CLASSIFICATION OF ANTIHISTAMINES DRUGS

1. H1-Antagonists with classical structures

According to the chemical features, they are further classified as follows:

a. Ethylene diamine derivatives

b. Amino alkyl ether analogues

c. Cyclic basic chain analogues

d. Mono amino propyl analogues

d. i. Saturated analogues

d. ii. Unsaturated analogues

e. Tricyclic ring system or Phenothiazine derivatives

f. Dibenzocyclo heptane’s

g. Miscellaneous agents

h. Newer agents

II. H1-Antagonists with nonclassical structures

i. Azelastine

ii. Tazifylline

iii. Astemizole

III. Nonsedative H1-antihistamines

Nonsedative antihistamines bind only to peripheral H1-receptors and produce with little or no sedation because of poor CNS penetration and lower affinity for central histaminic activity.

These are divided into two main classes:

1. Piperazine derivatives—Cetirizine

2. Pyridine and piperidine derivatives—Loratadine, Fexofenadine, Terfenadine, Astemizole, Acrivastine

i. Loratadine

ii. Epinastine

iii. Rocastine

iv. Cetirizine

v. Fexofenadine

vi. Acrivastine

IV. Inhibition of histamine release (mast cells stabilizers)

i. Cromolyn sodium

ii. Nedocromil sodium