Serum
phenytoin levels can be raised by the concurrent use of
chloramphenicol. Also, evidence from children suggests that
phenytoin may reduce or raise
serum chloramphenicol levels. Fosphenytoin, a prodrug of
phenytoin, may interact similarly.
Concurrent use should be avoided unless the effects can be closely monitored and appropriate
phenytoin dosage reductions made as necessary. The use of a single prophylactic dose of
phenytoin or fosphenytoin may be an exception to this. If both drugs are given, monitor for
phenytoin toxicity (indicators include blurred vision, nystagmus, ataxia or drowsiness). Take
phenytoin levels as necessary and adjust the dose accordingly. Also monitor for
chloramphenicol efficacy and
toxicity.