Model(s) | Differential equation |
---|---|

1 and 4 | dX(1)/dt = R(t) − [(CL_{INT} + CL_{SLOPE} × CL_{CR})/V_{c} + k_{12}] × X(1) + k_{21} × X(2) and dX(2)/dt = k_{12} × X(1) − k_{21} × X(2) |

2 | dX(1)/dt = R(t) − [k_{e} + k_{12}] × X(1) + k_{21} × X(2); dX(2)/dt = k_{12} × X(1) − k_{21} × X(2) |

3^{b} | dX(1)/dt = R(t) − [CL/(V_{c}0 · wt)] × X(1) + k_{21} × X(2); dX(2)/dt = k_{12} × X(1) − k_{21} × X(2) |

↵a

*X*(1) is the amount of drug in the central compartment, and*X*(2) is the amount of drug in the peripheral compartment. R(*t*) is a time-delimited zero-order drug input rate (piecewise input function) into the central compartment (milligrams per hour). CL is the clearance from the central compartment (liters per hour),*V*_{c}represents the apparent volume of distribution from the central compartment. and*k*_{12}and*k*_{21}are first-order intercompartmental transfer rate constants (per hour).*k*_{e}is the first-order elimination constant (per hour) from the central compartment. See also Table 2, footnote*a*, for additional definitions.↵b Model 3 included weight as a linear covariate, such that

*V*_{c}=*V*_{c}0 · weight, where*V*_{c}0 was the parameter to be estimated, normalized to weight.