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
