Plasma Halflife And Steadystate Concentration

The manner in which plasma drug concentration rises or falls when dosing is begun, altered or ceased follows certain simple rules, which provide a means for rational control of drug effect. Central to understanding these is the concept of half-life (t¥.) or half-time. Consider the time course of a drug in the blood after an i.v. bolus injection, i.e. a single dose injected in a period of seconds as distinct from a continuous infusion. Plasma concentration will rise quickly as drug enters the blood to reach a peak; there will then be a sharp drop as the drug distributes round the body (distribution phase), which will be followed by a steady decline as drug is removed from the blood by the liver or kidneys (elimination phase). If the elimination processes are first-order, the time taken for any concentration point in the elimination phase to fall to half its value is always the same; in other words, the t]/2, which is the time taken for the plasma concentration to fall by half, is a constant, as is illustrated in Figure 7.2. Note that from the peak concentration the drug is virtually eliminated from the plasma in 5 t^ periods.

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Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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