An elderly patient taking enalapril, thioridazine, hydrochlorothiazide, and glyburide presents with buccolingual movements and dry mouth. Which drug is most likely contributing to these symptoms?

• A. Hydrochlorothiazide
• B. Glyburide
• C. Enalapril
• D. Thioridazine

Answer: (D)

Movements of the lips and tongue with dry mouth point to tardive dyskinesia, an involuntary movement disorder that arises after prolonged dopamine D2 receptor blockade in the nigrostriatal pathway. Thioridazine is a low-potency typical antipsychotic with strong dopamine antagonism and notable anticholinergic effects, which together raise the risk of tardive dyskinesia and cause dry mouth. The other medications listed (an ACE inhibitor, a thiazide diuretic, and a sulfonylurea) do not typically produce tardive dyskinesia or significant anticholinergic-induced dry mouth.