Residual fraction of the area under the curve as a qualitative criterion in pharmacokinetic studies

The aim of the present study was to determine whether the residual area under the curve (AUCres%; expressed as % of total value of AUC) could be used as a parameter for the qualitative evaluation of pharmacokinetic studies. We propose new criteria for the qualitative evaluation of pharmacokinetic analysis. Two sets of hypothetical data that illustrate the relationship between concentration and time were used for the analysis of drug pharmacokinetics. Non-compartmental analysis was applied for the calculations. The results obtained from the hypothetical data were compared with those obtained from an in vivo study in which 3-week-old broiler chickens were administered 10 mg/kg b.w. enrofloxacin intravenously (iv) or per os (po). In the first set of data (A-D), AUCres% values were as follows: A= 16.29% and B = 20.79% for iv administration and C = 29.61% and D = 27.90% for po administration. In the next set of data (E-G), AUCres% values after oral administration were 25.30% (E), 23.18% (F), and 20.79% (G). The AUCres% values after iv administration of enrofloxacin were similar to po administration; the range of iv and po administration values were 14.35% to 17.50% and 11.14% to 28.33% of the total AUC, respectively. The analysis of the hypothetical data indicates that AUCres% is not an optimal method for the evaluation of pharmacokinetic studies.