Local Anesthetics: Vasoconstrictors

Adrenergic agonists, its important to know what the systemic effects of various vasoconstricors are.

Phenylephrine (a pure alpha agonist): doesn’t act on beta-receptors at all

Epinephrine (alpha, beta-1, beta-2 agonist): hydroxylated para position on the ring, epinephrine is a catecholamine. Dose concentration matters; low dose means that the concentration is below the alpha threshold. With respect to alpha-1, beta-1 and beta-2 receptors, epinephrine acts differently based on how much is present. If it is “below the alpha threshold” there is no alpha response (beta response only). If the epinephrine concentration is above the alpha threshold, alpha, beta-1 and beta-2 are activated, but the beta-2 response is masked because alpha and beta-1 are stronger.

Norepinephrine, levarterenol (Levophed) (alpha, beta-1 agonist; little beta-2): the structure lacks a terminal methyl group on the nitrogen. There is a small amount of beta-2 activation, mostly alpha and beta-1 are activated. When norepinephrine is marketed, it is called Levarterenol (Levophed).

Levonordefrin (Neo-Cobefrin): Syntetic vasoconstrictor, usually formulated with carbocaine. A methyl group is attached to the carbon chain. Levonordefrin has similar effects to epinephrine, but greater alpha/ beta-2 specificity and is 1/5 as potent for alpha (that’s why its used in 1:20,000 concentration).

Category: Pharmacology Notes