Core pharmacology

Class Group

ADRENERGIC

Legacy Cicm Level

Level 3

Introduction

synthetic sympathomimetic amine with alpha1 agonist effects and no beta effects.

Indications Uses

1. hypotension occurring during general or spinal anaesthesia
2. as a nasal decongestant and
3. as a mydriatic agent

Presentation

clear solution containing 10 mg/ml of phenylephrine
hydrochloride.

Main Action

Peripheral vasoconstriction

Mechanism of action

direct-acting sympathomimetic agent
that has agonist effects at alpha-1 adrenoceptors. The drug does not affect
beta-adrenoceptors.

Physiological effects

CVS
Phenylephrine causes a rapid increase in the systolic and diastolic
blood pressures due to an increase in the systemic vascular resistance.
A reflex bradycardia occurs, which may cause a decrease in cardiac output.

RS
The drug is not known to cause bronchodilatation or act as a respiratory stimulant.

CNS
Phenylephrine has no stimulatory effects on the CNs. Phenylephrine
causes mydriasis.

GU
The drug reduces uterine artery blood flow via its effect at alphaadrenoceptors. Renal blood flow is decreased.

Metabolic/other
The drug may cause alterations in glucose metabolism.

Adverse Effects Toxicity

Headaches, sweating, hypersalivation, tremor,
and urinary retention.
Extravascular
injection of the drug may lead to tissue necrosis.
Hypertension with MAOIs.
Dysrhythmias with cardiac glycosides, TCAs, Quinidine.

Absorption

no quantitative data available

Distribution

no quantitative data available

Metabolism

in the gastrointestinal tract and liver
by monoamine oxidase

Excretion

no quantitative data available

Route And Dose

SC/IM: 2-5mg
IV: 50-100mcg boluses