Interaction between doxycycline and barbiturates.

In a cross-over study of five hospitalized patients the half life of doxycycline was significantly shortened after 10 days' treatment with phenobarbitone. In five patients on continuous barbiturate therapy the half life of doxycycline was even shorter. Barbiturates or other agents inducing drug metabolism should be used cautiously in combination with doxycycline, since this might result in therapeutically inadequate serum concentrations of the antibiotic.