Structural diagram of Dextromethorphan

Epidemiology of Dextromethorphan Poisoning

The trend of dextromethorphan abuse among adolescents remains concerning. Data from the National Poison Data System (NPDS) show significant intentional abuse among teenagers aged 15-19 (Wilson et al., 2011). Studies indicate widespread abuse among adolescents, with rising recreational use and overdose incidents. In Texas, the age and gender distribution of dextromethorphan ingestions has been closely examined (Forrester, 2011).

Geographically, dextromethorphan abuse is prevalent among adolescents. A study from 2000 to 2015 identified a high number of abuse cases in individuals aged 14-17, with the rate of abuse calls peaking in 2006 before plateauing, likely due to public health measures (Karami et al., 2018).

Clinically, dextromethorphan abuse primarily affects the central nervous and autonomic systems, with most cases involving overdoses. Fortunately, supportive care is generally sufficient for recovery (Paul et al., 2017). Dextromethorphan abuse remains a significant issue, especially among adolescents and young adults, necessitating ongoing monitoring and intervention.

Pharmacokinetics

Absorption and Peak Concentration: After oral administration, dextromethorphan reaches peak serum concentrations within 2–3 hours, regardless of the formulation (Schadel et al., 1995).

Metabolism: The drug is primarily metabolized by the cytochrome P450 2D6 (CYP2D6) enzyme, with activity varying significantly among individuals due to genetic polymorphisms. About 85% of Americans are rapid metabolizers, meaning they process the drug quickly (Schadel et al., 1995). The main metabolite, dextrorphan, also exhibits pharmacological activity, contributing to both therapeutic effects and potential toxicity.

Half-Life: The serum half-life of dextromethorphan is approximately 3 hours in rapid metabolizers. In individuals with poor CYP2D6 metabolism, the half-life can extend significantly, sometimes up to 29.5 hours, leading to higher plasma concentrations and prolonged effects (Schadel et al., 1995; Kazis et al., 1996).

Excretion: Dextromethorphan and its metabolites are primarily excreted in urine. The drug's elimination depends largely on CYP2D6 activity rather than renal function (Schadel et al., 1995).

Bioavailability: Oral bioavailability of dextromethorphan is relatively low due to extensive first-pass metabolism. It can be influenced by factors such as gastrointestinal pH and the presence of food.

Mechanisms of Toxicity

Mechanisms of toxicity of dextromethorphan

Sigma-Opioid Receptor Activity: Dextromethorphan acts on sigma-opioid receptors, leading to psychotropic effects similar to drugs like phencyclidine (PCP) and ketamine, causing dissociative and hallucinogenic experiences.

NMDA Receptor Antagonism: It antagonizes NMDA receptors, causing symptoms similar to those caused by ketamine and PCP, including altered sensory perceptions and dissociation (Monte et al., 2010). While NMDA antagonism has neuroprotective properties, overdose can lead to significant neurotoxic effects (Afshar et al., 2014).

Serotonin Syndrome Risk: Dextromethorphan's affinity for serotonergic receptors increases the risk of serotonin syndrome, especially when combined with other serotonergic drugs. Symptoms include agitation, confusion, rapid heart rate, dilated pupils, loss of muscle coordination, and muscle rigidity (Monte et al., 2010).

Metabolism and Interaction with Other Drugs: Dextromethorphan is metabolized to dextrorphan, which also has NMDA receptor antagonistic properties, contributing to its toxicity (Schneider et al., 1991). Interactions with other medications, particularly monoamine oxidase inhibitors (MAOIs), can exacerbate toxic effects (Sinclair, 1973).

Neurotoxic Effects: High doses can lead to neurotoxic effects, including cognitive deterioration and severe neuropsychiatric symptoms, such as mania and psychotic states (Bernstein et al., 2020).

Developmental Toxicity: Animal studies show significant developmental toxicity, particularly affecting the developing brain, resulting in impaired motor skills and social behaviors (Richardson et al., 2017).

Toxic Dose

Adverse effects in children can occur at doses as low as 5 mg/kg. In adults, moderate toxicity typically occurs at 7.7 mg/kg or higher, while severe toxicity is associated with doses of 7.8 mg/kg or higher.

Sources

Dextromethorphan is found in over 140 prescription and nonprescription products, available in liquids, tablets, capsules, lozenges, and powders.

Therapeutic and Toxic Serum Concentrations

Therapeutic serum concentrations are generally low due to rapid metabolism. No defined toxic serum concentration thresholds exist; clinical effects guide severity assessment.

Clinical Presentation and Signs and Symptoms Based on Severity (Chyk aet al., 2007)

Mild: Vomiting, somnolence

Moderate: Agitation, lethargy, tachycardia, hypertension, nystagmus, ataxia

Severe: Hyperthermia, rigidity, seizures, coma, respiratory depression

Management of Toxicity Based on Severity

Mild: Observation and supportive care, including symptom control with benzodiazepines.

Moderate: Hospital observation, IV fluids, monitoring, and benzodiazepines for agitation.

Severe: Intensive care with airway protection, IV fluids, cooling measures for hyperthermia, anticonvulsants for seizures, and benzodiazepines for serotonin syndrome. Naloxone may be used for respiratory and CNS depression, though its efficacy is inconsistent. Orotracheal intubation might be necessary.

Antidote

Naloxone can be considered for patients with coma or respiratory depression, though its effectiveness in dextromethorphan poisoning varies.

Observation Criteria

Children: Ingestions under 10 mg/kg can be managed at home with follow-up from a poison center. Higher ingestions require hospital evaluation.

Adults: Asymptomatic patients who have ingested up to 7.5 mg/kg may be observed at home with follow-up. Deliberate overdoses, severe symptoms, or ingestions over 7.5 mg/kg require medical evaluation. Regular release forms should be observed for 4-6 hours, and sustained release forms for 8-12 hours.

Prevention and Public Health Measures

Increase public awareness about the risks of dextromethorphan abuse, especially among adolescents. Consider regulating dextromethorphan-containing products to reduce abuse.