Serum
phenytoin levels can be raised by amiodarone, markedly so in some individuals (4-fold rise reported).
Amiodarone serum levels are reduced by
phenytoin.
A 25 to 30% reduction in the
phenytoin dose has been recommended for those taking 2 to 4 mg/kg daily, but it should be remembered that small alterations in
phenytoin dose may result in a large change in
phenytoin levels, as
phenytoin kinetics are non-linear. The
clinical significance of the effects on
amiodarone are unclear.