Professional and Linguistic Assessments Board (PLAB) Practice Exam

When should lithium levels be monitored after administration?

1. 6 hours after last dose

2. 12 hours after last dose

3. 24 hours after last dose

4. Immediately after last dose

The correct answer is: 12 hours after last dose

Monitoring lithium levels is crucial for ensuring patient safety and effective treatment, especially since lithium has a narrow therapeutic range. The appropriate time to measure lithium levels is typically around 12 hours after the last dose. This timing provides a reliable estimate of the peak serum lithium concentration, which is important for assessing whether the dosage is within the therapeutic range or if adjustments need to be made. If levels are checked too soon, such as immediately after administration, the serum concentration may not accurately reflect the drug level in the system, leading to potential misinterpretations. Similarly, waiting too long, like 24 hours, could mean missing a chance to make any necessary dosage adjustments in a timely manner, especially since lithium can accumulate in the body, particularly in patients with renal impairment or those on other medications interacting with lithium metabolism. Therefore, monitoring at the 12-hour mark strikes the right balance for effective dosage management and patient safety.