Carbamazepine and Erythromycin

Carbamazepine serum levels can very rapidly rise to toxic concentrations if erythromycin is given concurrently. Intoxication has been described in many reports. Erythromycin appears not to interact with phenytoin.

Clinical evidence
A girl of eight taking 50 mg phenobarbitone and 800 mg carba-mazepine daily was additionally given 500 mg and later 1000 mg erythromycin daily. Within two days she began to experience balancing difficulties and ataxia which were eventually attributed to carbamazepine intoxication. Her serum carbamazepine levels were found to have risen from a little below 10 /jg/ ml to over 25 jig/ ml (therapeutic range 2-10 uglml).

Marked rises m serum carbamazepine levels11 and/or intoxication following the addition of erythromycin have been described. At least 24 cases of carbamazepine intoxication have been reported.3-1013~16 A study in eight normal subjects showed that 1 g erythromycin daily for five days reduced the clearance of carbamazepine by an average of 20% (range 5-41%). Another study confirmed this interaction.
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