This patient is now requesting sertraline as he believes it helped his depression in the past. However, antidepressant monotherapy is not indicated for patients with bipolar disorder due to the increased risk of inducing mania. The most appropriate next step is to educate the patient regarding the risks of antidepressants in his condition and explain why sertraline is not a good choice. This can be followed by a discussion of other treatment options for bipolar depression such as alternative mood stabilizers to lithium (eg, lamotrigine, valproate) and second-generation antipsychotics (eg, quetiapine, lurasidone).