Drugs affecting the respiratory system
I- Overview
Drugs can be deliverd to the lung by
inhalation : preferred as
The drug is deliverd directly to the target tissues
Effective in doses do not cause significant systemic side effects
oral route
parenteral route
Main mechanisms of action
Relaxing bronchial smooth muscles
Modulating the inflammatory response
II- Drugs used to treat asthma
Asthma is a chronic disease characterised by episodes of acute bronchoconstriction causing
Shortness of breath
Cough
Chest tightness
Wheezing
Rapid respirations
The goal of the therapy is to
Relieve symptoms
Prevent recurrence of asthmatic attacks if possible
Role of inflammation in asthma
Airflow obstruction in asthma is due to bronchconstriction resulting from
contraction of bronchial smooth muscle
inflammation of the bronchial wall
increased mucous secretions
Asthmatic attacks may be related to
Recent exposure to allergans
Inhaled irritants
leading to bronchial hyperactivity and inflammation of the airway mucosa
The symptoms of asthma may be effectively treated by several drugs but none of them provide a cure for this obsructive lung disease
A-Adrenergic agonists
Inhaled B2 agonists(as direct bronchodilators) ..are drug of choice for mild asthma (occurs occasionaly with intermittent symptoms)
Have no anti-inflammatory effects
Should not be used as the sole therapeutic agents for patient with chronic asthma
Short acting : used as a rescue agents to combat acute
bronchoconstriction
ex :terbutaline - albuterol - pirbuterol
Onset : rapid (15-30)minutes
Duration : (4-6)hours
Long acting drugs
ex:salmetrol
Onset :slow so should not be used in acute asthmatic attack
Duration : at least 12 hours
Prescriped only for administration at regular intervals and not to relieve symptoms
B- Corticosteroids
ex : beclomethazone - triamcinolone
Drug of first choice in patients with moderate to severe asthma who require inhalation of B2 agonists more than once daily
To be effective in controlling inflammation ,glucocorticoid must be taken continuously
Actions on the lung
Inhaled glucocorticoids decrease the number and activity of cells involved in airway inflammation
Prolonged(several months)inhalation of steroids reduces the hyperresponsiveness of the airway smooth muscle to a variety of bronchoconstriction stimuli such as
allergans - irritants - cold air - exercise
The most common adverse effect associated with the use of inhaled glucocorticoids is oropharyngeal candidiasis = oral thrush
C- Cromolyn & nedcromil - inhalations
Effective prophylactic anti-inflammatory agents
Not useful in management of acute ashmatic attack because they are not direct bronchodilators
Pretreatment with cromolyn blocks bronchoconsriction induced from allergans and exercise
Useful in reducing symptoms of allergic rhinitis
D- Cholinergic antagonists
ex: ipratropium
Has slow onset and nearly free of side effects
Less effective than B agonists but useful in patients unable to tolerate them
E- Theophylline
Relieves airflow obstruction in chronic asthma
Previously,it was the main stay of asthma therapy but now it is largely replaced with B agonists and corticoids
Has a narrow therapeutic window so overdose of it may cause seizures or potentially fatal arrythmias
III- Drugs used to treat allergic rhinitis
Rhinitis : an inflammation of the mucous membranes of the nose and is characterized by
Sneezing -nasal itching - watery rhinorrhea - congestion
A- Antihistamines = H1 receptor blockers
ex : diphenhydramine - chlorpheniramine - loratadine - terfenadine - astemizole
Useful in treating the symptoms of allergic rhinitis
When congestion is a feature of rhinitis , combination with decongestants is effective
B- Alpha adrenergic agonists = nasal decongestants
ex: phenylephrine - oxymetazoline
Constrict dilated arterioles in nasal mucosa and reduce airway resistance
Should not be used no longer than several days because rebound nasal congestion often occurs upon discontinuence of these drugs
C- corticosteroids
Topical steroids may be more effective than antihistamines in relieving the nasal symptoms of both allergic and non allergic rhinitis
Treatment of chronic rhinitis may not result in improvement until 1 to 2 weeks after starting therapy
D- Cromolyn
Intanasal cromolyn may be useful particularly when administerd before contact with an allergan
IV- Drugs used to treat chronic obstructive pulmonary disease COPD
It is a chronic irreversible obstruction of airflow
Smoking is the greatest risk factor for COPD
This disease may respond to
Anticholinergic agents
B adrenergic agents e.g : impratropium
Theophylline
These three classes does not cure the disease or even significantly slow its progress
Glucocorticoids : may be helpful in the treatment of acute exacerbations in some patients
V- Drugs used to treat cough
ex : codeine -hydrocodone -hydromorphone
at doses lower than required for analgesia they can
decrease the sensitivity of the CNS cough centers to peripheral stimuli
decrease mucosal secretion
Dextromethorphane : synthetic derivative of morphine
Supress the response of the cough center
Has no analgesic or addictive potential
Less constipating than codeine