ANTIARRHYTHMIC DRUGS
ADENOSINE
Adenosine
is an endogenous purine nucleotide that causes profound
conduction depression in the atrioventricular (AV) node,
without producing negative inotropic effects. It shortens
atrial action potential and refractory period, thus
rarely facilitating induction of atrial fibrillation.
There is no stable oral form of Adenosine, so that its
use is restricted to the short term intravenous infusion.
 Pharmacokinetics
Extremely short half life: 10-30 sec
Drug
interactions
Dipyridamole
inhibits
the breakdown of Adenosine: the dose of Adenosine
must be reduced.
Methylxantines (aminophylline,
theophylline, caffeine) antagonize the interactions
of Adenosine with receptors: larger doses of
Adenosine are required.
Indications
Interruption
of paroxysmal supraventricular tachycardias (either
AV nodal reentrant tachycardia or AV reentrant
tachycardia). Given the very short half life, the
drug is not useful in preventing early recurrences of
the arrhythmia (less than 10% of the cases).
A
"diagnostic" use as been proposed in:
a)
wide QRS complex tachycardias, in
differentiating the ventricular tachycardias
(unaffected by the drug) from supraventricular
tachycardias with aberrant conduction;
b)
latent preexcitation (in suspected
Wolff-Parkinson -White syndrome): the drug unmask
an otherwise absent delta-wave.
Contraindications
Atrial
flutter
(Adenosine - after slowing ventricular rate - may
trigger sympatetic stimulation and can induce1:1 AV
conduction with high ventricular rate)
Sick
sinus syndrome (may
cause sinus arrest)
Bronchial
asthma (may
cause bronchoconstriction)
Side effects
Side effects are the
rule and the patient has to be instructed about them.
All very transient, but sometimes very uncomfortable
for the patient that sometimes may refuse a repeat
dose.
Dyspnoea
Facial
flushing
Chest
pain
Hypotension
Nausea
Anxiety
Dosage
Adults: 6 mg over 1-2 seconds, into a
large peripheral vein, followed by a saline flush. If
no response is observed after 1-2 minutes, a second
12 mg dose may be infused with the same modalities. A
second 12 mg dose may be repeated once, if needed.
Children: 0.05 mg/Kg, followed, if
needed, by 0.05 mg/Kg increments every 1-2 min up to
a maximum 0.25 mg/Kg dose.
Leopoldo
Bianconi
Department of Heart Disease - Division
of Cardiology, S. Filippo Neri Hospital - Italy
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