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Allopurinol use while Breastfeeding

Drugs containing Allopurinol: Zyloprim, Aloprim, Lopurin

Allopurinol Levels and Effects while Breastfeeding

Summary of Use during Lactation

Limited information indicates that a maternal dose of allopurinol 300 mg daily provides near-therapeutic dose and plasma levels in an exclusively breastfed infant. If allopurinol is required by the mother, it is not a reason to discontinue breastfeeding, but exclusively breastfed infants should be monitored if this drug is used, including observation for allergic reactions (such as rash) and periodic CBC and differential blood counts.

Drug Levels

Allopurinol is metabolized to oxypurinol which has xanthine oxidase inhibitory activity equal to allopurinol's. Oxypurinol is well absorbed from the gastrointestinal tract.[1]

Maternal Levels. A woman who was 5 weeks postpartum had been taking allopurinol 300 mg orally for 4 weeks. Two hours after a dose her breastmilk contained 0.9 mg/L of allopurinol and 53.7 mg/L of its active metabolite oxypurinol. Four hours after the dose, her breastmilk contained 1.4 mg/L of allopurinol and 48 mg/L of oxypurinol. The authors calculated that the exclusively breastfed infant would receive between 0.14 and 0.2 mg/kg of allopurinol and between 7.2 to 8 mg/kg of oxypurinol daily. This dose of oxypurinol is slightly less than the infant allopurinol dose of 10 mg/kg daily.[2][3]

Infant Levels. A 5-week-old infant whose mother had been taking allopurinol 300 mg daily for 4 weeks had plasma levels of allopurinol that was undetectable (<0.5 mg/L) and of oxypurinol that was 6.6 mg/L 2 hours after nursing and 4 hours after the mother's dose of allopurinol. This plasma level was 33 to 48% of the measured maternal plasma oxypurinol levels.[2][3]

Effects in Breastfed Infants

One infant breastfed from age 1 week to age 7 weeks during maternal allopurinol therapy with 300 mg or allopurinol daily. The infant had no observable side effects and no changes in clinical chemistry and hematology values.[3]

Effects on Lactation and Breastmilk

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


1. Walter-Sack I , de Vries JX, Ernst B et al. Uric acid lowering effect of oxipurinol sodium in hyperuricemic patients - therapeutic equivalence to allopurinol. J Rheumatol. 1996;23:498-501. PMID: 8832991

2. Kamilli I, Gresser U, Schaefer C et al. Allopurinol in breast milk. Adv Exp Med Biol. 1991;309A:143-5. PMID: 1789194

3. Kamilli I, Gresser U. Allopurinol and oxypurinol in human breast milk. Clin Investig. 1993;71:161-4. PMID: 8461629

Allopurinol Identification

Substance Name


CAS Registry Number


Drug Class

Antigout Agents

Enzyme Inhibitors

Gout Suppressants

Administrative Information

LactMed Record Number


Last Revision Date



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