1.2 Risks and Special Precautions  

The main risk of beta blockers is that of provoking breathing difficulties as a result fo their blocking effect on beta receptors in the lungs. Cardioselective beta blockers, which act principally on the heart, are thought to be less likely than non-cardioselective ones to cause such problems. But all beta blockers are prescribed with caution for people who have asthma, bronchitis, or other forms of respiratory disease.

Beta blockers are not commonly prescribed for people who have poor circulation in the limbs because they reduce the flow of blood and may aggravate such conditions. They may be given, very cautiously, to people who are subject to heart failure because they may further reduce the force of the heart beat. Diabetics who need to take beta blockers should be aware that they may notice a change in the warning signs of low blood sugar; in particular, they may find that symptoms, such as palpitations and tremor are suppressed.

Beta blockers should not be stopped suddenly after prolonged use; this may provoke a sudden and severe recurrence of symptoms of the original disorder, even a heart attack. The blood pressure may also rise markedly. When treatment with beta blockers needs to be stopped, it should be withdrawn gradually under medical supervision.

2.Vasodilators                                                                                     

The following information is an excerpt from page 84 of "Canadian Pharmacists Association Guide to Drugs in Canada", Lalitha Raman-Wilms (Editor-In-Chief). Toronto, Ontario: Dorling Kindersley Limited, 2004.

2.1 Common Drugs

2.2 Risks and Special Precautions
The major risk is that blood pressure may fall too low. Therefore vasodilator drugs are prescribed with caution for people with unstable blood pressure. It is also advisable to sit or lie down after taking the first dose of a vasodilator drug.

Loop diuretics:
- Bumetanide
- Furosemide

Potassium-sparing diuretics:
- Amiloride
- Spironolactone
- Triamterene

Thiazides:
- Chlortalidone
- Hydrochlorothiazide
- Indapamide
- Metolazone

Others:
- Ethacrynic acid

3.2 Risks and Special Precautions
Diuretics can cause blood chemical imbalances, of which a fall in potassium levels (hypokalemia) is the most common. Hypokalemia can cause confusion, weakness, and trigger abnormal heart rhythms (especially in people taking digitalis drugs). Potassium supplements or a potassium-sparing diuretic usually corrects the imbalance. A diet that is rich in potassium (containing plenty of fresh fruit and vegetables) may be helpful.

Some diuretics may raise blood levels of uric acid, increasing the risk of gout. They may also raise blood sugar levels, causing some problems for diabetics.