ADRENERGIC BLOCKING DRUGS

The b – adrenergic receptor blocking drugs in use may be classified by their selectivity for receptors in different tissues.

1. Drugs blocking all the b receptor effects of adrenaline (non-selective beta blockers) e.g. propanalol, pinadolol, timolol etc
   1. Drugs blocking mainly the b1 effects (those on the heart) with less effect on the bronchi and blood vessels (beta1-selective blockers), e.g. atenolol, practalol acebutalol, etc.

PROPRANOLOL

Propranolol is a non- selective b adrenergic blocker; it has also other actions like membrane stabilization.

Pharmacokinetics

Propranolol is almost completely absorbed following oral administration. How ever, the liver, leaving only 1/3 rd of the dose to reach the systemic circulations, metabolizes most of the administered dose. It is bound to plasma to the extent of 90-95%. It is excreted in the urine.

Pharmacodynamics

The drug has the following main actions.

1. Cardiovascular system
   1. Bradycardia
   2. Reduces force of contraction
   3. Reduces blood pressure
2. Respiratory system
   1. Bronchoconstriction
3. Metabolic system
   1. Hypoglycemia
4. Central nervous system
   1. Anti-anxiety action
5. Eye
   1. Decrease the rate of Aqueous humor production
6. Kidneys:
   1. Decrease renin secretion

Indications

• Cardiac arrhythmias
  • Hypertension
  • Prophylaxis against angina
  • Myocardial infarction
  • Thyrotoxicosis
  • Anxiety states (suppression of the physical manifestations of situational anxiety)
  • Prophylaxis against migraine attacks
  • Glaucoma

Adverse reactions

• GI disturbances like nausea, vomiting
  • Heart failure
  • Heart block
  • Hypotension and severe bradycardia
  • Bronchospasm
  • Allergic reaction
  • Vivid dreams night mare and hallucinations
  • Cold hands
  • Withdrawal symptoms in case of abrupt discontinuation
  • Masking of hypoglycemia in diabetic patients

Contraindications and Precautions:

• Bronchial asthma
  • Diabetes mellitus
  • Heart failure
  • Peripheral vascular disease