L carnitine is primarily synthesized in the liver from the amino acids lysine and methionine through a series of four enzymatic reactions, with the liver and kidneys converting the precursor butyrobetaine into active L Carnitine Injection Levocarnitine IV Comparison of short term and long term effects of peroral L carnitine intake: clinical implications of elevated TMAO levels in cardiovascular complications Comprehensive review of the expanding roles of the carnitine pool in metabolic physiology: beyond fatty acid oxidation Journal of Translational Medicine Springer Nature Link l carnitine: Nutrition, pathology, and health benefits ScienceDirect