Serum
disopyramide levels are reduced by about 35% by
phenobarbital. Note that
primidone is metabolised to
phenobarbital and therefore may interact similarly.
The extent to which this interaction would reduce the antiarrhythmic effects of
disopyramide is unknown, but monitor the effects and the
serum levels of
disopyramide (if possible) if
phenobarbital is added or withdrawn. One manufac- turer suggests avoiding the combination.