Is amoxicillin and clarithromycin safe to use during pregnancy?

Safety of Amoxicillin and Clarithromycin in Pregnancy

Amoxicillin is safe to use during pregnancy, while clarithromycin should be avoided except when no alternative therapy is appropriate due to increased risk of miscarriage and potential fetal harm.

Amoxicillin Safety Profile

Pregnancy Use

• Amoxicillin is classified as FDA Pregnancy Category B and is compatible throughout all trimesters of pregnancy 1, 2, 3.
• Multiple guidelines recommend amoxicillin as a first-line antibiotic for pregnant women with bacterial infections, including respiratory tract infections, urinary tract infections, and as an alternative for chlamydial infections 4, 5, 3.
• Large population-based studies found no significant association between first-trimester amoxicillin exposure and major congenital malformations (adjusted relative risk 1.09,95% CI 0.98-1.20) 6.

Specific Considerations

• A very low risk of oral clefts has been reported with first-trimester exposure, though cohort studies have not confirmed a significant increase 1, 7.
• When combined with clavulanic acid (co-amoxiclav), the combination remains compatible in pregnancy but should be avoided in women at high risk of preterm delivery due to a very low but documented risk of neonatal necrotizing enterocolitis 1, 3.
• In high-risk preterm scenarios, alternative antibiotics such as cefuroxime or azithromycin should be selected instead of co-amoxiclav 3.

Breastfeeding

• Amoxicillin is compatible with breastfeeding with minimal risk to the infant 2.
• Clinicians should be aware that antibiotics in breast milk may cause false-negative cultures in febrile infants or transient gastroenteritis due to altered intestinal flora 1.

Clarithromycin Safety Profile

Pregnancy Use - Critical Warnings

• Clarithromycin is classified as FDA Pregnancy Category C and is NOT recommended for use in pregnant women except in clinical circumstances where no alternative therapy is appropriate 8, 9.
• The FDA drug label explicitly states that clarithromycin should not be used during pregnancy based on animal findings showing adverse fetal effects, and patients should be apprised of potential hazard to the fetus 9.
• Animal reproduction studies demonstrated cardiovascular anomalies in rats and cleft palate in mice at clinically relevant doses 8, 9.

Evidence of Fetal Risk

• A nationwide Danish cohort study found a 56% increased hazard of miscarriage among women using clarithromycin in early pregnancy (HR 1.56,95% CI 1.14-2.13) 10.
• A prospective controlled study reported a significantly higher spontaneous abortion rate in the clarithromycin-exposed group (14%) compared to controls (7%) (p = 0.04) 11.
• While major malformation rates were not significantly increased in human studies, the consistent finding of increased miscarriage risk across multiple studies is concerning 10, 11, 12.

When Clarithromycin Must Be Used

• If clarithromycin is absolutely necessary during pregnancy (e.g., for serious infections with no alternative), the European Respiratory Society classifies it as "probably safe" with the understanding that animal studies showed adverse effects but human data suggest low risk if any 1.
• An epidemiological study suggests a very low risk of hypertrophic pyloric stenosis in infants exposed to macrolides during the first 13 days of breastfeeding (not after 2 weeks) 1.

Breastfeeding

• Clarithromycin is considered "probably safe" during breastfeeding, though the same precautions regarding infantile hypertrophic pyloric stenosis apply during the first 2 weeks 1.

Clinical Decision Algorithm

For bacterial infections requiring antibiotic therapy in pregnancy:

1. First choice: Amoxicillin (with or without clavulanic acid if not at risk for preterm delivery) 1, 4, 3
2. Alternative penicillins or cephalosporins (e.g., cefuroxime) if penicillin allergy is not severe 1, 5
3. Azithromycin as an alternative macrolide if macrolide therapy is specifically indicated 1, 4
4. Avoid clarithromycin unless the infection is life-threatening and no other antibiotic is appropriate 9, 10

Common Pitfalls to Avoid

• Do not assume all macrolides have the same safety profile in pregnancy; clarithromycin carries higher risk than azithromycin or erythromycin 8, 1, 10.
• Do not prescribe co-amoxiclav to women with preterm labor, premature rupture of membranes, or cervical insufficiency due to neonatal necrotizing enterocolitis risk 3.
• Do not use clarithromycin for routine infections when safer alternatives exist, even if the patient has used it successfully before pregnancy 9.
• Remember that the very low risk of oral clefts with amoxicillin should not prevent its use when clinically indicated, as the absolute risk remains minimal 1, 7.