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ANTI-HYPERTENSIVE DRUGS

Contents 1 DIURETICS 1.1 Loop Diuretics 1.2 Thiazide Diuretics 1.3 Potassium Sparing Diuretics 2 BETA BLOCKERS 3 CALCIUM ANTAGONISTS 4 ACE INHIBITORS 5 ANGIOTENSIN II ANTAGONISTS 6 ALPHA BLOCKERS 7 VASODILATORS 7.1 Centrally Acting 7.2 Direct Acting 8 Comments

DIURETICS

There are three main types of diuretic used in the treatment of Hypertension.

Diuretics all reduce blood pressure by reducing the volume of the blood. Because they increase the amount of water lost in urine they should be taken early in the day, so that their effects don’t interfere with sleep.

Diuretics are cheap and effective, and are usually the first line treatment for hypertension and cardiac failure, especially in the elderly.

Side effects include Hypokalaemia, Uraemia and Dehydration.

Loop Diuretics

These act on the ascending limb of the Loop of Henle, and inhibit the re-absorption of water into the blood. Examples include Furosemide and Bumetanide.

Thiazide Diuretics

These inhibit sodium re-absorption in the distal convoluted tubule. Examples include Bendroflumethiazide and Metolazone

Potassium Sparing Diuretics

These drugs cause retention of Potassium, and, because they are generally weak diuretics, they are usually prescribed alongside others. Examples include Amiloride and Triamterene. Amiloride is often prescribed as a combination with Furosemide, in the drug Co-Amilofruse.

BETA BLOCKERS

β-adrenoreceptor blocking drugs act by blocking beta-adrenoreceptors in the heart and blood vessels. They slow the heart rate, therefore reduce cardiac output. Some beta blockers also cause vasodilation in the arteries. This reduces the total peripheral resistance.

They are cheap and effective, but adverse effects are common, including asthma, bradycardia, cold fingers and toes, cardia failure and fatigue.

They are particularly used as a first line treatment in patients with Ischaemic Heart Disease.

Examples include Atenolol, Propanolol, Metoprolol, Labetalol and Celiprolol.

CALCIUM ANTAGONISTS

These drugs block the calcium channels in peripheral blood vessels, as well as in the heart itself. This reduces total peripheral resistance. They are relatively efficient but also expensive, and are used particularly in patients with diabetes and ischaemic heart disease. They are also used in patients unable to tolerate beta-blockers.

Some, such as Amlodipine and Nifedipine, act mainly on the peripheral blood vessels, while verapamil and diltiazem act largely on the heart itself.

Side effects include flushing, headache, and bradycardia.

ACE INHIBITORS

These block the actions of Angiotensin Converting Enzyme, and prevent the conversion of angiotensin I to angiotensin II at the AT2 receptor. This results in vasodilation and potassium retention, as well as loss of sodium and water.

They are expensive, and no more effective than other treatments, but are particularly used in patients with diabetes or cardiac failure. Side effects include a cough (very common), renal failure, and angioedema.

Examples include Captopril, Enalapril, Lisinopril, Perindopril and Ramipril.

ANGIOTENSIN II ANTAGONISTS

These are an alternative to ACE inhibitors, and directly antagonise Angiotensin II. They are more expensive but also more effective, and do not have the common ACE Inhibitor side effect of the cough. However, they can cause Renal failure or Oedema.

Examples include Losartan, Valsartan and Irbesartan.

ALPHA BLOCKERS

These drugs antagonise alpha adrenoreceptors in the blood vessels, and cause vasodilation, reducing the total peripheral resistance. Side effects include Oedema and Hypotension, which are both common.

They are more expensive and less effective than other drugs, and are used as a second line treatment.

Examples include Prazosin, Doxazosin and Terazosin.

VASODILATORS

These can be split into two types, both of which ultimately act to reduce total peripheral resistance.

Centrally Acting

These inhibit sympathetic outflow from the brain. They are poorly tolerated and are used as a third line treatment in severe hypertension. They can cause tiredness and depression. Examples include methyldopa and moxonidine.

Direct Acting

These act directly on the blood vessels, but are also poorly tolerated, and are therefore only used in severe hypertension. They can cause oedema. Examples include diazoxide, minoxidil and nitroprusside.

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