A 76-year-old patient with chronic kidney disease and low se…

A 76-year-old patient with chronic kidney disease and low serum albumin is admitted for weakness and confusion. The patient takes eight prescription medications and recently started an herbal supplement recommended by a friend. Three days ago, an antibiotic was added. The nurse discovers that one medication has a narrow therapeutic index and is highly protein-bound. The patient’s serum concentration of that medication is elevated. Which explanation best accounts for the patient’s condition?