Objective: To evaluate the effectiveness of L-carnitine (LC) or L-acetyl-carnitine (LAC) or combined LC and LAC treatment in improving semen kinetic parameters and the total oxyradical scavenging capacity in semen.

Design: Placebo-controlled, double-blind, randomized trial.

Setting: Andrology unit, Department of Internal Medicine, Polytechnic University of Marche, Italy.

Patient(s): Sixty infertile men, ages 20 to 40 years, with the following baseline sperm selection criteria: concentration > 20 x 10(6)/mL, sperm forward motility < 50%, and normal sperm morphology > 30%; 59 patients completed the study.

Intervention(s): Patients underwent a double-blind therapy of LC 3 g/d, LAC 3 g/d, a combination of LC 2 g/d and LAC 1 g/d, or placebo. The study design was 1 month of run in, 6 months of therapy or placebo, and 3 months of follow-up evaluation.

Main outcome measure(s): Variations in semen parameters used for patient selection, and variations in total oxyradical scavenging capacity of the seminal fluid.

Result(s): Sperm cell motility (total and forward, including kinetic features determined by computer-assisted sperm analysis) increased in patients to whom LAC was administered both alone or in combination with LC; combined LC + LAC therapy led to a significant improvement of straight progressive velocity after 3 months. The total oxyradical scavenging capacity of the semen toward hydroxyl and peroxyl radicals also increased and was positively correlated with the improvement of kinetic features. Patients with lower baseline values of motility and total oxyradical scavenging capacity of the seminal fluid had a significantly higher probability of responding to the treatment.

Conclusion(s): The administration of LC and LAC is effective in increasing sperm kinetic features in patients affected by idiopathic asthenozoospemia and improves the total oxyradical scavenging capacity of the seminal fluid in the same population.