Phenylephrine Hydrochloride injection is indicated for the treatment of clinically significant hypotension, mainly due to vasodilation occurring during anesthesia.

Phenylephrine is a selective α-1 adrenergic receptor agonist. After intravenous administration, it causes an increase in systolic and diastolic blood pressure as well as mean arterial pressure due to peripheral vasoconstriction. The onset of action is rapid, usually within minutes.

Following IV administration of phenylephrine hydrochloride, increases in systolic pressure, diastolic pressure, mean arterial pressure, and total peripheral vascular resistance are observed. As blood pressure rises, vagal stimulation occurs, which may lead to reflex bradycardia. Phenylephrine acts on multiple vascular beds, including renal, pulmonary, and splanchnic circulation.

Dosing for treatment of hypotension during anesthesia: The recommended initial dose is 40 to 100 mcg administered by intravenous bolus. Additional boluses may be administered every 1-2 minutes as needed; not to exceed a total dosage of 200 mcg in a single administration. Do not use if the solution is colored or cloudy or if it contains particulate matter. Discard any unused portion.

The blood pressure–raising effect of Phenylephrine may be increased in patients receiving Monoamine Oxidase Inhibitors (MAOIs), oxytocin, oxytocic drugs, tricyclic antidepressants, and atropine. The pressor effect of Phenylephrine may be reduced in patients taking α-adrenergic antagonists, combined α and β blockers, calcium channel blockers, and benzodiazepines.

Adverse effects are mainly due to excessive pharmacological action. Reported side effects include reflex bradycardia, ischemia, hypertension, vomiting, nausea, neck pain, and tremors affecting different body systems.

Data from clinical studies and meta-analyses indicate that Phenylephrine injection used during cesarean section has not been associated with major birth defects or miscarriage. However, there is no sufficient data for use during the first or second trimester.There are also no data regarding the presence of Phenylephrine or its metabolites in human or animal milk, nor its effects on the breastfed infant or milk production.

Because of its vasoconstrictive and blood pressure–raising effects, Phenylephrine may worsen angina in patients with severe arteriosclerosis or a history of angina, aggravate heart failure, and increase pulmonary arterial pressure.

It may also cause severe bradycardia and reduced cardiac output.

In septic shock patients, it may increase the need for renal replacement therapy; therefore, renal function should be monitored.

Overdose may cause rapid and severe elevation of blood pressure. Symptoms include headache, vomiting, hypertension, reflex bradycardia, head fullness, tingling sensations in extremities, and cardiac arrhythmias.

Alpha adrenoceptor blocking drugs

Store below 30°C in a dry place, protected from light. Keep out of reach of children.