Respiratory System Pharmacology Course Notes Easy Simple Concise Understood
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Course
PHA311-7017 (PHA3117017)
Institution
BU - Accredited University
This course note provide students with simple & concise information about drugs acting on respiratory system and hep them understand respiratory drugs in easy way. The note includes: respiratory stimulants and depressants; expectorants; mucolytics; antitussives; bronchodilators; membrane shrinking ...
PHARMACOLOGY, RESPIRATORY SYSTEM (PHA311)
FOR STUDENTS ENROLLED IN PHARMACOLOGY PROGRAMS
RESPIRATORY DRUGS (Introduction - Stimulants)
INTRODUCTION
- Respiratory rate is controlled by two mechanisms:
o Nervous mechanism: The activity of respiratory center is modulated by impulses from the
cerebral cortex, hypothalamus, lungs, or circulatory system.
o Chemical mechanism: CO2 tension, O2 level and pH of the blood affect the respiration. It is
stimulated by CO2 and acidosis.
- The main function of respiration is gas exchange, i.e. continuous supply of oxygen and continuous
removal of CO2 and other wastes. The lack of oxygen is called hypoxia or anoxia which is a
diseased condition characterized by cyanosis and increase in respiratory rate to get as much
oxygen as possible. There are 4 types of hypoxias according to its cause:
o Anoxic hypoxia: due to inadequate availability of oxygen.
o Anemic hypoxia: due to decreased capacity of the blood to carry O2 because of lack of
hemoglobin or its change to nonfunctional one.
o Stagnant hypoxia: due to circulatory failure and stagnation of blood in its vessels.
o Histotoxic hypoxia: due to inability of tissue to utilize O2 in spite of its presence due to cellular
oxidative poisons such as cyanide.
- Hypoxia can be treated according to the cause together with respiratory stimulants.
- Bronchial muscles are controlled by autonomic nervous system. They are contracted by
parasympathetic stimulation (M receptors) and relaxed by sympathetic stimulation (2 receptors).
Bronchoconstrictors are of no therapeutic value; on the other hand, bronchodilators are very
important drugs for asthmatic patients and during respiratory infection.
- The bronchial gland secretions are one of the defense barriers in the body. During infection the
viscosity of the bronchial secretion may increase rendering it difficult for cilia to expel out. Such a
condition can be treated by mucolytics and expectorants.
- Non-productive cough due to continuous irritation of sensory nerve endings in the pharyngeal and
laryngeal mucosae can be treated by antitussives.
- Respiratory infection is usually associated with inflamed swollen bronchial mucosa which causes
dyspnea. Such condition can be helped by membrane shrinking drugs.
Respiratory system Pharmacology Surviving Revision
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RESPIRATORY STIMULANTS
Def.: are the drugs which increase the depth and rate of respiration.
Members:
Respiratory stimulants can be classified according to their mode of action into:
A. Direct stimulants of the respiratory center; including:
a. Medullary stimulants as picrotoxin, leptazole and nikethamide
b. Cerebral stimulants as caffeine, ephedrine, amphetamine, atropine and hyoscine.
c. Some analgesic drugs as salicylates.
d. Carbon dioxide is supplied as Carbogen (carbon dioxide-oxygen mixture; in which CO2
tension is 5~10%).
B. Reflex stimulants of respiratory center; including:
a. Stimulants of chemoreceptors in the carotid body and aortic arch by high CO2 and low O2
and acidic pH.
b. Irritants to skin and mucous membranes by ammonia inhalation, aromatic spirit of ammonia
oral administration, camphor or alcohol subcutaneous administration.
N.B. Some drugs act dually as you have studied in CNS.
Therapeutic uses of respiratory stimulants:
- During anesthesia.
- Coal tar poisoning.
- Conditions associated with hypoxia and bronchopneumonia.
RESPIRATORY DEPRESSANTS
Def.: are the drugs which decrease the rate and depth of respiration. They are of no therapeutic value.
Members:
Respiratory depressants can be classified according to mode of action into:
a. Depressants of respiratory center in the medulla as morphine and diamorphine.
b. Depressants of the sensitivity of respiratory center to CO2 as barbiturates.
Respiratory system Pharmacology Surviving Revision
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