###### Created: 2024-06-11 21:24 ###### Areas & Topics: #medicine #pharmacology ###### Note Type: #permanent ###### Connected to: [[Peri-Arrest Rhythms]] - Adenosine is a purine nucleoside base, found throughout the body. - It is an important part of metabolism and energy transfer as part of adenosine diphosphate (ADP) and adenosine triphosphate (ATP). - It acts on A1, A2a, A2b and A3 receptors throughout the body. - Adenosine alone also acts as a miscellaneous antiarrhythmic which is used for stopping supraventricular tachycardias. ### Mechanism of Action - Adenosine acts on and agonises A1 receptors found in the AV node in the heart. - It activates certain potassium channels, driving potassium out of cells and inhibiting calcium from moving in. - This causes depolarisation to require a longer time to normal, slowing conduction through the AV node and thereby limiting the signals that pass through when originating above it (as in supraventricular tachycardias). - The drug has a very short half-life of 0.6 to 10 seconds, making this heart block very transient. - This short half-life means it must be given via rapid IV bolus. - Its effects are enhanced by dipyridamole, as it inhibits adenosine uptake and thereby potentiates it. ### Adverse Effects The main adverse effects to be aware of include: - Chest Pain (thought to be caused by stimulating afferent nerve and/or causing ischaemia) - Bronchospasm (as it acts on adenosine receptors in the airways leading to bronchoconstriction) - Transient Flushing (activating of A2a receptors leads to increased myocardial output and thereby increased blood flow and flushing) ### Contra-Indications - Asthma (as it can induce bronchospasm) ### Antidote - Caffeine and other theophylline-like drugs inhibit the effects of adenosine by binding to adenosine receptors. - The main antidote for adenosine is aminophylline (as it preferentially binds to A2a receptors). - Theophylline can also be used to block its effects. ### Resources Singh S, McKintosh R. Adenosine. [Updated 2023 Aug 28]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519049/ Adenosine - BNF https://bnf.nice.org.uk/drugs/adenosine/ PassMed High Yield TextBook