phenylephrine hydrochloride (NeoSynephrine, Neofrin)

GENERIC NAME: phenylephrine hydrochloride

BRAND NAME: NeoSynephrine, Neofrin

DRUG CLASS AND MECHANISM: Phenylephrine is a man-made drug that stimulates receptors (alpha1 receptors) on blood vessels and cause blood vessels to constrict (vasoconstriction). It is a vasoconstrictor medication, structurally similar to epinephrine and ephedrine. Vasoconstriction increases blood pressure. Phenylephrine increases blood pressure and heart rate without affecting heart rhythm.



PREPARATIONS: Injection: 10 mg/ml

STORAGE: Store phenylephrine injections between 15 C to 30 C (59 to 86 F).

PRESCRIBED FOR: Phenylephrine is used for maintenance of blood pressure during anesthesia, for the treatment of vascular failure in shock or shock-like states, drug-induced hypotension, and to overcome paroxysmal supraventricular tachycardia (abnormally fast heart beats) during anesthesia.



  • Mild to moderate hypotension, hypotension during spinal anesthesia: 0.1 to 0.5 mg intravenously every 10 to 15 minutes or 1 to 5 mg subcutaneously or by intramuscular injection.
  • Severe Hypotension, shock: 100 to 180 mcg/minute continuous intravenous infusion until blood pressure is stable; decrease rate to 40 to 60 mcg/minute to maintain blood pressure.
  • Paroxysmal supraventricular tachycardia: 0.5 mg intravenous injection rapidly given within 20 to 30 seconds. Additional dose should not exceed 0.1 to 0.2 mg more than preceding dose, based on the initial blood pressure response; maximum dose is 1 mg.

DRUG INTERACTIONS: Phenylephrine should be used cautiously with MAO inhibitors like selegiline (Eldepryl, Zelapar), phenelzine (Nardil), isocarboxazid (Marplan), because they can also increase blood pressure and can cause a serious hypertensive episode. A similar reaction occurs when phenylephrine is combined with amphetamine and related drugs.

Phenylephrine should be used with caution with antidepressants like amitriptyline (Elavil, Endep), nortriptyline (Pamelor, Aventyl), doxepin (Sinequan, Adapin), and trazodone (Deyrel). Such anti-depressants may increase blood pressure if used together with phenylephrine.

PREGNANCY: There are no adequate studies done on phenylephrine to determine safe and effective use in pregnant women.

NURSING MOTHERS: It is not known whether phenylephrine enters breast milk; therefore, it is best to be cautious before using it in nursing mothers.

SIDE EFFECTS: Side effects of phenylephrine are headache, reflex bradycardia (slow heart beat), excitability, anxiety, restlessness, high blood pressure, and rarely abnormal heart beats.


FDA Prescribing Information.

Medscape. phenylephrine.

Medically Reviewed by a Doctor on 7/30/2014

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