The question concerns a 29-year-old woman who delivered a child less than 24 hours ago. She is bein

Fråga: The question concerns a 29-year-old woman who delivered a child less than 24 hours ago. She is being treated with Anafranil 110 mg per day and Buspar (buspirone) 10 mg three times daily. The question: is what is known about the extent to which buspirone is passed to the child during breast feeding?

Sammanfattning: Although there is no direct information available on the extent of the transfer of buspirone from the mother to the child during breast feeding, theoretical, physical, chemical and pharmacokinetic calculations suggest that only small amounts will actually reach the child. If the motivation to continue treatment of the mother is sufficiently strong it is suggested that, if breast feeding is also planned to continue, samples should be secured from the mother´s blood and milk and, if possible also from the child. However, it is emphasised that the general rule is to avoid using drugs during breast feeding for which documentation is not available.

Svar: Information on clomipramine and pregnancy and lactation is available in other Drugline documents (1). Neither a literature search of standard references, nor on Drugline or on Medline, gave any information on the kinetics or passage of buspirone to children during breast feeding (2-5). Direct contact with the manufacturer on the telephone did not provide any information concerning buspirone and breast feeding (6). In FASS (7) buspirone is classified as category IV, "no information available". Buspirone is a weak base with two pKa values of 1.22 and 7.32 respectively. Therefore the drug becomes ionised around physiological pH and an accumulation into breast milk, which is as most ten times the free concentration in plasma, may take place. The drug is strongly protein-bound, 95 per cent, and the volume of distribution can be calculated from the clearance and half-life given in FASS (7) to be at least eight litres per kilo body weight. Thus, a relatively small proportion of the body content of the drug resides in plasma. However, it can be assumed that the binding to milk proteins can be extensive and equal the plasma protein binding. Furthermore, the oral availability is around four per cent due to extensive first pass metabolism.

From these numbers it can be concluded that only a small amount of the body content of buspirone could actually reach the breast milk. Furthermore it can be suspected, although it has not been proven, that the oral availability is also very small in the breast-fed child. Thus, in spite of the risk of accumulation into breast milk due to the physicochemical properties of buspirone, the pharmacokinetic properties of the drugs suggest that only a very small amount will actually reach the child. If the patient is strongly dependent on the medication it seems rational to continue it. However, this decision should be accompanied by appropriate sampling from the mother´s blood and the breast milk and, when possible, a sample should be obtained from the child.