10-9 Bronchodilators and Asthma Drugs - Martin Lecture & DSA Flashcards
What is asthma?
Asthma is currently viewed primarily as an inflammatory illness that results in bronchial hyperreactivity and bronchospasm
Why are drugs so important in controlling asthma?
recommendations for prevention and treatment of asthma emphasize control of the inflammatory component as the underlying problem
- reserve bronchodilators primarily for symptomatic use.
The inflammatory component and the airway narrowing of asthma are largely reversible
- drug therapy plays a significant role in the management of the disease
Why is inflammation so pervasive in allergic asthma?
immediate hypersensitivity-type reactions can be continuously present at a sub-threshold level
- resulting in mild-to-moderate inflammation without overt bronchoconstriction
If inflammation is continuously present in allergic asthma, why is overt bronchospasm intermittent?
Overt bronchospasm then occurs upon exposure to a specific allergen or to a variety of nonspecific stimuli, e.g., cold air, dust, air pollution, exercise, etc
What is going on in COPD?
disease characterized by the presence of airflow obstruction due to chronic bronchitis or emphysema
- airflow obstruction is generally progressive
- may have airway hyperreactivity
- may be partially reversible
How is drug therapy helpful in treating COPD?
useful in addressing the reversible component of COPD
- induce bronchodilation
- decrease inflammatory reaction
- facilitate expectoration
What are the anti-inflammatory classes of drugs useful in asthma and related respiratory disease?
corticosteroids
cromolyn-like compounds
anti-leukotriene drugs
What are the bronchodilators helpful in treating asthma and related respiratory diseases?
b-adrenergic agonists,
muscarinic receptor antagonists
methylxanthines
In addition to bronchodilators and anti-inflammatories, what other types of drugs are helpful in addressing some respiratory disease?
decongestants, antitussives, expectorants and mucolytic agents
What happens in allergy that causes release of inflammatory mediators?
Allergen-specific IgE binds to Fc receptors on mast cell.
When allergen comes in contact with IgE, the mast cell is activated and releases a large number of mediators.
- enormous variety of mediators is released, each having more than one potent effect on airway inflammation.
Why are antihistamines not very effective in controlling allergic asthma?
many different mediators released
pharmacological blocker of any one mediator is ineffective in alleviating the symptoms or progression of asthma or the inflammatory component of other respiratory diseases
Corticosteroids, which can block many of the key steps in the inflammatory process, come closest to this ideal therapy
Mast cells release many inflammatory mediators, but why do airways become responsive to non-specific stimuli?
asthmatic airways respond to allergen challenge with an immediate airway narrowing and mast cell infiltration.
Reactive hyperemia, edema, and cellular inflammation become evident within hours of challenge
- frequently associated with a second, usually more severe, rise in airways resistance
- influx of white cells and changes in airways function may persist for days and weeks after a single challenge and can result in heightened bronchial sensitivity to a number of stimuli
What changes due to enzyme release from inflammatory cells contribute to bronchial sensitivity?
damage to the respiratory epithelium
enhanced neuropeptide release
exposed afferent nerve endings that can evoke enhanced vagal responses
Other than mast cells, what cells contribute to inflammation in asthma?
Inflammatory cells other than mast cells implicated in the pathogenesis of asthma include eosinophils, neutrophils, macrophages, lymphocytes, and platelets.
To sum, what are the 4 key features of asthma?
- Mast cell activation associated with early bronchospasm
- Inflammatory cell infiltration with subsequently mediator release
- Epithelial cell damage
- Increased responsiveness of the airways to a variety of non‑specific stimuli
What are the immediate mediators from mast cells? What are the effects?
Preformed:
Histamine, TNF-a, Proteases, Heparin
Effects:
Bronchoconstriction, itch, cough, vasodilation, edema
What are the lipid mediators from mast cells? What are the effects?
Mediators - lipids work in minutes
Leukotrienes, Prostaglandins
Effects:
Bronchoconstriction, chemotaxis, mucus secretion
What are the cytokine mediators from mast cells? What are their effects?
Cytokines - start working in hours:
Interleukins, GM-CSF
Effects:
Bronchoconstriction, chemotaxis, inflammatory cell proliferation
Why is aerosol delivery of asthma drugs beneficial?
pathophysiology of asthma appears to involve the respiratory tract alone.
- effective treatment could be achieved if drug administration was restricted to the lungs.
Aerosol application of drugs to the lungs can produce a high local concentration in the lungs with a low systemic absorption
- significantly improving the therapeutic ratio by minimizing side effects.
- both b2-agonists and corticosteroids have potentially serious side effects when delivered systemically.
What percentage of asthmatic patients can be managed by aerosols?
Probably more than 90% of asthmatic patients who are capable of manipulating inhaler devices can be managed by aerosol treatments alone.
What is are some important factors that determine effective deposition of drug into lung?
Particle size:
>10 mm deposit in mouth and oropharynx
<0.5 mm are inhaled and then exhaled
1-5 mm deposit in small airway and are most effective.
Rate of breathing and breath holding are important.
The recommendation technique is that a slow, deep breath be taken and held for 5 - 10 sec
How much of a dose of aerosol drugs for asthma reach the lung? Why is this important in formulating drugs for asthma, etc.?
under ideal conditions only 2 - 10 % of drug is deposited in lungs
- most of the remainder is swallowed
to have minimal systemic side effects, an aerosolized drug should be either poorly absorbed from the GI tract or be rapidly inactivated by first-pass liver metabolism.
- ipratropium Br is complexed to a salt and permanently charged, and cannot be absorbed will in the GI tract or cross membranes well
What are the different devices for aerosol delivery?
Metered Dose Inhalers (MDI) - with spacer device
Nebulizers
Dry powder inhalers
How do MDIs work?
pressurized canister with a metering valve that delivers drug with hydrofluoroalkane (HFA) propellant, co-solvents, and/or surfactants
Spacer devices that attach to the MDI markedly improve the ratio of inhaled to swallowed drug and reduce need for coordination.
Valved holding chambers (VHCs) have one-way valves that prevent the patient from exhaling into the device, minimizing the need for coordinated activation and inhalation.