Drug interactions
Guanfacine + Isoniazid
Severity: Moderate
Guanfacine and Isoniazid: 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
Guanfacine is cleared mainly by CYP3A4, and inhibitors raise its plasma levels, which can cause excess hypotension, bradycardia and sedation. Isoniazid is a weak-to-moderate CYP3A4 inhibitor, so the increase is likely smaller than with potent inhibitors.
What this interaction means in plain words
Guanfacine and Isoniazid 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.
Guanfacine belongs to Cardiovascular; Isoniazid belongs to Anti Bacterial.
Why it happens
Isoniazid inhibits CYP3A4, reducing the metabolism of guanfacine.
What to do
Monitor heart rate, blood pressure and sedation after starting isoniazid. Consider a guanfacine dose reduction if adverse effects occur.
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 Isoniazid
Other interactions of Guanfacine
- Clonidine + Guanfacine Major
- Guanfacine + Lofexidine Major
- Aldesleukin + Guanfacine Moderate
- Amiodarone + Guanfacine Moderate
- Amisulpride + Guanfacine Moderate
- Amitriptyline + Guanfacine Moderate
Frequently asked questions
Can I take Guanfacine with Isoniazid?
MediHelp rates the interaction as moderate. Guanfacine and Isoniazid 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. Guanfacine is cleared mainly by CYP3A4, and inhibitors raise its plasma levels, which can cause excess hypotension, bradycardia and sedation. Isoniazid is a weak-to-moderate CYP3A4 inhibitor, so the increase is likely smaller than with potent inhibitors.
How serious is the interaction between Guanfacine and Isoniazid?
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 heart rate, blood pressure and sedation after starting isoniazid. Consider a guanfacine dose reduction if adverse effects occur.
What other medicines interact with Isoniazid?
MediHelp also lists interactions of Isoniazid with, for example, Bacillus calmette-guerin substrain tice, Benzhydrocodone / acetaminophen, Carbamazepine. The full list is on the Isoniazid page.
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