Pharmacology Case File 1

A 12 year-old girl presents to your office with a sore throat and fever. You diagnose her with pharyngitis caused by Group A bete-hemolytic stretococcus. She is given an IM injection of penicillin. Approximately 5 minutes later, she is found to be in respiratory distress and audibly wheezing. Her skin is mottled and coo, she is tachycardic (rapid heart rate), and her blood pressure has fallen to 70/20 mmHg. You immediately diagnose her as having an anaphylactic reaction to the Penicillin and the you give a subcutaneous injection of Epinephrine.
Questions:
1. What effect will epinephrine have on this patient's vascular system?
2. Which adrenoreceptor primarily mediates the vascular response?
3. What effect will Epinephrine have on her respiratory system?
4. Which adrenoceptor primarily mediates the respiratory system response?

Note: The answers will be coming soon....


Lesson Review: 


Clinical correlation: 

Anaphylaxis is an acute, immune mediated response to an allergen characterized by bronchospasm, wheezing, tachycardia, and hypotension. Epinephrine is the drung of choice used to treat this condition because it appears, through the activation of alpha- and beta-adrenoceptors, to counteract the pathophysiological process underlying anaphylaxis. As with all emergencies, the ABCs ( Airway, Breathing, circulation) should be addressed first. Occasionally, the anaphylaxis causes laryneal edema to the extent that the airway is compromised, and intubation (tube placed in the trachea) is impossible. In these circumstances, an emergency airway, such as a surgical cricothyroidotomy, is required. 

The autonomic Sympathetic nervous system

Objectives: 

1. List the neurotransmitters of the autonomic sympathetic nervous system.

2. List the receptors and receptor-subtypes of the autonomic sympathetic nervous system. 

3. Predict the responses to activation and inhibition of autonomic sympathetic nervous system receptors. 

Definition:

Autonomic nervous system: Subdivision of the efferent peripheral nervous system that is largely under unconscious control (the somatic subdivision of the peripheral nervous system is largely under conscious control). Shown in Figure 1-1

Sympathetic nervous system: A division of the autonomic nervous system ( the other is the parasympathetic nervous system) that originates in nuclei of the central nervous system. Preganglionic fibers exit through the thoracic and lumbar spinal nerves to synapse on ganglia close to the spinal cord and also on the adrenal medulla (considered a modified ganglia). Postganglionic fibers innervate a wide variety of effector organs and tissues, including arteriole and bronchial smooth muscle, organs and tissues, including arteriole and bronchial smooth muscle. 

Antagonist: A drug that binds to receptors with little or no effect of its own but that can block the action of an agonist that binds to the same receptors. 

Agonist:  A drug that activates a receptor and results in a pharmacological response. 

Structure of Epinephrine: 

Epinephrine adn norepenephrine are catecholamines, synthesized from tyosine, that possesd a catechol nucleus with an ethylamine side chain (epinephrine is the methylated side chain derivative of epinephrine). The rate-limiting enzyme in this process is tyrosine hydroxylase.

Administration: 
Epinephrine is generally administered Parenterally (IM) for treatment of anaphylactic shock. For this and other conditions it is also available as IV, SC, ophtalmic, nasal, aerosol preparation. Norepinephrine is only available for parenteral administration.

the animation of Epinephrine action

Pharmacokinetic: 
Epinephrine released from the adrenal gland is metabolized primarily by catechol -O-methyltransferase (COMT) and monoamine oxidase (MAO). The action of norepinephrine released from nerve endings is terminated primarily by reuptake into nerve terminals and other cells.

Reference: The Pharmacology Case files, Published by LANGE
                   Author: Toy rosenfeld and Loose briscoe