Phenylehrine

Chemical

Direct acting synthetic non-catecholamine with α1 activity

Use

↑SVR
Nasal decongestant
Mydriatic to facilitate retinal exam

Presentation

Clear solution 10mg/mL

Dose

(IV) 50 – 100mcg
(SC/IM) 2 – 5mg

Route

IV, IM, SC

Onset

Immediate

DoA

5 mins

MoA

α1 agonist

α1 → Gq → stimulates Phospholipase C → ↑IP3 & DAG → opens Ca2+ channel

Effects of Ca2+

Smooth m.: VC

Cardiac: weak +ve inotropy

Metabolism: ↑BSL

PD

CVS

↑SVR

Reflex ↓HR

CNS

Mydriasis

Genitourinary

↓uterine artery BF

↓renal a. BF

GI

↑BSL

PK

A

IM/SC takes 15 mins to work

D

M

MAO of liver

E

Products of metabolism & route of elimination not identified

Adverse Effects

  • Only metabolised by MAO → C/I with MAOI
  • Headache
  • Sweating
  • Urinary retention
  • Tissue necrosis 

Everything else

  • Favourable cord gas profile → ∴used in obstetrics