Unique approach for calculation of absorption rate constant.

Several methods are employed to estimate an apparent first-order rate constant for absorption in a one-compartment model (Ka). These include curve-stripping, nonlinear least squares regression, and the Wagner-Nelson approach. The Wagner-Nelson method in particular requires extensive calculation and may be subject to error. A method for calculation of the absorption rate constant has been derived based on the relationship between area under the concentration-time curve, between time of maximum concentration (tmax) and infinity, and maximum concentration (cmax). The method obviates the need for large numbers of samples in the absorptive phase. The method also avoids extensive calculations and is less influenced by errors in data points prior to Cmax where the rate of change of concentration is very rapid and error is likely. The value for Ka is corrected for by the error found in tmax (calculated using the estimated Ka) relative to the observed tmax. The method has been tested on theoretical data with and without error generated using a range of a and KE. Errors in the estimate of Ka are proportional to error in the data.