CORRECT USE OF PROPAFENONE
| PHARMACOLOGICAL
INTERACTIONS |
DIGOXIN
Propafenone
causes a 35% increase in plasma concentrations of
Digoxin at a dose of 450 mg/day and a 65% increase at
900 mg/day.(6)
It is advisable, when using Digoxin and Propafenone
together, to reduce the Digoxin dosage accordingly
and to monitor its plasma levels.
WARFARIN
The
co-administration of Propafenone and Warfarin, with a
consequent prolongation of the prothrombin time
(circa 25%). (7)
Therefore, an adjustment to the Warfarin dosage and
an accurate monitoring of the prothrombin time or INR
are advisable.
ß-BLOCKERS
In a
clinical study in healthy subjects the concurrent
administration of Propafenone and Propranolol caused
an increase in Propranolol plasma concentrations and
half-life, without any change in the plasma levels of
Propafenone. Similar observations have been reported
for Metoprolol.(9) It is therefore
advisable to reduce the dosage of the ß-blocking
agents when they are associated with Propafenone
because of the possible cumulative inotropic effects
of the drugs.
CYCLOSPORIN
Propafenone
can increase the plasma concentrations of
Cyclosporin.
In a patient subjected to a heart transplant with
sustained ventricular tachycardia, the concentration
of Cyclosporin increased from 450 to 750 microg/L
after 5 days treatment with Propafenone (750 mg/day).
In this patient the dosage of Cyclosporin had to be
reduced from 240 to 200 mg/day.(10)
RIFAMPICIN
Rifampicin
reduces the steady state plasma concentrations of
Propafenone thus offsetting its therapeutic effect.
It is therefore advisable to administer another
antibiotic to patients on Propafenone.(11)
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