A patient receiving warfarin for atrial fibrillation experiences worsening of her chronic obstructive pulmonary disease with purulent sputum. You want to start an antibiotic. Her international normalized ratio (INR) has been rock stable at 2.5. Should you adjust the dose of warfarin? Would the answer be different if she was just ill and you were not going to use an antibiotic? Does it depend on the antibiotic? This is a common medicine (warfarin) and a common situation (upper respiratory tract infection), and yet there are no easy real-world answers.
Katz MH. Data for a Common Clinical Dilemma. JAMA Intern Med. 2014;174(3):416. doi:10.1001/jamainternmed.2013.13480