Drug interactions
Isoniazid + Methylene blue
Severity: Major
Isoniazid and Methylene blue: major 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
Methylene blue is a potent reversible MAO-A inhibitor, and isoniazid has weak MAO inhibitory properties. Combined serotonergic activity can precipitate serotonin syndrome with confusion, hyperthermia, clonus and autonomic instability.
What this interaction means in plain words
Isoniazid and Methylene blue can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Why it happens
Additive MAO-A inhibition leading to excess serotonergic activity.
What to do
Avoid the combination when possible. If methylene blue is essential, hold isoniazid and monitor for serotonin toxicity until the interval specified in labeling has passed.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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Other interactions of Isoniazid
Frequently asked questions
Can I take Isoniazid with Methylene blue?
MediHelp rates the interaction as major. Isoniazid and Methylene blue can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Methylene blue is a potent reversible MAO-A inhibitor, and isoniazid has weak MAO inhibitory properties. Combined serotonergic activity can precipitate serotonin syndrome with confusion, hyperthermia, clonus and autonomic instability.
How serious is the interaction between Isoniazid and Methylene blue?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid the combination when possible. If methylene blue is essential, hold isoniazid and monitor for serotonin toxicity until the interval specified in labeling has passed.
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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