A study and several case reports describe a reduction in
ciclosporin levels (37% reduction in the study) following the addition of
phenytoin. Other reports describe the need to make 2- to 4-fold increases in the
ciclosporin dose in patients also taking
phenytoin.
Ciclosporin levels and effects (e.g. on
renal function) should be monitored as a matter of routine, but it may be prudent to increase monitoring if
phenytoin is stopped, started, or the dose altered.