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Autocoids (Histamine and Serotonin)

1 out of 9

All are 2nd generation antihistaminic except (LQ)

A Azelastine
B Cyclizine

C Fexofenadine
D Loratidine

Ans. B Cyclizine (Ref. KDT pharmacology 6th ed. 156, 158)

Second Generation Antihistaminics

The second-generation antihistaminics (SGAs) may be defined as those H1 receptor blockers marketed after 1980, which have one or more of the following properties:

a. Higher H1 selectivity: no anticholinergic side effects.

b. Absence of CNS depressant property.

c. Additional antiallergic mechanisms apart from histamine blockade: some also inhibit late phase allergic reaction by acting on leukotrienes or by anti-platelet activating factor effect.

These newer drugs have the advantage of not impairing psychomotor performance (driving etc. need not be contraindicated. , produce no subjective effects, no sleepiness, and do not potentiate alcohol or benzodiazepines. Their principal indications are:

a. Allergic rhinitis and conjunctivitis, hay fever, pollinosis – control sneezing, runny but not blocked nose, and red,

watering, itchy eyes.

b. Urticaria, dermographism, atopic eczema.

c. Acute allergic reactions to drugs and foods.

They have poor antipruritic, antiemetic and antitussive actions.

a. Terfenadine It is the first SGA, highly HI selective, with a rapid onset (1-2 hr) and moderate duration (12-24 hr) of action.

b. Fexofenadine It is the active metabolite of terfenadine.

c. Astemizole Actions of astemizole are similar to terfenadine, but it has slow onset (2-4 hr) and long duration (2-5 days) of action.

d. Loratadine Another long acting selective peripheral H1 antagonist that lacks CNS depressant effects and is faster acting than astemizole.

e. Desloratadine It is the major active metabolite of loratadine effective at half the dose. Noninterference with psychomotor performance and cardiac safety are documented.

f. Cetirizine It is a metabolite of hydroxyzine with marked affinity for peripheral H1 receptors; penetrates brain poorly.

g. Azelastine This newer HI blocker has good topical activity; in addition inhibits histamine release and inflammatory reaction triggered by LTs and PAF; and has bronchodilator property.

h. Mizolastine nonsedating antihistaminic is effective in allergic rhinitis and urticaria by single daily dosing despite a t1/2 of 8-10 hr and no active metabolite.

Ebastine Another newer SGA that rapidly gets converted to the active metabolite carbastine having a t1/2 of 10-16 hr. It is

nonsedating and active in nasal and skin allergies.

Autocoids (Histamine and Serotonin) Flashcard List

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