Drug cabinet: ACE inhibitors

ACE inhibitors

ACE inhibitors are commonly used to treat heart failure and high blood pressure and are often prescribed to people following a heart attack. Doireann Maddock puts some common questions to Dr Terry McCormack.

What are ACE inhibitors and how do they work?

ACE inhibitors can reduce the activity of an enzyme called angiotensin-converting enzyme, or ACE for short. The enzyme is responsible for hormones that help control your blood pressure. It has a powerful narrowing effect on your blood vessels, which increases your blood pressure. ACE inhibitors inhibit or limit this enzyme, making your blood vessels relax and widen. This, in turn, lowers your blood pressure and improves blood flow to your heart muscle. A quarter of the blood pumped out in each heartbeat flows through the kidneys, so if your heart becomes less efficient, your kidneys also suffer. Therefore, ACE inhibitors improve kidney, as well as heart, function.

Why have I been prescribed an ACE inhibitor?

They are commonly prescribed if you’ve had a heart attack or if you have heart failure. They are also used to treat high blood pressure (hypertension).

There are various types of ACE inhibitor. What are the main differences?

ACE inhibitors make your blood vessels relax and widen. This, in turn, lowers your blood pressure

The main difference between the ACE inhibitors is how long their effects last; some are short-acting and others are long-acting. If the duration is long, you need to take them less often during the day. For example, perindopril is long-acting and only needs to be taken once a day, whereas captopril is short-acting and needs to be taken three times a day. Each drug comes in a range of strengths and we usually start on a low-strength drug and work our way up to the higher strengths as people get used to them.

What are the possible side effects?

About one in ten people experience a dry, irritating cough. If you have any side effects, let your GP know as soon as possible. In the event that your GP stops prescribing the ACE inhibitor and gives you alternative medication, it’s worth remembering that it can take eight to 12 weeks for the cough to disappear.

Fewer than one in 100 people have a problem with the blood supply to their kidneys (renal stenosis). There are no specific symptoms in renal stenosis so you should have a routine blood test to check your kidney function one to two weeks after starting the medication. Where early checks indicate a problem such as renal stenosis, patients will be advised to change the medication and there won’t be any lasting damage.

Dr Terry McCormackDr Terry McCormack

Dr Terry McCormack is a principal in general practice in Whitby, North Yorkshire. His cardiovascular interests include managing high blood pressure, lipids and heart failure. He was a member of the International Steering Committee for the Hypertension in the Very Elderly Trial (HYVET) and is Secretary of the British Hypertension Society.

About 1 per cent of people develop an allergic reaction, which causes swollen lips and breathing difficulties. This can develop any time from two weeks to two years after starting to take ACE inhibitors. If this happens, your GP will stop your ACE inhibitor and may prescribe an angiotensin receptor blocker (ARB) instead.

If you develop diarrhoea or vomiting due to a stomach bug, or any dehydrating illness, it’s important to consult your GP as they may advise you to temporarily stop taking your ACE inhibitor and restart when you feel better. The reason for this is that ACE inhibitors can increase the amount of potassium salts in your blood, particularly if you are dehydrated.

Are there any foods I should avoid?

Salt reduces the effects of ACE inhibitors, so you should avoid high salt foods and adding extra salt

Salt raises blood pressure and worsens heart failure. It also specifically reduces the effects of ACE inhibitors. You can’t avoid salt completely because it’s in lots of the food we already eat, to some degree. However, you should avoid high salt foods and avoid adding extra salt.

Are there any medications that may be prescribed with ACE inhibitors?

ACE inhibitors are often prescribed with other medications and it’s something we call a synergistic effect. They work well with diuretics, which are drugs that make you pass water, and with calcium channel blockers. With diuretics, ACE inhibitors have an enhanced effect at lowering blood pressure and controlling heart failure. They also help to minimise one of the side effects of calcium channel blockers, which is swollen ankles. If you are prescribed an ACE inhibitor and a diuretic, it’s important to be aware that the combination of the two may cause a sudden drop in blood pressure. So if you feel dizzy or unwell, tell your GP as soon as possible.

Why doesn’t my doctor want to prescribe me an ACE inhibitor?

People younger than 55 tend to benefit more from ACE inhibitors. This is because young people with high blood pressure often have a high level of renin in their blood (meaning they are renin sensitive). Renin is an enzyme that is released by the kidneys and plays a role in blood pressure regulation. If too much of it is released, it can raise the levels of the ACE enzyme, which we know can cause a rise in blood pressure.

They work well with diuretics, which are drugs that make you pass water, and with calcium channel blockers

Guidelines from NICE (National Institute for Health and Care Excellence) and the British Hypertension Society recommend ACE inhibitors as the most suitable drug for people under the age of 55. People over 55 are less responsive to renin so, for high blood pressure alone, ACE inhibitors would not be the first drug prescribed.

Black people are also not so sensitive to renin so the NICE guidelines recommend that they are not prescribed ACE inhibitors as a first drug of choice.

It’s a different matter with heart failure because the condition is more common in older people. So in terms of using ACE inhibitors to treat heart failure, the older you are, the more you benefit. However, the drug does have the potential to help people of all ages.

Is there anyone who should never be prescribed ACE inhibitors?

The angiotensin–renin system is involved in growth, therefore we are not sure if it’s wise for pregnant women to use ACE inhibitors. It is difficult to carry out research to test this theory, so the best advice is not to use them if you are pregnant or trying for a baby.

Are there any possible alternatives?

Angiotensin receptor blockers (ARBs) have a similar effect in lowering blood pressure and helping heart failure. They do not affect enzymes like ACE inhibitors do. Instead, they block a receptor that is stimulated by the hormones. Studies have shown that ARBs have the same beneficial effects as ACE inhibitors, but without causing patients to develop a cough.

Because there are more studies showing the benefits of ACE inhibitors in heart failure, they are usually used first. ARBs used to be more expensive than ACE inhibitors but now that many are the same price, ARBs are becoming more popular as the first drug to try for controlling blood pressure.

As with ACE inhibitors, ARBs should not be prescribed if you are pregnant or trying to get pregnant.

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