Phenylephrine

Question 1

Brand Name

Answer 1

Neosynephrine

Question 2

Pharmacological class

Answer 2

Selective alpha-1 agonist,
Synthetic noncatecholamine sympathomimetic

Question 3

Broad Category

Answer 3

Vasopressor

Question 4

MOA

Answer 4

Direct-acting alpha-1 agonist (Gq), binds directly on the receptor (not dependent on displacement or release of presynaptic endogenous NE)

Question 5

Indications / Clincal Uses

Answer 5

Hypotension
Decrease CO in pts with LV dysfunction
Obstetrics (agent of choice for regional anesthesia induced hypotension)

Topical: nasal decongestant, mydriatic

Question 6

Preparation and Dilution

Answer 6

Supplied as 1% (10 mg/mL) - MUST BE DILUTED
- 0.1 cc in 9.9 cc NS to yield 100 mcg/mL

Question 7

Bolus Dose

Answer 7

50-100 mcg

(or 0.5-1 mcg/kg)

Question 8

Continuous Infusion Dosing

Answer 8

20-200 mcg/min

(or weight based: 0.15-0.75 mcg/kg/min)

Question 9

Onset

Answer 9

Immediate (less than 1 min)

Question 10

CV effects

Answer 10

Vasoconstriction (venous and arterial)
Increased SVR/BP/MAP
INCREASES PVR
Reflex bradycardia

Organ perfusion: potent cutaneous, mesenteric, spenic, and renal vasoconstriction

Question 11

Respiratory effects

Answer 11

INCREASED PVR and PAP (worsens Pulm. HTN)

Question 12

Other effects / Adverse effects

Answer 12

Extravasation –> cause necrosis
Topical OD –> systemic absorption

Question 13

Contraindications (absolute)

Answer 13

PULM. HTN
- increases PVR and could cause death

Severe LV dysfunction/ Heart Failure
- Increases Afterload without increasing contractility results in CO reduction

Question 14

Tachyphylaxis?

Answer 14

Yes Acute tachyphylaxis can occur during continuous infusion, requiring progressive uptitrating to maintain pressure

Question 15

Drug-Drug Interactions?

Answer 15

Alpha-1 antagonists (prazosin, phentolamine, phenoxybenzamine) renders neo ineffective

Question 16

Metabolism

Answer 16

Extensive MAO metabolism
- Liver
- Plasma
- GI tract

Question 17

Excretion

Answer 17

Renal (inactive metabolites)

Question 18

Elimination half-life

Answer 18

2-3 hours

Question 19

Vd considerations

Answer 19

Relatively small
- hydrophilic, limited tissue penetration

Question 20

Duration

Answer 20

Short (10-15 mins)