Adenosine

Usage

• Adenosine is primarily used for the conversion of paroxysmal supraventricular tachycardia (PSVT), including PSVT associated with Wolff-Parkinson-White Syndrome, to sinus rhythm. It is also used as a pharmacologic stress agent, as an adjunct to thallium-201 myocardial perfusion scintigraphy in patients unable to exercise adequately.
• Pharmacological Classification: Antiarrhythmic, Vasodilator.
• Mechanism of Action: Adenosine slows conduction time through the atrioventricular (AV) node, interrupts re-entry pathways through the AV node, and can restore sinus rhythm in patients with PSVT. It is an endogenous nucleoside that activates A1 adenosine receptors, increasing potassium conductance and causing hyperpolarization. This leads to a transient slowing of the sinus rate and AV nodal conduction.

Alternate Names

• Adenocard (brand name)

How It Works

• Pharmacodynamics: Adenosine’s primary effect is on the heart, causing transient AV block and slowing sinus node discharge. It is a potent vasodilator of coronary and cerebral resistance vessels.
• Pharmacokinetics: Adenosine is rapidly absorbed and metabolized by adenosine deaminase, which is present in red blood cells and vascular endothelial cells. It has an extremely short half-life (less than 10 seconds).
• Mode of Action: Adenosine interacts with A1 adenosine receptors located in the sinoatrial (SA) and AV nodes. Receptor binding activates potassium channels, leading to hyperpolarization and slowed conduction.
• Elimination Pathways: Rapidly metabolized to inosine and subsequently uric acid, primarily in the liver and other tissues. Some renal excretion may also occur.

Dosage

Standard Dosage

Adults:

• PSVT: 6 mg rapid IV push over 1-3 seconds, followed by a 20 mL saline flush. If no conversion within 1-2 minutes, a second dose of 12 mg can be given. A third dose of 12 mg may be considered if necessary.
• Myocardial Perfusion Imaging: 140 mcg/kg/minute IV infusion over 6 minutes.

Children:

• PSVT: Initial dose: 0.1 mg/kg (max 6 mg) rapid IV push, followed by a saline flush. Second dose: 0.2 mg/kg (max 12 mg) if necessary. Third dose: 0.3 mg/kg (max 12 mg) may be considered.
• Pediatric Safety Considerations: Closely monitor heart rate, rhythm, and blood pressure. Be prepared to manage bradycardia or asystole.

Special Cases:

• Elderly Patients: Start with a lower dose (3 mg) and titrate cautiously.
• Patients with Renal Impairment: Dose reduction may be necessary.
• Patients with Hepatic Dysfunction: No specific adjustments are typically required due to rapid extrahepatic metabolism.
• Patients with Comorbid Conditions: Use with caution in patients with asthma, as bronchospasm may occur. Reduce initial dose to 3 mg for patients taking dipyridamole or carbamazepine and central line administration.

Clinical Use Cases

• Intubation, Surgical Procedures, Mechanical Ventilation, ICU Use, Emergency Situations: Dosage as per PSVT guidelines.

Side Effects

Common Side Effects:

Flushing, dyspnea, chest pain, headache, dizziness, nausea.

Rare but Serious Side Effects:

Severe bradycardia, asystole, bronchospasm, seizures, hypotension.

Adverse Drug Reactions (ADR):

Significant hypotension, high-grade AV block, severe bronchospasm.

Contraindications

• Second- or third-degree AV block (except in patients with a functioning pacemaker).
• Sinus node disease (sick sinus syndrome, symptomatic bradycardia) (except in patients with a functioning pacemaker).
• Known or suspected bronchoconstrictive or bronchospastic lung disease (e.g., asthma).
• Known hypersensitivity to adenosine.

Drug Interactions

• Dipyridamole and carbamazepine potentiate the effects of adenosine.
• Methylxanthines (caffeine, theophylline) antagonize adenosine’s effects.

Pregnancy and Breastfeeding

• Pregnancy Safety Category: C
• Breastfeeding: Adenosine is likely present in breast milk; caution is advised.

Drug Profile Summary

• Mechanism of Action: Slows AV nodal conduction, interrupts re-entry pathways.
• Side Effects: Flushing, dyspnea, chest pain, headache, bradycardia, asystole.
• Contraindications: AV block, sinus node disease, bronchospastic lung disease, hypersensitivity.
• Drug Interactions: Dipyridamole, carbamazepine, methylxanthines.
• Pregnancy & Breastfeeding: Category C, caution advised during breastfeeding.
• Dosage: Refer to detailed dosage section above.
• Monitoring Parameters: ECG, heart rate, blood pressure, respiratory status.

Precautions

• General Precautions: Cardiac monitoring is essential during administration. Resuscitation equipment should be readily available.
• Specific Populations: Refer to dosage section for adjustments in special populations.

FAQs (Frequently Asked Questions)

Q1: What is the recommended dosage for Adenosine in adults with PSVT?

A: 6 mg rapid IV push over 1-3 seconds, followed by 20 mL saline flush. 12 mg may be repeated twice if needed.

Q2: How does Adenosine work to terminate PSVT?

A: It slows AV nodal conduction, interrupting re-entry pathways responsible for PSVT.

Q3: What are the common side effects of Adenosine?

A: Flushing, dyspnea, chest pain, headache, dizziness, and nausea. These are typically transient.

Q4: What are the contraindications to using Adenosine?

A: Second- or third-degree AV block, sinus node disease, bronchospastic lung disease, and hypersensitivity.

Q5: What are the serious side effects of Adenosine that require urgent attention?

A: Severe bradycardia, asystole, bronchospasm, seizures, and hypotension.

Q6: How should Adenosine be administered?

A: Rapid IV bolus over 1-3 seconds, followed by a saline flush. Administer through a proximal IV site.

Q7: What drugs interact with Adenosine?

A: Dipyridamole and carbamazepine potentiate its effects, while methylxanthines (like caffeine and theophylline) can antagonize them.

Q8: Can Adenosine be used in pregnant or breastfeeding women?

A: It’s a Pregnancy Category C drug. Use with caution in pregnancy. Adenosine is likely present in breast milk, so caution is advised during breastfeeding.

Q9: What should be monitored during Adenosine administration?

A: Continuous ECG monitoring, heart rate, blood pressure, and respiratory status are essential.

Q10: What is the dose of adenosine for myocardial perfusion imaging?

A: 140 mcg/kg/minute IV infusion over 6 minutes.