ABSTRACT
In the previous discussion of the pharmacokinetic behavior of drugs after single and multiple drug administration by different routes, it was assumed that the drug absorption, distribution, and elimination processes follow rst-order kinetics. In this case, the drug CLT, Vd, k, and t1/2 are constant irrespective of the administered dose, that is, dose independent and concentration independent. After administration of increasing doses of the drug, the plasma drug concentration-time proles during the elimination phase are parallel when plotted on the semilog scale. Also, the AUC of the drug from 0 to ∞ after a single drug administration is directly proportional to the administered dose, which is known as the principle of superposition. Furthermore, at steady state during multiple drug administration, the AUC from 0 to τ and the average drug concentration are directly proportional to the administered dose. The drug is said to follow linear or dose-independent pharmacokinetics when there is a linear relationship between the dose and AUC after single dose administration and the dose and steady-state concentration during multiple drug administration.
