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Fosphenytoin

Classification: C

Drug products: Pro-Epanutin®

ATC code: N03AB05

Substances: fosphenytoin, fosphenytoin sodium

Summary

Fosphenytoin is a pro-drug of phenytoin and the anticonvulsant effect can thus be attriubuted to phenytoin.

Physiologic changes during pregnancy may alter plasma concentration of fosphenytoin and an increase of seizure frequency may occur in pregnant women.

Fosphenytoin can affect the metabolism of oral contraceptives and additional contraception should be used.

Additional information

Pharmacokinetics and dosing

According to the original manufacturer, sex has no significant impact on fosphenytoin pharmacokinetics [1, 2]. One study investigated the effects of age and sex on phenytoin pharmacokinetics using isotopes of phenytoin or fosphenytoin administrated IV or IM while patients remained on their oral maintenance regimen. Adult and elderly patients (39 men, 24 women) were given a single injection of 100 mg phenytoin or fosphenytoin, and serial blood samples were collected up to 196 hours after the dose. There was no difference between men and women in phenytoin clearance, distribution volume or elimination half-life [3]. Phenytoin pharmacokinetics is altered during pregnancy and an increase of seizure frequency may occur in pregnant women. For appropriate dose adjustment in pregnant women, periodic measurement of plasma phenytoin concentrations may be valuable [1].

Effects

Fosphenyotin is a prodrug of phenytoin and accordingly, its anticonvulsant effects are attributable to phenytoin [1].

Adverse effects

No studies with a clinically relevant sex analysis regarding adverse effects of fosphenytoin have been found.

Drug interactions

Fosphenytoin may affect the metabolism of estrogens and progestogens. Thus, the effect of these can be reduced. Additional contraceptive method should be used [4]. Swedish users, please consult Janusmed Interactions(Janusmed interaktioner).

Birth defects

Swedish users, please consult Janusmed Drugs and Birth Defects(Janusmed fosterpåverkan).

Updated: 2017-03-28

Date of litterature search: 2013-03-11

References

  1. Fosphenytoin. DailyMed [www]. US National Library of Medicine. [updated 2011-05-01, cited 2013-03-11]. länk
  2. Pro-Epanutin (fosfenytoin). Summary of Products Characteristics. Medical Products Agency Sweden; 2016.
  3. Ahn JE, Cloyd JC, Brundage RC, Marino SE, Conway JM, Ramsay RE et al. Phenytoin half-life and clearance during maintenance therapy in adults and elderly patients with epilepsy. Neurology. 2008;71:38-43. PubMed
  4. Patsalos PN, Perucca E. Clinically important drug interactions in epilepsy: general features and interactions between antiepileptic drugs. Lancet Neurol. 2003;2:347-56. PubMed
  5. Läkemedelsstatistik. Stockholm: Socialstyrelsen. 2015 [cited 2016-04-05.] länk

Authors: Linnéa Karlsson Lind, Desirée Loikas

Reviewed by: Expertrådet för neurologiska sjukdomar, Ellen Vinge

Approved by: Mia von Euler