ACE inhibitors are medicines that are used mainly in the treatment of high blood pressure (hypertension) and heart failure. They are also used in some people with diabetes, for some forms of kidney disease, and after a heart attack, to help protect the heart. They have a variety of effects on the body. Their ability to relax blood vessels is one of the most important. The side-effects most commonly associated with ACE inhibitors are usually minor. A common side-effect is a persistent dry cough.
What are ACE inhibitors?
ACE inhibitors are a group (class) of medicines that are used in the treatment of various disorders. Their correct name is angiotensin-converting enzyme inhibitors - which is usually shortened to ACE inhibitors. They include captopril, enalapril, fosinopril, imidapril, lisinopril, moexipril, perindopril, quinapril, ramipril and trandolapril. Each of these medicines also has various different brand names. Some ACE inhibitor medicines are also part of a combined tablet with a calcium-channel blocker medicine or 'water tablet' (diuretic) medicine.
What conditions are ACE inhibitors used to treat?
ACE inhibitors are used to treat a number of different conditions:
- High blood pressure (hypertension) - ACE inhibitors usually work well to lower blood pressure.
- Heart failure - ACE inhibitors reduce the strain on the heart by decreasing the amount of fluid pumped around the body. They also help the heart by relaxing blood vessels. This reduces the amount of force needed to eject blood from the heart.
- Diabetic kidney disease (diabetic nephropathy) - these medicines can help to maintain good kidney function.
- Chronic kidney disease - ACE inhibitors may help to slow the progress of kidney disease.
- After a heart attack (myocardial infarction).
For more information on the conditions see separate leaflets called High Blood Pressure (Hypertension), Heart Failure, Diabetic Kidney Disease, Myocardial Infarction (Heart Attack), and Chronic Kidney Disease.
How do ACE inhibitors work?
ACE inhibitors prevent the body from creating a hormone known as angiotensin II. They do this by blocking (inhibiting) a chemical called angiotensin-converting enzyme. This has a variety of effects but essentially relaxes blood vessels and helps to reduce the amount of water re-absorbed by the kidneys. These actions help to decrease blood pressure, as explained below.
Your body has a number of different ways of maintaining your blood pressure, but there are two main elements. One of the major factors is the resistance of the body's blood vessels. If the blood vessels tighten (constrict), resistance increases. If the blood vessels relax (dilate), the resistance is lower. If you have the same amount of fluid travelling in one vessel, the pressure will be higher when the vessel is constricted than when it is relaxed.
The other major factor influencing blood pressure is how much blood is pumped out of the heart. In a healthy person this depends on your heart rate (pulse) and the amount of blood that enters and leaves the heart's chambers. This is known as cardiac output.
Your blood pressure is the result of combining these two factors. It will be high if your vessels are constricted and there is lots of blood circulating through the heart. It will be lower if your vessels are dilated and there is less blood circulating through the heart. ACE inhibitors work by targeting both of these systems.
Blood is not just made up of red blood cells but also contains a large amount of fluid called plasma. Your kidneys control how much fluid you keep in your blood and how much you lose as urine. By retaining (re-absorbing) water that would otherwise become urine, the kidneys increase the amount of fluid in the blood. This increases blood volume.
In good health you have an intricate system set up to maintain your blood pressure. When your kidneys sense that your blood pressure has dropped, a substance called renin is released into the bloodstream. Renin works on another chemical to form angiotensin I. Then the angiotensin-converting enzyme changes angiotensin I to angiotensin II.
Angiotensin II is the active hormone. It has three main effects:
- Constriction of blood vessels.
- Re-absorption of water by the kidneys.
- Release of the hormone aldosterone which also causes water re-absorption by the kidneys.
Increasing the volume of the blood by adding more water and constricting your blood vessels increases blood pressure.
ACE inhibitors stop angiotensin I from becoming angiotensin II. This reduces the amount of angiotensin II which causes blood vessels to dilate. The amount of water put back into the blood by the kidneys decreases. These actions reduce blood pressure.
- In high blood pressure (hypertension), ACE inhibitors should help to reduce the blood pressure.
- In heart failure, there may be too much circulating fluid in the blood vessels. ACE inhibitors help to reduce this. They appear to have a protective effect on the heart and slow the progression of the heart failure.
There is another group of medicines called angiotensin-II receptor antagonists (for example, candesartan, losartan). These work in a similar way to ACE inhibitors. An angiotensin-II receptor antagonist may be used instead of an ACE inhibitor if you have problems or side-effects with taking an ACE inhibitor (such as a persistent cough).
Which is the best ACE inhibitor?
Clinical trials suggest ACE inhibitors are all about equally effective at treating high blood pressure (hypertension) and heart failure.
- Hypertension - NHS guidelines state that any ACE inhibitor may be prescribed for people with hypertension.
- Heart failure - NHS guidelines recommend enalapril, lisinopril, and ramipril for the treatment of heart failure. These medicines have the most medical evidence to support their use, and doctors generally have more experience in using them. However, other medicines are available for use in heart failure and, in certain cases, your doctor may prescribe an alternative.
- Chronic kidney disease - NHS guidelines recommend enalapril, lisinopril, or ramipril for people with chronic kidney disease. However, clinical trials suggest that no particular ACE inhibitor works better than another for chronic kidney disease.
Can I buy ACE inhibitors?
You cannot buy ACE inhibitors. They are only available from your pharmacist, with a doctor's prescription. These medicines require special monitoring of your kidneys.
How do I take ACE inhibitors?
Your doctor will advise you on how to take your medication, including how often. Generally, you will be started on a low dose to make sure you are coping well and that your blood pressure responds in an appropriate way.
In some people, the first dose can cause a drop in blood pressure immediately. The following is advice for starting ACE inhibitors:
- If you take a 'water tablet' (diuretic), you may be advised not to take it for a day or so before starting an ACE inhibitor.
- After the very first dose, on the first day you start an ACE inhibitor:
- Stay indoors for about four hours, as occasionally some people feel dizzy.
- If you do feel dizzy, sit or lie down and it will usually ease off.
- If you become very dizzy, contact your doctor immediately.
- Thereafter, there is no need to take any special precautions.
Do I need any tests when taking an ACE inhibitor?
A blood test is usually done before starting an ACE inhibitor, and about 1-2 weeks after the first dose. You may also require further blood tests as your dose increases. These tests check on the function of the kidneys. The kidneys are affected in a small number of people who take an ACE inhibitor.
For people with high blood pressure (hypertension), a blood test every year is then usual. If you have heart failure you will need more frequent blood tests - usually every 3-6 months.
A very small number of people may be required to start their treatment with ACE inhibitors in hospital so that careful monitoring can be undertaken.
How quickly do ACE inhibitors work?
These medicines can work very quickly in high blood pressure (hypertension). If you have heart failure it may be weeks or months before you notice an improvement in your symptoms.
What is the usual length of treatment?
Once you have started taking an ACE inhibitor you will generally keep taking it indefinitely, unless you experience an adverse effect.
Who cannot take ACE inhibitors?
A full list of people who should not take ACE inhibitors is included with the leaflet that comes with your medicine. If you are prescribed ACE inhibitors, read this to be sure you are safe to take it. For example, people who should not take ACE inhibitors include:
- Pregnant and breast-feeding women.
- Those with a known sensitivity to ACE inhibitors.
- Those with forms of swelling of the lips, eyes or tongue (angio-oedema).
- People with certain types of kidney disease - for example, renal artery stenosis.
What are the possible side-effects?
A common side-effect associated with an ACE inhibitor is low blood pressure (hypotension). You may have no symptoms of this, or it may make you feel dizzy. If you experience this you should report it to your doctor. Around one in ten people who take an ACE inhibitor have a persistent dry cough. Less common side-effects include swelling of the lips, eyes or tongue (angio-oedema) and a decline in kidney function.
Note: the above is not the full list of side-effects for these medicines. Please see the leaflet that comes with your particular brand for a full list of possible side-effects and cautions.
A number of medicines may interact with ACE inhibitors. In particular, non-steroidal anti-inflammatory drugs (NSAIDs), 'water tablets' (diuretics) and lithium. Your doctor will normally check what other medicines you take and give further advice about this.
So, make sure your doctor knows of any other medicines that you are taking, including ones that you have bought rather than been prescribed.
How to use the Yellow Card Scheme
If you think you have had a side-effect to one of your medicines you can report this on the Yellow Card Scheme. You can do this online at the following web address: www.mhra.gov.uk/yellowcard.
The Yellow Card Scheme is used to make pharmacists, doctors and nurses aware of any new side-effects that medicines or any other healthcare products may have caused. If you wish to report a side-effect, you will need to provide basic information about:
- The side-effect.
- The name of the medicine which you think caused it.
- The person who had the side-effect.
- Your contact details as the reporter of the side-effect.
It is helpful if you have your medication - and/or the leaflet that came with it - with you while you fill out the report.
Dr Tim Kenny
Dr Roger Henderson
Dr Hannah Gronow