Usage
Meclizine is primarily prescribed for the management of nausea, vomiting, and dizziness associated with motion sickness. It’s also used to treat vertigo associated with vestibular system disorders. It is pharmacologically classified as an antihistamine, specifically an antiemetic. Meclizine works by blocking acetylcholine’s action on the vestibular system in the inner ear, suppressing nerve impulses that trigger motion sickness symptoms and vertigo.
Alternate Names
Meclizine is also known as meclizine hydrochloride. Brand names for Meclizine include Antivert®, Bonine®, Dramamine® Less Drowsy, and others.
How It Works
Pharmacodynamics: Meclizine acts as an antagonist at H1 histamine receptors and muscarinic (M) cholinergic receptors. Its antiemetic and anti-vertigo effects primarily stem from its central anticholinergic action, which reduces the excitability of the vestibular and reticular systems. It also has antihistaminic properties.
Pharmacokinetics:
- Absorption: Meclizine is well-absorbed from the gastrointestinal tract after oral administration.
- Metabolism: It undergoes extensive first-pass metabolism in the liver, primarily by the CYP2D6 enzyme. Genetic polymorphisms affecting CYP2D6 activity can influence individual drug responses.
- Elimination: Meclizine is mainly excreted in the feces via biliary elimination, with a small portion eliminated through renal excretion.
Mode of Action: Meclizine’s primary mode of action is through central anticholinergic activity, primarily affecting the vestibular nuclei in the brainstem. It inhibits vestibular stimulation and reduces the transmission of nerve impulses that cause nausea, vomiting, and vertigo.
Receptor Binding/Enzyme Inhibition/Neurotransmitter Modulation: Meclizine acts as an antagonist at both H1 histamine receptors and muscarinic (M) cholinergic receptors. It also inhibits dopamine receptors to a lesser extent. Its central anticholinergic activity is the main driver behind its therapeutic effects.
Elimination Pathways: Meclizine is primarily eliminated through biliary excretion (feces), with a minor portion eliminated via renal excretion (urine).
Dosage
Standard Dosage
Adults:
- Motion Sickness: 25-50 mg orally, taken 1 hour before travel. This dose can be repeated every 24 hours as needed.
- Vertigo: 25-100 mg orally per day, divided into several doses.
Children:
- Motion Sickness (12 years and older): 25-50 mg orally 1 hour before travel and then repeated daily as needed.
- Vertigo (12 years and older): 25-100 mg/day orally, in a single or divided dose.
- Children younger than 12 years: Use and dosage must be determined by a doctor; not generally recommended.
Special Cases:
- Elderly Patients: Start with a lower dose (e.g., 12.5 mg) and increase cautiously due to increased sensitivity to anticholinergic effects. Monitor for cognitive impairment, urinary retention, and other side effects.
- Patients with Renal Impairment: Dosage adjustments may be required depending on the severity of renal impairment.
- Patients with Hepatic Dysfunction: Dosage adjustments may be necessary to avoid excessive drug accumulation.
- Patients with Comorbid Conditions: Caution advised in patients with glaucoma, prostatic hypertrophy, asthma, or pyloric/duodenal obstruction due to anticholinergic effects.
Clinical Use Cases
Meclizine is not typically indicated for use in clinical settings like intubation, surgical procedures, mechanical ventilation, ICU use, or emergency situations like status epilepticus or cardiac arrest. Its primary use is for managing motion sickness and vertigo.
Dosage Adjustments
Dosage adjustments may be necessary based on patient-specific factors including age, renal function, hepatic function, and concomitant medications. Always consider the patient’s overall clinical picture when determining the appropriate dose.
Side Effects
Common Side Effects:
Drowsiness, dry mouth, blurred vision, headache, fatigue, constipation, urinary retention.
Rare but Serious Side Effects:
Allergic reactions (e.g., rash, hives, itching, swelling), confusion, hallucinations, abnormal heart rhythms.
Long-Term Effects:
Limited data available; potential for chronic anticholinergic effects with prolonged use.
Adverse Drug Reactions (ADR):
Severe allergic reactions (anaphylaxis), severe drowsiness leading to impaired function.
Contraindications
Hypersensitivity to meclizine.
Drug Interactions
Meclizine may interact with other CNS depressants (alcohol, sedatives, tranquilizers), anticholinergics (antihistamines, tricyclic antidepressants), and MAO inhibitors. These interactions can increase the risk of drowsiness and other side effects. Interactions with alcohol should be avoided.
Pregnancy and Breastfeeding
- Pregnancy: Meclizine is generally considered safe to use during pregnancy, particularly for the treatment of nausea and vomiting. While animal studies have shown adverse effects at high doses, human data does not indicate an increased risk of birth defects.
- Breastfeeding: Meclizine is excreted in breast milk. Occasional use is likely safe, but prolonged use or high doses could potentially affect the infant or reduce milk supply. Consult with the patient regarding the risks and benefits.
Drug Profile Summary
- Mechanism of Action: Central anticholinergic, antihistaminic.
- Side Effects: Drowsiness, dry mouth, blurred vision, headache, fatigue.
- Contraindications: Hypersensitivity.
- Drug Interactions: CNS depressants, anticholinergics, MAO inhibitors.
- Pregnancy & Breastfeeding: Generally safe in pregnancy; caution advised during breastfeeding.
- Dosage: Motion sickness: 25-50 mg daily; Vertigo: 25-100 mg daily.
- Monitoring Parameters: Observe for drowsiness, cognitive impairment, and anticholinergic effects.
Popular Combinations
Meclizine is not commonly used in fixed combinations with other drugs.
Precautions
- General Precautions: Assess for hypersensitivity, renal/hepatic dysfunction, glaucoma, prostatic hypertrophy, and other relevant medical conditions.
- Specific Populations: Exercise caution in elderly patients, pregnant/breastfeeding women, and children under 12.
- Lifestyle Considerations: Avoid alcohol and other CNS depressants. Caution patients about driving or operating machinery while taking meclizine due to potential drowsiness.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Meclizine?
A: For motion sickness, the recommended dosage for adults and children 12 years and older is 25-50 mg taken one hour before travel, and can be repeated every 24 hours. For vertigo, the recommended dosage is 25-100 mg per day, in divided doses.
Q2: How does Meclizine work?
A: Meclizine primarily acts as a central anticholinergic, reducing the excitability of the vestibular system in the inner ear, thereby controlling nausea, vomiting, and vertigo.
Q3: What are the common side effects of Meclizine?
A: Common side effects include drowsiness, dry mouth, blurred vision, and headache.
Q4: Is Meclizine safe to use during pregnancy?
A: Generally considered safe for use during pregnancy, especially for nausea and vomiting. Consult with a physician for individualized recommendations.
Q5: Can Meclizine be used in children?
A: Not generally recommended for children under 12. For children 12 years and older, dosage should be determined by a physician.
Q6: Are there any drug interactions I should be aware of with Meclizine?
A: Avoid concurrent use with alcohol, CNS depressants, anticholinergics, and MAO inhibitors due to increased risk of side effects.
Q7: What should I advise my patients regarding driving or operating machinery while taking Meclizine?
A: Advise patients to avoid driving or operating machinery while taking meclizine as it can cause drowsiness and impair alertness.
Q8: What should I monitor in patients taking Meclizine long-term?
A: Monitor for anticholinergic side effects such as cognitive impairment, urinary retention, and constipation, particularly in elderly patients.
A: Meclizine is extensively metabolized in the liver, primarily by CYP2D6.
Q10: How is Meclizine eliminated from the body?
A: Meclizine is eliminated mainly through biliary excretion in the feces, with a small portion excreted in urine.
