Neo-Synephrine 1% Injection

Generic Name: Phenylephrine hydrochloride
Product Name: Neo-Synephrine 1% Injection

Indication

Neo-Synephrine 1% Injection is used to maintain an adequate level of blood pressure during spinal and inhalation anaesthesia, and also to treat low blood pressure in the following situations:

Vascular failure in shock
Shock-like states
Drug induced hypotension
Hypersensitivity

Other uses of Neo-Synephrine include:

Overcoming paroxysmal supraventricular tachycardia
Prolonging spinal anaesthesia
Vasoconstriction in regional anaesthesia

Action

Phenylephrine is a synthetic agent similar to adrenaline (which is normally found in the body), which stimulates the sympathetic nervous system. It has selectivity for alpha receptors, which are found on blood vessels. Once stimulated, these alpha receptors cause significant constriction of blood vessels, which increases resistance. This effect causes a rise in blood pressure and redirects blood to essential organs such as the brain and heart. Because of its selectivity for alpha receptors, Phenylephrine does not cause an associated increase in heart rate, which is governed by beta receptors. In fact, as a reflex response to the increased resistance, Phenylephrine actually causes a slowing of the heart rate. If this is undesirable it may be combated with the use of atropine.

Dose advice

Neo-Synephrine 1% Injection can be administered subcutaneously, intramuscularly, by slow intravenous injection or by continuous intravenous infusion. Mild or moderate hypotension subcutaneously or intramuscularly
2-5mg initially -dose range is 1-10mg
initial dose should not exceed 5mg Intravenously
usual dose is 0.2mg – dose range is 0.1-0.5mg
initial dose should not exceed 0.5mg
doses should be repeated no more often than every 10-15 minutes 5mg IM should increase BP for 1-2 hours, whilst a 0.5mg IV dose should last about 15 minutes.
Severe hypotension and shock
correct blood volume depletion before administering Neo-Synephrine
if hypotension is drug induced, Phenylephrine should be used as an adjunct to other measures (eg: antidotes) Continuous infusion
10mg of Phenylephrine (1ml of 1% solution) should be added to 500ml Dextrose 5% or sodium chloride 0.9% – start infusion at 100-180mcg/min
maintenance rate of 40-60mcg/min can be started when blood pressure has stabilised – if response is inadequate, additional 10mg doses can be added to the infusion solution
regularly monitor blood pressure to prevent hypertension Spinal anaesthesia, to prevent hypotension during spinal anaesthesia, Neo-Synephrine should be administered IM 3-4 minutes before injection of the spinal anaesthetic
3mg is required for high anaesthetic levels, 2mg for lower levels
for emergencies during spinal anaesthesia, 0.2mg may be injected intravenously – any further IV injections should not exceed the previous dose by 0.1-0.2mg and no more than 0.5mg should be administered as a single dose
in children, a dose of 0.5-1mg/11.36kg can be administered subcutaneously or intramuscularly Prolongation of spinal anaesthesia
2-5mg of Neo-Synephrine can be added to the anaesthetic solution to prolong motor block by up to 50%
no increased incidence of adverse effects is seen Vasoconstrictor for regional anaesthesia
1mg should be added to every 20ml of anaesthetic solution
2mg or more is required before blood pressure changes are seen Paroxysmal supraventricular tachycardia
rapid intravenous injection (over 20-30 seconds) is recommended – initial dose should not exceed 0.5mg
subsequent doses should never exceed the previous dose by 0.1-0.2mg – single dose should not exceed 1mg