2.  The respiratory agents presented here are divided into two primary categories.
 The first group includes drugs that treat acute and relatively minor problems, such as
 nasal congestion,
 coughing,
 and seasonal allergies.
 The second category includes drugs that treat more chronic and serious airway obstructions,
such as
 bronchial asthma,
 chronic bronchitis,
 and emphysema

3. Antitussives
Antitussive drugs are used to suppress coughing associated with the common cold and other
minor throat
irritations.
Antitussives are usually recommended for short-term use in relieving symptomatic coughing
Coughing is a type of defense mechanism that can help expel mucus and foreign material from the
upper respiratory tract
Antitussives may be helpful in treating an annoying dry cough, but use of these drugs to treat an
active and productive cough may not be justified

4. codeine and similar opiate derivatives suppress the cough reflex by a central inhibitory effect
Other nonopioid antitussives work by inhibiting the irritant effects of histamine on the respiratory
mucosa or by a local anesthetic action on the respiratory epithelium.

6. Adverse effects
The primary adverse effect associated with most antitussives is sedation. Dizziness and
gastrointestinal upset may also occur.

7. Decongestants
Congestion within and mucous discharge from the upper respiratory tract are familiar symptoms of
many
conditions. Allergies, the common cold, and various respiratory infections often produce a runny
nose and a stuffy head sensation
Decongestants used to treat these symptoms are usually alpha-1–adrenergic agonists
MOA: These agents bind to alpha-1 receptors located on the blood vessels of the nasal mucosa
and stimulate vasoconstriction, thus effectively drying up the mucosal vasculature and decreasing
local congestion in the nasal passages

8. Depending on the preparation, these agents may be taken systemically or applied locally to the
nasal mucosa via aerosol sprays
Adverse effects
The primary adverse effects associated with decongestants are headache, dizziness,
nervousness, nausea,
and cardiovascular irregularities (increased blood pressure, palpitations).

10. Antihistamines
Histamine is an endogenous chemical that is involved in the normal regulation of certain
physiologic
functions (gastric secretion, CNS neural modulation), as well as various hypersensitivity (allergic
reactions).
Histamine exerts its effects on various cells through four primary receptor subtypes:
 H1,
 H2,
 H3,
 and H4 receptors

11. H1-receptor blockers
Antihistamines are drugs that specifically block the H1 subtype of histamine receptors; that is, the
effects of histamine during allergic reactions, respiratory infections, and so forth are mediated
primarily through the H1 receptor located on vascular, respiratory, and other tissues.
H2-receptor blockers
H2 receptors are involved primarily in the regulation of gastric acid secretion. Drugs that
selectively block the H2 receptor (referred to simply as H2 antagonists) may help control gastric
secretion in conditions such as peptic ulcer;

12. H3-receptor blockers
A third receptor subtype, the H3 receptor, has been identified, and this subtype may be involved in
the local regulation of histamine release from CNS nerve terminals
H4-receptors
► a new H4 receptor has been identified on blood cells or cells derived from blood cells.
► The clinical and pharmacologic significance of H3 and H4 receptors remains to be determined.

13. Therapeutic indications of Antihistamines
By blocking the effects of histamine on the upper respiratory tissues, these drugs help decrease
nasal congestion, mucosal irritation and discharge (rhinitis, sinusitis), and conjunctivitis that are
caused by inhaled allergens. Similarly, antihistamines may decrease the coughing and sneezing
associated with the common cold.
Antihistamines may be used as an adjunct in patients with asthma to help control rhinitis and
sinusitis

14. Adverse effects
The primary adverse effects associated with antihistamines are sedation, fatigue, dizziness,
blurred
vision, and incoordination. Gastrointestinal distress (nausea, vomiting) is also quite common.
Certain side effects, however, are related directly to each drug’s ability to cross the blood-brain
barrier
First-generation antihistamines
The original or “first-generation” antihistamines readily cross the blood-brain barrier and enter the
brain, thus causing CNS-related side effects such as sedation and psychomotor slowing
Second-generation antihistamines
do not easily cross the blood brain barrier, and the risk of sedation and other CNS side
effects is reduced substantially

15. Newer “second-generation” antihistamines, also known as nonsedating antihistamines, include
cetirizine, loratadine, desloratidine and fexofenadine

16. Mucolytics and Expectorants
Mucolytic drugs attempt to decrease the viscosity of respiratory secretions
Expectorant drugs facilitate the production and ejection of mucus. These drugs are used to
prevent the accumulation of thick, viscous secretions that can clog respiratory passages and lead
to pulmonary problems.

18. Acetylcysteine
The primary mucolytic drug currently in use is acetylcysteine. This drug is thought to work by
splitting the disulfide bonds of respiratory mucoproteins, thus forming a less viscous secretion.
Acetylcysteine is usually administered directly to the respiratory mucosa by inhalation or
intratracheal instillation (through a tracheostomy)
Adverse effects
The primary adverse effects associated with this drug include nausea, vomiting, inflammation of
the oral mucosa (stomatitis), and rhinorrhea. However, serious adverse effects are relatively rare.

19. Guaifenesin
Several expectorant agents have been used in the past, but guaifenesin is the only drug currently
acknowledged by the FDA to have evidence of therapeutic effects
This drug is administered to increase the production of respiratory secretions, thus encouraging
ejection of phlegm and sputum