Phenytoin is predicted to decrease abacavir levels. Zidovudine may alter the
pharmacokinetics of
phenytoin, although this may be due to HIV
infection itself. Fosphenytoin, a prodrug of
phenytoin, may interact similarly.
The
clinical significance of these interactions is unclear. However, it may be prudent to monitor the
efficacy of abacavir. Be aware that larger
phenytoin doses may be needed in the presence of zidovudine.