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Drugs Affecting Respiratory System. Antihistamines. Drugs that directly compete with histamine for specific receptor sites Two histamine receptors H 1 (histamine 1 ) H 2 (histamine 2 ). Histamine-mediated disorders Allergic rhinitis (hay fever, mould and dust allergies) Anaphylaxis

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Drugs that directly compete with histamine for specific receptor sites

  • Two histamine receptors
    • H1 (histamine1)
    • H2 (histamine2)
Histamine-mediated disorders
    • Allergic rhinitis (hay fever, mould and dust allergies)
    • Anaphylaxis
    • Drug fevers
    • Insect bite reactions
    • Urticaria (itching)
H1 antagonists are commonly referred to as antihistamines
  • Antihistamines have several properties
    • Antihistaminic
    • Anticholinergic
    • Sedative
mechanism of action
Mechanism of Action
  • Block action of histamine at the H1 receptor sites
  • Compete with histamine for binding at unoccupied receptors
  • Cannot push histamine off the receptor if already bound
The binding of H1 blockers to the histamine receptors prevents the adverse consequences of histamine stimulation
  • Prevent smooth muscle contraction of the bronchial airways
  • Decrease mucus secretion
  • Prevent increase of vascular permeability
More effective in preventing the actions of histamine rather than reversing them
  • Should be given early in treatment, before all the histamine binds to the receptors
  • Nasal allergies
  • Seasonal allergic rhinitis (hay fever)
  • Allergic reactions
  • Motion sickness
  • Sleep disorders
  • Also used to relieve symptoms associated with the common cold such as sneezing, runny nose (Palliative treatment, not curative)
side effects
Side Effects
  • Anticholinergic effects, most common
    • Dry mouth
    • Difficulty urinating
    • Constipation
    • Changes in vision
  • Drowsiness
    • Mild drowsiness to deep sleep
first generation
First generation
  • Diphenhydramine (Benedryl )
  • Chlorpheniramine (Piriton)
  • Promethazine hydrochloride (Phenergan)
second generation
Second generation
  • Loratidine
  • Ceterizine/cetrizine

They are much less likely to have side effects of sedation and dry mouth

Use with caution in increased intraocular pressure, cardiac or renal disease, hypertension, asthma, COPD, peptic ulcer disease

What is nasal congestion?

  • Excessive nasal secretions
  • Inflamed and swollen nasal mucosa
  • Primary causes
    • Allergies
    • Upper respiratory infections (common cold)
Two decongestant forms
  • Oral/systemic
  • Inhaled/topically applied to the nasal membranes
topical nasal decongestants
Topical Nasal Decongestants
  • Adrenergics
  • Intranasal steroids
mechanism of action1
Mechanism of Action
  • Adrenergics
    • Constrict small blood vessels that supply Upper Respiratory Tract structures
    • As a result these tissues shrink, and nasal secretions in the swollen mucous membranes are better able to drain
    • Nasal stuffiness is relieved
Nasal steroids
    • Anti-inflammatory effect
    • Work to turn off the immune system cells involved in the inflammatory response
    • Decreased inflammation results in decreased congestion
    • Nasal stuffiness is relieved
    • Ephedrine hydrochloride
  • Intranasal steroids
    • Beclomethasone dipropionate
side effects1
Side Effects


Nervousness Local mucosal dryness

Insomnia and irritation



(systemic effects due to adrenergic stimulation of theheart, blood vessels, and CNS)

oral decongestants
Oral decongestants
  • Not that effective
  • Have unwanted sympathomymetic effects
  • Pseudoephridine
  • Drugs used to stop or reduce coughing
  • What is cough? Respiratory secretions and foreign objects are naturally removed by the Cough reflex initiated by irritation of sensory receptors in the respiratory tract
  • Productive cough
    • Congested, removes excessive secretions
  • Nonproductive cough
    • Dry cough
  • Suppress the cough reflex by direct action on the cough centre in the medulla


    • Codeine
    • Hydrocodone
  • Suppress the cough reflex by numbing the stretch receptors in the respiratory tract and preventing the cough reflex from being stimulated


    • Dextromethorphan
  • Used to stop the cough reflex when the cough is nonproductive and/or harmful
  • Drugs that aid in the expulsion (removal) of mucus/ bronchial secretions
  • Reduce the viscosity of secretions
  • Disintegrate and thin secretions
By loosening and thinning sputum and bronchial secretions, the tendency to cough is indirectly diminished
  • Used for the relief of nonproductive coughs
asthma causes a narrowing of the breathing airways
Asthma causes a narrowing of the breathing airways
  • The narrowing that occurs in asthma is caused by three major factors: inflammation, bronchospasm, and hyperreactivity.
  • In inflammation the bronchial tubes become red, irritated, and swollen
  • The muscles around the bronchial tubes tighten during an attack of asthma. This muscle constriction of the airways is called bronchospasm
In patients with asthma, the chronically inflamed and constricted airways become highly sensitive, or reactive, to triggers such as allergens, irritants, and infections.
  • Exposure to these triggers may result in progressively more inflammation and narrowing and this is called hyperreactivity
The combination of these three factors results in difficulty with breathing out, or exhaling.
  • As a result, the air needs to be forcefully exhaled to overcome the narrowing, thereby causing the typical "wheezing" sound.
  • People with asthma also frequently "cough" in an attempt to expel the thick mucus plugs.
Reducing the flow of air may result in less oxygen passing into the bloodstream, and if very severe, carbon dioxide may dangerously accumulate in the blood
management of asthma
Management of asthma
  • some drugs are given to treat acute asthma exacerbations
  • Some drugs are used as long term maintenance therapy
  • Adrenoceptor agonists
  • Antimuscarinic bronchodilators
  • Xanthene derivatives –theophilline
  • Antileukotriene agents/Leukotriene receptor antagonists
  • Cromones
adrenoceptor agonists
Adrenoceptor agonists
  • Used during acute phase of asthmatic attacks
  • Quickly reduce airway constriction and restore normal airflow
  • Stimulate beta2-adrenergic receptors throughout the lungs
Selective beta2 drugs
    • Stimulate only beta2-receptors
    • Commonly used
    • Example: salbutamol
selective beta2 agonists
Selective beta2 agonists
  • Salbutamol
  • Terbutaline
  • Salmeterol
  • Formeterol
side effects2
Side Effects
  • Tremor
  • Headache
  • Peripheral venous dilatation
  • Palpitations
antimuscarinic bronchodilators anticholinergics
Antimuscarinic bronchodilators/ Anticholinergics
  • Acetylcholine (ACh) causes bronchial constriction and narrowing of the airways
  • Anticholinergics bind to the ACh receptors, preventing ACh from binding
  • Ex-ipratropium bromide
mechanism of action2
Mechanism of Action
  • Leukotrienes are substances released when expose to a trigger, such as cat hair or dust, and starts a series of chemical reactions in the body
  • Leukotrienes cause inflammation, bronchoconstriction, and mucus production
  • Result: coughing, wheezing, shortnessof breath
Antileukotriene agents prevent leukotrienes from attaching to receptors on cells in the lungs and in circulation
  • Inflammation in the lungs is blocked, and asthma symptoms are relieved
mast cell stablizers
Mast cell stablizers

Sodium cromoglicate

  • Mechanism of action is not very clear, but known to affect on inflammatory mediated cells
  • Indicated in prophylaxis of asthma by inhalation
  • Very effective in asthma
  • Mechanism of action :
  • Enter cells where they combine with steroid receptors in cytoplasm
  • Inhibit inflammation/reduce synthesis of inflammatory mediators

IN asthmatics inhalers are used to deliver drugs more effectively with minimal side effects

Relievers have to be taken when they get worsening of asthma

Preventers should be used daily for it to be effective

Patients should be clearly educated on this …

oxygen therapy
Oxygen Therapy
  • Oxygen therapy is the administration of oxygen as a medical intervention
  • Administration of oxygen at concentrations greater than that in room air ( 21%) to treat or prevent hypoxemia (not enough oxygen in the blood)
high concentration o 2 therapy
High concentration O2 therapy
  • Concentrations up to 60%
  • Use in pneumonia and many other conditions
low concentration o 2 therapy
Low concentration O2 therapy
  • The concentration should not exceed 28%
  • Used in COPD
  • Improve the hypoxemia with out worsening existing CO2 retention