Is Metoprolol safe while breastfeeding?

Effects on the breastfed infant

A study of mothers taking beta-blockers during nursing found a numerically, but not statistically significant increased number of adverse reactions in those taking any beta-blocker. Although the ages of infants were matched to control infants, the ages of the affected infants were not stated. Of 6 mothers taking metoprolol, none reported adverse effects in her breastfed infant.[ 11 , 12 ] A prospective study of pregnant patients taking a beta-blocker asked mothers to complete a questionnaire about postpartum breastfeeding and any side effects in their breastfed infants. Two mothers reported taking metoprolol in unreported dosages while breastfeeding. Neither reported any adverse reactions in their breastfed infants.[ 13 ]

Effects on milk supply

Relevant published information on the effects of beta-blockade or metoprolol during normal lactation was not found as of the revision date. A study in 6 patients with hyperprolactinemia and galactorrhea found no changes in serum prolactin levels following beta-adrenergic blockade with propranolol.[ 14 ]

Levels in milk

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.[ 1 ] Accumulation of the drugs in the infant is related to the fraction excreted in urine. With 10% protein binding, 40% renal excretion and a moderate half-life, metoprolol presents moderately low risk for accumulation in infants. Maternal Levels. With metoprolol doses of 50 mg orally twice daily, milk levels are usually less than 420 mcg/L.[ 2 - 4 ] Five women taking oral metoprolol 100 to 200 mg daily had average milk metoprolol levels of 316 mcg/L.[ 5 ] It is estimated that a breastfed infant would receive a dose of about 0.07 mg/kg daily in breastmilk with a maternal dose of 200 mg daily.[ 4 ] Peak milk levels of 106 to 689 mcg/L have been reported following doses of 100 mg orally twice daily.[ 4 , 6 ] Peak milk levels occurred about 30 minutes after peak serum levels, at 1.5 hours after the dose in two patients, and 6 hours after the dose in a third.[ 6 ] Two women who were taking metoprolol (dosage not specified). Milk samples were obtained over one dosage interval. The dosage of metoprolol and alpha-hydroxymetoprolol in breastmilk was less than 2% of the mother's weight-adjusted dose.[ 7 ] Three mothers who took metoprolol in unspecified dosages during breastfeeding had breastmilk samples collected every 2 to 3 hours over one dosage interval. The average amount of metoprolol excreted in breast milk was 71.5 mcg daily (range 17.0 to 158.7 mcg daily). The average relative infant dosage was 0.5% of the mother's weight-adjusted dosage. Renal clearance of metoprolol was increased during lactation at 3 to 4 months postpartum, possibly related to increased maternal prolactin.[ 8 ] Infant Levels. Metoprolol was undetectable ( 2.7 mcg/L) in the plasma of 3 infants aged 4, 10 and 60 days after maternal oral doses of 100 mg daily.[ 2 ] Metoprolol serum levels in 3- to 5-day-old breastfed in

Alternatives LactMed lists

• Propranolol
• Labetalol