L15 - Principles of Respiratory Pharmacology Flashcards
Definition of Agonist
- Drugs bind to a receptor and initiate a change in cellular function (i.e. mimic physiologic activation)
- An agonist has both high affinity and efficacy
Definition of antagonist
Function of Respiratory Stimulants
- to help increase the urge to breathe in the treatment of respiratory failure
Example of respiratory stimulants
Doxapram
Doxapram properties (function, mechanism, effect, administration, usage)
1) Function: as respiratory stimulant to help increase the urge to breathe in the treatment of respiratory failure
2) Mechanism: a CNS stimulant drug that acts on both carotid chemoreceptors and the respiratory centre in the brainstem to increase respiration
3) Effect: increase in respiratory rate and tidal volume with a fall in pCO2 and a rise in pO2
4) Administration: Intravenous administration (patients ususally connected to machines)
5) Usage: used primarily to help preterm infants who have apnea, but also helpful in older patients with sleep apnea and in COPD patients with acute respiratory failure
Examples of drugs depressing respiration
1) Ethanol
2) Narcoltic analgesics (opioids) - morphine and codeine
3) H1-histamine receptor antagonists – promethazine
4) Psychotic drugs - Antidepressants, barbiturates, benzodiazepines
Mechanism of respiratory depression by ethanol
by diffusing into the cell membranes of nerve cells and inhibiting the passive neuronal flux of Na+
Consequence of excess dosage of respiratory depressants
Excessive dosage - decrease in sensitivity of respiration to CO2 and hypoxic drive (a form of respiratory drive)
Drugs that provokes asthma
1) Aspirin and other nonsteroidal anti-inflammatory drugs (NSAID; e.g. ibuprofen)
2) Beta-adrenergic receptor antagonists (blockers)
How NSAID provokes asthma
Through lipoxygenase that converts membrane arachidonic acid to leukotrienes (LT), which will then cause bronchoconstiction
How beta blockers provoke asthma
By binding to ß2-receptors and preventing bronchodilation
Three categories of drugs to treat coughs
1) Antitussives
2) Expectorants
3) Mucolytics
Two basic types of coughs (characteristics and treatment)
1) Productive cough (aka congestive cough)
- removes excess secretions
- do not use antitussives
2) Non-productive cough (i.e. dry cough)
- use antitussives
What are antitussives
Drugs used to suppress the intensity and frequency of coughinh
Possible sites of action of antitussives
Peripheral (above and below larynx) or central (CNS)
Dosage form and mechanisms of peripheral antitussives
- Above larynx: syrups and lozenges as demulcent
- Below larynx: water aerosol inhalation and warm environment
- Mechanism: decreasing the sensitiveity of peripheral sensory ‘cough receptors’ in the pharynx to irritation
Mechanism of central antitussives
By decreasing the cough reflex in the medulla; decreasing the sensitivity of CNS cough centres to peripheral stimulus