What is the standard practice for drawing trough levels in therapeutic drug monitoring?

The standard practice for drawing trough levels in therapeutic drug monitoring is to do so before the next scheduled dose. This timing is critical because the trough level represents the lowest concentration of the drug in the patient's bloodstream, ensuring that it is at its most effective level before the next dose is administered. This helps healthcare providers assess whether the patient is within the therapeutic range, thereby allowing for appropriate dosage adjustments if necessary.

Drawing the sample immediately after the last dose would not accurately reflect the drug's effectiveness or potential toxicity, as the levels would still be decreasing and may not represent the trough. Timing the draw at peak concentration would measure the highest level of the drug instead of indicating how well the patient is metabolizing and responding to treatment. Taking samples every three days does not align with the need for precise timing related to the patient’s dosing schedule and would not provide relevant information regarding drug levels at the necessary therapeutic intervals.