Effect of antiepileptic drugs on the elimination of various tetracycline derivatives.

Elimination of the bacteriostatics tetracycline, doxycycline, methacycline, oxytetracycline, demethylchlortetracycline and chlortetracycline was studied in healthy control persons and in patients on long-term antiepileptic therapy. The half-life of doxycycline was significantly shorter in patients than in the controls. The half-lives of other tetracycline derivatives and their excretion in urine were not significantly different between the two groups. Accordingly, in order to maintain an adequate serum level of doxycycline it should be given twice daily to patients on long-term therapy with barbiturates, diphenylhydantoin or carbamazepine. The classical tetracycline derivatives studied may be administered according to conventional principles.