ADRENERGIC BLOCKERS

Adrenergic receptor blockers may be considered in two groups:

1. Drugs blocking the ą adrenergic receptor
2. Drugs blocking theβ Adrenergic receptor
   These drugs prevent the response of effectors organs to adrenaline, noradrenaline and other
   sympathomimetic amines whether released in the body or injected. Circulating catecholamines
   are antagonized more readily than are the effects of sympathetic nerve stimulation. The drugs
   act by competing with the catechoamines for α or β receptors on the effectors organs. They
   don’t alter the production or release of the substances.
   α- Adrenergic blockers
   Alpha adrenergic receptor antagonists may be reversible or irreversible. Reversible antagonists
   dissociate from the receptors e.g. phentolamine, tolazoline, prazosin,yohimbine, etc. Irreversible
   antagonists tightly bind to the receptor so that their effects may persist long after the drug has
   been cleared from the plasma e.g. phenoxybenzamine
   Pharmacologic Effects:
   Alpha receptor antagonist drugs lower peripheral vascular resistance and blood pressure.
   Hence, postural hypotension and reflex tachycardia are common during the use of these drugs.
   Other minor effects include miosis, nasal stuffiness, etc.
   Prazosin
   This is an effective drug for the management of hypertension. It has high affinity for alpha1
   receptor and relatively low affinity for the alpha2 receptor. Prazosin leads to relaxation of both
   arterial and venous smooth muscles due to the blockage of alpha1 receptors. Thus, it lowers
   blood pressure, reduces venous return and cardiac output. It also reduces the tone of internal
   sphincter of urinary bladder.
   Indications:

• Essential hypertension
• Raynaud’s syndrome
  Benign prostatic hyperplasia
  β – ADRENERGIC BLOCKING DRUGS
  The β – adrenergic receptor blocking drugs in use may be classified by their selectivity for
  receptors in different tissues.

• Drugs blocking all the β receptor effects of adrenaline (non-selective beta blockers) e.g.
• propanalol, pinadolol, timolol etc

Drugs blocking mainly the β1 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 β 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.

Cardiovascular system

• Bradycardia
• Reduces force of contraction
• Reduces blood pressure

1. Respiratory system

• Bronchoconstriction

1. Metabolic system

• Hypoglycemia

1. Central nervous system

• Anti-anxiety action

1. Eye

• Decrease the rate of Aqueous humor production

1. Kidneys:

• 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