Fosphenytoin | clinical impact review Clinical value Fosphenytoin retains the pharmacologic properties of phenytoin with the advantage of an improved adverse event profile. Two factors that influence outcome following therapy for SE are good drug tolerability and rapid administration, and the available evidence suggests that fosphenytoin is superior to phenytoin in both instances. Evidence from available studies in SE patients shows that fosphenytoin is at least as effective as phenytoin both in terms of speed of seizure resolution and the number of patients that respond in the treatment of the condition. There is moderate evidence that therapeutic phenytoin blood levels after intravenous fosphenytoin administration are achieved at least at a similar rate compared with intravenous phenytoin. There is also evidence confirming that the risk of venous adverse events with fosphenytoin is lower than with phenytoin, when administered at the recommended rate. Blood pressure and cardiac monitoring should be maintained with fosphenytoin, particularly during and immediately after the infusion, because hypotension and arrhythmias can occur with the active principle (phenytoin). There are patient populations for whom treatment with phenytoin may not be appropriate, in particular those with poor peripheral vascular access (e.g. children, the elderly, and intravenous drug abusers). Fosphenytoin may therefore be a preferred option in these patients although there is very limited evidence to confirm this benefit. Clearly the higher acquisition cost of fosphenytoin compared with phenytoin is an issue. Nevertheless, there is evidence that when fosphenytoin is administered as recommended the incidence of adverse events is lower than with phenytoin, thereby avoiding costly management and treatment of these events, which would influence the cost-effectiveness of fosphenytoin. 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