Is Meclizine (Antihistamine) safe to use during pregnancy?

Safety of Meclizine During Pregnancy

Meclizine should be considered relatively safe for use during pregnancy, particularly after the first trimester, as it has not been shown to be teratogenic in humans despite animal studies suggesting potential risks.

Evidence on Meclizine Safety in Pregnancy

FDA Classification and Animal Data

• Meclizine is classified as FDA Pregnancy Category B, which means:
  • Animal studies have shown adverse effects, but adequate studies in pregnant women have not demonstrated risk to the fetus 1
  • In animal studies, oral administration of meclizine to pregnant rats during organogenesis resulted in fetal malformations at doses approximately 2 times the maximum recommended human dose 1

Human Data

• Epidemiological studies on meclizine use during pregnancy have not identified an association between its use and increased risk of major birth defects 1
• A large study of 16,536 women who used meclizine in early pregnancy showed no increased risk of congenital malformations; in fact, the rate of malformations was actually reduced compared to the general population 2
• Meclizine has been extensively studied and has not been shown to be teratogenic in humans despite the concerning animal data 3

Recommendations for Use During Pregnancy

First Trimester Considerations

• It is generally best to avoid all antihistamines during pregnancy if possible, especially during the first trimester 4
• If antihistamine therapy is necessary during the first trimester, caution is recommended 4

Second and Third Trimester Use

• Meclizine presents one of the lowest risks of teratogenicity among antiemetics and has been considered a drug of first choice for nausea and vomiting in pregnancy 3
• The benefits of treating severe nausea and vomiting during pregnancy may outweigh the minimal risks associated with meclizine use

Breastfeeding Considerations

• The FDA label states there are no data on the presence of meclizine in human milk, effects on the breastfed infant, or effects on milk production 1
• The developmental and health benefits of breastfeeding should be considered along with the mother's clinical need for meclizine and any potential adverse effects 1

Clinical Decision Algorithm

1. First assess severity of symptoms and necessity for treatment:

   • For mild symptoms: Consider non-pharmacological approaches first
   • For moderate to severe symptoms affecting nutrition or quality of life: Consider medication

2. If medication is necessary:

   • First trimester: Use with caution, only if benefits clearly outweigh risks
   • Second and third trimesters: Can be used with greater confidence based on human epidemiological data

3. Dosing considerations:

   • Use the lowest effective dose (typically 25-50 mg daily) 1
   • Consider divided doses to minimize peak concentrations

4. Monitor for side effects:

   • Drowsiness (most common) - advise against driving or operating machinery 1
   • Dry mouth, headache, fatigue (less common) 1

Important Caveats and Precautions

• Meclizine has anticholinergic properties and should be used with caution in patients with asthma, glaucoma, or enlargement of the prostate gland 1
• Avoid concurrent use with CNS depressants including alcohol due to increased risk of sedation 1
• Meclizine is metabolized by CYP2D6, so potential drug interactions with CYP2D6 inhibitors should be monitored 1
• If the patient has hepatic or renal impairment, use with caution as the drug may accumulate 1

In summary, while animal studies raised concerns about meclizine's safety during pregnancy, human epidemiological data have been reassuring. When treatment for nausea, vomiting, or vertigo is necessary during pregnancy, meclizine represents one of the safer antihistamine options, particularly after the first trimester.