Isoprenaline Macure: Uses, Dosage & Side Effects

What Is Isoprenaline Macure and What Is It Used For?

Isoprenaline Macure contains the active substance isoprenaline hydrochloride at a concentration of 0.2 mg/ml in a ready-to-use solution for intravenous infusion. Isoprenaline (known as isoproterenol in the United States) is a synthetic catecholamine and one of the most potent non-selective beta-adrenergic receptor agonists available in clinical medicine. It was first synthesized in the 1940s and has been used in clinical practice since the early 1950s, making it one of the longest-established sympathomimetic agents in emergency and critical care medicine.

As a non-selective beta-agonist, isoprenaline stimulates both beta-1 and beta-2 adrenergic receptors throughout the body. The activation of beta-1 receptors in the myocardium (heart muscle) produces three key pharmacological effects that are central to its therapeutic use: positive chronotropy (increased heart rate), positive inotropy (enhanced force of cardiac contraction), and positive dromotropy (improved conduction velocity through the atrioventricular node and His-Purkinje system). These combined effects make isoprenaline uniquely effective for increasing heart rate in patients with severe bradycardia and for overcoming conduction blocks in the cardiac conduction system.

The simultaneous stimulation of beta-2 adrenergic receptors causes relaxation of smooth muscle in the bronchi (bronchodilation), peripheral blood vessels (vasodilation), and the uterus. The peripheral vasodilation results in a decrease in diastolic blood pressure and total peripheral resistance, while the increased cardiac output from beta-1 stimulation tends to maintain or increase systolic blood pressure. This hemodynamic profile is an important consideration when using isoprenaline in critically ill patients, as the reduction in diastolic pressure can potentially reduce coronary perfusion pressure.

Isoprenaline Macure is indicated for the following clinical situations, all of which represent medical emergencies requiring immediate hospital treatment:

• Severe symptomatic bradycardia: When a dangerously slow heart rate (typically below 40–50 beats per minute) causes hemodynamic compromise with symptoms such as syncope (fainting), presyncope (near-fainting), altered mental status, hypotension, or signs of shock, and when atropine (the first-line pharmacological treatment for bradycardia) has failed or is considered unlikely to be effective.
• Complete (third-degree) atrioventricular block: When the electrical signals from the atria completely fail to reach the ventricles, resulting in an escape rhythm that is too slow to maintain adequate cardiac output. Isoprenaline can increase the ventricular rate by enhancing automaticity in subsidiary pacemaker cells and improving conduction through partially blocked pathways.
• Mobitz type II second-degree AV block: A form of AV block that carries a high risk of progression to complete heart block and is typically unresponsive to atropine because the block occurs below the AV node in the His-Purkinje system.
• Bridge to pacemaker insertion: Isoprenaline is frequently used as a temporary pharmacological measure to maintain an adequate heart rate while arrangements are being made for temporary transvenous pacing or permanent pacemaker implantation. This bridging role is one of the most common clinical applications of the drug.
• Torsades de pointes: A specific type of polymorphic ventricular tachycardia associated with QT interval prolongation, where isoprenaline can be used to increase the heart rate and thereby shorten the QT interval, reducing the likelihood of recurrent arrhythmia episodes while other definitive treatments (such as magnesium sulfate and overdrive pacing) are being initiated.

According to the American Heart Association (AHA), American College of Cardiology (ACC), and Heart Rhythm Society (HRS) 2018 guidelines for the evaluation and management of patients with bradycardia and cardiac conduction delay, isoprenaline (isoproterenol) is recommended as an alternative chronotropic agent when atropine is ineffective and temporary pacing is not immediately available. The European Resuscitation Council (ERC) 2021 guidelines similarly position isoprenaline as a second-line agent in the bradycardia algorithm after atropine, alongside other options such as dopamine and adrenaline infusions.

What Should You Know Before Taking Isoprenaline Macure?

Contraindications

Isoprenaline Macure is contraindicated in several clinical scenarios where its potent beta-adrenergic stimulating properties could cause serious harm. Understanding these contraindications is essential for the safe use of this medication in emergency settings. The primary contraindications include:

• Tachyarrhythmias: Isoprenaline must not be administered to patients who already have a rapid heart rate or cardiac arrhythmias (except for torsades de pointes, where it is specifically indicated). The drug's positive chronotropic effect can dangerously accelerate pre-existing tachycardias and may precipitate ventricular fibrillation.
• Hypertrophic obstructive cardiomyopathy (HOCM): In patients with this condition, the increased contractility and heart rate caused by isoprenaline can worsen the dynamic outflow tract obstruction, potentially leading to severe hypotension, syncope, or sudden cardiac death.
• Pheochromocytoma: This catecholamine-secreting tumor already produces excessive sympathetic stimulation. Adding isoprenaline can precipitate a hypertensive crisis or life-threatening arrhythmias.
• Hypersensitivity: Known allergy to isoprenaline hydrochloride or any of the excipients in the formulation is an absolute contraindication.
• Digitalis toxicity with tachycardia: In patients experiencing cardiac glycoside (digoxin) toxicity with associated tachyarrhythmias, isoprenaline can exacerbate the arrhythmia risk due to the synergistic proarrhythmic effects of both drugs.

Warnings and Precautions

Before initiating isoprenaline therapy, healthcare professionals must carefully consider the following precautions and risk factors:

• Ischemic heart disease: Patients with known or suspected coronary artery disease are at increased risk of myocardial ischemia because isoprenaline increases myocardial oxygen consumption while potentially decreasing coronary perfusion pressure (through reduced diastolic blood pressure). If isoprenaline must be used in these patients, the lowest effective dose should be employed, and continuous 12-lead ECG monitoring for ischemic changes is recommended.
• Hypokalemia: Isoprenaline, like other beta-agonists, can cause a shift of potassium from the extracellular to the intracellular compartment, resulting in hypokalemia. Low serum potassium levels increase the risk of cardiac arrhythmias, particularly in patients receiving concurrent digitalis glycosides. Serum potassium should be monitored and corrected before and during isoprenaline infusion.
• Diabetes mellitus: Beta-2 adrenergic stimulation can promote glycogenolysis and gluconeogenesis, leading to hyperglycemia. Blood glucose monitoring should be intensified in diabetic patients receiving isoprenaline.
• Hyperthyroidism: Patients with thyrotoxicosis have an increased sensitivity to catecholamines, and isoprenaline may cause exaggerated cardiovascular responses. Dose reduction and careful monitoring are required.
• Elderly patients: Older patients are more susceptible to the arrhythmogenic effects of isoprenaline and may have underlying coronary artery disease. Lower starting doses and more cautious titration are recommended in this population.

Pregnancy and Breastfeeding

The use of isoprenaline during pregnancy should be considered only when the potential benefit to the mother clearly outweighs the potential risk to the fetus. There are limited controlled data on the use of isoprenaline in pregnant women. As a beta-adrenergic agonist, isoprenaline can cross the placenta and may affect fetal heart rate and metabolism. Beta-2 stimulation can also cause uterine relaxation (tocolysis), which may be relevant in pregnant patients near term.

Animal reproduction studies have shown that high doses of sympathomimetic amines can cause fetal abnormalities, although the relevance of these findings to clinical doses of isoprenaline in humans is uncertain. In life-threatening situations such as severe maternal bradycardia or complete heart block, the decision to use isoprenaline must be made by the treating physician based on the clinical urgency and the availability of alternative treatments.

It is not known with certainty whether isoprenaline is excreted in human breast milk. Given its very short half-life (2–5 minutes) and the fact that it is rapidly metabolized, significant accumulation in breast milk is unlikely. However, as a precautionary measure, breastfeeding should be temporarily suspended during isoprenaline infusion and for a reasonable period afterward, as determined by the treating physician.

Required Monitoring During Administration

Due to the potent cardiovascular effects of isoprenaline and its narrow therapeutic window, comprehensive monitoring is mandatory during administration. This includes continuous electrocardiographic (ECG) monitoring with real-time display of heart rate and rhythm, continuous arterial blood pressure monitoring (preferably invasive via arterial line in critically ill patients), continuous pulse oximetry, regular assessment of clinical status including level of consciousness, urine output, and peripheral perfusion, and periodic measurement of serum electrolytes (particularly potassium and magnesium) and blood glucose. Access to a defibrillator and full resuscitation equipment must be immediately available throughout the duration of isoprenaline infusion.

How Does Isoprenaline Macure Interact with Other Drugs?

Isoprenaline has a number of clinically important drug interactions that must be considered in the emergency and critical care setting. Because patients requiring isoprenaline are often acutely ill and receiving multiple medications, awareness of these interactions is essential for safe prescribing. The interactions are primarily pharmacodynamic in nature, arising from the combined cardiovascular effects of isoprenaline with other agents.

The following table summarizes the most important drug interactions with isoprenaline:

Major Interactions

The interaction between isoprenaline and halogenated inhalational anesthetics is particularly significant in the perioperative setting. Halothane, in particular, is well known to sensitize the myocardium to the arrhythmogenic effects of catecholamines, and the concurrent use of isoprenaline with halothane has been associated with fatal ventricular fibrillation. Although halothane is less commonly used in modern anesthesia practice, newer agents such as sevoflurane and desflurane can also sensitize the myocardium to a lesser degree. When isoprenaline is required in a patient under general anesthesia, the anesthetist should be informed, the anesthetic agent should be changed if feasible, and the isoprenaline dose should be kept to an absolute minimum.

The interaction with beta-blockers is of special clinical relevance because beta-blocker-induced bradycardia is one of the clinical scenarios in which isoprenaline may be required. In patients with severe bradycardia caused by beta-blocker overdose or toxicity, isoprenaline may be less effective because the beta-receptors are already occupied by the beta-blocking agent. In these cases, higher doses of isoprenaline may be needed, or alternative approaches such as glucagon, high-dose insulin-euglycemia therapy, or temporary transcutaneous pacing may be more appropriate.

Minor Interactions

Antidiabetic medications may require dose adjustment during isoprenaline infusion because the drug's beta-2 agonist activity can promote glycogenolysis and gluconeogenesis, leading to elevated blood glucose levels. This interaction is generally manageable with blood glucose monitoring and adjustment of insulin or oral hypoglycemic doses. Diuretics that cause potassium loss (loop diuretics and thiazides) can compound the hypokalemia caused by isoprenaline, increasing the risk of cardiac arrhythmias. Serum potassium should be monitored at regular intervals and supplemented as necessary.

What Is the Correct Dosage of Isoprenaline Macure?

The dosage of Isoprenaline Macure must be individualized for each patient based on the clinical situation, the severity of bradycardia, and the hemodynamic response to treatment. Because of the drug's extremely short half-life and potent cardiovascular effects, all dosing is performed as a continuous intravenous infusion with real-time titration. There is no fixed oral or intramuscular dose, as isoprenaline is administered exclusively by the intravenous route in current clinical practice.

Adults

Children

Elderly

Elderly patients (over 65 years) are generally more sensitive to the cardiovascular effects of isoprenaline and are more likely to have underlying coronary artery disease, which increases the risk of myocardial ischemia. Treatment should be initiated at the lower end of the adult dosing range (0.5 micrograms per minute), and upward titration should be performed more cautiously with close monitoring for signs of ischemia (chest pain, ST-segment changes on ECG). The target heart rate in elderly patients should generally be more conservative, aiming for 50–70 beats per minute rather than higher rates, to minimize myocardial oxygen demand.

Missed Dose

The concept of a “missed dose” does not apply to isoprenaline in the traditional sense, as the drug is administered as a continuous intravenous infusion in a monitored hospital setting. If the infusion is accidentally interrupted, the effects of isoprenaline will rapidly diminish within minutes due to its very short half-life (2–5 minutes). The infusion should be restarted as soon as possible if the patient still requires chronotropic support. If the infusion line becomes disconnected or occluded, the patient may experience a rapid return of bradycardia, and the clinical team should be prepared to provide alternative pacing support if necessary.

Overdose

Overdose with isoprenaline can occur if the infusion rate is accidentally set too high or if the drug concentration is miscalculated during preparation. Signs and symptoms of isoprenaline overdose include severe tachycardia (heart rate exceeding 150–200 beats per minute), palpitations, chest pain, ventricular arrhythmias (including ventricular tachycardia and ventricular fibrillation), hypotension (due to severe peripheral vasodilation), tremor, headache, flushing, nausea, and anxiety.

Management of isoprenaline overdose consists of immediately stopping or reducing the infusion rate, which will typically lead to rapid resolution of symptoms given the drug's short half-life. If life-threatening tachyarrhythmias develop, a short-acting beta-blocker (such as esmolol) may be cautiously administered, although this must be balanced against the risk of causing rebound bradycardia in patients who required isoprenaline in the first place. Supportive care includes continuous ECG monitoring, correction of any electrolyte abnormalities (particularly hypokalemia), and management of hypotension with intravenous fluids. In cases of cardiac arrest due to ventricular fibrillation, standard advanced life support protocols should be followed.

What Are the Side Effects of Isoprenaline Macure?

Like all potent sympathomimetic agents, isoprenaline can cause a range of side effects that are largely predictable extensions of its pharmacological actions on the adrenergic nervous system. Most side effects are dose-related and can be managed by reducing the infusion rate or temporarily stopping the infusion. Because isoprenaline has a very short half-life (2–5 minutes), side effects typically resolve rapidly once the infusion rate is decreased or discontinued.

The following side effect frequency grid categorizes adverse effects based on their frequency of occurrence as reported in clinical studies and post-marketing surveillance data:

It is critically important to understand that many of these side effects represent dose-dependent extensions of the desired pharmacological action of isoprenaline. The primary therapeutic goal is to increase heart rate, but excessive stimulation of beta-adrenergic receptors can lead to tachycardia, arrhythmias, and myocardial ischemia. This is why continuous ECG monitoring and careful dose titration are mandatory during isoprenaline administration. The infusion rate should always be maintained at the lowest level necessary to achieve the desired clinical effect.

Patients with pre-existing coronary artery disease are at the highest risk of experiencing ischemic side effects, as the combination of increased heart rate (which reduces diastolic filling time and coronary perfusion), increased contractility (which raises myocardial oxygen demand), and decreased diastolic blood pressure (which further reduces coronary perfusion pressure) creates a particularly unfavorable oxygen supply-demand balance in the myocardium. In these patients, the target heart rate should be kept as low as clinically acceptable, and alternative methods of rate support (such as temporary pacing) should be prioritized.

How Should You Store Isoprenaline Macure?

Proper storage of Isoprenaline Macure is essential to maintain its chemical stability and therapeutic efficacy. Isoprenaline, like other catecholamines, is susceptible to oxidative degradation when exposed to light, heat, or air. Degradation products may be inactive or potentially harmful, and the solution may change color (turning pink or brown) as it deteriorates. The following storage guidelines must be strictly adhered to:

• Unopened vials: Store in a refrigerator at 2–8°C (36–46°F). Keep the vials in the original outer carton to protect from light. Do not freeze the solution, as freezing may alter the concentration or cause precipitation of the active substance.
• Protection from light: Isoprenaline is photosensitive and degrades when exposed to light. The solution should be kept in the carton until immediately before use, and infusion lines should ideally be covered with light-protective material during prolonged infusions.
• After dilution: Once diluted for intravenous infusion, the solution should be used immediately. If immediate use is not possible, the diluted solution may be stored for up to 24 hours at 2–8°C. Chemical and physical in-use stability has been demonstrated for 24 hours at this temperature when diluted with glucose 5% or sodium chloride 0.9%.
• Visual inspection: Before administration, the solution must be visually inspected for discoloration and particulate matter. The solution should be clear and colorless to very pale yellow. Do not use if the solution has turned pink, brown, or any other color, or if it contains visible particles or precipitates.
• Shelf life: Refer to the expiry date printed on the vial and outer carton. Do not use Isoprenaline Macure after the expiry date stated on the packaging.
• Disposal: Any unused medicinal product or waste material should be disposed of in accordance with local hospital pharmacy guidelines for cytotoxic and pharmaceutical waste. Do not dispose of via household waste or down drains.

In the hospital pharmacy setting, stock rotation should follow first-expiry-first-out (FEFO) principles to ensure that older stock is used before newer supplies. Temperature monitoring of refrigerators storing isoprenaline should be performed regularly, and temperature excursions should be investigated and documented to ensure product integrity.

What Does Isoprenaline Macure Contain?

Isoprenaline Macure is formulated as a sterile, preservative-free, ready-to-use aqueous solution for intravenous infusion. Understanding the complete composition of the product is important for healthcare professionals, particularly when considering potential allergies to excipients or calculating sodium content for patients on sodium-restricted regimens.

Active Substance

The active substance is isoprenaline hydrochloride, present at a concentration of 0.2 mg per milliliter (0.02%). Isoprenaline hydrochloride is the salt form of isoprenaline (free base), which is a synthetic catecholamine structurally related to adrenaline (epinephrine) and noradrenaline (norepinephrine). The molecular formula is C₁₁H₁₇NO₃·HCl, and the molecular weight is 247.72 g/mol. It is a white to off-white crystalline powder that is freely soluble in water.

Excipients (Inactive Ingredients)

• Sodium chloride: Used as a tonicity agent to make the solution isotonic with blood and body fluids. This ensures that the infusion does not cause hemolysis (destruction of red blood cells) or pain at the injection site due to osmotic effects.
• Hydrochloric acid: Used for pH adjustment. The solution is adjusted to a slightly acidic pH (approximately 2.5–4.5) to optimize the chemical stability of isoprenaline, which is more stable in acidic conditions.
• Water for injections: Serves as the solvent for all the other components. Meets pharmacopoeial standards for sterility and endotoxin content.

Isoprenaline Macure contains sodium from the sodium chloride excipient. The sodium content per vial should be considered for patients on a controlled sodium diet or those receiving sodium-restricted intravenous fluids. The exact sodium content per milliliter should be verified from the product-specific prescribing information or by consulting the hospital pharmacy.

The solution is preservative-free, which means it does not contain antimicrobial preservatives such as benzyl alcohol, methylparaben, or propylparaben. While this makes the product safer for neonates and patients sensitive to preservatives, it also means that the vial is intended for single use only. Any unused portion remaining in the vial after the required dose has been withdrawn must be discarded and should not be stored for later use, in accordance with good manufacturing practice and infection control guidelines.