Verapamil and simvastatin: higher statin exposure and muscle symptoms

The NHS describes verapamil as a calcium channel blocker used to treat irregular heart rhythms and high blood pressure, and to prevent chest pain caused by angina. It relaxes and widens blood vessels and slows the heart rate. The NHS also notes that a specialist can prescribe it for cluster headaches.

Simvastatin is a statin. The NHS describes it as a medicine used to treat high cholesterol and prevent heart attacks and strokes, available on prescription, usually as tablets or a liquid that you swallow. The NHS says most adults can take it.

The NHS lists angina and high blood pressure among the uses of verapamil and high cholesterol and cardiovascular disease among the uses of simvastatin, so the same person may be prescribed both. The question is whether the doses are chosen with the interaction in mind.

In the BNF interaction list for verapamil, the simvastatin entry states that verapamil moderately increases the exposure to simvastatin. The manufacturer advice is to monitor and adjust the dose. The severity is marked severe and the evidence is study evidence.

The word moderately in the entry describes the size of the rise in exposure, while the severity label reflects the potential consequences if the exposure rises too far. Both appear because the BNF separates how large an effect is from how much it could matter clinically.

The simvastatin interaction list repeats the picture from the statin side. Diltiazem moderately increases exposure with advice to monitor and adjust the dose, amlodipine causes a small increase with advice to adjust the simvastatin dose, and clarithromycin and erythromycin are among the antibiotics for which the advice is to avoid. The NHS diltiazem page adds a specific point, listing more than 20mg a day of simvastatin among the medicines to tell your doctor about.

The NHS simvastatin page lists inflammation and damage to the muscles, called muscle toxicity, among the possible serious side effects, with symptoms such as muscle cramps, pain and weakness. It says to call NHS 111 if you are taking simvastatin and think you might be having serious side effects.

The NHS atorvastatin page, which describes the same type of problem for another statin, adds that you may also have a high temperature and red or brown pee. Those extra features are described on the atorvastatin page, not the simvastatin one, but they illustrate why unexplained dark urine with muscle pain on any statin should be taken seriously.

This site has separate guides to statin side effects and to statin-induced myopathy for readers who want the topic in more depth.

• New or unexplained muscle cramps, pain or weakness.

• Dark red or brown urine with muscle symptoms.

• Feeling generally unwell with a high temperature alongside muscle pain.

• Any of the above soon after a new medicine was added.

If you are prescribed verapamil while taking simvastatin, or the reverse, ask whether the simvastatin dose has been considered. A pharmacist can check the combination at the point of dispensing. The prescriber may keep the dose, lower it or choose a different statin, depending on your situation.

Do not stop either medicine on your own. The NHS says that if you stop taking statins your cholesterol levels may go up again, and that you should keep taking simvastatin unless your doctor tells you to stop.

Grapefruit is a separate point. The NHS verapamil page advises not to eat grapefruit or drink grapefruit juice, and the NHS simvastatin page advises avoiding grapefruit juice. The BNF also lists grapefruit juice as increasing simvastatin exposure with advice to avoid.

In the NHS the GP practice usually manages both medicines, and community pharmacists review new prescriptions. Cardiology clinics may start verapamil, and the GP may not see the letter at once, so telling the pharmacist yourself is useful. Private cardiologists and GPs use the same BNF, so the medicine list is what carries the safety check from one service to another.