PharmSim

Formulas for single vascular bolus administration

After single vascular bolus administration, the plasma concentration of a drug at a certain moment in time depends on:

• the administered dose

• the volume of distribution

• the clearance

The dose and the volume of distribution together determine the initial plasma concentration. After t=0, the plasma concentration decreases with a power of e, which depends on the elimination rate constant k, calculated by deviding the clearance by the volume of distribution. In formulas, the plasma concentration (Cp) at a certain time is given by:

where and

The drug action over time depends on the plasma concentration, and, in addition on the maximal effect of the drug (Emax), which is 100% in this applet, and the EC50. If the plasma concentration equals the EC50, the drug action should be 50% by definition. Furthermore, when the plasma concentration is approaches 0, the action should also approach zero, and when the plasma concentration equals a number of times the EC50, the action equals 1. In a formula, this looks as follows:

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