Na₂ Fe(CN)₅ NO

Nitroprusside (NP) is a powerful arteriovenous vasodilator that decreases peripheral vascular resistance, and is used in hypertensive crises ^{(Pediamecum 2016)}. It is metabolized producing nitric oxide (vasodilator) and cyanide which is metabolized to thiocyanate which is eliminated by urine ^{(AEMPS 2017, FDA 2017)} and can be toxic if the doses have been high or very prolonged ^{(Moffett 2008)}, especially if there is kidney or liver failure. Administration via intravenous infusion continues for a few hours (usually less than 3 days). After that time, plasma cyanide levels should be monitored so that they do not exceed 1 microgram/mL and thiocyanate levels remain below 80 nanograms/mL.

Sine the last update we have not found published data on Nitroprusside excretion in breastmilk.

The rapid elimination half-life of nitroprusside (T½ of 2 minutes) makes it very unlikely it will be excreted in breastmilk and, in addition, its oral bioavailability is almost zero, therefore it would not be absorbed by the infant's intestine.

Cyanide and thiocyanate have a T ½ of 7 hours and of 3 to 7 days respectively ^{(Hale, Kirsten 1998, Schulz 1984)}. Thiocyanate also has a 100% oral bioavailability. Both, but especially thiocyanate, would be excreted in breastmilk.

Thiocyanate is a common component of breastmilk ^{(Kirk 2007, Funderburk 1967)} with concentrations dependent on smoking ^{(Meberg 1979)}, exposure to certain industrial products, the consumption of certain foods (cassava or manioc, some pulses and almonds) and intake of medication such as nitroprusside. ^{(Dorea 2004, Laurberg 2004)}

There is low excretion in breastmilk, milk levels being lower than plasma ones, with a milk/plasma index of 0.4 to 0.7. ^{(Dorea 2002, Funderburk 1967)}

Nitroprusside is used in Pediatrics even in premature infants, especially in serious situations ^{(Deliu 2018, Pediamecum 2016, Drover 2015, Hammer 2015, Clark 2006, Cachat 2004, Benitz 1985)} with good tolerance and very low and infrequent toxicity if normal doses are respected. ^{(Drover 2015, Hammer 2015, Thomas 2009, Benitz 1985)}

Although the possibility that thiocyanate may interfere with thyroid function has been put forward ^{(Lee 2017, Kirk 2007, Laurberg 2004)}, other authors have not found this link. ^{(Leung 2012).}

In summary, nitroprusside has good tolerance in pediatrics and is not likely to be eliminated in breastmilk or absorbed orally; the risk to the infant comes from the potential toxicity of its cyanogenic metabolites. Breastmilk contains thiocyanate and only if a breastfeeding mother has been treated with high doses or over many days with nitroprusside is it likely that the levels of thiocyanate in breastmilk would be high enough to cause problems in the infant. In cases of prolonged treatment, the plasma levels of cyanide and thiocyanate in the mother should be monitored as well as the appearance of clinical symptoms in the infant.