Mrs. Oza, age 69, has hypertension and has one functioning kidney. She loves chocolates and enjoys an alcoholic beverage twice a week. Her hobby is gardening and she goes for long walks despite having arthritis. Which one of the following pieces of information is likely to have the greatest significance if she is prescribed vancomycin?

A. She enjoys an alcoholic beverage twice a week: While alcohol can affect kidney function, occasional moderate intake might not be a major concern for vancomycin. B. She remains outdoors for long periods of time: Sun exposure is not a major concern for vancomycin. C. She only has one functioning kidney: This is the most significant factor. Vancomycin is primarily excreted by the kidneys. With only one functioning kidney, there's an increased risk of drug accumulation and potential toxicity if the dose is not adjusted for renal function. D. She has hypertension: Hypertension itself might not significantly affect vancomycin use, although some medications for hypertension can interact with other drugs.