A patient is admitted after having multiple seizures. Fosphenytoin is administered. When the patient's phenytoin blood level is checked later, it is 19 mcg/ml. At this level, which of the following side effects of the drug might be observed?


• Fosphenytoin is a phenytoin prodrug; both are hydantoin anticonvulsants. It works by modulating neuronal sodium and calcium channels.

• The therapeutic phenytoin level is 10–20 mcg/ml. Even at therapeutic levels, side effects such as nystagmus can occur. 

• Hypotension or constipation, not hypertension or diarrhea, are side effects of fosphenytoin. 

• Agitation is not a side effect of fosphenytoin. However, the drug may cause confusion and/or somnolence.

• Other side effects include paresthesia, sedation, ataxia, rash, bradycardia, hypokalemia, tinnitus, and gingival hyperplasia.

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