Phenylephrine
Phenylephrine is an alpha1-adrenergic agonist vasopressor.
Group
Alpha1-adrenergic agonist vasopressor
Mechanism of Action
Contracts vascular smooth muscle through alpha1 receptors, increasing resistance and blood pressure.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Hypotension | 10 mcg/kg | IV | Every 0.25 h | Repeat as required. |
| Hypotension | 0.1 mg/kg | IM, SC | Every 0.25 h | Repeat as required. |
| Vasopressor infusion — Loading | 10 mcg/kg | IV | Once | |
| Vasopressor infusion — Maintenance | 3 mcg/kg/min | IV | Continuous | |
| Vasopressor infusion | 1–3 mcg/kg/min | IV | Continuous | Titrate to perfusion and BP; monitor reflex bradycardia and organ vasoconstriction. |
| Septic vasodilation | 2–10 mcg/kg/min | IV | Continuous | Titrate to perfusion and BP; monitor reflex bradycardia and organ vasoconstriction. |
| Hypovolemic shock vasopressor | 1–3 mcg/kg/min | IV | Continuous | Titrate to perfusion and BP; monitor reflex bradycardia and organ vasoconstriction. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Hypotension | 10 mcg/kg | IV | Every 0.25 h | Repeat as required. |
| Hypotension | 0.1 mg/kg | IM, SC | Every 0.25 h | Repeat as required. |
| Vasopressor infusion — Loading | 10 mcg/kg | IV | Once | |
| Vasopressor infusion — Maintenance | 3 mcg/kg/min | IV | Continuous | |
| Vasopressor infusion | 1–3 mcg/kg/min | IV | Continuous | Titrate to perfusion and BP; monitor reflex bradycardia and organ vasoconstriction. |
| Septic vasodilation | 2–10 mcg/kg/min | IV | Continuous | Titrate to perfusion and BP; monitor reflex bradycardia and organ vasoconstriction. |
| Hypovolemic shock vasopressor | 1–3 mcg/kg/min | IV | Continuous | Titrate to perfusion and BP; monitor reflex bradycardia and organ vasoconstriction. |
| Vasodilatory hypotension | 1–2 mcg/kg/min | IV | Continuous |
Horses
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Nephrosplenic entrapment | Reference only | IV | Infuse 10-20 mg in 500 mL saline over 10-15 minutes, or 20 mg in 1000 mL over 10 minutes. Admixture volume and duration must remain linked. | |
| Reported vasoconstrictor treatment | 5 mg/animal | IV | Specific indication and repeat frequency are not given in this dose line. |
Indications
- Hypotension
- Topical vasoconstriction
- Equine nephrosplenic entrapment
- Vasopressor infusion
- Septic vasodilation
- Hypovolemic shock vasopressor
- Vasodilatory hypotension
- Reported vasoconstrictor treatment
Contraindications
- Compromised cardiovascular status
Interactions
- Other alpha agonists, including alpha2 sedatives, can intensify cardiovascular effects.
Adverse effects
- Reflex bradycardia, excessive vasoconstriction and local irritation; equine hemorrhagic shock has occurred.
Toxicity
Marked exposure can cause hypertension, tachyarrhythmias, agitation, tremor, vomiting or seizures. Monitor ECG and BP; treatment depends on the cardiovascular state rather than the oral amount alone.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Phenylephrine injection 10 mg/mL | Injection | 10 mg / mL | IV |
Monitoring and Administration
During systemic treatment monitor blood pressure, pulse and rhythm. Equine nephrosplenic-entrapment use has potentially severe complications.
Protect from light and discard darkened solution; alkaline conditions accelerate oxidation.