A nurse is caring for a client who has heart failure and a prescription for digoxin. Which of the following statements by the client indicates an adverse effect of the medication?

A. A backache is not a common adverse effect of digoxin. B. Being able to walk a mile a day is an improvement in physical activity and not an indication of digoxin toxicity. C. Increased urination could be due to improved cardiac output and is not necessarily an adverse effect of digoxin. D. Nausea and loss of appetite are classic symptoms of digoxin toxicity, which requires immediate attention.