6.7: Adrenergic Agonists: Mixed-Action Agents
Mixed-action adrenergic agonists, like ephedrine and pseudoephedrine, directly and indirectly affect adrenergic receptors. These agents stimulate adrenoceptors and indirectly release stored neurotransmitters, amplifying the adrenergic response.
Ephedrine and pseudoephedrine lack a catecholamine group, making them less susceptible to degradation by metabolic enzymes. They have increased oral bioavailability and lipophilicity, resulting in a longer duration of action. Their response is reduced by prior treatment with catecholamine-depleting agents like guanethidine or reserpine.
Ephedrine, the first orally active sympathomimetic, is used for asthma and nasal congestion. However, its potential for secondary abuse and the availability of safer alternatives have limited its use. Pseudoephedrine is primarily used as a nasal decongestant but is strictly regulated due to its potential for the illicit synthesis of methamphetamine.
