Phenytoin can make your body clear caffeine faster, so caffeine citrate may not work as long or as well as expected. If both are used together, a higher dose of caffeine citrate may be needed. This is based on data from adults, and the dose should be adjusted by the doctor.
These medicines are often taken together with some care. Your doctor may change a dose, space them apart or check on you more often. Make sure your doctor and pharmacist know you take both.