Does Doxycycline Interact with Phenobarbital Sodium?
Doxycycline and Phenobarbital Sodium have a major drug interaction according to U.S. FDA drug labeling data. Phenobarbital shortens the half-life of doxycycline for up to 2 weeks after discontinuation; clinical response should be monitored closely. The mechanism involves induction of hepatic microsomal enzymes that metabolize the antibiotic. Patients taking both medications should consult their healthcare provider before starting, stopping, or changing the dosage of either drug. This information is based on official FDA drug labeling sourced from OpenFDA and the NIH National Library of Medicine.
- Severity
- Major
- Doxycycline Class
- Tetracycline-class Drug
- Management
- Close medical supervision required
- Data Source
- U.S. FDA via OpenFDA
How This Interaction Works
The interaction between Doxycycline and Phenobarbital Sodium occurs because induction of hepatic microsomal enzymes that metabolize the antibiotic. Clinically, this means phenobarbital shortens the half-life of doxycycline for up to 2 weeks after discontinuation; clinical response should be monitored closely. This is classified as a major interaction, meaning it could cause serious harm if not properly managed. Your healthcare provider may need to adjust dosages, substitute one medication, or increase monitoring frequency.
What To Tell Your Doctor or Pharmacist
If you are taking Doxycycline and your doctor is considering prescribing Phenobarbital Sodium (or vice versa), make sure to:
- Inform your doctor and pharmacist of all current medications, including over-the-counter drugs and supplements
- Ask whether the benefits of combining these medications outweigh the risks for your specific situation
- Ask what symptoms to watch for that would indicate the interaction is causing problems
- Ask how frequently you should be monitored while these are co-prescribed
- Ask whether any dosage adjustments are needed
- Never stop or change either medication without first consulting your healthcare provider