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Does Isoniazid Interact with Fosphenytoin Sodium?

CDI records a moderate classification for Isoniazid and Fosphenytoin Sodium. The stored summary is: May increase phenytoin serum levels; monitoring of phenytoin levels recommended. The mechanism involves inhibition of phenytoin metabolism. Patients taking both medications should consult their healthcare provider before starting, stopping, or changing the dosage of either drug. This record was extracted from drug labeling through openFDA. NIH/NLM RxNorm is used for drug identities. The summary and severity classification are CDI's processed information, not a verbatim source quotation. Product, route, and patient circumstances matter.

Severity: Moderate
Isoniazid Class: Antimycobacterial
Management: Monitor for effects
Data Source: U.S. FDA via OpenFDA

Recorded Mechanism

Inhibition of phenytoin metabolism

What To Tell Your Doctor or Pharmacist

If you are taking Isoniazid and your doctor is considering prescribing Fosphenytoin 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 whether any dosage adjustments are needed
Never stop or change either medication without first consulting your healthcare provider

💊 Isoniazid(Isoniazid)+💊 Fosphenytoin Sodium(Cerebyx)

Severity & Interaction Details

🟡

moderate

Be aware — moderate interaction

Documented interaction with manageable risk. May require dose adjustment or monitoring.

Severity scale

MinorContra

On record

Yes

Drug A class

Antimycobacterial

Drug B class

—

Source

NLP:fosphenytoin sodium

What this means in plain English

May increase phenytoin serum levels; monitoring of phenytoin levels recommended.

About Isoniazid and Fosphenytoin Sodium

Isoniazid is an Antimycobacterial. Fosphenytoin Sodium is also sold under the brand name Cerebyx. Both Isoniazid and Fosphenytoin Sodium carry an FDA boxed warning — the agency's most serious safety designation.

Source and Limitations

This record was produced by automated extraction from drug-label information, including AI processing. The summary and mechanism are not verbatim FDA quotations. The drug profiles below may describe different formulations from the source label. Confirm the exact product and route with your pharmacist. This page does not establish independent clinical review.

📖 Source: NLP:fosphenytoin sodium

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How this information is prepared: CDI uses automated extraction, including AI, to summarize drug labeling from openFDA and includes separately identified curated-reference records. RxNorm helps identify medications; it does not verify interaction claims. Extracted summaries and CDI severity classifications can contain errors and are not verbatim FDA statements or independent clinical review. Maintained by CheckDrugInteractions.com. See our methodology or report a correction at support@checkdruginteractions.com.

Data sourced from U.S. FDA drug labeling via openFDA and the NIH National Library of Medicine, supplemented with a small number of well-established interactions from curated clinical references. For informational purposes only. Always consult your pharmacist or physician.