Clin Invest Med 2009; 32 (1): E13-E19. AbstractPurpose: To investigate the pharmacokinetics of Lcarnitine (LC) and its analogues, acetyl-L-carnitine (ALC) and propionyl -L-carnitine (PLC) in healthy volunteers after single L-carnitine administration. Methods: Liquid L-carnitine (2.0 g) was administered orally as a single dose in 12 healthy subjects. Plasma and urine concentrations of L-carnitine, ALC and PLC were detected by HPLC. Results:The maximum plasma concentration (Cmax) and area under the curve (AUC0-) of L-carnitine was 84.7±25.2 μmol·L -1 ·h and 2676.4±708.3 μmol·L -1 ·h, respectively. The elimination half-life of L-carnitine and the time required to reach the Cmax (Tmax) was 60.3±15.0 and 3.4±0.46 h, respectively. The Cmax of ALC (12.9±5.5 μmol·L -1 ) and PLC (5.08±3.08 μmol·L -1 ) was lower than Lcarnitine (P<0.01), so as the AUC0-(166.2±77.4 and 155.6±264.2μmol·L -1 ·h, respectively, P<0.01). The half-life of ALC (35.9±28.9h) and PLC (25.7±30.3 h) was also shorter than L-carnitine (P<0.01). The 24h accumulated urinary excretion of L-carnitine, ALC and PLC were 613.5±161.7, 368.3±134.8 and 61.3±37.8μmol, respectively. Conclusion: L-carnitine has a greater maximum plasma concentration than ALC and PLC. L-carnitine also has a longer half-life than ALC and PLC. These data may have important implications in the designing of dosing regimens for L-carnitine or its analogues, such as ALC or PLC.L-carnitine (3-hydroxy-4-N-trimethylammonium butyrate) is an endogenous compound mainly derived from food stuff, such as meat and dairy products. [1][2][3] It is also synthesized in the human, in the liver and kidneys, from the essential amino acids lysine and methionine. [1][2][3] In humans, the endogenous carnitine pool, which comprises free L-carnitine and a range of short-, medium-and long-chain esters, such as acetyl-L-carnitine (ALC) and propionyl-L-carnitine (PLC), is maintained by absorption of L-carnitine from dietary sources, biosynthesis within the body and extensive renal tubular reabsorption from glomerular filtrate. [1][2][3] L-carnitine has important roles in intermediary metabolism, including the transport of long chain fatty acids across the mitochondrial inner membrane; more than 90% of the human body's store is present in skeletal and cardiac muscle. 1,2 L-carnitine is an essen-ORIGINAL RESEARCH