Betamethasone is a corticosteroid with mainly glucocorticoid activity. It induces phospholipase A2 inhibitory lipase (lipocortins) and sequentially inhibits the release of arachidonic acid, thereby depressing the formation, release, and activity of prostaglandins, leukotrienes, and other inflammatory mediators.
Phenylephrine is a sympathomimetic with mainly direct effects on alpha-adrenergic receptors and weak beta-adrenergic activity. It causes vasoconstriction of the arterioles of the nasal mucosa and conjunctiva; activates the dilator muscle of the pupil to cause contraction; produces vasoconstriction of arterioles in the body and produces systemic arterial vasoconstriction.
Lidocaine alters signal conduction in neurons by blocking the fast voltage-gated Na+ channels in the neuronal cell membrane responsible for signal propagation. With sufficient blockage, the membrane of the postsynaptic neuron will not depolarize and will thus fail to transmit an action potential.