Decongestants

Question 1

α-adrenergic agonists

Answer 1

Vasoconstriction by α-adrenergic agonists is prominent in the vessels of the nasal mucosa, making these medications effective decongestants.

Phenylephrine, xylometazoline, and oxymetazoline are used as topical preparations for the treatment of allergic rhinitis and common cold associated congestion and rhinitis

. rapidly declining effect after a few days of use. This phenomenon is called tachyphylaxis

occurs because of decreased production of endogenous norepinephrine from the nerve terminals due to a negative feedback mechanism, resulting in relative vasodilation (ie, removal of normal vasoconstrictive tone) and subsequent edema and congestion.

leads to exacerbation of the nasal congestion symptoms. Rebound rhinorrhea (ie, rhinitis medicamentosa) is described as nasal congestion without cough, sneezing, or postnasal drip.

Rebound rhinorrhea is associated with the use of topical decongestants for > 3 days. The use of adrenergic agonists should be stopped to allow the restoration of normal norepinephrine feedback pathways.

Question 2

nitroglycerine

Answer 2

decrease in its effect is explained by the diminished release of NO from the target cells.

Drug-free intervals of 8–10 hours should be maintained during the use of nitroglycerine to prevent tachyphylaxis.