Isoprenaline
Isoprenalin APL · Isuprel
Pharmacological pacemaker. Potent β₁-stimulation produces marked chronotropy and inotropy, while equally potent β₂-stimulation dilates the vessels — completely without alpha effect. The result is that heart rate rises while systemic vascular resistance and diastolic blood pressure fall, so the drug raises rate but not pressure. Used where rate itself is the problem: bradycardia while awaiting pacing, bradycardia-dependent torsades de pointes, and electrical storm in Brugada syndrome.
Isoprenaline increases myocardial oxygen consumption while diastolic pressure and therefore coronary perfusion fall. In ischaemic heart disease it can trigger infarction and ventricular arrhythmias. Not given in tachyarrhythmia, digoxin toxicity, or marked hypovolaemia, and never without continuous telemetry and standby for transcutaneous or transvenous pacing.
Dosing in adults
| Indication | Regimen | Comment |
|---|---|---|
| Symptomatic bradycardia or AV block II–III | 0,5–10 μg/min iv, titrate to heart rate and symptoms | bridge to pacing, not definitive treatment |
| Bradycardia-dependent torsades de pointes | 0,5–10 μg/min iv targeting heart rate 90–110 per minute | after magnesium; rate increase shortens QT and breaks the arrhythmia |
| Electrical storm in Brugada syndrome | Bolus 1–2 μg iv, then infusion 0,5–5 μg/min | normalises ST elevation in V₁–V₂ and suppresses arrhythmia burden |
| Beta-blocker intoxication (second choice) | 0,5–10 μg/min iv, often high doses | glucagon and high-dose insulin are the primary treatment |
| Discontinuation | Taper when pacing or causal treatment is in place | short duration, effect wanes within minutes |
No established dose adjustment.
No established dose adjustment.
0,05–2 μg/kg/min on paediatric cardiology prescription; titrated to heart rate.
Avoid in ischaemic bradycardia in the acute phase of myocardial infarction: the increased rate and reduced diastolic coronary perfusion can extend the infarct, and pacing is the safer choice. Also avoid as a blood pressure agent — isoprenaline lowers mean arterial pressure and is the wrong tool in hypotension.
Pharmacokinetics
- BIOAVAIL.
- Intravenous only
- ONSET
- Immediate
- t½
- 2–5 minutes
- DURATION
- Under 10 minutes after the infusion stops
- RECEPTORS
- β₁ +++++, β₂ +++++, α 0
- METABOLISM
- COMT and sulfate conjugation
- EXCRETION
- Renal as metabolites
- HAEMODYNAMICS
- Raises heart rate and cardiac output, lowers diastolic pressure