Oral Anti-allergy Medicines

(i) Antihistamines

Histamines are released when your body defends against attack. If you have an allergy, your immune system treats the allergen as an invader. Histamine release causes inflammation characterized by expansion of small blood vessels and swelling of surrounding skin or tissues. Antihistamines block the effects of histamine and thus relieve symptoms of allergy. Oral antihistamines are used for the treatment of a number of allergies, including allergic rhinitis in which they reduce runny nose and sneezing but are usually less effective for nasal congestion. They are also used to treat urticarial rash (hives), itchy skin and eyes (eczema and conjuctivitis). They are also of some value in preventing hives and in treating drug allergies.

The term antihistamine is referred to medicines which act by blocking the histamine-1 receptor. They are classified as first generation (sedating) and second generation (non-sedating) antihistamines.

(a) Sedating Antihistamines

These are the older type of antihistamines and are characterized by their sedating and antimuscarinic effects. Classical examples of sedating antihistamines include brompheniramine, chlorpheniramine, cinnarizine, cyclizine, cyproheptadine, diphenhydramine, promethazine and triprolidine. Their sedative effect can vary from slight drowsiness to deep sleep. Diphenhydramine and promethazine are associated with more severe sedative effects and can be used for short-term sedation. Cyproheptadine is often associated with increase in appetite and weight gain.

(b) Non-sedating Antihistamines

Examples of non-sedating antihistamines include cetirizine, desloratadine, fexofenadine and loratadine. These are newer antihistamines and generally cause little or no drowsiness due to their poor penetration into the central nervous system.

(ii) Corticosteroids

The role of oral corticosteroids in the treatment of allergies is reserved only for severe cases, such as severe attacks of hives non-responsive to standard treatment and resistant severe eczema. (Please refer to the following link of the previous article ‘Information on oral corticosteroid for more detail:
http://www.drugoffice.gov.hk/eps/en/consumer/news_informations/dm_02.html )

(iii) Decongestants

Decongestants relieve nasal congestion and thus provide symptomatic relief to allergic rhinitis and hay fever. They reduce swelling of blood vessels inside your nasal cavity in the upper airway to make breathing easier. However, use of decongestants for more than 7 days can lead to rebound congestion and therefore they are not recommended to be used regularly or for long term. Examples of commonly used decongestants include pseudoephedrine and phenylephrine.

(iv) Montelukast

Montelukast, a leukotriene antagonist, has been used for the management of allergic rhinitis. Montelukast blocks the effect of potent inflammatory substances released from cells including mast cells and eosinophils, thus improving symptoms of allergic rhinitis, such as nasal congestion, rhinorrhea, sneezing and nasal itching.