When should blood samples for trough drug levels be collected?

Blood samples for trough drug levels should be collected immediately before the next dose is given to ensure that the measurement reflects the lowest concentration of the drug in the bloodstream. Trough levels are particularly important for drugs that have a narrow therapeutic range, as they help determine whether the drug concentration is adequately controlled before the next administration. Collecting the sample at this time allows healthcare professionals to assess if the previous dose was sufficient or if adjustments are needed based on the drug’s pharmacokinetics and the patient’s individual response.

Gathering samples at other times, such as after peak levels or shortly after the last dose, would not accurately represent the drug's lowest concentration and could lead to misinterpretation of the drug's effectiveness or safety in the given patient population. Thus, obtaining the sample just prior to the next dose is critical for appropriate monitoring and management of therapy.