Drug interactions
Phenobarbital + Tolbutamide
Severity: Moderate
Phenobarbital and Tolbutamide: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Phenobarbital is an enzyme inducer that can increase the metabolism of tolbutamide and shorten its half-life. With chronic use, glycemic control may deteriorate.
What this interaction means in plain words
Phenobarbital and Tolbutamide can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Why it happens
Induction of CYP2C9 and other hepatic enzymes increases tolbutamide clearance.
What to do
Monitor blood glucose and HbA1c when phenobarbital is started or withdrawn, and adjust the tolbutamide dose accordingly. Watch for hypoglycemia after the inducer is stopped.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Tolbutamide
- Glyburide-metformin + Tolbutamide Major
- Insulin degludec-liraglutide + Tolbutamide Major
- Aceclofenac + Tolbutamide Moderate
- Acemetacin + Tolbutamide Moderate
- Acetylsalicylic acid + Tolbutamide Moderate
- Albiglutide + Tolbutamide Moderate
Frequently asked questions
Can I take Phenobarbital with Tolbutamide?
MediHelp rates the interaction as moderate. Phenobarbital and Tolbutamide can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Phenobarbital is an enzyme inducer that can increase the metabolism of tolbutamide and shorten its half-life. With chronic use, glycemic control may deteriorate.
How serious is the interaction between Phenobarbital and Tolbutamide?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor blood glucose and HbA1c when phenobarbital is started or withdrawn, and adjust the tolbutamide dose accordingly. Watch for hypoglycemia after the inducer is stopped.
What other medicines interact with Tolbutamide?
MediHelp also lists interactions of Tolbutamide with, for example, Glyburide-metformin, Insulin degludec-liraglutide, Aceclofenac. The full list is on the Tolbutamide page.
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