User:Ely.yatun/Fosphenytoin

Pharmacogenomics
Fosphenytoin is metabolized by CYP2C9 so it is important to make sure hat patient that take have adequate activity of this gene. As this medication is classified as an actionable pharmacogenetic medication by the FDA it is a good idea to do a genetic test and verify the activity of the CYP2C9 gene. On top of that verifying the allele of HLA-B can also help measure the safety of Fosphenytoin in the patient. If HLA-B *15:02 is present in patients Fosphenytoin can increase the risk of Stevens-Johnson syndrome/toxic epidermal necrolysis, because of that it is suggested to avoid this medication in those patients.

When deciding on a starting dose use the following criteria as a guide (based on activity score of CYP2C9):

Activity score of 2 (normal metabolizer)

 * Use regular dose.
 * Use regular duration of treatment.
 * Low chance of adverse effects.

Activity score of 1.5 (intermediate metabolizer)

 * Use regular dose.
 * Use regular duration of treatment.
 * no significant increase in side effects.

Activity score of 1 (intermediate metabolizer)

 * Use regulars loading dose but reduce subsequent doses by 25%.
 * Increased chance of side effects.

Activity score of 0 - 0.5 (poor metabolizer)

 * Use regulars loading dose but reduce subsequent doses by 50%.
 * Increased chance of side effects.