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9780521704632c14 CUFX213A/Peck 9780521618168 December 28, 2007 12:32
14 Anti-arrhythmicswhile ventricular excitability is increased and may predispose to re-entry arrhyth-
mias. Cardiac failure and cardiogenic shock occur rarely.
Non-cardiac – anticholinergic effects (blurred vision, dry mouth and occasionally
urinary retention) often prove unacceptable.Kinetics
Disopyramide is well absorbed from the gut and has an oral bioavailability of 75%.
Itis only partially metabolized in the kidney, the majority of the drug being excreted
in the urine unchanged. Its elimination half-life is about 5 hours but this increases
significantly in patients with renal or cardiac failure.Propafenone
Propafenone is similar in many respects to flecainide.Presentation
Itis available only as film-coated tablets in the UK although it has been used intra-
venously at a dose of 1–2 mg.kg−^1 .The oral dose is initially 600–900 mg followed by
150–300 mg bd or tds.Uses
Propafenone is used as second-line therapy for resistant SVT, including atrial fibril-
lation and flutter, and also for ventricular tachyarrhythmias.Mechanism of action
Propafenone prevents the fast Na+flux into cardiac tissue and prolongs phase 0 of
the action potential. The duration of the action potential and refractory period is pro-
longed especially in the conducting tissue. The threshold potential is increased and
cardiac excitability reduced by an increase in the ventricular fibrillation threshold.
Athigher doses it may exhibit someβ-blocking properties.Side effects
Propafenone is generally well tolerated.
Cardiac – owing to its weakβ-blocking actions it should be used with caution in
those with heart failure.
Non-cardiac – it may produce minor nervous system effects and at higher doses
gastrointestinal side effects may become more prominent. It may worsen myas-
thenia gravis. Propafenone increases the plasma levels of concurrently admin-
istered digoxin and warfarin. It may precipitate asthma due to itsβ-blocking
properties.