ACE Inhibitors

What are ACE inhibitors?

ACE inhibitors are a class (group) of drugs 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, cilazapril, enalapril, fosinopril, imidapril, lisinopril, moexipril, perindopril, quinapril, ramipril and trandolapril. Each of these drugs also has various different brand names. Some ACE inhibitor drugs are also part of a combined tablet with a calcium channel blockers or diuretic (water tablet).

What conditions are ACE inhibitors used to treat?

ACE inhibitors are used to treat a number of different conditions:

• Hypertension – ACE inhibitors are usually effective at lowering 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 nephropathy (diabetic kidney disease) – these drugs can help to maintain good kidney function.
• Chronic kidney disease – ACE inhibitors may help to slow the progress of kidney disease.
• After a myocardial infarction (heart attack).

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 special 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 constrict (tighten), resistance increases. If the blood vessels dilate (relax), 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 (heart) 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 re-absorbing (retaining) 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 (ACE) 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 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 also appear to have some form of protective effect on the heart and may slow the progression of the heart failure.

Drugs in the class of drugs called angiotensin II receptor antagonists work in a similar way to ACE inhibitors. One 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 hypertension and heart failure.

• NHS guidelines suggest enalapril, lisinopril, perindopril, ramipril, or trandolapril for people with hypertension. There is good medical evidence that these ACE inhibitors reduce your long-term likelihood of suffering from a heart attack or stroke.
• NHS guidelines recommend enalapril, lisinopril, and ramipril for the treatment of heart failure. These drugs have the most medical evidence to support their use, and doctors generally have more experience using them. However other drugs are available for use in heart failure and in certain cases your doctor may prescribe an alternative.

Can I buy ACE inhibitors or are they just available on prescription?

These drugs are prescription only as they require special monitoring of your kidneys.

How do I take ACE inhibitors?

A blood test is usually done before starting an ACE inhibitor, and about 7-10 days 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. A blood test every year is then usual.

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.

Your doctor will advise you 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 diuretic ('water tablet'), 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.

How quickly do ACE inhibitors work?

These drugs can work very quickly in hypertension. If you have heart failure it may be weeks or months before you notice an improvement in your symptoms.

How long is treatment needed?

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 information leaflet that comes in the drug packet. 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 breastfeeding women.
• Those with a known sensitivity to ACE inhibitors.
• Those with forms of angio-oedema (swelling of the lips, eyes or tongue).
• People with certain types of kidney disease, for example, renal artery stenosis.

What about side-effects?

The most common side effect associated with an ACE inhibitor is hypotension (low blood pressure). 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 angio-oedema (swelling of the lips, eyes or tongue) and a decline in kidney function.

A number of drugs may interact with ACE inhibitors. In particular, non-steroidal anti-inflammatory drugs (NSAIDs), diuretics (water tablets) and lithium. Your doctor will normally check what other drugs you take and give further advice about this.

For a full list of all the side effects and possible interactions associated with your drug consult the leaflet that comes with your medication.