GHB levels in breast milk of women with narcolepsy with cataplexy treated with sodium oxybate.

Objective: To determine GHB levels in breast milk of women taking sodium oxybate (Xyrem) for treatment of narcolepsy and cataplexy.

Methods: Two women with narcolepsy and cataplexy treated with sodium oxybate before pregnancy collected breast milk for analysis of GHB concentration after resuming sodium oxybate postpartum. One woman collected samples across two consecutive nights (doses: 3.0 gm and 4.5 gm twice per night) five months after delivering her first child; the other collected samples on three separate days (doses: 2.25 gm and 3.0 gm twice per night) nine months after the births of her first two children. GHB concentration was determined by gas chromatography/mass spectrometry.

Results: Milk GHB levels before sodium oxybate ranged from 5.81 to 7.60 μM. Levels were 2-4 times higher four hours after the first sodium oxybate dose (10.44-23.58 μM) and 3-5 times higher four hours after the second dose (ie, eight hours after first dose; 14.60-34.01 μM). GHB levels returned to endogenous levels 6-10 h following the second dose, however variability was observed between patients and pregnancies. Higher breast milk GHB levels were observed with higher doses for both patients.

Conclusions: Sodium oxybate is transmitted to breast milk. Despite its short half-life, GHB concentrations remained two-to-five times higher than endogenous levels four hours after both nighttime doses. To avoid excess GHB exposure, breastfeeding mothers who take sodium oxybate should consider expressing and discarding their morning milk. Future work should examine milk GHB levels after chronic sodium oxybate and determine whether levels change as milk composition changes across the postpartum period.