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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 Affecting Respiratory System

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Drugs affecting respiratory system

Drugs Affecting Respiratory System



Drugs that directly compete with histamine for specific receptor sites

  • Two histamine receptors

    • H1 (histamine1)

    • H2 (histamine2)

Drugs affecting respiratory system

  • Histamine-mediated disorders

    • Allergic rhinitis (hay fever, mould and dust allergies)

    • Anaphylaxis

    • Drug fevers

    • Insect bite reactions

    • Urticaria (itching)

Drugs affecting respiratory system

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

Drugs affecting respiratory system

  • 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

Drugs affecting respiratory system

  • 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

Drugs affecting respiratory system

  • 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)

Drugs affecting respiratory system

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

Drugs affecting respiratory system

  • 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

Drugs affecting respiratory system

  • Adrenergics

    • 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

Drugs affecting respiratory system


  • Suppress the cough reflex by direct action on the cough centre in the medulla


    • Codeine

    • Hydrocodone

Drugs affecting respiratory system


  • 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

Drugs affecting respiratory system

  • By loosening and thinning sputum and bronchial secretions, the tendency to cough is indirectly diminished

  • Used for the relief of nonproductive coughs

What happens in asthma

What happens in ASTHMA ?

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

Drugs affecting respiratory system

  • 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

Drugs affecting respiratory system

  • 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.

Drugs affecting respiratory system

  • 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

Drugs affecting respiratory system

  • 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

Drugs affecting respiratory system

  • Contraindicated: clients with severe cardiac disease

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

Drugs affecting respiratory system

  • Side effects: dry mouth, nausea, constipation, headache

Antileukotriene agents leukotriene receptor antagonists

Antileukotriene agents/Leukotriene receptor antagonists

  • Montelukast

  • Zafirlukast

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

Drugs affecting respiratory system

  • 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

Drugs affecting respiratory system

  • Oxygen can deliver to the respiratory system via nasal canula, tracheostomy and face mask

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