Drug Levels and Effects:

Summary of Use during Lactation:

Because of the low levels of clarithromycin in breastmilk and administration directly to infants, it is acceptable in nursing mothers. The small amounts in milk are unlikely to cause adverse effects in the infant. Monitor the infant for possible effects on the gastrointestinal flora, such as diarrhea, candidiasis (thrush, diaper rash). Unconfirmed epidemiologic evidence indicates that the risk of hypertrophic pyloric stenosis in infants might be increased by maternal use of macrolide antibiotics during breastfeeding.

Drug Levels:

Maternal Levels.

Twelve mothers were given clarithromycin 250 mg orally twice daily for puerperal infections. Both clarithromycin and its active metabolite, 14-hydroxyclarithromycin, were found in milk. The peak clarithromycin milk level was 0.85 mg/L at 2.2 hours after the dose; the peak 14-hydroxyclarithromycin level was 0.63 mg/L at 2.8 hours after the dose. Respective trough values were 0.21 and 0.36 mg/L. The half-lives of the drug and metabolite were 4.3 hours 9 hours, respectively.[1] Using the milk level data from this study, an exclusively breastfed infant would receive an estimated average of 150 mcg/kg daily of drug plus metabolite with this maternal dosage regimen or about 2% of the maternal weight-adjusted dosage.

Infant Levels.

Relevant published information was not found as of the revision date.

Effects in Breastfed Infants:

A cohort study of infants diagnosed with infantile hypertrophic pyloric stenosis found that affected infants were 2.3 to 3 times more likely to have a mother taking a macrolide antibiotic during the 90 days after delivery. Stratification of the infants found the odds ratio to be 10 for female infants and 2 for male infants. All of the mothers of affected infants nursed their infants. Most of the macrolide prescriptions were for erythromycin, but only 1.7% were for clarithromycin. However, the authors did not state which macrolide was taken by the mothers of the affected infants.[2]

A study comparing the breastfed infants of mothers taking amoxicillin to those taking a macrolide antibiotic found no instances of pyloric stenosis. However, most of the infants exposed to a macrolide in breastmilk were exposed to roxithromycin. Only 6 of the 55 infants exposed to a macrolide were exposed to clarithromycin. Adverse reactions occurred in 12.7% of the infants exposed to macrolides which was similar to the rate in amoxicillin-exposed infants. Reactions included rash, diarrhea, loss of appetite, and somnolence.[3]

Possible Effects on Lactation:

Relevant published information was not found as of the revision date.

Alternate Drugs to Consider:



1. Sedlmayr T, Peters F, Raasch W et al. [Clarithromycin, a new macrolide antibiotic. Effectiveness in puerperal infections and pharmacokinetics in breast milk]. Geburtshilfe Frauenheilkd. 1993;53:488-91. PMID:8370491
2. Sorensen HT, Skriver MV, Pedersen L et al. Risk of infantile hypertrophic pyloric stenosis after maternal postnatal use of macrolides. Scand J Infect Dis. 2003;35:104-6. PMID:12693559
3. Goldstein LH, Berlin M, Tsur L et al. The safety of macrolides during lactation. Breastfeed Med. 2009;4:197-200. PMID:19366316

Substance Identification:

Substance Name:


CAS Registry Number:


Drug Class:

  • Anti-Bacterial Agents

  • Anti-Infective Agents

  • Macrolides

  • Administrative Information:

    LactMed Record Number:


    Last Revision Date:

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