INTRODUCTION:• Antihistamines and nasal decongestants are drugs used to treat the common cold and allergic rhinitis, conditions that collectively cause more discomfort and lost work time than all other known illnesses combined.
• Nasal decongestants may be used in treating nasal congestion associated with sinusitis, middle ear infections, and upper respiratory infections.
• Allergic rhinitis is a condition caused by an immunological response resulting from the contact of one or more environmental allergens with the nasal mucosal tissue of an allergy-prone individual.
ANTIHISTAMINES• Histamine is a naturally occurring substance in the body released in response to tissue damage and the presence of microorganisms and allergens invading body tissue. Histamine dilates arterioles to allow increasing blood supply to capillaries and the tissues supplied by capillaries.
• Another manifestation of histamine is itching common at the site of insect bites or other sources of contact inflammation.• Antihistamines do not affect the release of histamine, but act primarily to block the action of histamine at the H1 histamine receptor sites.
• Antihistamines are capable of causing a wide variety of adverse effects. Many of these agents will produce varying degrees of sedation, particularly when used in combination with other depressant drugs or alcoholic beverages.
• Because of their chemical similarity to anticholinergic drugs, many antihistamines will cause dry mouth, constipation, blurred vision, and urinary retention. The effects are most prominent and troublesome in elderly, particularly those with glaucoma or prostatic hyperthropy.
• The most commonly used antihistamines for symptoms of allergies, desloratadine (Clarinex), loratadine (claritin, Alavert), fexofenadine (Allegra), and cetirizine HCl (Zyrtec),have been shown to be more specific in blocking peripheral H1 histamine receptors than those located in the CNS.
• Although most antihistamines are administered orally or by injection, several are available for rectal or topical administration.
DECONGESTANTS• Nasal decongestants are agents that constrict dilated blood vessels in the nasal mucosa by stimulating alpha !-adrenergic nerve receptors in vascular smooth muscle.
• Nasal decongestants are administered either topically, by inhalation, or orally. Topically used decongestants are effective rapidly.• A common problem in the use of these agents is rebound nasal congestion.
• Excessive use causes local ischemia and irritation of the nasal mucosa that may lead to extensive secondary vasodilation and congestion. Rebound congestion is the return of excessive tissue fluid occurring as a result of using nasal decongestions for time periods or dosages beyond the those recommended by the manufacturer.
• Although topical administration of decongestants results in only minimal absorption of drug through the nasal mucosa, adverse systemic effects, such as elevation of blood pressure and CNS stimulation, may occur if the decongestant solution drains through the nasal passage and is swallowed by the client.
• Some decongestants drugs are administered by inhalation using specially designed inhalers. Such inhalers are generally plastic containers containing an inert fibrous material impregnated with a volatile decongestant drug.
• Oral decongestants also act by constricting blood vessels in the nasal mucosa. They generally have a longer duration of action than the topical agents, but tend to have less constrictive effect. Oral decongestants may affect vascular beds other than those found in the nasal mucosa.
• It is important to realize that antihistamines and decongestants exert only a palliative effect on symptoms of the common cold and allergic rhinitis and are not curative. Symptomatic treatment of nasal congestion is useful, however, it relieves discomfort and prevents blowing of the nose, which may further irritate the nasal mucosa.