If you have been taking phenytoin for a long time, the muscle relaxation from drugs like cisatracurium has been seen to work less well. This has been shown with the same kind of muscle-relaxing medicines, but nobody knows for sure whether it happens with cisatracurium itself. Still, doctors may expect the muscle relaxation to wear off a little sooner. They may also need to give cisatracurium at a faster drip rate to keep you relaxed during surgery or intensive care. Cisatracurium is given only in hospital by an anaesthetist or ICU team. Tell them if you take phenytoin regularly.
Little or no effect is expected. You usually do not need to change anything, but still tell your doctor or pharmacist about every medicine you take.