Nursing

In the know: Therapy and adverse reactions

Stressed Out Nurses Weekly, August 9, 2010

It is common practice to administer drugs in repeated doses so a steady state can be achieved. A steady state means the amount of drug administered is equal to that of the amount of being metabolized or excreted. Some drugs require careful monitoring of plasma levels due to difficulties in obtaining and maintaining equilibrium. In such cases, blood levels may be drawn to achieve drug ranges within what is referred to as a therapeutic window or index.

The therapeutic window (index) is considered the concentration above which the drug is toxic and below which the drug is ineffective. This therapeutic range is usually small, and increments in between are significant. There is little difference between toxic and therapeutic dosages, so monitoring of blood levels of the drug is critical. The peak level of a drug is the highest therapeutic blood level, and the trough is the lowest blood concentration level. Peak levels are drawn 30 minutes to two hours after the drug is administered, depending upon the route. Trough levels are obtained approximately 30 minutes prior to the next scheduled dose.

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