C₁₉ H₂₁ N₅ O₄

An antihypertensive and antiadrenergic agent with peripheral action indicated in the treatment of hypertension and Raynaud's phenomenon. Oral administration in two daily doses.

According to the manufacturer, it is excreted in small amount in breast milk ^{(Pfizer 2016 & 2009)}, with a relative dose of at most 3%. ^{(Schaefer 2015, p 716)}

Its pharmacokinetic data - large volume of distribution, high percentage of protein binding and short half-life ^{(Pfizer 2016, Kirsten 1998)}-, makes transfer into breastmilk in significant quantities unlikely.

Its low oral bioavailability hinders transfer to infant plasma from breastmilk, except in premature infants and the immediate neonatal period when there may be increased intestinal permeability.

It is structurally similar to doxazosin, which is excreted in breast milk in negligible amounts.

There is contradictory data regarding its action on prolactin, not affecting its levels according to some (Laakmann 1986, Barbieri 1980) or decreasing it according to others ^{(Gumbatov 1992)}, but when breastfeeding is well established, milk production does not depend as much on levels of prolactin.^{(Messinis 1985).}

Until there is more published data on this drug in relation to breastfeeding, safer known alternatives may be preferable ^{(Anderson 2018, Malachias 2018, Schaefer 2007 p685)}, especially during the neonatal period and in cases of prematurity.