Treatment of Bronchial Asthma is done by ß agonist ( selective ß2 agonist such as Salbutamol ). It acts by relaxing the human airway tract. ß2 agonist stimulates the ß2 adrenergic receptor present in Bronchus and dialates it.
Propanolol is a non-selective beta blocker opposite to the medication of broncial asthma. It is mainly used in patients to treat hypertension.
Propanolol can block both the ß1 and ß2 receptors.
Propanolol → ß1 + ß2 receptor antagonist → Blocks ß2 receptor in Bronchial smoot muscle → Broncospasm
So, Propanolol is contradicted in patients of Bronchial Asthma and COPD ( Chronic Obstructive Pulmonary Disorder )
That explain why Propranolol Should be avoided in bronchial asthma.
EXPLAIN WHY ADRENALINE IS USED IN ANAPHYLACTIC SHOCK