Allergic rhinitis, or hay fever, is a type I hypersensitivity reaction just like extrinsic asthma. Symptoms include:
- Nose and eyes are itchy
- Rhinorrhoea (runny nose)
- Congestion (stuffy nose)
Histamine H1 receptor antagonists are useful because histamine is important in allergy. We use second generation drugs because they have a smaller sedative effect than the first generation. Common examples include:
They can be taken orally or applied topically on the eye or nasal cavity. These drugs don’t help with the stuffy nose though. For that, we have:
Nasal decongestants. Your nose becomes stuffy because the mucous membranes in the nasal cavity are swollen because the vessels are inflamed and vasodilated from the hypersensitivity I reaction. We treat this by giving α adrenergic agonists or indirect sympathomimetics. These constrict the vessels again and therefore reduce the volume of the mucosa. They’re mostly used topically, by spray. Commonly used types are:
- α agonists
- Indirect sympathomimetic agents
Muscarinic receptor antagonists reduce the secretion but doesn’t affect the vasodilation. Ipratropium is commonly used as nasal spray.
Nasal glucocorticoids like budesonide, ciclesonide and beclomethasone can be used nasally. They have good effect on all symptoms.
Anti-leukotrienes can be given orally. Zafirlukast, montelukast and pranlukast can be used.
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 isn’t productive, like in pleuritis or dry trachea
- the cough is exhausting, like in patients with hypertension or heart failure
The cough centre is in the brain stem, so to suppress coughing must we get to work on the CNS.
Opioids like codeine, dihydrocodeine, hydrocone and dextromethorphan have addictive potential, but they do suppress coughing efficiently.
Non-opioids like butamirate and pentoxyverine are also used. As they’re not can they be used in children.
There are some peripherally-acting cough suppressants that can be used as well. These are thought to block receptors of the cough reflex in the bronchi. Benzonatate and prenoxdiazine can be used.
Expectorants and mucolytics
Expectorants increase the volume and decrease the viscosity of the airway secretions, thereby making it easier to cough up.
Commonly used expectorants are saponines, emetine, guaifenesin, citrus oil, eucalyptus oil and inhaled salts.
Mucolytics cleave macromolecules in the secretion which also makes it less viscous, but by a different mechanism.
Acetylcysteine, carbocysteine and bromhexine can be given orally or by inhalation. They break down macromolecules in the secretions.
Analeptics stimulate the respiratory centre. They can be used to treat apnoea in preterm infants or in respiratory failure. Commonly used drugs are theophylline, aminophylline and doxapram.
24. Drugs used to treat bronchial asthma