PHARMACOKINETICS OF PIRACETAM - A STUDY ON THE BIOAVAILABILITY WITH SPECIAL REGARD TO RENAL AND NONRENAL ELIMINATION

The basis of this investigation was a trial on the relative bioavailab ility of a recently developed galenic formulation of piracetam. The op en, randomized, single-blind crossover study was performed in 16 healt hy male volunteers aged between 20 and 31 years. Under fasting conditi ons, they were given a single oral dose of 1600 mg piracetam either of the test drug or the reference drug. Blood samples and urine specimen s were collected over 24 hours. The quantitative analysis was performe d with a high sensitive HPLC-method. The pharmacokinetic analysis was carried out with the PC-based program TopFit. An identical bioavailabi lity of the test drug was found (AUC(0-24), AUC(0-infinity), C-max, by comparison to the reference drug. No relevant difference in piracetam excretion between test and reference drug was found, however, in cont rast to previous references only about two thirds of the given oral do se could be detected in the urine after administration. A statisticall y significant difference (p = 0.001) between total clearance and renal clearance was observed. Because an incomplete absorption of the drug in the upper gastrointestinal tract is excluded, an additional extrare nal pathway of piracetam must be discussed; the hypothesis of an exclu sive renal elimination of this drug should be overruled.