As discussed in Chapter 15 ‘Methods of administration’ (p. 120), the thin, highly vascular lining of the sinuses makes it easy to reach with soluble orthodox medication (in the form of sprays) and vapourized aromatic oils. This, combined with their fat solubility, ensures rapid absorption into the body and also the brain.

Because of this feature, it is usually one of the first areas in a patient to be affected by allergens.

Airborne allergens react with IgE-sensitized mast cells in the nasal mucosa and the mucous membranes around the eyes. This is treated by oral antihistamines or nasal spray.

• Antihistamines

Histamine

• Found in most of the tissues of the body, but is in higher concentrations in the lungs, skin and the gut.

• Usually found in basophils and mast cells.

• Released from mast cells during inflammatory or allergic reactions.

• H2 histamine receptors are found in the acid-secreting cells in the stomach.

There are two types of antihistamine drug: H1-receptor antagonists, the classic antihistamine drugs, and H2-receptor antagonists, which affect gastric secretion:

• Cimetidine (Figure 34.1), an H2 antagonist, is used to treat stomach ulcers.

• Ceterizine, an H1 antagonist, is used to treat allergies.

Figure 34.1 The structure of histamine and two different types of antihistamine.

H1-Receptor Antagonists (H1 Antihistamines)

Ceterizine

• Blocks the classical histamine H1 receptors and interferes with the actions of histamine released in type 1 immune reactions.

• Used in hay fever, allergic rhinitis, urticaria and other acute allergic reactions.

• Used to settle down itching and skin reactions such as wheals and hot allergic lumps.

• Potential for drowsiness but not as sedative as effects of the older antihistamines as it is more specific for peripheral H1 receptors.

Asthma occurs as a result of a restriction of airflow caused by the contraction of the smooth muscles of the bronchioles and mucosal oedema. It is due to an increased responsiveness of the trachea and bronchi to various stimuli. This reaction is reversible, but in some cases a severe asthma attack can be fatal if not treated quickly. Triggers can be:

Childhood asthma or extrinsic asthma is associated with increased levels of IgE antibodies. In adult or intrinsic asthma the symptoms appear in middle age and tend to be persistent.

The initial response occurs suddenly and is due to spasm of the smooth muscles of the bronchioles. The antibodies attach to the mast cell, which reacts to the allergen by releasing histamine, leukotrienes, eosinophils, macrophages, platelets and bradykinins. Leucocytes are attracted into the area, which leads to the second or delayed response.

The delayed response does not occur immediately and is a progressive inflammatory reaction. The usual inflammatory cells are found at the site, with cytokine-releasing T cells and eosinophils, the contents of which damage the epithelium. The products of these cells stimulate the nerve cells to constrict the bronchioles. A thickening of the mucosal walls along with copious amounts of mucus, which accumulate over a period of time, decrease the lumen of the bronchioles further. There is often a family history of hay fever or eczema.

• Beta-2 Adrenoceptor Agonists

Beta-2 adrenoceptor agonists (see Chapter 31 ‘The nervous system’, p. 244) are used; these:

• act on the smooth muscles

• inhibit the release of contents from the mast cells

• inhibit the action of the vagus nerve

• increase the action of the cilia to improve mucus clearance.

Usually, different types of medication are given:

• Short-acting drugs: salbutamol (Figure 34.2) is a beta-2 agonist that works within 30 minutes, the effects of which last 4–6 hours.

• Longer-acting drugs: salmeterol is a beta-2 agonist, its effects last 12 hours. It should therefore not be used more than twice a day.

Figure 34.2 Examples of respiratory medication and histamine.

Doses are given by inhalation.

Adverse Effects

• Tremor: due to the beta receptors being stimulated.

Inflammation of the mucosa occurs in chronic asthma.

Corticosteroids can be used in chronic asthma. The actions of corticosteroids on the bronchi are not properly understood, but they might be effective due to the reduction of the inflammation of the mucosal oedema. They are no use for acute episodes, as they do not work fast enough. The dose is given via an inhaler, which is effective at limiting the dose because the liver clears corticosteroids administered in this way very quickly. So there is a good local effect that should not spread systemically.

Drugs such as beclometasone and budesonide can be used. In chronic asthma that is deteriorating, a short course of an oral glucocorticoid can be given, e.g. prednisolone.

Obstruction of the airflow is progressive and generally not reversible because of the tissue changes that have taken place. The two diseases associated with COPD are:

The two very often coexist.

Most common causes due to: