Familial juvenile hyperuricemic nephropathy requiring the use of febuxostat during the perinatal period: a case report including evaluation of transfer into cord blood and breast milk

Background There are no case reports or epidemiological studies on the use of febuxostat, a drug used to treat hyperuricemia, during pregnancy or breastfeeding. We encountered a case of familial juvenile hyperuricemic nephropathy in which the patient required febuxostat during the perinatal period. This case provides valuable insights into placental and breast milk transfer of febuxostat. Case presentation A 30-year-old woman presented with familial juvenile hyperuricemic nephropathy. She strongly desired to have children. She was found to be pregnant while her condition was being controlled with febuxostat 40 mg/day and sodium bicarbonate 500 mg/day. When pregnancy was confirmed, the patient was 9 weeks pregnant. Following consultation, febuxostat administration continued during pregnancy. The patient gave birth at 38 weeks of gestation. The maternal plasma concentration of febuxostat immediately prior to delivery (before medication) was 169 ng/mL, and the umbilical cord blood concentration at birth (4 h after medication) was 154 ng/mL. No major congenital abnormalities were observed at birth. The patient chose to breastfeed after delivery. She continued taking 40 mg/day of febuxostat orally. Febuxostat concentrations in breast milk immediately before dosing and at 1, 3.5​, 7 h after dosing were 37, 40, 58, and 81 ng/mL, respectively. At the one-month checkup, a deformity of the infant’s second toenail was noted. However, its association with a congenital malformation could not be confirmed, and there were no functional abnormalities. No problems with the infant’s growth or development were observed. Conclusion The patient continued to febuxostat throughout pregnancy and subsequently gave birth. Further data are required to draw conclusions regarding the risks to infants associated with febuxostat use during the perinatal period.