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 receptors (β1 = 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