Differences in the Prediction of Area Under the Curve for a Protease Inhibitor Using Trough Versus Peak Concentration: Assessment Using Published Pharmacokinetic Data for Indinavir

In the present day antiretroviral therapy, Ctrough is a key tool for efficacy assessment. The present work explored the feasibility of using Ctrough or Cmax in the area under the concentration-time curve (AUC) prediction of indinavir. A simple unweighted linear regression model was developed to describe the relationship between Cmax versus AUC (r = 0.8101, P < 0.001) and Ctrough versus AUC (r = 0.8127, P < 0.001) for indinavir. The regression lines were used to predict the AUC values from literature Cmax or Ctrough data of indinavir in HIV and healthy subjects. The fold difference, defined as the quotient of the observed and predicted AUC values, was evaluated along with statistical comparison, including root mean square error (RMSE) prediction for the 2 models. The correlation between Cmax versus AUC and Ctrough versus AUC was established. Majority of the predicted values for Cmax versus AUC were within 0.75- to 1.5-fold differences. However, the Ctrough versus AUC model showed larger variability with approximately one-third of the predictions within 0.75- to 1.5-fold differences. The r value and %RMSE for observed versus predicted AUC for Ctrough (r = 0.5925, n = 65, P < 0.001, and RMSE: 67%) were inferior to the Cmax (r = 0.8773, n = 86, P < 0.001, and RMSE: 46%). In conclusion, Cmax versus AUC and Ctrough versus AUC relationships were established for indinavir showing the utility of a single concentration time point for therapeutic drug monitoring purpose. The Cmax model for indinavir may be more relevant for AUC prediction as determined by the statistical criteria.