistamines diphenhydramine and hydroxyzine are more ciliostatic than the antitussives dextromethorphan and vadocaine on the rat tracheal cilia in vitro. The results suggest further in vivo studies. The used photoelectric detection method proved to be suitable for evaluating drug effects on the CBF of respiratory mucosa.

Animals↗
PubMed1994

The inhibitory effect of amiodarone and desethylamiodarone on dextromethorphan O-demethylation in human and rat liver microsomes.

Amiodarone has been shown in-vitro to inhibit the activity of cytochrome P4502D6 (CYP2D6) in nonhuman primates. However, the influence of its major metabolite, desethylamiodarone, on this isozyme activity has not been studied. To determine the effect of these drugs on dextromethorphan O-demethylation, we carried out studies in 10 human and 10 rat liver microsomal preparations. In human microsomal studies, amiodarone and the metabolite competitively inhibited dextromethorphan metabolism with mean Ki values of 52.70 +/- 5.27 and 34.40 +/- 3.30 microM, respectively. Similar studies in rat microsomes showed a competitive inhibitory effect of amiodarone and its metabolite on dextromethorphan metabolism. These data suggest that amiodarone and desethylamiodarone have an inhibitory effect on CYP2D6 in man and CYP2D1 in rats. However, it cannot be concluded that both of them are substrates of this isozyme activity.

Amiodarone↗
PubMed2002

Characterization of cytochrome P450 2D6.1 (CYP2D6.1), CYP2D6.2, and CYP2D6.17 activities toward model CYP2D6 substrates dextromethorphan, bufuralol, and debrisoquine.

Over 50 allelic variants of cytochrome P450 2D6 (CYP2D6) encoding fully functional, reduced-activity, or nonfunctional proteins have been described. Compared with Caucasians, studies in black populations demonstrate a tendency toward slower CYP2D6 activity, attributed in part to the presence of a variant allele associated with reduced activity, the CYP2D6*17 allele. To investigate the kinetic characteristics of this variant protein, expression constructs coding for CYP2D6.1, CYP2D6.2, and CYP2D6.17 gene products were prepared and transfected into mammalian COS-7 and insect (Trichoplusia ni) cells for expression. Microsomal fractions containing the expressed proteins were used to determine the kinetic parameters K(m), V(max), and intrinsic clearance (Cl(int)) for the model substrates dextromethorphan, bufuralol, and debrisoquine. Relative to the wild-type CYP2D6.1 protein expressed in COS-7 cells, CYP2D6.17 exhibited a 2-fold higher K(m) and a 50% reduction in V(max) using dextromethorphan as the substrate. In contrast, no appreciable change in bufuralol K(m) was observed with CYP2D6.17 whereas V(max) was decreased by 50%. When expressed in the baculovirus expression system, CYP2D6.17 exhibited a 6-fold increase in K(m) but no change in V(max) with dextromethorphan as the substrate, a 2-fold higher K(m) and 50% reduction in V(max) with bufuralol, and a 3-fold increase in K(m) and no change in V(max) with debrisoquine relative to CYP2D6.1. These data indicate that CYP2D6.17 exhibits reduced metabolic activity toward all three commonly used CYP2D6 substrates, although specific effects on substrate affinity and turnover demonstrate some substrate dependence.

Animals↗
PubMed1993

A pilot trial of dextromethorphan in amyotrophic lateral sclerosis.

Assuming the presence of glutamate-induced neurotoxicity in amyotrophic lateral sclerosis 14 patients were treated with dextromethorphan, an N-methyl-D-aspartate receptor antagonist. The patients were treated with 150 mg dextromethorphan or placebo daily for 12 weeks in a double-blind crossover trial, with a wash out period of 4 weeks between the two treatment periods. Thereafter the surviving patients were treated with 300 mg dextromethorphan daily for up to 6 months in an open trial. No positive effects on clinical or neurophysiological parameters (relative number of axons, and compound muscle action potentials in the abductor digiti minimi muscle) were observed either in the double-blind trial or in the open trial.

Aged↗
PubMed1991

Safety and tolerance of oral dextromethorphan in patients at risk for brain ischemia.

Experimental ischemia models have shown the antitussive dextromethorphan to be an N-methyl-D-aspartate antagonist with neuroprotective properties. We treated 10 patients with a history of recent stroke or transient ischemic attack with oral dextromethorphan (60 mg q.i.d.) for 3 weeks in a placebo-controlled, double-blind, crossover tolerance study. We documented no clinical evidence of toxicity attributable to dextromethorphan in this preliminary study.

Administration, Oral↗
PubMed2002

Effect of ketamine, dextromethorphan, and MK-801 on cochlear dysfunction induced by transient ischemia.

Overstimulation of the N-methyl-D-aspartate (NMDA) glutamate receptor has been implicated as a factor in the pathogenesis of hypoxic-ischemic injury in the central nervous system. To evaluate the role played by NMDA antagonists in ischemia-reperfusion injury of the cochlea, 3 noncompetitive NMDA antagonists--ketamine, dextromethorphan, and MK-801--were administered to 53 albino guinea pigs subjected to transient ischemia of 30 minutes' duration, and the threshold shifts of the compound action potential were compared with those of nontreated animals 4 hours after the onset of recirculation. Ketamine and dextromethorphan moderately ameliorated the compound action potential threshold shifts, whereas MK-801, the most potent NMDA receptor antagonist among these 3 agents, did not show any protective effect. These results indicate that the action antagonizing the NMDA receptor has no protective effect against ischemia-reperfusion injury of the cochlea, and that ketamine and dextromethorphan act as protective agents for the cochlea via other pathways.

Action Potentials↗
PubMed2001

Lack of gender differences and large intrasubject variability in cytochrome P450 activity measured by phenotyping with dextromethorphan.

Gender-based differences in cytochrome P450 (CYP) activity may occur due to endogenous hormonal fluctuations with the menstrual cycle, which are altered by oral contraceptives. This study assessed the average activity and within-subject variability in CYP3A4 and CYP2D6 in men, women taking Triphasil, and regularly menstruating women not receiving oral contraceptives. Thirty-three healthy volunteers participated in this 28-day pilot study (12 women receiving Triphasil) (OCs), 11 regularly menstruating women not on exogenous progesterone or estrogen (no OCs), and 10 men. CYP3A4 and CYP2D6 activities were phenotyped with dextromethorphan (DM) on study days 7, 14, 21, and 28 using urinary ratios of DM:3-methoxymorphinan (3MM) and DM:dextrorphan (DX), respectively. Serial blood concentrations of estrogen and progesterone and menstrual diaries were used to determine menstrual phase in both groups of women. Average urinary DM:3MM and DM:DX in the 28 extensive metabolizers of CYP2D6 did not differ between the three study populations (p = 0.86 and 0.93, respectively). Post hoc power analysis indicated that more than 1000 subjects would be needed for 80% power (alpha = 0.05) to detect a +/- 15% difference from the population mean in the urinary ratios of dextromethorphan and its metabolites 3MM and DX. Variability in CYP3A4 and CYP2D6 activity, characterized by intrasubject standard deviation, also did not differ. The varying doses of levonorgesterol and ethinyl estradiol in Triphasil, fluctuations in estrogen and progesterone, and menstrual phase did not influence CYP3A4 or CYP2D6 activity. It was concluded that CYP3A4 and CYP2D6 activity and intrasubject variability were not different in the three study populations, and thus a clinically important difference between men, women on Triphasil, and women not receiving oral contraceptives is unlikely. High inter- and intrasubject variability in DM:3MM and DM:DX were clearly demonstrated and limit the use of dextromethorphan to phenotype endogenous CYP3A4 and CYP2D6 activity.

Adult↗
PubMed1983

Dextromethorphan and codeine: objective assessment of antitussive activity in patients with chronic cough.

Dextromethorphan, the most widely used cough suppressant in the U.S.A., was compared with codeine, the traditional European antitussive, in a double-blind, crossover trial using both an objective and subjective assessment of efficacy in sixteen patients with chronic, stable cough. Both preparations, at a dose of 20 mg, were similarly effective in reducing cough frequency. Dextromethorphan lowered cough intensity to a greater degree than codeine (p less than 0.0008) and was considered the better antitussive by the majority of patients (p less than 0.001). In view of its lack of side-effects, its safety even in overdose and its non-narcotic status, the increasing trend in Europe to use dextromethorphan as a substitute for codeine in the treatment of cough is to be welcomed.

Adult↗
PubMed2007

A placebo double-blind pilot study of dextromethorphan for problematic behaviors in children with autism.

We used a mixed group/single-case, double-blind, placebo-controlled, ABAB design to examine the safety and efficacy of the glutamate antagonist dextromethorphan for the treatment of problematic behaviors and core symptoms in eight children diagnosed with autism. All participants had increased levels of irritability at baseline as measured by the Aberrant Behavior Checklist, and demonstrated a wide variety of problematic behaviors. Group analyses revealed that dextromethorphan was equivalent to placebo in the treatment of problem behaviors and core symptoms. Analyses at the single-subject level demonstrated that three of the eight participants who had a behavioral profile consistent with attention-deficit hyperactivity disorder responded positively to dextromethorphan. Future research that employs a larger, more homogeneous sample is necessary to replicate the findings from this study.

Adolescent↗
PubMed1998

Dextromethorphan and other N-methyl-D-aspartate receptor antagonists are teratogenic in the avian embryo model.

N-Methyl-D-aspartate (NMDA) receptors are a calcium-conducting class of excitatory amino acid receptors that are involved in neuronal development and migration. Certain well known teratogens (e.g. homocysteine, ethanol, and chloroform) that induce congenital neural tube and neural crest defects also have the capacity to act as NMDA receptor antagonists. We hypothesized that teratogenicity was a general property of NMDA receptor antagonists, and that high affinity NMDA receptor antagonists would induce neural tube and neural crest defects. Chicken embryos were given 5, 50, or 500 nmol/d of selected NMDA receptor antagonists for 3 consecutive days during the process of neural tube closure, beginning 4 h after the beginning of incubation. Selected NMDA receptor antagonists represented three classes of antagonists: ion channel blockers, glycine site antagonists, and glutamate site agonists and antagonists. All classes of NMDA receptor antagonists induced embryonic death and congenital defects of the neural crest and neural tube; however, the channel blockers were the most potent teratogens. Dextromethorphan at 500 nmol/embryo/d killed more than half the embryos and induced congenital defects in about one-eighth of the survivors; dextromethorphan was also highly lethal at 50 nmol/embryo/d. Glutamate site NMDA receptor agonists (NMDA and homoquinolinic acid) displayed weak toxicity relative to their known NMDA receptor potency. Taken together, these data indicate that NMDA receptor antagonists, particularly channel blockers, are potent teratogens in the chicken embryo model. Because dextromethorphan is a widely used nonprescription antitussive, its strong teratogeneticity using this model is particularly noteworthy.

Abnormalities, Drug-Induced↗
PubMed1993

Nonketotic hyperglycinemia: clinical and electrophysiologic effects of dextromethorphan, an antagonist of the NMDA receptor.

A 10-week-old girl with nonketotic hyperglycinemia was treated with increasing amounts of dextromethorphan, an NMDA receptor antagonist. She improved neurologically; at 35 mg/kg/d, seizures ceased and EEG normalized. Dextromethorphan withdrawal resulted in a dramatic clinical deterioration coinciding with epileptic and high-voltage slow activity in the EEG. After reintroduction of dextromethorphan (35 mg/kg/d), recovery occurred within 24 hours.

Amino Acid Metabolism, Inborn Errors↗
PubMed1995

Dextromethorphan shows efficacy in experimental pain (nociception) and opioid tolerance.

The oral antitussive dextromethorphan is a clinically available N-methyl-D-aspartate receptor antagonist. Dextromethorphan has analgesic efficacy in the experimental formalin test, blocks the nociceptive activation of the immediate-early gene, c-fos proto-oncogene, and prevents and reverses the development of opiate analgesic tolerance in experimental models. These data suggest that dextromethorphan should be evaluated in a controlled clinical trial for analgesic efficacy in zoster-associated neuralgia.

Dextromethorphan↗
PubMed2002

Protective effects of dextromethorphan and tizanidine on ouabain-induced arrhythmias.

The effects of the opioid agonist dextromethorphan and the alpha 2-adrenoceptor agonist tizanidine on ouabain-induced cardiac arrhythmias were investigated in rats. Ouabain (10 mg/kg i.v.) elicited ventricular arrhythmias in all of the control rats. Administration of dextromethorphan (25 mg/kg i.v.) and tizanidine (0.1 mg/kg i.v.) 30 min before ouabain treatment significantly reduced the incidence of arrhythmias. We suggest that dextromethorphan and tizanidine showed these effects by decreasing excitatory amino acid (EAA) activity. It can be speculated that opioids and other EAA antagonists may have antiarrhythmic actions through both their central and peripheral effects as well.

Adrenergic alpha-Agonists↗