Simvastatin is a great drug, one I happen to take. But new restrictions on its use are going to pluck it right off of doctors' prescription pads. It's not the recommendation against using the highest dose (80 mg) that's going to deliver the death blow; it's the restrictions on its use with other common drugs.
The FDA's new warnings on simvastatin restrict its use with many other common drugs, including a couple of commonly used antibiotics such as erythromycin. That's not too difficult---people only take antibiotics for short periods of time. But its use is also limited with some popular heart medications, and since simvastatin is often used in patients with heart disease, this will be a problem. For example, amlodipine, a popular blood pressure medication marketed as Norvasc, can raise levels of simvastatin. New recommendations cap simvastatin at 20 mg for patients on amlodipine.
None of these individual recommendations are that difficult to follow, but given our wide range of choices for statins, physicians will have fewer reasons to deal with the hassle. Why prescribe 40 mg of simvastatin when 40 mg of pravastatin may do just as well (and doesn't carry similar warnings)? If you suspect your patient is going to eventually need a high dose, why not just bite the bullet and prescribe a branded statin such as atorvastatin (Lipitor) or rosuvastatin (Crestor)? They are both more potent, and atorvastatin will soon lose its patent.
I can easily see physicians restricting simvastatin to patients with mildly elevated cholesterol and those without too many other medical problems requiring drugs that may interact unfavorably.
Simva, I still like you, but your market share is about to tank.