18.4 : 上気道薬：充血除去薬

Decongestants relieve nasal congestion caused by allergies, colds, sinusitis, and other upper respiratory infections.

Nasal decongestants activate α-adrenergic receptors, constricting small blood vessels in nasal membranes and opening clogged nasal passages for sinus drainage.

Most nasal decongestants are available over the counter for topical and oral use, while some have restricted access.

Decongestants can be β-phenylethylamine derivatives or imidazoline derivatives.

β-phenylethylamine derivatives such as epinephrine, phenylephrine, and pseudoephedrine act on α₁-adrenoreceptors, while imidazoline derivatives such as oxymetazoline, naphazoline, tetrahydrozoline, and xylometazoline act on α₂-adrenoreceptors, resulting in vasoconstriction.

While topical decongestants provide short-term relief, they should not be used for more than three days to avoid rebound nasal congestion.

In addition, they may occasionally cause nasal burning, stinging, and dryness.

Conversely, oral decongestants provide longer-lasting relief but may cause systemic effects such as nervousness, tachycardia, blurred vision, vomiting, and insomnia.