Risk factors for statin-associated myopathy:
(1) hepatic dysfunction
(2) renal dysfunction
(3) hypothyroidism
(4) diabetes mellitus
(5) drug interactions (see below)
(6) > 1 quart of grapefruit juice per day
(7) debilitation
(8) high statin dosage
(9) myotoxin or myotoxic drug
Drugs that may interact with statins to increase the risk for myopathy:
(1) fibrates (fibric acid derivatives), especially gemfibrozil
(2) niacin (nicotinic acid)
(3) cyclosporine
(4) azole antifungals
(5) macrolide antibiotics
(6) protease inhibitors (for HIV infection)
(7) nefazodone
(8) verapamil and diltiazem
(9) amiodarone
(10) warfarin
(11) digoxin
(12) mibefradil (a calcium channel blocker)
Mechanisms:
(1) increased plasma concentration of statins, often due to decreased metabolism by the CYP3A4 system.
(2) predisposition to or pre-existing muscle disease
