Simvastatin and Grapefruit
Grapefruit products are known to interact with several medications, and one of which is simvastatin. Taking this cholesterol-lowering statin together with grapefruit (including grapefruit juice and grapefruit-containing supplements) can lead to serious drug interactions. Healthcare providers caution patient on simvastatin therapy against taking grapefruit products.
How Grapefruit Affects Simvastatin Metabolism
Simvastatin, and other cholesterol-lowering statins, are metabolized in the body through an enzyme system called cytochrome P450 system. This enzyme system is chiefly responsible for the first-pass metabolism of simvastatin which transforms it into more usable chemicals in the body. Grapefruit contains bergamottin, a compound that can interact with cytochrome P450. When grapefruit is taken together with simvastatin, its compounds interfere with the enzyme system resulting in altered drug metabolism and eventually accumulation of the drug in the body.
This can lead into potentially life-threatening adverse effects and complications, such as liver impairment and, rarely, rhabdomyolysis (a severe muscle problem that results in kidney damage).
What Studies Say
Clinical studies indicate that grapefruit juice can significantly increase simvastatin levels in the blood. In one clinically study, a 12-fold increase has been noted when simvastatin was taken together with a large amount of grapefruit juice. The study further suggests that taking one glass of grapefruit juice everyday can significantly increase the simvastatin levels in the blood by about four-fold. A four-fold increase means that if you take 40 mg of this drug the effect is equal to 160 mg. This certainly puts you at increased risk of experience side effects.
Studies have shown that a small amount of grapefruit can increase the cholesterol-lowering effect of the drug as much as the adverse effects. However, it is difficult to predict the increase in the cholesterol-reducing effect of simvastatin because of the many variables that can potentially interact with the drug metabolism and mechanism of action.
Since clinical studies show that even a glass of grapefruit juice, taken each day, can considerably increase simvastatin levels in the blood, it is best to avoid grapefruit products throughout the treatment.
Healthcare providers recommend that patients on statin therapy, including simvastatin, atorvastatin (Lipitor) and lovastatin, avoid taking any grapefruit product, such as grapefruit, grapefruit juice and grapefruit supplement. Instead of grapefruit juice, patients can consume common orange juice and other fruit juices which are thought to be safe with statins. Alternatively, your healthcare provider may recommend a statin which is not known to have adverse reactions with grapefruit juice. These include: Crestor, Livalo and Pravastatin (Pravachol).
If you think you cannot stop taking grapefruit products, you should consult your healthcare provider for a possible dose adjustment or a change in medication. You and your healthcare provider must come up with a shared decision so that you can continue enjoying grapefruit while avoiding potential adverse effects.