Women with rheumatoid arthritis (RA) appear to be at a high risk of preterm delivery, preeclampsia and low birth weight infants.1 Reduction of inflammatory activity is of particular importance in those desirous of having children.2 3 The use of disease-modifying antirheumatic drugs, including biological preparations, has been shown to be essential for suppression of the activity of RA. Tumour necrosis factor inhibitors have been introduced for the treatment of RA, with the expectation of obtaining immediate and certain effect. Although no teratogenicity of these drugs has been recognised in animal experiments,4 5 the safety of their use in pregnancy has not yet been adequately established. In this report, we discuss the clinical usefulness of etanercept with reference to the drug concentration in maternal and neonatal blood and breast milk.

A 40-year-old active RA patient (51.5 kg body weight; 153 cm height; body mass index 22), with a past history of two miscarriages at 7 weeks of pregnancy, was started on treatment with etanercept at 25 mg sq twice a week. She became pregnant soon after the drug produced a dramatic improvement in the clinical symptoms of RA, and strongly desired to continue the treatment with etanercept and prednisolone (9 mg/day) even during the pregnancy. Based on previous reports,6 7 8 we decided to continue the treatment after obtaining informed consent from the patient. She delivered a female infant weighing 1906 g by caesarean section at 36 weeks and 2 days of gestation. The infant Apgar scores at one minute and 5 minutes were 8 and 9, respectively, and no abnormalities were observed.

To determine the alterations in the blood concentrations of etanercept during pregnancy and to determine the transfer ratio of the drug to the fetus during pregnancy, the etanercept concentrations in the maternal blood in each trimester of pregnancy and the cord blood immediately after delivery were measured.9 The concentrations in the maternal blood were stable during pregnancy and the concentration in the cord blood, which was considered to represent the level in the blood of the infant, was approximately 1/30th of the concentration in the maternal blood. After childbirth, to confirm the degree of the transfer of etanercept to breast milk and to determine the possibility of the drug being detected in the blood of the infant during breast feeding, the etanercept concentrations in breast milk and serum of the baby were measured (see table 1). While the infant continued to be completely breast fed, the serum concentration of the drug in the infant decreased rapidly. By 12 weeks after delivery, etanercept could no longer be detected in the infant’s serum, despite its detection in the breast milk,10 and the infant (3885 g body weight; 51.9 cm height) had at least 800 ml/day of breast milk. The decrease in concentration with time in the infant’s serum despite continuation of breast feeding indicates placental transfer, but not transfer via the breast milk. These findings suggest that etanercept may be relatively safe during lactation.

In conclusion, unchanging levels in the maternal serum during pregnancy, low levels in the cord blood and progressively decreasing concentrations in the infant’s serum despite breast feeding were observed in this study.