A drug may be classified by the chemical type of the active ingredient or by the way it is used to treat a particular condition. Each drug can be classified into one or more drug classes.
Ophthalmic antihistamines and decongestants are products designed especially so that it can be applied in the eyes to treat hay fever symptoms such as runny eyes and redness.
Antihistamines block the histamine receptors and inhibit the action of histamine, which when activated cause runny eyes, redness, itching and so on. Decongestants are sympathomimetic drugs that relieve redness in the eyes.
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