Dexchlorpheniramine

Usage

Dexchlorpheniramine is prescribed for the symptomatic relief of various allergic conditions. These include:

• Perennial and seasonal allergic rhinitis (hay fever)
• Vasomotor rhinitis
• Allergic conjunctivitis
• Mild, uncomplicated allergic skin manifestations (urticaria and angioedema)
• Itching associated with skin conditions such as eczema, dermatitis, and insect bites.
• Adjunctive therapy in anaphylactic reactions.

It is classified pharmacologically as a first-generation antihistamine, specifically an alkylamine derivative.

Dexchlorpheniramine’s mechanism of action involves competitively antagonizing histamine at the H1 receptor sites. This inhibits the effects of histamine, a chemical mediator released during allergic reactions responsible for symptoms like itching, sneezing, and runny nose. It also exhibits anticholinergic activity.

Alternate Names

Dexchlorpheniramine is the generic name. It is also known as the dextrorotatory isomer of chlorpheniramine.

Popular brand names include Polaramine and RyClora.

How It Works

Pharmacodynamics: Dexchlorpheniramine primarily acts as a histamine H1-receptor antagonist. By binding to these receptors, it blocks the actions of histamine, reducing the allergic response. The drug also has anticholinergic effects, contributing to some of its side effects like dry mouth and blurred vision.

Pharmacokinetics:

• Absorption: Dexchlorpheniramine is well-absorbed from the gastrointestinal tract after oral administration.
• Metabolism: It is extensively metabolized in the liver, primarily by CYP450 enzymes.
• Elimination: Primarily eliminated through renal excretion. The half-life ranges from 20-30 hours, necessitating dosing every 4-6 hours.

Mode of Action: The primary mode of action is competitive antagonism at the histamine H1 receptor. Binding prevents histamine from activating the receptor, reducing vasodilation, capillary permeability, and smooth muscle contraction associated with allergic reactions.

Receptor Binding/Enzyme Inhibition/Neurotransmitter Modulation: Dexchlorpheniramine binds to the H1 receptor. It does not significantly inhibit enzymes or modulate neurotransmitters other than histamine.

Elimination Pathways: Primarily eliminated renally, with some hepatic metabolism.

Dosage

Standard Dosage

Adults:

2 mg orally every 4-6 hours, not to exceed 12 mg in a 24-hour period. Timed-release formulations: 4-6 mg at bedtime or every 8-10 hours.

Children:

• 2-5 years: 0.5 mg orally every 4-6 hours (maximum 3 mg/24 hours). Do not use timed-release formulations.
• 6-11 years: 1 mg orally every 4-6 hours (maximum 6 mg/24 hours) or 4 mg of a timed-release formulation at bedtime.
• 12 years and older: Same as adult dose.

Special Cases:

• Elderly Patients: Start with the lower end of the dosage range (2 mg every 4-6 hours) or administer less frequently due to increased sensitivity to side effects like dizziness, sedation, and hypotension. Non-anticholinergic antihistamines are generally preferred in this population.
• Patients with Renal Impairment: Dose adjustment might be necessary, although specific recommendations are lacking. Monitor closely for adverse effects.
• Patients with Hepatic Dysfunction: Dosage adjustments might be necessary due to altered metabolism. Close monitoring is crucial.
• Patients with Comorbid Conditions: Caution is advised in patients with cardiovascular disease, narrow-angle glaucoma, prostatic hyperplasia, urinary obstruction, or thyroid dysfunction.

Clinical Use Cases

Dosage recommendations for specific medical settings are not well-defined in the literature. Standard dosing applies to most situations unless otherwise directed by a specialist. It’s not generally recommended for use in situations like intubation, surgical procedures, mechanical ventilation, ICU use, or emergency situations.

Dosage Adjustments

Dosage modifications should be considered in elderly patients, those with renal or hepatic dysfunction, and based on individual response. Monitor closely for side effects and efficacy.

Side Effects

Common Side Effects:

Drowsiness, dizziness, dry mouth/nose/throat, blurred vision, constipation, upset stomach, and trouble sleeping. Children may experience paradoxical excitation.

Rare but Serious Side Effects:

Severe allergic reactions (anaphylaxis), confusion, hallucinations, difficulty urinating, and irregular heartbeat.

Long-Term Effects:

Chronic complications from prolonged use are rare but may include tolerance to the sedative effects.

Adverse Drug Reactions (ADR):

Clinically significant ADRs requiring immediate intervention include severe allergic reactions (anaphylaxis), seizures, and cardiac arrhythmias.

Contraindications

• Hypersensitivity to dexchlorpheniramine or other similar antihistamines.
• Narrow-angle glaucoma.
• Pyloroduodenal obstruction.
• Symptomatic prostatic hypertrophy.
• Bladder neck obstruction.
• Concurrent use with MAOIs (monoamine oxidase inhibitors).
• Newborns and premature infants.
• Breastfeeding mothers.
• Lower respiratory tract symptoms, including asthma.

Drug Interactions

• CNS depressants (alcohol, sedatives, opioids): Increased sedation.
• Tricyclic antidepressants: Additive anticholinergic effects.
• MAOIs: Prolonged and intensified anticholinergic and CNS depressant effects.
• Hormonal contraceptives: Reduced contraceptive efficacy.

Pregnancy and Breastfeeding

Pregnancy Category: Generally considered safe in the first two trimesters if clearly needed. Use in the third trimester is not recommended due to potential adverse effects on the newborn. Breastfeeding: Dexchlorpheniramine is excreted in breast milk and may cause drowsiness or irritability in infants. It’s generally not recommended during breastfeeding.

Drug Profile Summary

• Mechanism of Action: Histamine H1 receptor antagonist with anticholinergic properties.
• Side Effects: Drowsiness, dizziness, dry mouth, blurred vision, constipation.
• Contraindications: Hypersensitivity, MAOI use, newborns/premature infants, breastfeeding.
• Drug Interactions: CNS depressants, TCAs, MAOIs, hormonal contraceptives.
• Pregnancy & Breastfeeding: Use with caution during pregnancy, avoid while breastfeeding.
• Dosage: Adults: 2 mg q4-6h (max 12 mg/day); Children: Dose adjusted by age.
• Monitoring Parameters: Observe for sedation, anticholinergic effects, allergic reactions.

Popular Combinations

Dexchlorpheniramine is often combined with pseudoephedrine (a decongestant) in over-the-counter cold and allergy medications.

Precautions

Pre-existing medical conditions like glaucoma, prostatic hypertrophy, or urinary obstruction require caution. Avoid in patients with asthma or lower respiratory tract symptoms. Dosage adjustments are often necessary for elderly patients and those with renal or hepatic impairment. Avoid alcohol and driving while taking this medication.

FAQs

Q1: What is the recommended dosage for Dexchlorpheniramine?

A: Adults: 2 mg orally every 4-6 hours, not to exceed 12 mg/day. Children: Dosage varies by age.

Q2: What are the common side effects?

A: Drowsiness, dizziness, dry mouth/nose/throat, blurred vision, constipation.

Q3: Is it safe during pregnancy?

A: Generally considered safe in the first two trimesters if clearly needed. Avoid during the third trimester.

Q4: Can I take it while breastfeeding?

A: Not recommended as it can be passed through breastmilk and affect the infant.

Q5: What medications should I avoid while taking Dexchlorpheniramine?

A: Alcohol, other CNS depressants, MAOIs, and tricyclic antidepressants.

Q6: Can I drive while taking this medication?

A: Avoid driving or operating machinery as it can cause drowsiness and impair alertness.

Q7: What should I do if I miss a dose?

A: Take the missed dose as soon as you remember unless it’s almost time for your next dose. Do not double the dose.

Q8: What are the signs of an overdose?

A: Extreme drowsiness, confusion, hallucinations, seizures, and dilated pupils. Seek immediate medical attention if overdose is suspected.

Q9: What is the mechanism of action of Dexchlorpheniramine?

A: It works by blocking the action of histamine at H1 receptors.

Q10: Is Dexchlorpheniramine suitable for long-term use?

A: While generally safe for short-term use, consult a physician regarding long-term use to assess benefits and potential risks.