216 Section 5/ AutacoidsANTIHISTAMINICSAntihistaminics are classified in table 5.1.1.
Pharmacological Actions
Most of the antihistaminics (H 1 -receptor
antagonists) have similar pharmacological
actions and conventionally can be discussed
together.
- Antihistaminic action: The antihista-
minics blocks histamine effects at a
variety of sites. They inhibit most re-
sponses of smooth muscles to hista-
mine. They antagonize the stimulant
actions of histamine on various smooth
muscles of the respiratory system, gas-
trointestinal tract, the uterus and the
blood vessels. They inhibit the hyperten-
sive effect (in rabbits & guinea pigs) and
hypotensive effect (in cat & dog) pro-
duced by histamine. They also reduced
the triple response induced by histamine
injection.
Histamine induced bronchospasm in
many animal species, especially in guinea
pigs can easily be antagonized by antihis-
taminics.Table 5.1.1: Classification of antihistaminic agents.
I. Ethanolamines
Diphenhydramine (BENADRYL) 25-50 mg/day
Dimenhydrinate (DRAMAMINE) 25-50 mg/day, IM
II. Ethylenediamines
Pyrilamine maleate (DORANTAMIN) 25-50 mg/day
Tripelennamine 25-50 mg/day
III.Alkylamines
Pheniramine maleate (AVIL) 25-50 mg/day, IM
Chlorpheniramine maleate (PIRITON) 2-4 mg/day, IM
Triprolidine (ACTIDIL) 2.5-5 mg/day
IV.Phenothiazines
Promethazine (PHENERGAN) 25-50 mg/day, IM
Promethazine chlorotheophyllinate (AVOMINE) 25-75 mg/day
V. Piperazines
Cyclizine hydrochloride (MAREZINE) 50 mg/day
Meclizine hydrochloride (ANCOLAN) 25-50 mg/day
Buclizine (LONGIFENE) 25-50 mg/day
VI.Piperidines:
Loratidine (LORMEG) 10 mg OD
Fexofenadine (ALLEGRA) 60-180 mg OD
Astemizole (STEMIZ) 10 mg/day
VII.Miscellaneous compounds
Cetirizine (CETZINE) 10 mg/day
Levocetirizine (TECZINE) 5 mg/day
Cyproheptadine (Antihistaminic/antiserotonin; PERIACTIN) 4 mg/day
Cinnarizine (Antivertigo; STUGERON) 25-50 mg/day