Antenatal mgnesium sulfate and ritodrine increased potassium levels in preterm infants: A cohort study

Ritodrine and magnesium sulfate are administered to prevent preterm labor. Magnesium sulfate is also administered to prevent preeclampsia. These drugs have been reported to increase potassium levels in pregnant women and neonates. The aim of this study was to investigate the relationship between potassium levels in preterm infants and antenatal treatment.

This prospective cohort study was conducted at Saiseikai Suita Hospital. Preterm infants born at <35 weeks' gestation between October 2012 and September 2014 were recruited and divided into four groups based on the antenatal treatment their mothers received. Serum and urine electrolyte levels at birth and serum potassium levels 1 day after birth were measured.

The mothers of 16 infants received no antenatal treatment (condition C); the mothers of 29 infants received antenatal ritodrine (R); the mothers of seven infants received magnesium sulfate (M); and the mothers of 15 infants received both magnesium sulfate and ritodrine (M + R). At birth, potassium levels were similar among the four groups. However, potassium levels a day after birth were significantly higher in the M + R group than in the other groups: median (min.-max.) mEq/L 4.8 (3.8-6.2), 4.8 (3.6-6.0), and 4.4 (3.8-5.9) vs. 5.8 (4.9-7.2), in the C, R, and M groups versus the M + R group, respectively (P < 0.01). Significantly more infants in the M + R group exhibited a fractional excretion of potassium of <10% compared with those in the other groups.

The increased potassium levels we observe in preterm infants of mothers who received antenatal magnesium sulfate and ritodrine administration on postnatal day 1 warrant monitoring by neonatologists.