P22: Respiratory System

What are the types of drugs used in the respiratory system?

mucolytics, expectorants, antitussives, bronchodilators, respiratory stimulants

What are expectorants used for?

facilitate the removal of secretions from airways by increasing the output of bronchial secretions, enhance clearance of bronchial exudate, and promote a productive cough

What are the groups of expectorants?

saline expectorants, direct stimulants, guaifenesin

What are saline expectorants?

stimulate bronchial mucous secretions via vagally mediated reflex action on the gastric mucosa

What are examples of saline expectorants?

ammonium chloride, ammonium carbonate, potassium iodide, calcium iodide, ethylenediamine dihydroiodide

What are direct stimulant expectorants?

direct stimulants of respiratory secretions believed to increase respiratory tract secretions

What are examples of direct stimulants of respiratory secretions?

volatile oils like eucalyptus oil and lemon oil

What is guaifensin (glyceryl guaiacolate)?

centrally acting muscle relaxant that may also have an expectorant effect by stimulating bronchial secretions by vagal pathways

What is guaifenesin used for?

coughing associated with chronic bronchial diseases

What are mucolytics used for?

facilitate the removal of secretions from airways by exposed sulfhydryl groups on the compound interacting with disulfide bonds on mucoprotein

What are examples of mucolytics?

N-acetylcysteine, dembrexine

What considerations should be made when using N-acetylcysteine?

aerosolisation of acetylcysteine can cause reflex bronchoconstriction due to irritant receptor stimulation, so its use should be preceded by bronchodilator therapy

What is the proposed mode of action of dembrexine?

alteration of the constituents and viscosity of abnormal respiratory mucus and an improved efficiency of respiratory clearance mechanisms
(also has antitussive action and enhances concentrations of antibiotics in lung secretions)

What are antitussive drugs used for and how do they work?

reduce the incidence of coughing, usually by central depression of the cough centre in the medulla oblongata

What types of drugs are most antitussives?

opiates or opioids

What are the classifications of antitussives?

narcotic, non-narcotic

What are examples of narcotic antitussives?

morphine, codeine, hydrocodone

What is an example of non-narcotic antitussives?

dexmethorphan

What is dextromethorphan used for?

suppressed coughing in dogs that are suffering from mild irritation of the airway, thereby reducing the risk of condition worsening through the strenuous act of coughing

What are the groups of bronchodilators?

β-adrenergic receptor agonists, methylxanthines, anticholinergic drugs

What is the mode of action of β-adrenergic receptor agonists?

bronchial smooth muscles are innervated by β2-adrenergic receptors and stimulation of these receptors leads to increased activity of the enzyme adenylate cyclase, increased cAMP, and relaxation of bronchial smooth muscle

Compare the duration of action of non-selective β-receptor agonists and β2-selective agonists?

non-selective β-receptor agonists are short-acting
β2-selective agonists are longer-acting

What receptors do non-selective β-receptor agonists stimulate?

β1, β2

What are examples of non-selective β-receptor agonists?

epinephrine, ephedrine, isoproterenol

What are non-selective β-receptor agonists used to treat?

acute therapy of respiratory diseases

What receptors do β2-selective agonists stimulate?

β2

What are examples of β2-selective agonists?

terbutaline, clenbuterol

What is the mode of action of terbutaline?

stimulates β2-adrenergic receptors found principally in bronchial, vascular and uterine smooth muscle causing bronchial and vascular smooth muscle relaxation with resultant reduced airway resistance

What is clenbuterol used for?

management of airway obstruction, such as chronic obstructive pulmonary disease in horses

What is an example of methylxanthines?

theophylline

What is theophylline used for?

treatment of respiratory diseases in dogs and cats

What is the mode of action of anticholinergic bronchodilator drugs?

reduce sensitivity of irritant receptors by inhibiting vagally mediated cholinergic smooth muscle tone in respiratory tract

What is an example of anticholinergic bronchodilator drugs?

atropine

What is atropine used for as a bronchodilator?

acute bronchodilation in horses (low IV dosage is more effective and less toxic than IV theophylline)

What is an example of respiratory stimulants?

doxapram

What is the mode of action of doxapram?

direct stimulation of the medullary respiratory centres and possibly through the reflex activation of carotid and aortic chemoreceptors

What effect does doxapram have?

increases respiratory rate and volume, but does not cause increase in arterial oxygenation

What is doxapram used for in cats, dogs, and horses?

stimulate respiration during and after general anaesthesia and/or to speed awakening and reflexes after anaesthesia

What is doxapram used for in neonatal dogs and cats?

initiate or stimulate respirations following dystocia or caesarean section