Estimation of Rate constant from measurement during free dosage regimen

The estimation procedure for pharmakokinetic rate constants of blood and/or urine levels which have been taken during a free dosage regimen is described under the assumption of a classical open two-compartment model of first order. In an example phenylbutazone concentration measurements are used to demonstrate the iteration estimation procedure and to discuss the specific problems in order to receive unbiased and best estimates. Advantages and disadvantages of multiple-dose studies in free dosage regimen are itemised, and model functions for the free dosage regimen are suggested.