Drug Levels and Effects:

Summary of Use during Lactation:

Limited information from an old study indicates that maternal doses of cycloserine of 1 gram daily produce moderate levels in milk. If cycloserine is required by the mother, it is not a reason to discontinue breastfeeding, especially if the infant is older than 2 months. Exclusively breastfed infants should be monitored if this drug is used during lactation, possibly including measurement of serum levels to rule out toxicity if there is a concern.

Drug Levels:

Maternal Levels.

In 5 women (time postpartum not stated) receiving oral cycloserine 250 mg 4 times daily, single milk levels from each of the mothers (collection times not stated) averaged 13.4 mg/L (range 6 to 19 mg/L).[1] It is estimated that a fully breastfed infant would receive 1.7 mg/kg daily or 11 to 28% of a usual infant dosage.[2][3]

Infant Levels.

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

Effects in Breastfed Infants:

No adverse effects were noted in 5 in breastfed infants (ages not stated) whose mothers were taking oral cycloserine 250 mg 4 times daily.[1]

Cycloserinewas used as part of multi-drug regimens to treat 5 women with multidrug-resistant tuberculosis, 4 throughout pregnancy and postpartum and the other postpartum only. The infants were breastfed (extent and duration not stated). At age 1.25, 1.8, 3.9, 4.6 and 5.5 years, the children were developing normally except for a mild speech delay in one and hyperactivity in another.[4]

Possible Effects on Lactation:

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


1. Morton RF, McKenna MH, Charles E. Studies on the absorption, diffusion, and excretion of cycloserine . Antibiot Annu 1955-1956. 1956;31:169-72. PMID:13355263
2. Snider DE Jr, Powell KE. Should women taking antituberculosis drugs breast-feed? Arch Intern Med. 1984;144:589-90. PMID:6367682
3. Tran JH, Montakantikul P. The safety of antituberculosis medications during breastfeeding. J Hum Lact. 1998;14:337-40. PMID:10205455
4. Drobac PC, del Castillo H, Sweetland A et al. Treatment of multidrug-resistant tuberculosis during pregnancy: long-term follow-up of 6 children with intrauterine exposure to second-line agents. Clin Infect Dis. 2005;40:1689-92. PMID:15889370

Substance Identification:

Substance Name:


CAS Registry Number:


Drug Class:

  • Antibiotics, Antitubercular

  • Administrative Information:

    LactMed Record Number:


    Last Revision Date:

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