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). |
| Molecular Weight | 481 |
| Action Class | Antihistamine (H1 receptor antagonist), Antiemetic, Antivertigo agent |
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 | Animal studies have shown teratogenic effects at high doses, but human data are limited. Use only if clearly needed and benefit outweighs risk. |
| 2nd trimester | Not associated with major teratogenicity in human studies; caution advised due to anticholinergic effects. |
| 3rd trimester | May cause respiratory depression or sedation in neonates if used near term; avoid use during labor. |
Clinical note
CNS depressants may enhance sedative effects May cause drowsiness and impair mental and physical abilities.
| Placental transfer | Crosses the placenta; extent unknown but likely due to molecular weight <500 Da. |
| Breastfeeding | Excreted into breast milk in small amounts; unlikely to cause adverse effects in infants but use caution due to potential sedation or anticholinergic effects. |
■ FDA Black Box Warning
None.
| Common Effects | motion sickness |
| Serious Effects | Drowsiness and sedation, Extrapyramidal symptoms (rare), Hypotension, Tachycardia, Urinary retention, Blurred vision, Dry mouth, Constipation, Confusion (especially in elderly), Seizures (rare, with overdose) |
Hypersensitivity to meclizine or any componentAcute porphyria
| 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. |
| Food/Dietary | Alcohol should be avoided due to additive sedative effects. Grapefruit juice may theoretically increase meclizine absorption, but no significant clinical interaction reported. |
Loading safety data…
| Lactation Rating |
| L3 (Moderately Safe) |
| 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. |
| 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. |
| Clinical Pearls | Meclizine is a first-generation antihistamine with central anticholinergic effects, used primarily for vertigo and motion sickness. Onset is delayed (~1 hour); administer at least 1 hour before travel. Can cause sedation and dry mouth; avoid with alcohol. Antiemetic efficacy is modest; consider ondansetron or promethazine for severe nausea. |
| Patient Advice | Take meclizine 1 hour before travel or as needed for vertigo. · Do not drive or operate heavy machinery until you know how this drug affects you, as it may cause drowsiness. · Avoid alcohol while taking meclizine. · Notify your doctor if you have glaucoma, enlarged prostate, or urinary retention. · If you miss a dose, take it when you remember; do not double the next dose. |