Co-Phenylcaine Forte Spray Mechanism of Action

Pharmacology: Pharmacodynamics and Pharmacokinetics: Co-Phenylcaine Forte Spray contains two active ingredients: Lidocaine hydrochloride 50 mg/mL, a local anaesthetic and phenylephrine hydrochloride 5 mg/mL, an agent that causes blood vessel constriction.
Lidocaine hydrochloride is a local anaesthetic which stabilizes the neuronal membrane and prevents initiation and transmission of nerve impulses, thereby effecting local anaesthetic action. Like other anaesthetics, lidocaine impairs the generation and conduction of the nerve impulses by slowing depolarization. This results from blocking of the large transient increase in permeability of the cell membrane to sodium ions that follows initial depolarization of the membrane. Onset of action is rapid and may last for 1 hour. It does not produce irritation to mucous membranes due to its non-ester structure and it is not detoxified by circulating plasma esterases. The liver is the chief site of biotransformation of lidocaine and both free and conjugated forms of the drug are excreted in the urine.
Phenylephrine hydrochloride is a sympathomimetic agent with direct effects on the α-1 adrenoreceptors. It has mainly α-1 adrenergic activity. Phenylephrine is a relatively selective α-1-adrenoreceptor agonist. α-1 receptors are widely expressed in vascular beds and their activation leads to vasoconstriction. The phenylepherine in Co-Phenylcaine Forte Spray constricts the blood vessels locally, which can decrease the systemic absorption of lidocaine and restrict bleeding. It also decreases the onset of action and increases the duration of action of lidocaine. Its nasal decongestant action can assist in easier passage of endoscopes.
Systemic bioavailability of phenylephrine is only about 40% following administration. Peak plasma concentrations are achieved in 1-2 hours. The mean plasma half-life is in the range of 2-3 hours. Penetration into the brain appears to be minimal.