Elimination rate continuous intravenous infusion

Figure 10.5 Scheme for constant input rate, continuous intravenous infusion. Q, constant input or infusion rate X, mass (amount) of drug in the blood or body at time f X , mass of unchanged drug in urine at time t K, first-order elimination rate constant. 

Fig. 39.10. (a) One-compartment open model for continuous intravenous infusion of a dose D from a reservoir. The rate of infusion is k. (b) Time courses of the content in the reservoir Xn of the plasma concentration Cp and of the content of the elimination pool... 

With continuous intravenous infusion, the rate of drug entry into the body is constant. In the majority of cases, the elimination of a drug is first-order, that is, a constant fraction of the agent is cleared per unit time. Therefore, the rate of drug exit from the body increases proportionately as the plasma concentration increases and at every point in time is proportional to the plasma concentration of the drug. 

Following an intravenous injection of 10 mg propranolol, McAllister (1976) found the values of the elimination rate constant (K) and the apparent volume of distribution (V) to be 0.00505 0.0006min and 295 SSL, respectively (mean SD for six patients). These values were then used to calculate the loading dose (I ) and infusion rate (Q) necessary to instantly obtain and then continuously maintain propranolol plasma concentrations of 12, 40 and 75 ngmL . ... 

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