Because of the low levels of labetalol in breastmilk, amounts ingested by the infant are small and would not be expected to cause any adverse effects in full-term breastfed infants. No special precautions are required in most infants. However, other agents may be preferred while nursing a preterm infant.
The excretion of beta-adrenergic blocking drugs into breastmilk is largely determined by their protein binding. Those with low binding are more extensively excreted into breastmilk. Accumulation of the drugs in the infant is related to the fraction excreted in urine. With 50% protein binding, 5% renal excretion and a moderate half-life, labetalol presents moderately low risk for accumulation in infants.
Random milk levels from 15 women on the third day postpartum averaged 27.5 mcg/L after maternal doses ranging from 330 to 400 mg daily. One of the women who took labetalol 400 mg daily for 5 weeks had no detectable drug in breastmilk (assay limit not specified). In another 9 women taking 600 to 800 mg daily, the average random milk level was 41 mcg/L. In one patient taking 1200 mg daily, a random milk level of 600 mcg/L was found.
Peak milk levels averaging 70 mcg/L were found after a single 200 mg oral dose in 9 women. Peak milk levels of 129, 223 and 662 mcg/L were found in 3 women taking 600, 600 and 1200 mg daily, respectively. Peak milk levels occur 1 to 3 hours after the dose.
The average dose received by breastfed infants is estimated to be between 0.004% and 0.07% of the maternal dose.
In a 6-day-old breastfed infant whose mother was taking labetalol 600 mg daily, labetalol in plasma was 18 and 21 mcg/L at 4 and 8 hours after the maternal dose; labetalol was undetectable in a 7-day-old infant whose mother was taking the same dosage. Although the authors estimated the infant's dose to be 100 mg/kg daily, a recalculation using their data indicates that the infant's dose was only 100 mcg/kg daily.
Effects in Breastfed Infants:
One investigator reported that no adverse effects occurred in breastfed infants whose mothers were taking labetalol in doses of 330 to 800 mg/day.
A 26-week premature infant weighing 640 g developed sinus bradycardia (80 to 90 bpm) and isolated atrial premature beats after nasogastric feeding with mother's pumped breastmilk was begun on day 8 of life. The mother was taking labetalol 300 mg twice daily by mouth for hypertension. Bradycardia and premature beats resolved within 24 hours of substitution of formula for breastmilk. No other causes for the bradycardia could be identified. One untimed sample of the mother's breastmilk contained 710 mcg/L of labetalol. Although the authors estimated the infant's dose to be 100 mg/kg daily, a calculation using their data indicates that the dose was only 100 mcg/kg daily.
Possible Effects on Lactation:
Intravenous labetalol can increase serum prolactin in men and non-nursing women, although the increase is greater in women. Oral labetalol does not increase serum prolactin. The maternal prolactin level in a mother with established lactation may not affect her ability to breastfeed.
1. Riant P, Urien S, Albengres E et al. High plasma protein binding as a parameter in the selection of betablockers for lactating women. Biochem Pharmacol. 1986;35:4579-81. PMID:2878668 2. Michael CA. Use of labetalol in the treatment of severe hypertension during pregnancy. Br J Clin Pharmacol. 1979;8(suppl):211S-5S. 3. Leitz F, Bariletto S, Gural R et al. Secretion of labetalol in breast milk of lactating women. Fed Proc. 1983;42:378. Abstract. 4. Lunell NO, Kulas J, Rane A. Transfer of labetalol into amniotic fluid and breast milk in lactating women. Eur J Clin Pharmacol. 1985;28:597-9. PMID:4043203 5. Atkinson HC, Begg EJ, Darlow BA. Drugs in human milk. Clinical pharmacokinetic considerations. Clin Pharmacokinet. 1988;14:217-40. PMID:3292101 6. Mirpuri J, Patel H, Rhee D, Crowley K. What's mom on? A case of bradycardia in a premature infant on breast milk. J Invest Med. 2008;56:409. Abstract. 7. Barbieri C, Ferrari C, Caldara R et al. Endocrine and metabolic effects of labetalol in man. J Cardiovasc Pharmacol. 1981;3:986-91. PMID:6168866 8. Barbieri C, Larovere MT, Mariotti G et al. Prolactin stimulation by intravenous labetalol is mediated inside the central nervous system. Clin Endocrinol (Oxf). 1982;16:615-9. PMID:7105431
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