Which client should the licensed practical nurse follow up on first?

The situation involving the client taking lithium who reports nausea and vomiting should be prioritized for follow-up due to the potential risks associated with lithium therapy. Lithium is a mood stabilizer commonly used in the treatment of bipolar disorder, but it has a narrow therapeutic window, meaning that the difference between therapeutic and toxic doses is small. Nausea and vomiting can be indicative of lithium toxicity or significant side effects, especially if the client has not maintained adequate hydration or if their serum lithium levels are elevated.

In this context, monitoring lithium levels is crucial because any fluctuations can lead to serious consequences, including neurological or renal impairment. Therefore, this client's symptoms warrant immediate attention to ensure they are not experiencing toxicity that could lead to life-threatening complications.

While the other clients also present important issues, such as medication adherence and side effects, they do not carry the same immediate risk of severe complications that would require urgent intervention. Focusing on the client with symptoms related to lithium is the best course of action for ensuring patient safety and effective management of their health.