Simvastatin

Fat-soluble statin, which acts by reducing cholesterol synthesis.
Indicated in the treatment of hypercholesterolemia, primary, familial (hetero and homozygous) and combined familial hyperlipidaemia.
Authorized use from 10 years of age.
Oral administration in a daily dose.

At the date of the last update, the authors did not find any published data on its excretion in breast milk.

Its pharmacokinetic data (very high percentage of protein binding and moderately high molecular weight) make it highly unlikely that significant quantities will pass into breast milk.

The tiny known secretion in breast milk, of pravastatin (Pan 1988) and rosuvastatin (Lwin 2018, Schutte 2013) and presumably from the rest of statins, is very unlikely to alter the lipid composition of breast milk and decrease its cholesterol concentration.

Because of its low oral bioavailability it has difficulty passing to the infant plasma from ingested breast milk, except in premature infants and in the immediate neonatal period in which there may be greater intestinal permeability.

Mothers homozygous for familial hypercholesterolemia took statins for 18 pregnancies and 11 lactations lasting 3 to 9 months. Infants had no developmental or school learning problems (Botha 2018).

Expert authors consider the use of statins, especially rosuvastatin or pravastatin, safe or probably compatible or of minimal risk during pregnancy and/or lactation (Hale 2021, Botha 2018, Holmsen 2017, Amir 2011).

Other authors advise postponing statin treatment from 3 months before pregnancy and until breastfeeding ends or is not exclusive (Shala 2020, Lawrence 2016 p 393).
Except in severe forms of hypercholesterolemia (Moss 2018), postponing drug treatment for a few months is unlikely to alter the long-term outcome of the disease in the mother. It is advisable to follow a lipid-lowering diet.

Cholesterol levels are normally increased (40%) during pregnancy and lactation in healthy women (Lawrence 2016 p590).
The cholesterol in breast milk is synthesized in the mammary gland and its concentration in breast milk ranges from 30 mg/dL in colostrum to 10 - 20 mg/dL in mature breast milk (Lawrence 2016 p98, 105 and 767).
The cholesterol concentration is greatly increased (up to 3 times higher) in the milk of lactating mothers with homozygous familial hypercholesterolemia (Holmsen 2017, Tsang 1978). Statin treatment would, at best, reduce it to normal levels (Holmsen 2017).

Cholesterol is necessary for the development of brain tissue, myelination of nerves, and is the basis for many enzymes. Breastfed infants have higher plasma cholesterol levels than those fed artificial formulas and this will protect them against the consequences of hypercholesterolemia in adult life (Lawrence 2016 p108).

Infants fed substitute formulas “artificial milk” do not receive cholesterol in their diet, as these products do not contain cholesterol (Lawrence 2016 p 109 and 215). The amount of cholesterol in breast milk that would remain after the hypothetical reduction in cholesterol produced by statins taken by the mother, would still be much higher than that provided by artificial formulas (Holmsen 2017).