Definition of Peak Level
A drug’s peak level may occur within minutes to several hours of taking or receiving it. Injectable drugs enter the blood circulation rapidly; oral medications (taken by mouth) take longer to reach the blood as they must first go through digestion.
Foods and liquids also consumed affect the rate of digestion and absorption, as do other factors such as the person’s activity level, age, body weight, and any health conditions.
A drug’s peak level establishes the upper limit of the drug’s therapeutic range. For most drugs it is not necessary for the doctor to determine peak level and trough level (lowest concentration) as the drug’s informational literature provides the expected levels. Improvement in the person’s symptoms or condition is clinical evidence that the drug dosage is therapeutically appropriate.
The doctor may more closely monitor blood concentrations for narrow therapeutic index (nti) drugs, for which the peak and trough levels are critical. Because the goal of most medication therapy is to achieve a fairly constant level of the drug in the blood circulation, peak and trough levels are primarily significant at the onset of treatment.
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