MECLIZINE HYDROCHLORIDE
Clinical safety rating: safe
Animal studies have demonstrated safety
Meclizine is a histamine H1 receptor antagonist that acts centrally in the vestibular system to suppress nausea and vomiting. It also has anticholinergic and sedative effects.
| Metabolism | Hepatic metabolism via CYP450 enzymes, primarily CYP2D6 and CYP3A4. |
| Excretion | Renal (unchanged and metabolites): 50%; fecal: 40%; biliary: 10% |
| Half-life | Terminal elimination half-life: 6 hours (range 5-10 hours). Clinical context: Supports twice-daily dosing; steady-state achieved in approximately 24 hours. |
| Protein binding | 50-75% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | 2.7 L/kg. Clinical meaning: Indicates extensive distribution into tissues, including the central nervous system. |
| Bioavailability | Oral: 50-60% (due to first-pass metabolism). |
| Onset of Action | Oral: 30-60 minutes; intravenous: 15 minutes. |
| Duration of Action | Oral: 8-24 hours (clinical effect for motion sickness persists up to 24 hours). |
25-50 mg orally, 3 to 4 times daily for vertigo; 25-50 mg orally 1 hour before travel, may repeat every 24 hours as needed for motion sickness.
| Dosage form | TABLET |
| Renal impairment | No specific dose adjustment required for renal impairment; use with caution in severe impairment. |
| Liver impairment | No specific dose adjustment required for hepatic impairment; use with caution in severe impairment. |
| Pediatric use | Children ≥12 years: 25-50 mg orally, 3 to 4 times daily for vertigo; 25-50 mg orally 1 hour before travel, may repeat every 24 hours as needed for motion sickness. Children <12 years: not recommended. |
| Geriatric use | Start at lower end of dosing range due to increased sensitivity to anticholinergic effects; 25 mg orally, 3 to 4 times daily for vertigo; 25 mg orally 1 hour before travel for motion sickness. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
CNS depressants may enhance sedative effects May cause drowsiness and impair mental and physical abilities.
| Breastfeeding | Meclizine is excreted into breast milk in small amounts; the milk-to-plasma ratio is not established. Due to potential for adverse effects (e.g., drowsiness, anticholinergic effects) in nursing infants, caution is advised. Consider alternative agents with more safety data. |
| Teratogenic Risk | Meclizine hydrochloride is classified as FDA Pregnancy Category B. Animal reproduction studies have not demonstrated fetal risk, but no adequate and well-controlled studies in pregnant women exist. First trimester: limited human data show no increased risk of major birth defects. Second and third trimesters: no specific fetal risks reported; use only if clearly needed. |
■ FDA Black Box Warning
None.
| Common Effects | motion sickness |
| Serious Effects |
["Hypersensitivity to meclizine or any component of the formulation","Acute asthmatic attack","Lower respiratory tract symptoms"]
| Precautions | ["Use with caution in patients with glaucoma, prostatic hypertrophy, or urinary retention due to anticholinergic effects.","May cause drowsiness; avoid driving or operating heavy machinery.","Caution in elderly patients due to increased risk of sedation and falls."] |
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| Fetal Monitoring | No specific fetal monitoring is required. Monitor maternal response to therapy and adverse effects such as drowsiness, dizziness, and anticholinergic signs. In pregnant women, routine prenatal care should continue. |
| Fertility Effects | Animal studies have not shown impaired fertility. No human data suggest meclizine adversely affects fertility. However, because sedation and anticholinergic effects may impact overall health, use with caution in women attempting conception. |