Is amoxicillin (amoxicillin) safe to use during the third trimester of pregnancy?

Amoxicillin Safety in Third Trimester

Yes, amoxicillin is safe to use during the third trimester of pregnancy and is considered a first-line antibiotic for treating bacterial infections in pregnant women. 1, 2

Evidence from FDA Drug Labeling

The FDA label for amoxicillin provides reassuring data from animal studies:

• Reproduction studies in mice and rats at doses up to 2000 mg/kg (3-6 times the human dose) showed no evidence of harm to the fetus 2
• However, the label notes that "there are no adequate and well-controlled studies in pregnant women" and recommends use "only if clearly needed" 2
• This cautious language reflects standard FDA pregnancy labeling rather than evidence of harm 2

Guideline Recommendations

Amoxicillin is explicitly listed as "Compatible" for use throughout pregnancy, including the third trimester, according to multiple clinical practice guidelines 1:

• The CDC recommends amoxicillin as an alternative treatment for Chlamydia trachomatis infections during pregnancy with high cure rates 1
• Amoxicillin is recommended for treating Salmonella gastroenteritis in pregnant women to prevent extraintestinal spread that could threaten the placenta and amniotic fluid 1
• For anthrax post-exposure prophylaxis in pregnancy, amoxicillin 500 mg every 8 hours is specifically recommended when the organism is penicillin-susceptible 1
• The American College of Obstetricians and Gynecologists recommends amoxicillin 500 mg IV/PO every 8 hours for uncomplicated urinary tract infections during pregnancy 1

Clinical Context and Advantages

Penicillins, including amoxicillin, are considered first-line antibiotics during pregnancy 3:

• Unlike tetracyclines and fluoroquinolones (which are contraindicated in pregnancy), amoxicillin has no known teratogenic effects 1
• Amoxicillin is preferred over many other antibiotic classes that carry specific pregnancy risks 3

Important Pharmacokinetic Consideration

Amoxicillin clearance increases significantly during pregnancy, which may affect dosing 4:

• Renal clearance of amoxicillin is approximately 60% higher in the third trimester (24.0 L/h) compared to postpartum (15.3 L/h) 4
• This increased clearance means standard doses may result in lower drug concentrations during pregnancy 4
• For serious infections, higher or more frequent dosing may be necessary to achieve adequate therapeutic levels 4

Common Pitfalls to Avoid

• Do not confuse amoxicillin with amoxicillin-clavulanic acid: While generally safe, the combination should be used with caution in women at risk of preterm delivery due to theoretical risk of necrotizing enterocolitis in the fetus 1
• Do not avoid necessary antibiotic treatment due to pregnancy: Untreated bacterial infections pose greater risks to both mother and fetus than appropriate antibiotic use 3
• Do not assume standard dosing is always adequate: The increased renal clearance during pregnancy may necessitate dose adjustments for serious infections 4

Breastfeeding Compatibility

Amoxicillin is also compatible with breastfeeding, as supported by the American Academy of Dermatology 1. Penicillins are excreted in breast milk but are considered safe for nursing infants 2.