1. Antihistamines and Nasal
Decongestants

2. 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.

3. • Nasal decongestants may be used in treating nasal
congestion associated with sinusitis, middle ear
infections, and upper respiratory infections.

4. • 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.

5. 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.

6. • 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.

7. • 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.

8. • 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.

9. • 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.

10. • Although most antihistamines are administered
orally or by injection, several are available for rectal
or topical administration.

11. DECONGESTANTS
• Nasal decongestants are agents that constrict
dilated blood vessels in the nasal mucosa by
stimulating alpha !-adrenergic nerve receptors in
vascular smooth muscle.

12. • 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.

13. • 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.

14. • 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.

15. • 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.

16. • 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.

17. • 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.