Final answer:
The nurse should instruct the client to take medications at a consistent time each day to maintain therapeutic blood levels in their medication teaching plan.
Step-by-step explanation:
The nurse should include the instruction to take medications at a consistent time each day to maintain therapeutic blood levels in the client's medication teaching plan. This is important because maintaining steady blood levels of phenytoin helps prevent seizures and promotes the effectiveness of the medication. It is also important to note that abrupt discontinuation of phenytoin can lead to withdrawal seizures, so the client should not taper the medication without consulting their healthcare provider.