Drug Therapy

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DRUG THERAPY

Blood pressure can be lowered by a large class of drugs. The choice of a drug depends therefore on the associated problems and the life style of the patient.

What makes a doctor choose a particular drug for treating hypertension (HT)?

Situation Possible choice
Diabetes with Hypertension ACE inhibitor
Heart Failure with Hypertension ACE inhibitor and / or Diuretics
Raised Systolic blood pressure Diuretics and / or Calcium Channel Blockers
Following Heart Attack Beta Blockers and / or ACE Inhibitors
Anginal pain on exertion Beta Blockers and / or Calcium Channel Blockers other than nifedipine
Enlarged prostate Alpha Blockers and / or low dose diuretics
Fine tremors of hands, migraine or excessive activity of Thyroid gland (hyperthyroidism) Beta Blockers
Before an operation Beta Blockers
Thinning down of bone due to loss of calcium in elderly people (osteoporosis) Thiazide type of Diuretics
Reduced function of kidneys ACE Inhibitors

In contrast to the above, the following drugs may have an unfavorable effect when used in hypertension.

Situation Possible problem drug
Bronchitis and Bronchial asthma Beta blockers
Disturbances in peripheral blood flow Beta blockers
Diabetes, High blood lipids (cholesterol) Beta blockers, diuretics
Heart Block Beta blockers, Verapamil
Pregnancy, disease of kidney arteries ACE inhibititors
Gout (high blood uric acid) Diuretics
Depression Beta blockers, Centrally acting alpha agonists

Brief notes on different classes of drugs

  1. DiureticsThe kidney filters out about 180 liters of salt and water daily, and then selectively reabsorbs back about 178.5 liters, so that ultimately only 1.5 liters of salt and water, now called urine, is passed out. Diuretics are drugs that reduce the re-absorption of salt, and thus the water. Diuretics initially throw out a lot of salt and water, but soon the body develops tolerance by raising the level of a counter-regulating hormone called Renin, that blocks salt excretion. However, by this time the body has developed a slight imbalance of salts in muscle cells of the arteries. This prevents them from contracting forcefully, thus relaxing them and reducing blood pressure, provided the diuretic usage is maintained. Diuretics in common usage include a class called Thiazides, Furosemide, Spiranolactone, Triamterene, and Amiloride. The last three are usually always used in combination with either of the first two drugs. Diuretics in high dose may increase blood uric acid, blood sugar and blood cholesterol.
  2. Beta Blockers One of the stimulant hormones of the body is called Adrenaline (hormone produced by a gland Adjacent to Ren or kidney). It acts on the various cells at sites called Adrenergic Receptors. There are various types of Receptors, divided into Alpha and Beta types. The beta receptors are present in
  • Lungs (Beta2 Receptors that on stimulation relax air passages)
  • Heart  (Beta1 Receptors that on stimulation make the heart beat stronger and faster)

Atenolol, Metoprolol, Acebutolol reduces the effect of vasoconstrictor drive by blocking the beta receptors through which the vasoconstrictors work thereby, reducing the blood pressure.

Beta Blockers may precipitate bronchial asthma and raise blood sugar.
III. ACE Inhibitors  Renin (see above) is released by the kidneys in response to decreased blood flow or fall in blood pressure. It activates a chemical called Angiotensinogen to Angiotensin I. Angiotensin I is further converted to Angiotensin II by Angiotensinogen converting enzyme. Angiotensin II is a potent blood vessel constricting agent that increases blood pressure. Drugs that prevent the conversion of Angiotensin I to Angiotensin II are called Angiotensinogen Converting Enzyme Inhibitor or ACE inhibitors. They are potent blood pressure reducing agents, and are noted for improving blood flow through the kidneys to protect them from damage as in case of diabetes. They also reduce the enlargement of heart which may be associated with long standing hypertension. Commonly used drugs are Enalapril, Lisinopril, Ramipril.Newer drug Losarton acts by blocking the receptor (AT1) through which angiotensin II exerts its effect. ACE inhibitors do not affect blood lipid or blood sugar levels, but may cause cough. The newer drug Losarton is less likely to cause cough. ACE inhibitors are contraindicated in pregnancy.
  1. Calcium Channel Blockers  The arterial and heart muscles are made to contract under the influence of calcium ions which enters into the heart and arterial muscle through the ionic channels. Calcium Channel Blocker drugs act by blocking the calcium channels thereby preventing the entry of calcium ions, resulting in relaxation and dilatation of the blood vessels.
Nifedipine, Felodipine, Amlodipine, Isradipine, Diltiazem are commonly used drugs. These drugs are generally very safe. However, they may cause swelling in ankles and constipation.
  1. Alpha Blockers  These drugs block Alpha Adrenergic receptors that are predominantly found in arteries, to make them relax and lower blood pressure. In addition, they also relax the muscle coat around the prostate gland in males, and has been found useful in relieving to some extent the urinary obstruction caused by benign enlargement of prostate. Prazosin, Terazosin, Doxazosin are commonly used drugs. These drugs may cause sudden fall of blood pressure while getting up, causing giddiness. This is called Postural Hypotension. The newer drugs in this class are better tolerated.