Drugs in Pregnancy and Lactation: Tenth Edition


Nutrient (Amino Acid)

PREGNANCY RECOMMENDATION: No Human Data—Probably Compatible



L-Lysine is an essential amino acid that has been occasionally used for the treatment and prophylaxis of herpes simplex infections (the effectiveness of this indication is questionable). No reports on the use of the commercial formulation in human pregnancy have been located.


L-Lysine is actively transported across the human placenta to the fetus with a steady-state fetal:maternal ratio of approximately 1.6:1 (1,2). Fetal tissues retain most of the essential amino acids, including l-lysine, in preference to the nonessential amino acids (3).

One published case has been located that described a woman with familial hyperlysinemia because of deficiency of the enzymes lysine ketoglutarate reductase and saccharopine dehydrogenase (4). The woman gave birth to a normal child. No details of the pregnancy or the child were provided other than that the child was normal. Serum lysine levels, which were regularly >10 mg/dL and may have been as high as 20 mg/dL or more when the disorder was detected, were not measured during the pregnancy or in the baby.


No reports describing the use of l-lysine during human lactation have been located.


1.Schneider H, Mohlen KH, Dancis J. Transfer of amino acids across the in vitro perfused human placenta. Pediatr Res 1979;13:236–40.

2.Schneider H, Mohlen KH, Challier JC, Dancis J. Transfer of glutamic acid across the human placenta perfused in vitro. Br J Obstet Gynaecol 1979;86:299–306.

3.Velazquez A, Rosado A, Bernal A, Noriega L, Arevalo N. Amino acid pools in the feto-maternal system. Biol Neonate 1976;29:28–40.

4.Dancis J, Hutzler J, Ampola MG, Shih VE, van Gelderen HH, Kirby LT, Woody NC. The prognosis of hyperlysinemia: an interim report. Am J Hum Genet 1983;35:438–42.