*k*_{12} (min^{−1}) | First-order transfer rate constant between central and peripheral compartments | 0.404 (46.9) | 0.363 (46.4) |

*k*_{21} (min^{−1}) | | 0.143 (72.9) | 0.113 (69.5) |

*k*_{10} (min^{−1})^{a} | First-order elimination constant from central compartment | 0.0711 | 0.0735 |

*k*_{m} (min^{−1}) | First-order rate constant describing formation of MG from M | 0.048 (24.3) | 0.047 (20.9) |

*k*_{m,others} (min^{−1}) | First-order rate constant describing forming other metabolites from M | 0.001 (24.1) | 0.001 (25.0) |

*k*_{bile} (min^{−1}) | First-order rate constant describing biliary secretion of M | 0.0001 (31.0) | 0.0004 (31.0) |

*k*_{renal} (min^{−1}) | First-order rate constant describing renal excretion of M | 0.022 (26.8) | 0.021 (23.6) |

*V*_{1} (ml) | Volume of distribution of central compartment for M | 140 (59.1) | 120 (58.0) |

*k*_{a} (min^{−1}) | First-order absorption rate constant of M | 0.036 (37.3) | 0.034 (35.2) |

CL_{tot} (ml·min^{−1}) | Total clearance of M | 9.95 | 8.82 |

*g*_{mi} = *k*_{m}/*k*_{10} | Fraction of total morphine clearance responsible for forming MG | 0.675 | 0.642 |

*F*_{abs} | Fraction of dose absorbed | 0.94 (30.0) | 0.95 (24.8) |

*k*{mi}_{bile} (min^{−1}) | First-order rate constant describing biliary excretion of MG | 0.045 (59.1) | 0.040 (46.4) |

*k*{mi}_{renal} (min^{−1})^{b} | First-order rate constant describing renal excretion of MG | 0.020 (12.5) | 0.020 (12.1) |

*V*{mi} (ml) | Volume of distribution of metabolite compartment | 306 (36.0) | 292 (29.8) |