Oral Antihypertensive Drugs

High blood pressure

Blood pressure is the force of blood pushing against the wall of the arteries as your heart pumps out blood into the arteries. Its level varies with age, sex, level of physical activity and emotional changes.

Hypertension refers to the sustained elevation of blood pressure above normal range. According to the World Health Organization, “hypertension” is defined as systolic/diastolic pressure persistently higher than 140/90mmHg. Risk factors for hypertension include increasing age, family history, overweight and smoking. Sometimes, high blood pressure may also be caused by certain medications or underlying diseases such as kidney or endocrine diseases.

There is usually no obvious symptom associated with hypertension and many patients may not be aware until they check their blood pressures or when complications develop. Poorly controlled hypertension may lead to severe complications such as stroke, coronary heart disease, aneurysm (a balloon-like bulge in the artery) and kidney function impairment, etc.

Treatment

Treatment modality depends on the level of your blood pressure, and your risk of developing cardiovascular diseases. If there are underlying conditions for your hypertension, your blood pressure will be controlled by removing the cause. Work with your doctor to devise the appropriate treatment plan. In general, lifestyle modification, such as having a healthier diet, exercising more regularly, quit smoking and drinking less alcohol, is good for your blood pressure. However, pharmacological treatment may also be needed, especially when your blood pressure is much higher than normal and your risk of cardiovascular diseases is high.

Antihypertensive Drugs

A variety of blood pressure lowering medicines (antihypertensive drugs) is available in the market. Your doctor will use the most appropriate drug or a combination of drugs after considering their risks and benefits. Good blood pressure control is important for preventing cardiovascular or cerebrovascular events. In most cases, your blood pressure needs to be monitored life-long. Antihypertensive drugs may have some side effects but these can often be resolved by adjusting the dosage or changing the type of drugs. Patients are advised to follow doctor’s instructions in using the drugs and consult their doctors if they have any concerns or queries.

In Hong Kong, antihypertensive drugs can only be obtained from pharmacy with a prescription. They should be used under close supervision by healthcare professionals. Antihypertensive drugs are available in different dosage forms. They include oral (e.g. tablet and capsule) and injectable (e.g. intramuscular and intravenous injection). The most widely used medications for treating hypertension includes:

1. ACE inhibitors

Angiotensin-converting enzyme (ACE) inhibitors reduce blood pressure by relaxing your blood vessels, e.g. enalapril, lisinopril, perindopril.

2.Angiotensin II receptor blockers

Angiotensin II receptor blockers help relax your blood vessels which lower your blood pressure and makes it easier for your heart to pump blood,e.g. losartan, valsartan.

3.Calcium channel blockers

Calcium channel blockers keep calcium from entering the muscle cells of the heart and blood vessels. This widens your arteries and reduces your blood pressure, e.g. diltiazem, nifedipine and amlodipine.

4.Diuretics

Sometimes known as water pills, diuretics work by flushing excess water and salt from the body through urine, e.g. amiloride, frusemide, indapamide.

5.Beta-blockers

Beta-blockers work by making your heart beat more slowly and with less force, thereby reducing blood pressure, e.g. atenolol, metoprolol, propanolol.

6.Alpha-blockers

Alpha-blockers work by relaxing your blood vessels, making it much easier for blood to flow through them, e.g.doxazosin, prazosin.

7.Centrally acting antihypertensive drugs

Centrally acting antihypertensive drugs, like methyldopa and clonidine, act by stimulation of alpha 2 adrenoceptors in the central nervous system which results in a reduction in sympathetic tone and a fall in blood pressure. Methyldopa may be used for the management of hypertension in pregnancy.

8.Vasodilators

Vasodilators reduce blood pressure by dilatation of blood vessels, e.g. hydralazine.

General advice on taking antihypertensive drugs

• Be familiar with the name and dosage of the drugs you are taking. Be cautious about their possible side effects

• Take the drugs regularly as instructed by your doctor in order to have effective control of hypertension. Keep taking the same dosage of drugs even if your conditions improve unless your doctor suggested you to change your antihypertensive regime.

• Do not stop medication without your doctor’s instruction. Take your medicines at the same fixed time every day as far as possible. If you miss a dose, take it as soon as possible unless it is almost time for the next scheduled dose. In that case, skip the missed dose and take the next dose as directed. Do not take double doses

• The drugs should not be taken with alcoholic drinks to avoid dizziness or fainting

• Some types of antihypertensive drugs can cause dizziness or drowsiness, usually when you first start taking your medicine or if your doctor changes your dose. If you do feel light-headed or dizzy, you should not drive or operate machinery and seek your doctor’s advice if the symptom persists.

• Make sure you have sufficient drug stocks for several days. Do not wait till the last minute to refill the prescription