The psychiatric-mental health nurse practitioner has just diagnosed a 23-year-old man with bipolar disorder. He has had one manic episode with suicidal ideation and no depressive episodes to date. Which of the following is the most appropriate at this time?

Choice A reason: Divalproex is an effective mood stabilizer, especially for rapid cycling or mixed episodes, but lithium is generally first-line for classic mania with suicidal ideation. Choice B reason: Lamotrigine is more effective for bipolar depression than mania and is not ideal for initial treatment of a first manic episode. Choice C reason: Carbamazepine is an alternative mood stabilizer but has more drug interactions and is not the preferred first-line for initial mania. Choice D reason: Lithium is considered first-line treatment for acute mania in bipolar disorder and provides prophylactic benefits; it is particularly indicated for patients with suicidal ideation.