A 38-Year-Old Woman with a History of Bipolar I Disorder

A 38-year-old woman with a history of bipolar I disorder comes to the office due to low energy.  The patient felt well until 4 months ago when she noticed she was reacting slowly at work and was reluctant to meet with friends on weekends due to fatigue.  She is afraid she is becoming depressed again.  The patient says, "I am so discouraged.  I really felt so much better on my medication, and now I feel like I'm slipping."  She has a history of multiple hospitalizations for manic and depressive episodes since late adolescence.  She attempted suicide at age 20 by taking an overdose of aspirin.  The patient was previously treated with valproate and olanzapine and has been taking lithium for the past year.  Her other medical issues include hypertension and allergic rhinitis, for which she takes hydrochlorothiazide and loratadine, respectively.  On review of systems, the patient reports fatigue and difficulty concentrating over the past few weeks.  Mental status examination shows a tired appearance and sad affect.  She has no suicidal ideation.  Physical examination shows no abnormalities.  The patient's blood lithium level is 0.9 mEq/L (range: 0.6-1.2 mmol/L) .  Other laboratory results are as follows: Which of the following is the best next step in management of this patient?

A) Continue lithium and add an antidepressant
B) Continue lithium and add levothyroxine
C) Continue lithium and discontinue hydrochlorothiazide
D) Decrease lithium dose and repeat lithium blood level in 3 days
E) Discontinue lithium and treat with another mood stabilizer