The most appropriate treatment for this patient is moderate-intensity statin therapy, such as with rosuvastatin. This patient has peripheral arterial disease, a form of clinical atherosclerotic cardiovascular disease (ASCVD), and therefore meets the criteria for one of four patient groups that have been shown to benefit from the treatment of hyperlipidemia with statin therapy. Patients with clinical ASCVD benefit most from high-intensity statin therapy; however, for those with risk factors for statin-associated adverse effects, moderate-intensity therapy is recommended. This patient is best treated with a moderate-intensity statin because he has three such risk factors: age older than 75 years, chronic kidney disease, and use of a medication known to interact with statins (diltiazem).

The use of high-intensity rosuvastatin in this patient has significant potential to cause adverse effects, including myopathy and liver dysfunction. In this patient, the risks associated with high-dose statin therapy outweigh the potential benefits, especially since moderate-intensity statin therapy can reduce the LDL cholesterol level 30% to 49% and provide secondary prevention of cardiovascular events.

Niacin monotherapy has not been shown to reduce the incidence of cardiovascular events and is not considered first-line therapy for the prevention of ASCVD. Niacin and other nonstatin drugs are only recommended for patients who have severe hypertriglyceridemia, do not respond to statin therapy, or have a history of statin intolerance.

Providing no additional treatment in this patient with ASCVD would be inappropriate. Current American College of Cardiology/American Heart Association guidelines recommend statin therapy for all patients with clinical ASCVD, regardless of LDL cholesterol levels, to reduce the risk of cardiovascular events.