Pharmacology
Cardiovascular
Adenosine has a half-life of approximately:
Answer:
Adenosine stimulates A1-adenosine receptors and opens acetylcholine sensitive K+ channels, increasing K+ efflux. This hyperpolarises the cell membrane in the atrioventricular node and, by inhibiting the calcium channels, slows conduction in the AVN. As it has a very short duration of action (half-life only about 8 - 10 seconds), most side effects are short lived.Adenosine
Pharmacology / Cardiovascular
Last Updated: 6th June 2021
Adenosine is usually the treatment of choice for terminating paroxysmal supraventricular tachycardia.
Mechanism of Action
Adenosine stimulates A1-adenosine receptors and opens acetylcholine sensitive K+ channels, increasing K+ efflux. This hyperpolarises the cell membrane in the atrioventricular node and, by inhibiting the calcium channels, slows conduction in the AVN. As it has a very short duration of action (half-life only about 8 - 10 seconds), most side effects are short lived.
Administration
For a regular narrow-complex tachycardia the first step is to attempt vagal manoeuvres. If this is unsuccessful and the tachyarrhythmia persists, 6 mg intravenous adenosine should be administered into a central/large vein over 2 seconds, followed by 12 mg after 1 - 2 minutes if required, then a further 18 mg after 1 - 2 minutes if required (max 36 mg, as per the 2021 ALS Guidelines).
The effects of adenosine are potentiated by dipyridamole, therefore if it is essential to give adenosine in a patient taking dipyridamole the dose should be quartered.
The patient should be warned that they will feel unwell and may experience chest discomfort for a few seconds following the injection. An ECG (preferably multi-lead) should be recorded during the injection. If adenosine is contraindicated, or fails to terminate a regular narrow-complex tachycardia, the administration of verapamil 2.5 - 5 mg IV over 2 mins should be considered.
Contraindications
Adenosine is contraindicated in:
- Asthma and COPD (can cause bronchospasm)
- Decompensated heart failure
- Long QT syndrome
- Second- or third-degree AV block and sick sinus syndrome (unless pacemaker fitted)
- Severe hypotension
Side Effects
Common side effects of adenosine include:
- Apprehension
- Dizziness, flushing, headache, nausea, dyspnoea
- Angina (discontinue)
- AV block, sinus pause and arrhythmia (discontinue if asystole or severe bradycardia occur)
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
