The patient who was started on warfarin sodium for the treatment of atrial fibrillation has reached steady state with the current dose. Which instruction is most important to give the patient?

The 71-year-old previously healthy patient is admitted to the hospital for dehydration after 3 days of malaise and productive cough with green sputum. Right lower lobe consolidation is noted on x-ray. Leukocytosis is revealed by a complete blood count. Vitals are notable for a temp of 40.4°C, heart rate of 122 bpm, respiratory rate of 22, and blood pressure of 104/62 mm Hg. Oxygen saturation is 84% on room air, but improves to 100% with 2L 100% FiO2 via nasal cannula. The nurse prepares to administer which medications? Select all that apply.

Which adverse effect of gabapentin is of greatest concern for the 85-year-old patient?