Question

An antihistamine is a drug that inhibits the physiological effects of histamine. Their mechanism of action involves the competitive inhibition of histamine receptors.

a. Define what is meant by a competitive antagonist.

b. Discuss the physiological effects of antihistamines. Consider the anticholinergic and sedative effects as well as the effects on skin and the cardiovascular system.

c. Explain the advantage of using peripherally acting antihistamines.

Answer 1

a) competitive antagonist define as it binds to the same site as the agonist but does not activate it , thus blocks the agonist action. A non competitive antagonist binds to an non agonist site on the receptor to prevent activation of the receptor.

b) antihistamine suppresses histamine induced wheal response ( swelling) and flare response ( vasodilation) by blocking the binding of histamine to it's receptorsor reducing histamine receptor activity on nerves, vascular smooth muscles, glandular cells, endothelium and mast cells.

Antihistamine block the effect of a substance is called histamine in your body.Histamine normally released when your body detect something harmful such as an infection.

The effect of anticholinergic are included, dry mouth constipation , urinary retention, bowel obstruction, dilated pupils, blurred vision, increased heart rate, and decreased sweating

M2 receptors are present in the heart are responsible for slowing the heart rate ,thus blocking this receptors may lead to tachycardia . This cause imay lead to increases the risk of cardiovascular comorbidities.

The side effects of sedation are , drowsiness, feeling of heaviness or sluggishness,loss of memory, slow reflexes,low blood pressure, headache , feeling sick.

c) The advantages are ;

* It helps to reduce watery eyes,

* Helps to reduce itchy eyes or thorat or nose,

* It helps to reduce running nose and sneezing.

* Decongestants help to relieve stuffy nose

* Helps to relieve ear congestion symptoms.