Final answer:
When administering Phenytoin, all of the following should be monitored: behavior, therapeutic blood levels, and for Steven Johnson syndrome as they are critical to ensure the safety and effectiveness of the medication.
Step-by-step explanation:
When administering Phenytoin, it is important to monitor for behavior changes, therapeutic blood levels, and signs of Steven Johnson syndrome. Phenytoin is a medication used primarily for the treatment of epilepsy. Monitoring for behavior is essential as this drug can affect the central nervous system and may alter mood or cognitive function. Keeping track of therapeutic blood levels is crucial for ensuring that the drug is present in the blood at a concentration that is both effective and non-toxic. Additionally, it is pertinent to be vigilant for any signs of Steven Johnson syndrome, a rare but serious skin reaction. Therefore, the correct answer is 'D. all of the above'.