Carnitine metabolism was studied in 16 pediatric patients with various infections under the treatment with cefditoren pivoxil (CDTR-PI) in granular form. Pivalic acid released from pivaloyloxymethyl ester of the drug was metabolized to pivaloylcarnitine. As results, an increase in urinary carnitine excretion (predominantly as pivaloylcarnitine) and, a decrease in free carnitine concentration and a high acyl/free carnitine ratio in serum (plasma) were observed during the treatment. When the dosing was terminated, pivaloylcarnitine in plasma and then in urine disappeared, and the concentration of free carnitine, acyl/free carnitine ratio returned to the normal range. No carnitine-related side effects were observed throughout the study.