Phenylephrine
Synthetic α1-agonist
Pure α1 agonist → vasoconstriction. No β activity.
Indications
- •Anesthesia-induced hypotension
- •OB spinal hypotension (preferred over ephedrine for fetal pH)
- •Mydriasis (ophthalmic)
Dosing
| Context | Adult | Pediatric |
|---|---|---|
| Bolus | 50–200 mcg IV | — |
| Infusion (general OR) | 0.15–1.5 mcg/kg/min | — |
| OB spinal prophylaxis (SOAP 2018) | 25–50 mcg/min infusion at spinal placement; titrate to baseline SBP; OR variable-rate 50 mcg bolus PRN | — |
Pharmacokinetics
Onset 1 min. Duration 10–20 min.
Hemodynamic effects
↑SVR, ↑BP. Reflex bradycardia (often ↓CO).
Side effects
- !Bradycardia + ↓CO (relevant in poor LV function)
- !Reduced uteroplacental flow at high dose
Contraindications
- ×Severe LV dysfunction (relative — reduced CO with vasoconstriction)
Clinical pearls
- ★OB spinal: phenylephrine maintains umbilical artery pH better than ephedrine.
- ★Cardiac surgery off-pump: phenyl preferred for systemic pressure during graft anastomoses.
- ★Watch for reflex bradycardia in LVH/HOCM patients.
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