Phenylephrine

Phenylephrine is a vasopressor with activity at the alpha-1 adrenergic receptor with no affinity for the beta-adrenergic receptors (see table below). It is used for severe hypotension and does not affect heart rate.

Per Clinical Pharmacology:

For the treatment of hypotension or shock:

•for mild to moderate hypotension:

Subcutaneous or Intramuscular dosage:

Adults: 2—5 mg IM or SC (range: 1—10 mg), repeated no more often than every 10—15 minutes. Maximum initial IM or SC dose is 5 mg.

Intravenous dosage:

Adults: 0.2 mg IV (range: 0.1—0.5 mg), given no more frequently than every 10—15 minutes. Maximum initial IV dose is 0.5 mg.

•for severe hypotension or shock:

NOTE: Patients with hypovolemia should receive adequate fluid resuscitation prior to administration of phenylephrine.

NOTE: Although FDA-approved for the treatment of severe shock states, phenylephrine is not recommended as first-line therapy for septic shock. Dopamine and norepinephrine have been recommended as first-line vasopressor.

Intravenous dosage:

Adults: The FDA-approved dosage is 100—180 mcg/min IV as a brief initial infusion until the blood pressure stabilizes, with dosage titration to the desired mean arterial pressure (MAP) and systemic vascular resistance (SVR).The usual maintenance infusion rate ranges between 40 and 60 mcg/min IV.

Alternatively, IV infusion rates have been recommended according to body weight for septic shock patients. A recent evidence-based medicine review has recommended an initial infusion of 0.5 mcg/kg/min IV, followed by titration up to 5—8 mcg/kg/min IV based on limited clinical trials of septic shock patients.

A dosage range of 0.5 to 9 mcg/kg/min IV has been reported to maintain MAP > 70 mmHg in 13 septic shock patients; however, these patients also received dopamine 5 mcg/kg/min IV for renal perfusion and possibly dobutamine for inotropic support.

See Clinical Pharmacology for more details.

Comparison of Inotropes and Vasopressors Circulation 2008;118;1047-1056