Hypothyroidism increases statin toxicity. “I can’t overstate how important it is to check the thyroid-stimulating hormone to see if we’re dealing with something really simple,” Dr. Paauw said, “because trust me, treating hypothyroidism is much easier than treating statin-associated muscle symptoms.”
It has long been known that fibrates increase the risk of statin toxicity. Much less well recognized is that not all fibrates are the same in this regard: The risk is 15 times greater with gemfibrozil than with fenofibrate. The risk is also higher with verapamil or diltiazem than with nifedipine or amlodipine. Other important causes of drug interactions that increase statin toxicity include amiodarone, azole antifungals, protease inhibitors, erythromycin, and clarithromycin, but not azithromycin.
“Simvastatin and lovastatin are probably the worst as far as drug interactions,” Dr. Paauw cautioned. “They’re cheap, they’ve been generic for a long, long time, and a lot of times insurance companies want to move people to them. I try to move patients away from those two, because they are the dirtiest of the statins as far as side effects and drug interactions.”
When a drug interaction simply cannot be avoided, it’s best to have patients take the drugs 12 hours apart so peak levels don’t overlap, he added.