Major indications
In the ED, adenosine is used to terminate supraventricular tachycardias (SVTs). It is also used by cardiologists for pharmacologic stress testing. Paroxysmal SVT .
How it works
Adenosine is one of the components of RNA, but given intravenously, it works to terminate SVTs by binding to the AV node's A1 receptors. This inhibits adenylyl cyclase, ultimately increasing potassium efflux from the cell, causing hyperpolarization, and thereby "blocking" the AV node. This prevents atrial impulses from reaching the ventricles through the AV node, and also blocks re-entrant tachycardias that rely on conduction through the AV node.
Recently in the news
A recent retrospective study of the use of adenosine for termination of SVT in children found that adenosine was effective in 75% of cases, and that, . In an unrelated development, a recent clinical trial .
Notable History
The first report of adenosine used for SVT was published in 1976. At that time, (adenosine triphosphate). In the following decades, .
Adverse Events
The time from administration to effect is about 10-40 seconds. Expected side effects include a transient bradycardia or heart block during which time the patient may have a sense of anxiety or chest pain. Patients should be warned of this prior to administration. Other side effects include hypotension and in rare cases, prolonged heart block or dysrhythmias. However, the short half-life of adenosine (less than 10 seconds) means the side effects are typically brief and self-limiting.
Cautions
Adenosine is class C in pregnancy, but is the recommended first-line medication for termination of SVTs in pregnant patients when vagal maneuvers fail. If adenosine is ineffective, then propranolol or metoprolol can be used. Verapamil is less favorable as it can cause more maternal hypotension and potential decreased perfusion to the placenta and fetus. In unstable pregnant patients, cardioversion is still the recommended treatment. .
Dose adjustments
Typical doses for terminating SVT are 6-mg rapid IV push and flush in a proximal, large bore IV. If this is ineffective, then two subsequent doses of 12 mg can be attempted. In children under 50 kg, the dose is 0.05-0.1 mg/kg. This dose can be increased by 0.05-0.1 mg/kg and attempted twice more, with a maximum dose of 0.3 mg/kg or 12 mg. There are no dosing adjustments needed for patients with renal or liver disease. Caffeine and other methylxanthines, such as theophylline, have adenosine receptor blocking activity as a result of their purine structure, so or (caffeine's effectiveness as a stimulant is largely accomplished through blocking adenosine's inhibitory effects on the CNS).
If you are administering adenosine through a central line, then (starting at 3 mg) to avoid side effects, such as prolonged bradycardia or heart block.
Special considerations
Adenosine is not typically effective for the termination of atrial flutter. When given to patients with flutter, the drug may 'uncover' the underlying flutter waves and help clarify the diagnosis if it was initially thought to be an SVT. In cases of rapid, regular, wide-complex tachycardia, it can be difficult to differentiate between SVT with aberrant conduction and ventricular tachycardia (VT). However, in the vast majority of cases, the patient should be presumed to have VT and treated as such.
Cost
Approximately $40 per 6-mg dose in the United States.
Christina Shenvi, MD, PhD, is an assistant professor in the department of emergency medicine at the University of North Carolina. A version of this article originally appeared at .