phenylephrine

Prolongation of the duration of spinal anesthesia.
Localization of the effect of regional anesthesia.

High Alert

Management of hypotension associated with shock that may persist after adequate fluid replacement.
Management of hypotension associated with anesthesia.

Anesthesia adjunct

Action ⬆ ⬇

Constricts blood vessels by stimulating alpha-adrenergic receptors.

Therapeutic effects:

Increased BP.

Pharmacokinetics ⬆ ⬇

Absorption: Well absorbed from IM sites. IV administration results in complete bioavailability.

Distribution: Widely distributed to tissues.

Metabolism/Excretion: Metabolized by the liver into inactive metabolites.

Half-Life: 2.5 hr.

Time/Action Profile ⬆ ⬇

(vasopressor effects)

ROUTE	ONSET	PEAK	DURATION
IV	immediate	unknown	15–20 min
IM	10–15 min	unknown	0.5–2 hr
SUBQ	10–15 min	unknown	50–60 min

Contraind./Precautions ⬆ ⬇

Contraindicated in:

Hypersensitivity to bisulfites.

Use Cautiously in:

HF, coronary artery disease, or peripheral arterial disease;
OB: Has been used safely during Caesarean section procedure; safety of use during first or second trimester of pregnancy not established;
Lactation: Use while breastfeeding only if potential maternal benefit justifies potential risk to infant;
Pedi: Safety and effectiveness not established in children.

Adv. Reactions/Side Effects ⬆ ⬇

CV: ARRHYTHMIAS, bradycardia, chest pain, hypertension, ischemia, tachycardia

Derm: pruritus

GI: epigastric pain, nausea, vomiting

Local: phlebitis, sloughing at IV sites

Neuro: blurred vision, headache, insomnia, nervousness, tremor

Resp: dyspnea

Interactions ⬆ ⬇

Drug-drug:

Use with general anesthetics may result in myocardial irritability; use with extreme caution.
Use with MAO inhibitors, ergot alkaloids (methylergonovine), oxytocics, tricyclic antidepressants, atropine, corticosteroids, or atomoxetine results in severe hypertension.
Alpha-adrenergic blockers, PDE-5 inhibitors, calcium channel blockers, benzodiazepines, ACE inhibitors, or guanfacine may antagonize vasopressor effects.

Route/Dosage ⬆ ⬇

Hypotension

SC IM (Adults ): 2–5 mg.
SC IM (Children ): 0.1 mg/kg/dose every 1–2 hr as needed, maximum dose 5 mg.
IV (Adults ): 0.2 mg (range 0.1–0.5 mg), may be repeated every 10–15 min or as an infusion at 100–180 mcg/min initially, 40–60 mcg/min maintenance.
IV (Children ): 5–20 mcg/kg/dose every 10–15 min as needed or 0.1–0.5 mcg/kg/min infusion, titrate to effect.

Hypotension During Anesthesia

SC IM (Adults ): 2–3 mg has been used 3–4 min before spinal anesthesia to prevent hypotension.
IM SC (Children ): 0.5–1 mg/25 lb body weight.
IV (Adults ): 40–100 mcg; may repeat every 1–2 min as needed (not to exceed total dose of 200 mcg); if BP remains low, initiate continuous infusion at 10–35 mcg/min (not to exceed 200 mcg/min).

Vasoconstrictor for Regional Anesthesia

Local
(Adults ): Add 1 mg to every 20 mL of local anesthetic (yields a 1:20,000 solution).

Prolongation of Spinal Anesthesia

Spinal
(Adults ): 2–5 mg added to anesthetic solution.

Availability ⬆ ⬇

(Generic available)

Solution for injection: 0.1 mg/mL; 10 mg/mL
Premixed infusion: 20 mg/250 mL 0.9% NaCl; 25 mg/250 mL 0.9% NaCl; 40 mg/250 mL 0.9% NaCl; 50 mg/250 mL 0.9% NaCl

Assessment ⬆ ⬇

Monitor BP every 2–3 min until stabilized and every 5 min thereafter during IV administration.
- Monitor ECG continuously for arrhythmias during IV administration.
- Assess IV site frequently throughout infusion. Antecubital or other large vein should be used to minimize risk of extravasation, which may cause tissue necrosis.

Implementation ⬆ ⬇

Patient harm and fatalities have occurred from medication errors with phenylephrine. Prior to administration, have second practitioner independently check original order, dose calculations, concentration, route of administration, and infusion pump settings.
Anesthesia: Phenylephrine 2–5 mg may be added to spinal anesthetic solution to prolong anesthesia.
- Phenylephrine 1 mg may be added to each 20 mL of local anesthetic to produce vasoconstriction.

IV Administration:

IV: Blood volume depletion should be corrected, if possible, before initiation of IV phenylephrine.
Diluent: Dilute each 1 mg with 9 mL of sterile water for injection or D5W.
- For Biorphen, the 0.1 mg/mL solution must NOT be diluted prior to administration.
- For Biorphen 10 mg/mL solution, Diluent: dilute 1 mL (10 mg) with 99 mL of D5W or 0.9% NaCl before bolus or continuous infusion.Concentration: 100 mcg/mL. Solution is stable for 4 hr at room temperature or 24 hr if refrigerated.
Rate: Administer each single dose over 1 min.
Diluent: Dilute 10 mg in 250 or 500 mL of D5W or 0.9% NaCl. For Biorphen, dilute 10 mg in 500 mL of D5W or 0.9% NaCl.Concentration: 20 or 40 mcg/mL.
Rate: Titrate rate according to patient response. Infuse via infusion pump to ensure accurate dose rate.

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Pronunciation ⬇

Classifications ⬆ ⬇

Indications ⬆ ⬇