Figure 5. The absorption function after oral administration of morphine: The inverse Gaussian density (Equation 16, appendix 1) was chosen as an input function for the description of morphine absorption. [15]It provides flexibility and appropriate asymptotic behavior. The graph of the function f^A(t)=[radical] MAT/2 [Greek small letter pi] CV^A2t³e sup [-(t-MAT)(2)/2CV^A2MATt] is drawn using the original parameters of participant 1 (i.e., MAT = 3.793 and CV^A2= 1.68 [thick line]). For comparison, the traditional approach to absorption is depicted as a dotted line. In the traditional approach, the rate of absorption dA/dt is given by the product of the absorption rate constant, k (^a), and the amount remaining to be absorbed, A^a: da/dt = k^a[middle dot] A^a. The amount remaining to be absorbed is given by A^a= F [middle dot] D^or[middle dot] e^-kat. Thus, the rate of absorption over time is calculated as d/dt=k^a[middle dot] D^or[middle dot] e^-kot(dotted line).