Phenergan Vc (Promethazine HCl and Phenylephrine HCl Syrup) Drug Information: Clinical Pharmacology

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May 27, 2012

Phenergan Vc

Vertigo »

Vertigo introduction

Balance is defined as a state of equilibrium. It takes significant amount of work for this to occur in the body. The brain uses inputs from many sources to understand where the body is located in relationship to the world and to allow it to function. Sensory information from the eyes, ears, and position receptors in the rest of the body help keep the body upright and allow it to move in a coordinated fashion.

Information comes to cerebellar lobes located in the base of the brain from the vestibular system in the inner ear, vision from the eyes, and proprioception (position) receptors located throughout the body that send signals through the spinal cord. The cerebellum uses that information to maintain posture, coordinate body motions like walking and also coordinate fine motor skills like using a pen to write.

Vertigo, a feeling of spinning movement and sometimes accompanied by nausea and vomiting, occurs when an...

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Please Note: This Brand Name drug is no longer available in the US.
(Generic versions may still be available.)

CLINICAL PHARMACOLOGY

Promethazine

Promethazine is a phenothiazine derivative which differs structurally from the antipsychotic phenothiazines by the presence of a branched side chain and no ring substitution. It is thought that this configuration is responsible for its relative lack (1/ 10 that of chlorpromazine) of dopaminergic (CNS) action. Promethazine is an H₁ receptor blocking agent. In addition to its antihistaminic action, it provides clinically useful sedative and antiemetic effects. In therapeutic dosages, promethazine produces no significant effects on the cardiovascular system. Promethazine is well absorbed from the gastrointestinal tract. Clinical effects are apparent within 20 minutes after oral administration and generally last four to six hours, although they may persist as long as 12 hours. Promethazine is metabolized by the liver to a variety of compounds; the sulfoxides of promethazine and N-demethylpromethazine are the predominant metabolites appearing in the urine.

Phenylephrine

Phenylephrine is a potent post- synaptic a- receptor agonist with little effect on b- receptors of the heart. Phenylephrine has no effect on b-adrenergic receptors of the bronchi or peripheral blood vessels. A direct action at recep- tors accounts for the greater part of its effects, only a small part being due to its ability to release norepinephrine. Therapeutic doses of phenylephrine mainly cause vasoconstriction. Phenylephrine increases resistance and, to a lesser extent, decreases capacitance of blood vessels. Total peripheral resistance is increased, resulting in increased systolic and diastolic blood pressure. Pulmonary arterial pressure is usually increased, and renal blood flow is usually decreased. Local vasoconstriction and hemostasis occur following topical application or infiltration of phenylephrine into tissues. The main effect of phenylephrine on the heart is bradycardia; it produces a positive inotropic effect on the myocardium in doses greater than those usually used therapeutically. Rarely, the drug may increase the irritability of the heart, causing arrhythmias. Cardiac output is decreased slightly. Phenylephrine increases the work of the heart by increasing peripheral arterial resistance. Phenylephrine has a mild central stimulant effect.

Following oral administration or topical application of phenylephrine to the mucosa, constriction of blood vessels in the nasal mucosa relieves nasal congestion associated with allergy or head colds. Following oral administration, nasal decongestion may occur within 15 or 20 minutes and may persist for up to 4 hours. Phenylephrine is irregularly absorbed from and readily metabolized in the gastrointestinal tract. Phenylephrine is metabolized in the liver and intestine by monoamine oxidase. The metabolites and their route and rate of excretion have not been identified. The pharmacologic action of phenylephrine is terminated at least partially by uptake of the drug into tissues.

Last reviewed on RxList: 12/8/2004
This monograph has been modified to include the generic and brand name in many instances.