17.03.3 Sympathomimetic

The sympathomimetic most commonly used in rhinitis/rhinorrhea is ephedrine, which is also known as pseudoephedrine. Ephedrine, as discussed in the Chapter on the sympathetic nervous system, is a mixed acting amine, which means it has both direct and indirect effects at adrenoceptors. The direct action is that ephedrine is a weak agonist at a- and b- adrenoceptors. The indirect action is that ephedrine releases noradrenaline, which in turn stimulates the a- and b- adrenoceptors.

Ephedrine is active after oral administration, and after oral administration it causes an a-adrenoceptor-mediated vasoconstriction, which overcomes the nasal decongestant. After oral administration, ephedrine also causes a b₂-adrenoceptor-mediated bronchodilation, which is useful in bronchial congestion, which often occurs with nasal congestion. In addition to being active after oral administration, ephedrine can be applied topically to the nasal mucosa in a nasal spray. With topical administration, this limits the effects to the nose. Topical administration limits adverse effects, but also reduces the beneficial bronchodilation. After oral administration, the adverse effects observed with ephedrine include central nervous system stimulation, and sympathomimetic actions such as an increased heart rate (tachycardia) and an increased blood pressure.