Interference of oral phenytoin absorption by enteral tube feedings

The medical records of 11 brain-injured patients, simultaneously on enteral tube feeding and phenytoin, were retrospectively reviewed for evidence of interference of phenytoin absorption. One case demonstrated no interference. Three cases suggested depression of serum phenytoin levels by enteral formula, but the contribution of other factors could not be ruled out. Seven cases did appear to reflect a direct alteration of phenytoin levels by enteral formula. To achieve adequate serum phenytoin levels, patients may need (1) large oral phenytoin doses above that recommended while on continuous enteral feedings, (2) administration of oral phenytoin between intermittent enteral feedings, or (3) a choice of alternative anticonvulsants which have been shown to be unaffected by enteral formula.