Effects of furosemide in the newborn

The effects of furosemide on electrolyte and water excretion were determined in 9 neonates with fluid overload states. Hourly measurements of urine volume, serum and urine Na+, K+, Cl−, creatinine, and blood urea nitrogen were done before and after the intravenous or intramuscular injection offurosemide (1 mg/kg). Mean (±SE) birth weight was 2,261.7 ± 284.4 gm; gestational age was 35.1 ± 1.4 wk, postnatal age was 13.8 ± 6.9 days, blood urea nitrogen was 10.0 ± 1.0 mg%, creatinine was 0.7 ± 0.1 mg%, and glomerular filtration rate was 21.9 ± 3.8 ml · min−1/1.73 m2. Compared with the values obtained before the administration of furosemide, there were significant increases in percent fractional Na+ excretion, percent fractional Cl− excretion, urine volume (ml · hr−1), and free water clearance (ml · hr−1), each of which peaked within 1 hr of furosemide administration and were sustained for another hour thereafter. These effects were discernible for about 5 hr and returned to baseline by 6 hr after administration of the drug. A 2.5‐fold increase in K+ excretion (µEq · hr−1) was noted I hr after furosemide; this increase was sustained for 2 hr and decreased to the predrug level in 4 hr. Although all infants showed increases in urine volume and electrolyte excretion within 1 hr of furosemide administration, the magnitude of the response exhibited remarkable variability. There is some suggestion that perinatal asphyxia may decrease the response to furosemide.