Dextromethorphan exerts its antitussive effects through the following mechanisms:

1. Central Cough Suppression:
   • Acts on the medullary cough center in the brainstem to elevate the threshold for coughing (BNF).
   • Does not depress respiratory function at therapeutic doses (Lippincott).
2. NMDA Receptor Antagonism:
   • Blocks NMDA receptors, which may contribute to its cough-suppressant effects and potential neuroprotective properties (Lange).
3. Sigma-1 Receptor Agonism:
   • Modulates neurotransmitter release, influencing cough reflex pathways (Lippincott).
4. Serotonin and Norepinephrine Reuptake Inhibition:
   • At high doses, it weakly inhibits reuptake of serotonin and norepinephrine, contributing to side effects like agitation or serotonin syndrome in combination with other drugs (Lange).

Dextromethorphan is indicated for:

1. Non-Productive Cough Relief:
   • Temporary relief of dry cough caused by colds, upper respiratory infections, or irritants (BNF).
2. Off-Label Uses:
   • Investigated for neuropathic pain, depression, and pseudobulbar affect (emotional lability), though these uses are not BNF-approved (Lange).

Dosage varies by formulation and patient age. Always follow the prescribing physician’s instructions.

Adults and Children Over 12 Years:

• Immediate-Release: 10–20 mg every 4–6 hours, up to 120 mg/day.
• Extended-Release: 30–60 mg every 12 hours (BNF).

Children 6–12 Years:

• Immediate-Release: 5–10 mg every 4–6 hours, up to 60 mg/day.

Administration Tips:

• Avoid use in children under 6 years due to overdose risk.
• Do not exceed recommended doses to prevent toxicity.

Dextromethorphan is generally safe at therapeutic doses but may cause:

Common:

• Drowsiness, dizziness, or fatigue.
• Nausea, stomach upset.
• Mild headache.

Rare but Serious:

• Serotonin Syndrome: Confusion, hyperthermia, tachycardia (with serotonergic drug combinations).
• Hallucinations or Dissociation: At high doses (>100 mg).
• Respiratory Depression: Rare, typically with extreme overdose.

Before using dextromethorphan, inform your healthcare provider if you have:

• Chronic respiratory conditions (e.g., asthma, COPD).
• Liver impairment (reduces drug metabolism).
• History of substance abuse or psychiatric disorders.
• Allergies to dextromethorphan or formulation components.

Special Populations:

• Pregnancy: Limited data; use only if benefits outweigh risks (BNF Category: Not formally classified).
• Breastfeeding: Avoid due to potential excretion in breast milk.
• Elderly: Increased sensitivity to CNS effects like dizziness.

Dextromethorphan interacts with several medications:

1. MAO Inhibitors (MAOIs):
   • Risk of serotonin syndrome or hypertensive crisis (contraindicated within 14 days of MAOI use) (BNF).
2. SSRIs/SNRIs (e.g., fluoxetine, venlafaxine):
   • Increased serotonin levels, raising risk of serotonin syndrome (Lippincott).
3. CNS Depressants (e.g., alcohol, benzodiazepines):
   • Enhanced sedation or respiratory depression.
4. CYP2D6 Inhibitors (e.g., quinidine):
   • Increase dextromethorphan levels due to reduced metabolism (Lange).

Generic Names in Pharmacy

• Dextromethorphan hydrobromide (active ingredient)
• Common brand names: Robitussin DM®, Delsym®, Benylin Dry Cough®