Antihistamines appear to compete with histamine for histamine H1-receptor sites on effector cells and antagonize the vasodilator effect of endogenously released histamine. Consequently antihistamines antagonize the physiological manifestations of histamine release in the nose following antigen-antibody interaction, such as congestion related to vascular engorgement, mucosal edema, and profuse, watery secretion, and irritation and sneezing resulting from histamine action on afferent nerve terminals.
Pseudoephedrine is an orally effective nasal decongestant.
In effective recommended oral dosage, pseudoephedrine produces minimal other sympathomimetic effects, such as pressor activity and CNS stimulation. The relief of the symptoms of upper respiratory mucosal congestion in perennial and allergic rhinitis, and for the relief of nasal congestion and eustachian tube congestion. Antihistamines should not be used to treat lower respiratory tract symptoms. Trinalin should be used with caution in patients with glaucoma, stenosing peptic ulcer, pyloroduodenal obstruction, prostatic hypertrophy or bladder neck obstruction, cardiovascular disease, those with increased intraocular pressure or diabetes mellitus. Because of the atropine-like action of antihistamines, this product should be used with caution in patients with a history of bronchial asthma.