Isoprenaline

Chemical

Synthetic catecholamine with β adrenergic action

Use

Bradycardia/CHB

Presentation

Clear solution, 1mg/mL for dilution

Aerosol 400mcg INH dose

Dose

1 – 20mcg/min

Route

Infusion, inhaled for bronchodilation

Onset

Immediate

DoA

MoA

The most potent sympathomimetic of β receptors1 = β2)

 β1 receptor → GS → activates AC → ↑cAMP → ↑Ca2+

Effects of ↑Ca2+

Heart: +ve inotropy, +ve chronotropy, +ve dromotropy

Metabolic: lipolysis, ↑FFAs

Renal: ↑renin, ↑AII, VC

 β 2 receptor → GS → activates AC → ↑cAMP → ↑Ca2+

Effects of ↑Ca2+

Heart: ↑Ca2+ → ↑FoC

Smooth m.: inhibits MLCK → relaxes smooth m.

Liver: activates glycogen phosphorylase

PD

CVS

↑HR

↑FOC

↑Automaticity

↑CO

BP: ↓SVR 2° β2 smooth m. relaxation but ↑CO enough so MAP unchanged

Myocardial O2 demand ↑ & ↑HR = less time for coronary perfusion, but coronary VD (β2) offsets this

RESP

Potent bronchodilation

Stabilises mast cells (β2 receptor)

↑anatomical DS & ↑V/Q mismatch

GI

↑splanchnic BF

METABOLIC

↑Plasma glucose

↑FFA

PK

A

Extensive 1st pass by liver

D

65% PPB

M

Liver COMT

E

15 – 75% excreted, unchanged in urine. Rest conjugated metabolites.

Adverse Effects

Tachycardia / arrhythmias

Palpitations

Angina

Tachyphylaxis

Co-admin with some volatiles ↑arrhythmia risk