25. Drug treatment of allergic rhinitis. Antitussives, expectorants and mucolytics

Last updated on November 25, 2019 at 12:06

Treatment of allergic rhinoconjuctivitis

Allergic rhinoconjuctivits, or hay fever, is a type I hypersensitivity reaction just like extrinsic asthma. Symptoms include:

  • Nose and eyes are itchy
  • Sneezing
  • Rhinorrhoea (runny nose)
  • Nasal congestion (stuffy nose)

Drugs used in the treatment of allergic rhinitis:

  • Intranasal sprays
    • Histamine H1 receptor antagonists
      • Azelastine
    • Decongestants (α1 agonists)
      • Oxymetazoline
      • Xylometazoline
    • Anticholinergics
      • Ipratropium (bromide)
    • Corticosteroids
      • Budenoside
      • Fluticasone
  • Oral drugs
    • Histamine H1 receptor antagonists (2nd generation)
      • Cetirizine
      • Loratadine
      • Fexofenadine
    • Decongestants (α1 agonists)
      • Phenylephrine
      • Pseudoephedrine
    • Anti-leukotrienes
      • Montelukast

Indications:

Antihistamines relieve most symptoms of hay fever, but they have minimal effects on nasal congestion. A combination of an oral antihistamine and a nasal spray with a decongestant is sufficient to treat the symptoms in most cases. Both intranasal and oral application of antihistamines has fast onset of action.

Decongestants decrease the nasal congestion. Topical application is preferred over oral.

Anticholinergic drugs like ipratropium decrease the nasal secretions but has no effect on other symptoms.

Topical glucocorticoids treat all symptoms effectively but are mostly reserved for cases with more severe symptoms.

Anti-leukotrienes are usually reserved for treatment-resistant cases.

Mechanism of action:

α1 agonists constrict venules in the nasal mucosa. This reduces the volume of venous blood in the mucosa, thereby decreasing the oedema.

Anticholinergics like ipratropium block the M3-receptor-mediated nasal secretion.

Glucocorticoids decrease the allergen-mediated inflammation.

Tolerance:

Tolerance develops quickly to the decongestant effect of α1 agonists, most likely due to a down-regulation of α receptors. This occurs after continous use of nasal decongestant for 10 days straight and results in rebound-congestion.

To combat this tolerance the nasal decongestant addict usually starts to take the intranasal spray more and more often. This can lead to systemic symptoms of α-adrenergic agonism like vasoconstriction, palpitation, tachycardia and anxiety.

Treatment of cough

Coughing is a good thing; it removes foreign material and secretions from the airways. We never want to stop coughing completely, but we can suppress the reflex in cases where:

  • the cough is dry (not productive) and painful
  • the cough is exhausting, like in patients with hypertension or heart failure

Anti-tussive drugs:

  • Centrally acting cough suppressants
    • Opioids
      • Codeine
      • Dihydrocodeine
      • Hydrocodone
      • Ethylmorphine
    • Opioid-like drugs
      • Noscapine
    • Non-opioids
      • Butamirate
      • Pentoxyverine
  • Peripherally acting cough suppressants
    • Benzonatate

Indications:

Opioids antitussives can’t be used in children, but the non-opioids can.

Mechanism of action:

Opioids act on a “cough centre” in the CNS and suppresses cough centrally.

Noscapine is an alkaloid of the opium plant but it’s not an opioid. It’s mechanism of action of cough is not precisely known but probably doesn’t involve opioid receptors.

Butamirate and pentoxyverine also act centrally, most likely on the cough centre.

Benzonatate is chemically related to local anaesthetics like tetracaine. It acts by blocking receptors of the cough reflex in the lung.

Adverse effects:

  • Opioids
    • Addictive potential
    • Constipation
    • Respiratory depression
    • Decreased mucociliary clearance
Expectorants and mucolytics

Expectorants are drugs which increase the volume and decrease the viscosity of the airway secretions, thereby making them easier to cough up.

Mucolytics cleave macromolecules in the secretion which also makes it less viscous.

Drugs:

  • Expectorants
    • Guaifenesin
    • Saponines
  • Mucolytics
    • Acetylcysteine
    • Bromhexine

Mechanism of action:

Expectorants directly stimulate glands in the airways, and/or they indirectly stimulate these glands by stimulating the vagus nerve.

Acetylcysteine cleaves disulfide bonds in big macromolecules in sputum, which decreases its viscosity. Bromhexine acts by similar mechanism.

Analeptic drugs

Analeptic drugs are drugs which stimulate the respiratory centre. Their respiratory stimulant effect can be useful in conditions like respiratory failure or apnoea, but nowadays they’re replaced by mechanical ventilation.

Drugs:

  • Theophylline
  • Doxapram

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