Propafenone (Fenopraine)
·
Propafenone is a class IC
antiarrhythmic drug which blocks the fast sodium channel of the myocardial cell. It has some
negative inotropic and beta-adrenoceptor blocking activity. Propafenone is
structurally related to propranolol and is administered orally for the
treatment of life-threatening ventricular arrhythmias. It is indicated in
patients without structural heart disease to treat paroxysmal atrial
fibrillation/flutter (PAF) or paroxysmal supraventricular tachycardia (PSVT)
associated with disa-bling or life-threatening symptoms. It can have
proarrhythmic effects and its use is not recommended in lesser ventricular
arrhythmias.
·
It is 95% absorbed, peaks in 2 to 3 hours, has a plasma
half-life varying from 2 to 32 hours, and less than 1% is excreted unchanged in
the urine. Apparent volume of distribution is 1.1 to 3.6 L/kg and protein
binding is to the extent of 97%. Therapeutic plasma levels should preferably
not exceed 2 mcg/ml. Propafenone is metabolised by the cytochrome P-450 pathway
which produces the major metabolites 5-hydroxy propafenone and N-desalkyl
propafenone.
·
Bradycardia, cardiac conduction
anomalies, hypoten- sion, proarrhythmias, worsening of heart failure, vertigo,
headache, GI distress, alteration of taste (metallic or bitter taste), visual
blurring. Constipation and nausea have been commonly reported side effects with
propafenone therapy. Liver damage has been reported rarely with therapeutic
use.
·
Potentiation of effects with local
anaesthetics, beta blockers.
·
Increases digoxin plasma levels.
·
Poentiates anticoagulant effects of
warfarin.
·
The adult therapeutic dose range is
600 to 900 mg/day. Therapeutic levels range from 90 to 3,000 ng/ml.
·
Toxicity is usually most severe
within 3 hours of inges-tion. Effects of overdose can include gastrointestinal
upset, blurred vision, hypotension, drowsiness, prolonga-tion of the QRS
interval, atrioventricular blocks, brady-cardia, A-V dissociation and
conduction disturbances, ventricular arrhythmias, asystole, convulsions,
acidosis and coma.
·
Neurologic disturbances are
relatively common with propafenone overdose, and several types of convul-sions
have been described including minor motor and tonic-clonic seizures. Dizziness,
amnesia, disorientation, neuropathy, paraesthesias, coma and mania have also
been reported.
· Admit to intensive care and monitor
cardiac function and tidal volume. Obtain an ECG, institute continuous cardiac
monitoring and administer oxygen. Evaluate for hypoxia, acidosis, and
electrolyte disorders (particularly hypoka-laemia, hypocalcaemia, and
hypomagnesaemia).
· Lignocaine and amiodarone are
generally first line agents for stable monomorphic ventricular tachycardia,
particu-larly in patients with underlying impaired cardiac function. Sotalol is
an alternative for stable monomorphic ventricular tachycardia. Amiodarone and
sotalol should be used with caution. Unstable rhythms require cardioversion.
Atropine may be used when severe bradycardia is present and PVCs are thought to
represent an escape complex.
· The class IC agents have been shown
to be moderately refractory to conventional antiarrhythmic drug therapy,
cardioversion, and ventricular pacing. Because of cross-over in
electrophysiologic properties, class IA agents (quinidine, procainamide,
disopyramide) are relatively contraindicated. Class IB agents (lignocaine, phenytoin,
mexiletine, tocainide) may be the best alternative based on electrophysiologic
properties, but could also exacerbate toxicity.
· Stomach wash and/or activated
charcoal, upto 4 to 6 hours post-ingestion.
· Sodium loading : molar sodium
lactate, sodium bicarbonate, or hypertonic saline may be administered. Serum
alkalini-sation with sodium bicarbonate may be useful in treating arrhythmias.
A reasonable starting dose is 1 to 2 mEq/kg as an intravenous bolus, repeated
as needed to maintain arterial pH 7.45 to 7.55. Monitor ECG, arterial blood
gases and electrolytes.
· Diazepam for convulsions. If
seizures persist or recur administer phenobarbitone.
· For hypotension: Infuse 10 to 20
ml/kg of isotonic fluid and place in Trendelenburg position. If hypotension persists,
administer dopamine or noradrenaline. Consider central venous pressure
monitoring to guide further fluid therapy. Atropine and pressor amines
(dopamine, dobutamine) may be used as necessary.
·
There are a few cases reported of beneficial effects following
the use of infused adrenaline and temporary internal pacemaker.
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