Dextromethorphan

BRAND NAMES:

Delsym 12-hour cough comprises the principal active component, dextromethorphan polistirex extended-release solution for cough suppression.

Robitussin cough long-acting- This medication comprises the active components dextromethorphan and chlorpheniramine. Robitussin cough and cold long-acting is ideal for controlling and relieving your child's frequent cough for up to 8 hours.

Triaminic long-acting cough - This medicine comprises dextromethorphan and acetaminophen. Dextromethorphan HBr suppresses coughs, while paracetamol relieves pain and fevers.

Vicks DayQuil Cough - Comprises the active substances dextromethorphan HBr, guaifenesin, and phenylephrine hydrochloride. They suppress coughs, create chest congestion, loosen and thin mucus, and produce nasal congestion.

MECHANISM OF ACTION:

The drug is a lipophilic molecule with an ionizable amine at one end. It is structurally related to alkaloid opioids such as morphine but does not interact with the receptor. It derives from levorphanol, first designed as a morphine alternative. The main mechanism of action for its use in the cough suppressant is not completely understood. One proposed mechanism is dextromethorphan works on the nucleus tractus solitaries, the estimated site where the pulmonary vagal afferent fibers synapse in the central nervous system. The site in the brain stem functions as a gate for the cough reflex. Dextromethorphan is known for its many interactions with several different receptor sites.

PHARMACOKINETICS:

Absorption: The oral administration of dextromethorphan is 30 mg it reaches a Cmax of 2.9ng/ml with a Tmax of 2.86h and an AUC of 17.8 ng h/ml.

Distribution: The mean volume of distribution of dextromethorphan is 5-6.7L/kg.

Metabolism: CYP3A4, CYP2D6, and CYP2C9 can N-demethylate dextromethorphan to 3-methoxymorphinan, while CYP2D6 and CYP2C9 can O-demethylate it to dextrorphan. CYP3A4 and CYP2D6 are dextrorphan N-demethylases. Both are converted to 3-hydroxymorphinan. Dextrorphan and 3-hydroxymorphinan are O-glucuronidated or O-sulfated.

Excretion: Dextromethorphan is eliminated through urine.

PHARMACODYNAMICS:

Dextromethorphan's therapeutic window is moderate, as intoxication can occur at higher doses. Dextromethorphan has a moderate duration of action. Patients should be advised about the risk of intoxication. It is an opioid-like molecule used in combination with other medications to treat coughs and pseudobulbar effects.

DOSAGE AND ADMINISTRATION:

• Combination liquid cough syrups, the common OTC formulation contain 15mg/ml of dextromethorphan, recommended adult dosing is 2 tsp (810ml) every 4 hours.
• Sustained-release cough syrup suspension, another OTC product contains 30mg/5ml.
• Liquid-filled capsules containing 15 or 30 mg of dextromethorphan.
• Oral strips containing 7.5 or 15 mg of dextromethorphan.
• Lozenges containing 5, 7.5, and 10 mg of dextromethorphan.
• The recommended dosing for dextromethorphan is 0.5mg/kg up to 30 mg. administered three or four times a day.

Dextromethorphan is available as liquid capsules, chewable tablets, dissolving strips, extended-release suspensions, and lozenges for oral administration. It is usually taken every 4 to 12 hours, as needed. It is used exactly as specified on the label or as directed by your doctor. Do not exceed the recommended dose or time of use. Cough medicine is typically used for a short period until the symptoms resolve.

DRUG INTERACTIONS:

The drug interactions of dextromethorphan include

• MAO inhibitor- isocarboxazid, phenelzine, rasagiline, selegiline, tranylcypromine
• Anti-arrhythmic medication- amiodarone, propafenone, quinidine and flecainide
• Opioid analgesics-codeine tramadol, morphine, methadone
• Anti-anxiety medications- fluoxetine, paroxetine, sertraline 
• Anti-fungal- terbinafine

CONTRAINDICATIONS:

• It is not recommended for patients with known or established hypersensitivity, as well as those who experience an idiosyncratic reaction after receiving the drug. 
• It should not be administered to patients taking selective serotonin reuptake inhibitors due to the risk of serotonin syndrome.
• It is not recommended to administer dextromethorphan concurrently with monoamine oxidase inhibitors or for two weeks after discontinuing MAOI drugs. 
• Because dextromethorphan is used in conjunction with other medications, consider the contraindications of each ingredient when prescribing combination products to ensure safety.

ADVERSE EFFECTS:

Experienced signs of an allergic reaction like trouble breathing, hives, or swelling on the face, tongue, throat, or lips. The less severe and more likely side effect of taking dextromethorphan can be an upset stomach.

Side effects can include:

• Anxiety, dizziness
• Convulsions
• Confusion
• Hallucinations
• Slow and shallow breathing
• Dry mouth 
• Constipation
• Rapid heartbeat
• Breathing problems

OVERDOSE:

Symptoms of overdose may include

• Nausea
• Vomiting
• Drowsiness
• Dizziness
• Changes in vision
• Difficult breathing
• Fast heartbeat
• Seizures
• coma

TOXICITY:

Dextromethorphan overdose may lead to toxicity. Overdose should be managed through symptomatic and supportive measures. Dextromethorphan should taken as per prescription only.

STORAGE:

Keep the medicine safe and out of the reach of children. Keep the drug at room temperature between 20° to 25°C (68°to 77°F). Keep the medicine away from direct contact with heat, light, and moisture.