Avonex

Approved Indications:

• Motion Sickness: For prevention and treatment of nausea, vomiting, and dizziness associated with travel.
• Vertigo: Used in the management of vertigo due to vestibular disorders such as:
• Ménière’s disease
• Vestibular neuronitis
• Labyrinthitis
• Nausea and Vomiting in Pregnancy (NVP): Combination therapy is commonly used to manage mild to moderate nausea and vomiting during pregnancy.

Clinically Accepted (Off-label) Uses:

• Postoperative Nausea and Dizziness
• Radiation-induced Nausea
  Utilized in specific cases to relieve dizziness and nausea secondary to vestibular involvement.

Route of Administration: Oral only

Adults:

• Motion Sickness:
  25 mg Meclizine + 50 mg Pyridoxine orally, 1 hour before travel; may be repeated every 24 hours as needed.
• Vertigo:
  25–100 mg Meclizine per day (with equivalent Pyridoxine dose), in divided doses depending on symptom severity.

Pregnancy-related Nausea:

• 25 mg Meclizine + 50 mg Pyridoxine orally once or twice daily, based on clinical assessment. Maximum: 100 mg Meclizine/day.

Pediatrics (≥12 years):

• Motion Sickness or NVP:
  25 mg Meclizine + 50 mg Pyridoxine orally once daily; not to exceed 50 mg Meclizine in 24 hours.

Elderly:

• Start at the lower end (12.5–25 mg Meclizine with 25–50 mg Pyridoxine), due to increased sensitivity to CNS and anticholinergic effects.

Renal Impairment:

• No specific dosage adjustment is required, but use cautiously.

Hepatic Impairment:

• Use with caution; adjust dose if needed due to hepatic metabolism of Meclizine.

Duration of Use:

• Use as needed for motion sickness. In pregnancy, continue only as long as required, under medical supervision.

Meclizine is a first-generation antihistamine that acts by antagonizing H1 histamine receptors in the vestibular system and vomiting center of the brain. It has anticholinergic and CNS depressant activity, which reduces vestibular stimulation and suppresses nausea, vomiting, and dizziness.

Pyridoxine (Vitamin B6) plays a role in neurotransmitter metabolism and may reduce nausea by stabilizing neural transmission in the vomiting center. Though its precise antiemetic mechanism is not fully understood, it is believed to complement Meclizine's effects by normalizing brainstem activity related to nausea control.

Meclizine:

• Absorption: Well absorbed orally
• Onset of Action: 1 hour
• Peak Plasma Time: ~3 hours
• Bioavailability: Moderate
• Distribution: Crosses the blood-brain barrier
• Metabolism: Hepatic (primarily via CYP2D6)
• Half-life: 6–12 hours
• Excretion: Urinary (as metabolites)

Pyridoxine:

• Absorption: Rapidly absorbed in the small intestine
• Bioavailability: High
• Metabolism: Hepatic conversion to pyridoxal phosphate (active form)
• Half-life: 15–20 days for tissue stores; shorter for plasma levels
• Excretion: Renal (as 4-pyridoxic acid)

• Pregnancy Category: Category B (Meclizine and Pyridoxine individually) – Safe for short-term use under medical supervision in pregnancy.
• Lactation:
• Meclizine: Excretion in human milk unknown; use cautiously.
• Pyridoxine: Present in breast milk in small amounts and considered safe.
• Recommendation: May be used during pregnancy for NVP if benefits outweigh risks. Monitor infant if used during breastfeeding.

• Primary Class: Antiemetic and Antivertigo Combination
• Components:
• Meclizine: First-generation H1 antihistamine
• Pyridoxine: Water-soluble vitamin (Vitamin B6), antiemetic co-therapy

• Hypersensitivity to Meclizine, Pyridoxine, or any excipients
• Severe hepatic impairment
• Acute angle-closure glaucoma
• Urinary retention or prostatic hypertrophy
• Concurrent use of other strong CNS depressants (relative)

• CNS Depression: Risk of drowsiness and impaired coordination; avoid driving or operating machinery.
• Elderly Patients: Prone to confusion, sedation, or falls.
• Seizure Disorders: Use cautiously; Meclizine may lower seizure threshold.
• Over-supplementation with Pyridoxine: Long-term high doses may cause sensory neuropathy.
• Use with CNS Depressants: Increased sedation when combined with alcohol, sedatives, or opioids.
• Monitoring: Observe for anticholinergic effects and hypersensitivity reactions.

Common Adverse Effects:

• Central Nervous System: Drowsiness, dizziness, fatigue, headache
• Gastrointestinal: Dry mouth, nausea, constipation
• Visual: Blurred vision
• General: Coordination difficulties

Pyridoxine-specific (high dose or chronic use):

• Paresthesia, numbness, sensory neuropathy

Serious/Rare Effects:

• Hypersensitivity reactions (rash, itching, anaphylaxis – rare)
• Confusion or hallucinations (particularly in elderly)
• Tachycardia or palpitations
• Urinary retention

Onset: Usually within 1–2 hours of administration
Severity: Mostly mild and dose-dependent

• CNS Depressants (alcohol, opioids, sedatives): Additive CNS depression with Meclizine
• Anticholinergic Drugs (e.g., atropine): Additive effects—risk of dry mouth, blurred vision, urinary retention
• CYP2D6 Inhibitors (e.g., fluoxetine, paroxetine): May increase Meclizine levels
• Levodopa: Pyridoxine may reduce efficacy of levodopa unless combined with carbidopa
• Alcohol: Increases sedative effects—avoid use

• Pregnancy Guidelines: Still included in recommended therapy options for NVP in updated clinical practice guidelines.
• Formulation Availability: Newer formulations include chewable tablets and fixed-dose combinations for ease of use.
• Practice Note: Long-term use of high-dose Pyridoxine should be avoided to prevent neurotoxicity.

• Temperature: Store at 20°C to 25°C (68°F to 77°F)
• Humidity: Protect from moisture
• Light: Store in a tightly closed container, away from direct sunlight
• Handling: Do not freeze. Chewable and orally disintegrating forms should be used immediately after opening.
• Special Instructions: Keep out of reach of children; store in original packaging