(3-Carboxy-2-hydroxypropyl)trimethylammonium hydroxide, inner salt; 3-Hydroxy-4-trimethylammoniobutyrate

Carnitine is a derivative of the amino acids L-lysine and L-methionine. It is widely distributed in all mammalian tissues and is very abundant in muscle tissue and is essential in fatty acid metabolism ^{(AESAN 2021)}. It is used as levocarnitine in the treatment of primary (extremely rare) and secondary deficiency (due to hemodialysis, cardiomyopathy or HIV) of carnitine ^{(Evans 2003)}. Oral or intravenous administration 2 to 4 times a day. In the form of acetylcarnitine it is used in various psychiatric disorders.

Carnitine is present breast milk: Mean concentration level the first month is about 7 to 12 mg/L ^{(Mitchell 1991, Penn 1987, Rovamo 1986, Cederblad 1986, Sandor 1982)}, with lower levels in the next following months. ^{(Rovamo 1986, Sandor 1982)}

Milk carnitine levels are not affected by carnitine supplementation: breastfed infants of carnitine-deficient mothers require carnitine supplementation. ^{(Studinski 2011)}

Due to its protein nature it would be digested and inactivated in the gastrointestinal tract. Its very low oral bioavailability, < 20% ^{(Evans 2003)}, minimizes the passage into plasma of the infant from ingested breast milk, except in the premature and in the immediate neonatal period in which there may be greater intestinal permeability.

The maximum daily amount of levocarnitine as a food supplement should not exceed 2 g. ^{(AESAN 2011)}