A 24-year-old patient with a history of bipolar I disorder presents to the clinic and reports excessive fatigue over the past 2 months.

A 24-year-old patient with a history of bipolar I disorder presents to the clinic and reports excessive fatigue over the past 2 months. The patient also has an increased need for sleep, difficulty concentrating, and constipation. The patient has been taking lithium (Lithobid) 600 mg twice daily for > 2 years with achievement of euthymia at this dose for > 1 year. The patient tried many other agents for this disorder without a good response. One week ago, this patient had the following laboratory test results: lithium (Lithobid) level of 0.7 mEq/L, TSH of 8.5 mU/L, free T4 of 0.2 ng/dL, and a normal CMP. The patient’s physical examination is unremarkable. What is the most appropriate treatment for this patient’s condition? Collaborating regarding levothyroxine (Synthroid) prescribing Decreasing lithium (Lithobid) dosing to 300 mg twice daily Discontinuing lithium (Lithobid) therapy permanently Immediately starting fluoxetine (Prozac) 20 mg once daily