Phenylephrine

1. Health Canada Product Monograph — Phenylephrine

• Phenylephrine injection maintains adequate blood pressure during spinal or inhalation anesthesia.
• Phenylephrine injection treats vascular failure in shock, shock-like states, and drug-induced or other hypotension.
• Phenylephrine injection is used to convert (stop) paroxysmal supraventricular tachycardia, a fast, regular abnormal heart rhythm.
• Phenylephrine can be added to local anesthetic solutions to prolong spinal anesthesia or used as a vasoconstrictor for regional analgesia.

• Phenylephrine injection should be given to a pregnant woman only if clearly needed, since safety in pregnancy has not been established.
• In obstetric use, phenylephrine and other vasopressors used to correct hypotension or added to local anesthetic can interact with oxytocic drugs to cause severe, persistent high blood pressure, with a risk of rupturing a blood vessel in the brain around the time of delivery.

• It is not known whether phenylephrine passes into human breast milk, so caution is advised when giving it to a breastfeeding woman.

• Older adults should receive phenylephrine only with extreme caution, since they are more likely to have underlying heart disease and are more sensitive to its blood-pressure-raising effects.

• In children undergoing spinal anesthesia, phenylephrine may be used to prevent or treat low blood pressure, with the dose calculated according to body weight.

• For mild to moderate hypotension, phenylephrine is usually given by subcutaneous or intramuscular injection, or by slow intravenous injection, with the dose adjusted according to the blood pressure response.
• For severe hypotension or shock, phenylephrine may be given as a continuous intravenous infusion added to a dextrose or saline solution, with the infusion rate adjusted until the desired blood pressure is reached.
• Blood volume depletion should be corrected as fully as possible before giving any vasopressor, though phenylephrine can be started before and alongside fluid replacement in an emergency.
• For spinal-anesthesia-related hypotension, phenylephrine is usually given a few minutes before the anesthetic, by injection under the skin or into the muscle, or intravenously if hypotension develops during the procedure.
• For fast heart rhythm (paroxysmal supraventricular tachycardia), phenylephrine is given as a rapid intravenous injection, with each subsequent dose based on the blood pressure response.
• Injections should not be repeated more often than every 10 to 15 minutes, and higher initial and maintenance doses may be needed in patients with persistent or severe hypotension.
• To prolong spinal anesthesia, phenylephrine may be added directly to the anesthetic solution, which can increase the duration of motor block without increasing complications such as nausea or blood pressure swings.
• As a vasoconstrictor for regional analgesia, a small, specific amount of phenylephrine is added to the local anesthetic solution.

If overdose is suspected, seek emergency medical attention immediately or contact your regional Poison Control Centre without delay.

• When phenylephrine is given intravenously to treat a fast heart rhythm, an excessive dose can cause extra heart beats (ventricular extrasystoles) and brief runs of a dangerous fast heart rhythm (ventricular tachycardia).
• Overdose can also cause a sensation of fullness in the head and tingling in the arms or legs.
• Excessive blood pressure elevation from overdose can be reversed promptly with an alpha-adrenergic blocking agent such as phentolamine.

• Headache may occur.
• A slower heart rate (reflex bradycardia) may occur as the body responds to rising blood pressure.
• Excitability or restlessness may occur.
• Discomfort or a burning feeling at the injection site may occur.
• A feeling of anxiety or nervousness may occur.
• Pale skin may occur due to the drug's vessel-narrowing effect.

Serious side effects require immediate discussion with the prescriber or emergency care.

• Abnormal heart rhythms (arrhythmias) may occur, though rarely.
• Severe high blood pressure can occur if the dose is excessive, which can cause headache and a slow heart rate as warning signs.
• Reduced blood flow to the heart or brain can occur if blood pressure rises too high, particularly in patients with underlying heart or blood vessel disease.
• Tissue damage or death (necrosis) can occur at the injection site if the drug leaks outside the vein (extravasation), because of its strong vessel-constricting effect; prompt local treatment with an alpha-blocking agent such as phentolamine can help prevent lasting tissue injury.
• Reduced blood flow to the fingers or toes has been reported with vasopressor use, due to severe peripheral vasoconstriction.
• Allergic-type reactions, including severe asthma-like breathing difficulty, can occur in susceptible individuals due to the sodium metabisulfite preservative in the product.
• Rebound low blood pressure can occur if an infusion is stopped too abruptly, particularly after prolonged use.
• Reduced blood flow to the kidneys or other organs can occur with prolonged or high-dose use, since phenylephrine strongly constricts blood vessels throughout the body.
• Seek immediate medical attention for chest pain, severe headache, a very slow or irregular heartbeat, sudden vision changes, or signs of a severe allergic reaction such as difficulty breathing or swelling of the face or throat.

• Use with caution in patients with high blood pressure or an irregular heartbeat, since phenylephrine can worsen both.
• Use with caution in older adults, who are more sensitive to its pressor effects.
• Use with caution in patients with an overactive thyroid (hyperthyroidism), heart block, significant heart disease, or severe hardening of the arteries.
• Use with caution in patients with known sulfite sensitivity, since this product contains sodium metabisulfite, which can trigger allergic or asthma-like reactions, especially in people with asthma.
• Use with caution in patients taking monoamine oxidase inhibitors or tricyclic antidepressants, since these substantially increase phenylephrine's blood-pressure-raising effect.
• Use with caution when correcting hypotension caused by phenothiazine antipsychotics, ganglionic blockers, or reserpine, since these patients may need larger-than-usual doses to achieve a response.
• Use with caution when giving by peripheral intravenous line, since extravasation can cause serious local tissue injury; a central line is often preferred for infusions.
• Use with caution in patients with diabetes or peripheral vascular disease, given the risk of further reduced blood flow to the extremities.
• Use with caution in patients also receiving other alpha-adrenergic stimulant drugs, including certain nasal decongestants, due to additive blood-pressure-raising effects.
• Inspect the solution before use, and do not use it if it appears hazy or discoloured or contains visible particles.

• Should not be used in patients who are hypersensitive to phenylephrine or any ingredient in the formulation.
• Should be avoided, or used only with extreme caution, in patients with significant high blood pressure or ventricular tachycardia, given the drug's strong pressor effect.

• Monoamine oxidase (MAO) inhibitors markedly increase the pressor effect of phenylephrine, so the starting dose should be reduced and used with caution in patients on these drugs.
• Tricyclic antidepressants can also increase the blood-pressure-raising effect of phenylephrine.
• Oxytocic drugs used in obstetrics, combined with phenylephrine, can cause severe and persistent high blood pressure.
• Other vasopressors, particularly metaraminol, combined with phenylephrine during halothane anesthesia can cause serious abnormal heart rhythms and should be used together only with great caution.
• Ganglionic and adrenergic blocking agents, certain antihistamine tranquilizers (such as chlorpromazine and promethazine), and reserpine can cause exaggerated drops in blood pressure that phenylephrine may be used to correct, often requiring larger-than-usual doses.
• Digitalis glycosides combined with phenylephrine may increase the risk of abnormal heart rhythms.

• Not applicable; phenylephrine injection is given by a healthcare professional and is not taken by mouth, so food timing does not apply.

• Phenylephrine injection is given by a healthcare professional in hospital or clinical settings, timed to the clinical situation, such as before anesthesia or during treatment of low blood pressure, rather than on a fixed home dosing schedule.

• Store between 20°C and 25°C, protect from light, and discard any unused portion since each vial is for single use only.

• Phenylephrine injection is a fast-acting medicine given by a healthcare professional to raise blood pressure or treat a fast heart rhythm, and it is closely monitored with frequent blood pressure and heart rate checks during and after administration.