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Chapter 4. Dosing to Cure > PK/PD Indices Help Determine Antibiotic Dosage

PK/PD Indices Help Determine Antibiotic Dosage

As a part of the licensing process, the U.S. Food and Drug Administration and the European Medicines Agency approve particular doses for each antibiotic. These doses are usually proposed by the manufacturer with support from laboratory tests, animal studies, and clinical trials. Two general properties are paramount: effectiveness and safety. Because not all toxicity problems can be identified using animal tests and small clinical studies, companies have tended to keep doses low, hoping to minimize toxic side effects. Part of the challenge has been to find doses likely to be effective before expensive clinical trials are carried out.

Efforts to identify effective antimicrobial doses use analyses involving pharmacokinetics and pharmacodynamics, commonly abbreviated as PK/PD. Pharmacokinetics describes drug concentration changes that occur in our bodies during therapy. Drug concentration generally rises quickly after we take a dose, and then it gradually drops (see Figure 4-2). When we take the next dose, the concentration again rises and gradually drops. This behavior is described quantitatively in two ways. One is to measure the maximum drug concentration achieved, commonly abbreviated as Cmax. Another is to draw a graph of concentration versus time and then measure the area under the concentration-time curve (AUC) over a specified time, such as 24 hours. This area is abbreviated as AUC24. Both Cmax and AUC24 change when the dose is changed and both serve as a way to relate dose to drug concentration in the patient.


  

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