One hundred-twenty men (mean age, 66 years) with symptoms of androgen decline (decreased libido and erectile quality, depressed mood, decreased cognitive function, and fatigue) and a low free-testosterone concentration were randomly assigned to receive, in double-blind fashion, either 1) testosterone undecanoate (160 mg/day orally), 2) 2 g/day each of propionyl-L-carnitine and acetyl-L-carnitine (carnitines group), or 3) placebo for 6 months. Erectile function, as determined by the International Index of Erectile Function (IIEF) score, increased (improved) from a mean of 8 in each group at baseline to 16 in the testosterone group, 24 in the carnitines group, and 9 in the placebo group. The increase in IIEF score was significantly greater in the carnitines group than in the testosterone group. Carnitines and testosterone were effective for as long as they were administered, but symptoms recurred when treatment was discontinued.

Comment: Propionyl-L-carnitine is a carnitine derivative that has been found to have greater affinity than L-carnitine for certain tissues and is apparently hydrolyzed to release free L-carnitine in those tissues. L-Carnitine plays a role in energy production by facilitating the transport of fatty acids into mitochondria. Acetyl-L-carnitine functions as a neurotransmitter, with activity similar to that of acetylcholine. The results of the present study indicate that the combination of propionyl-L-carnitine and acetyl-L-carnitine was significantly more effective than testosterone in the treatment of erectile dysfunction associated with age-related androgen decline. The mechanism of action is not clear.

Cavallini G, et al. Carnitine versus androgen administration in the treatment of sexual dysfunction, depressed mood, and fatigue associated with male aging. Urology 2004;63:641-646.