title: A novel approach for prediction of tacrolimus blood concentration in liver transplantation patients in the intensive care unit through support vector regression.
abstract: BACKGROUND
  Tacrolimus is an important immunosuppressive drug for organ transplantation patients. It has a narrow therapeutic range, toxic side effects, and a blood concentration with wide intra- and interindividual variability. Hence, it is of the utmost importance to monitor tacrolimus blood concentration, thereby ensuring clinical effect and avoiding toxic side effects. Prediction models for tacrolimus blood concentration can improve clinical care by optimizing monitoring of these concentrations, especially in the initial phase after transplantation during intensive care unit (ICU) stay. This is the first study in the ICU in which support vector machines, as a new data modeling technique, are investigated and tested in their prediction capabilities of tacrolimus blood concentration. Linear support vector regression (SVR) and nonlinear radial basis function (RBF) SVR are compared with multiple linear regression (MLR).
  
  
  METHODS
  Tacrolimus blood concentrations, together with 35 other relevant variables from 50 liver transplantation patients, were extracted from our ICU database. This resulted in a dataset of 457 blood samples, on average between 9 and 10 samples per patient, finally resulting in a database of more than 16,000 data values. Nonlinear RBF SVR, linear SVR, and MLR were performed after selection of clinically relevant input variables and model parameters. Differences between observed and predicted tacrolimus blood concentrations were calculated. Prediction accuracy of the three methods was compared after fivefold cross-validation (Friedman test and Wilcoxon signed rank analysis).
  
  
  RESULTS
  Linear SVR and nonlinear RBF SVR had mean absolute differences between observed and predicted tacrolimus blood concentrations of 2.31 ng/ml (standard deviation [SD] 2.47) and 2.38 ng/ml (SD 2.49), respectively. MLR had a mean absolute difference of 2.73 ng/ml (SD 3.79). The difference between linear SVR and MLR was statistically significant (p < 0.001). RBF SVR had the advantage of requiring only 2 input variables to perform this prediction in comparison to 15 and 16 variables needed by linear SVR and MLR, respectively. This is an indication of the superior prediction capability of nonlinear SVR.
  
  
  CONCLUSIONS
  Prediction of tacrolimus blood concentration with linear and nonlinear SVR was excellent, and accuracy was superior in comparison with an MLR model.
authors.affiliation: Ghent University, Department of Information Technology, Gaston Crommenlaan 8, Ghent, Belgium.
authors.forename: Stijn
authors.initials: S
authors.lastname: Van Looy
authors.forename: Thierry
authors.initials: T
authors.lastname: Verplancke
authors.forename: Dominique
authors.initials: D
authors.lastname: Benoit
authors.forename: Eric
authors.initials: E
authors.lastname: Hoste
authors.forename: Georges
authors.initials: G
authors.lastname: Van Maele
authors.forename: Filip
authors.initials: F
authors.lastname: De Turck
authors.forename: Johan
authors.initials: J
authors.lastname: Decruyenaere
mesh_terms: D000328:Adult; D000368:Aged; D003422:Critical Care / Q000379:methods*; D005260:Female; D006801:Humans; D007166:Immunosuppressive Agents / Q000097:blood*; D016014:Linear Models; D016031:Liver Transplantation / Q000706:statistics & numerical data*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D016559:Tacrolimus / Q000097:blood*
chemical_list: D007166:Immunosuppressive Agents; D016559:Tacrolimus