A 48-year-old woman with seizure disorder previously stabili…

A 48-year-old woman with seizure disorder previously stabilized on carbamazepine was prescribed alprazolam for anxiety. After one month of increased dosage adjustments, her alprazolam serum levels stabilized at 15 ng/mL and her anxiety symptoms were controlled. Due to unforeseen circumstances, she was forced to switch doctors and her new doctor advised her to try a new antiseizure medication. Within a week of switching to the new drug, she began feeling very sluggish with signs of sedation. Serum levels of the alprazolam were now nearly 40 ng/mL A pharmacist suggested that she talk to her doctor immediately to either reduce the alprazolam dosage or switch to a new antianxiety drug. Explain the reasoning behind the pharmacist’s advice and how the dosage should be changed.   Which of the following could best explain these observations?