Question

Anaphylaxis is a severe allergic reaction that can be life threatening. Symptoms of anaphylaxis include wheezing or shortness of breath, and low blood pressure.

The primary treatment for anaphylaxis is administration of adrenaline (epinephrine) by intramuscular injection.

a) Describe the mechanism of action for adrenaline, and explain how adrenaline relieves the symptoms of anaphylaxis

b) Identify ONE drug that could reduce the effectiveness of adrenaline as a treatment for anaphylaxis, and explain why this would occur.

Answer 1

A) Adrenaline acts on receptors and produces the following effects.

By acting on beta 1 receptors it increases the rate of spontaneous depolarization in SA node thus increasing the heart rate . It shows positive ionotropic and dromotropic effect and increases the cardiac output.

It acts on alpha 1 receptors on blood vessels thus increasing the blood pressure.

Adrenaline rapidly relaxes the bronchial smooth muscles by acting on beta 2 receptors hence relieving the symptoms of shortness of breath and wheezing. It also reduces the secretions and relieves mucosal congestion by vasoconstrictor effect.

B) Guanethidine is a antihypertensive drug which reduces the release of adrenaline so that the blood vessels are relaxed and blood passes through them more easily thus lowering the blood pressure.