Phenytoin
| Evidence Level: L5 | Predicted Indications: 10 |
Table of Contents
Phenytoin: From Epilepsy to Trigeminal Nerve Neoplasm
One-Sentence Summary
Phenytoin is a long-established antiseizure medicine, originally used to treat epilepsy, including generalized tonic-clonic seizures, partial seizures and status epilepticus. The TxGNN model predicts it may be effective for trigeminal nerve neoplasm, but there are no clinical trials and only 2 publications retrieved, and these concern trigeminal neuralgia and Sturge-Weber syndrome rather than neoplasm. The prediction is therefore supported by model output alone.
Quick Overview
| Item | Content |
|---|---|
| Original Indication | Epilepsy (generalized tonic-clonic, partial, status epilepticus, Lennox-Gastaut syndrome). The approved indication text is not available in the New Zealand licence data, so this is taken from the knowledge-graph indication list. |
| Predicted New Indication | Trigeminal nerve neoplasm |
| TxGNN Prediction Score | 99.99% |
| Evidence Level | L5 |
| New Zealand Market Status | Cancelled only (no currently valid licence) |
| Number of Authorizations | 5 (all cancelled) |
| Recommended Decision | Hold |
Why is This Prediction Reasonable?
Detailed mechanism of action data is not currently available in the data compiled for this report. Phenytoin is generally known as a voltage-gated sodium channel blocker. It limits repetitive neuronal firing, and the pharmacology data compiled here list the sodium channel Nav1.2 (SCN2A) as a target. That mechanism fits epilepsy well.
The link to a trigeminal nerve neoplasm is weak. The very high TxGNN score most likely reflects network proximity to trigeminal neuralgia and seizure-related nodes, not any antitumour activity. Phenytoin has no established antineoplastic mechanism in this setting. The retrieved literature covers trigeminal neuralgia treatment and Sturge-Weber syndrome, not tumours. This looks like a model artefact, not a real repurposing opportunity.
The related condition trigeminal neuralgia (rank 9, score 99.97%) is much better supported mechanistically and clinically. It is covered under Conclusion and Next Steps.
Clinical Trial Evidence
Currently no related clinical trials registered.
Literature Evidence
| PMID | Year | Type | Journal | Key Findings |
|---|---|---|---|---|
| 17997704 | 2007 | Review | Expert Rev Neurother | Overview of medical and surgical treatments for trigeminal neuralgia. It concerns a pain syndrome, not neoplasm. |
| 9157801 | 1997 | Case series | An Esp Pediatr | Experience with 14 cases of Sturge-Weber syndrome (clinical features, course, treatment response). Not about neoplasm. |
New Zealand Market Information
| Authorization Number | Product Name | Dosage Form | Approved Indication |
|---|---|---|---|
| 2619466 | Dilantin Paediatric | Oral liquid 30 mg per 5 ml | Not available (cancelled) |
| 2619431 | Dilantin | Capsule 100 mg | Not available (cancelled) |
| 2619458 | Dilantin | Capsule 30 mg | Not available (cancelled) |
| 2619474 | Dilantin Infatab | Tablet 50 mg | Not available (cancelled) |
| 391646 | Hospira | Injection 50 mg per ml, 5 ml ampoule | Not available (cancelled) |
All five authorizations are cancelled, so no phenytoin product currently holds a valid New Zealand licence.
Safety Considerations
The knowledge graph flags the following conditions as contraindication-related for phenytoin (this comes from graph data, not from package insert text):
- Cardiac: long QT syndrome (including familial), torsades de pointes, hypotensive disorder
- Liver: liver failure, liver disease, hepatic coma, hepatic encephalopathy, gallbladder disease
- Kidney: kidney disease, pyoureter
- Blood: thrombocytopenia, neutropenia, agranulocytosis
- Metabolic: hyperglycemia, diabetes mellitus, diabetic ketoacidosis, inherited porphyria / porphyria
- Autoimmune: systemic lupus erythematosus (including paediatric)
- Respiratory and sleep: obstructive sleep apnea, sleep apnea syndrome, congenital central hypoventilation syndrome, Haddad syndrome
- Psychiatric: anxiety disorder, neurotic disorder, dysthymic disorder, substance abuse/dependence
Published case reports in the retrieved literature also describe phenytoin-associated thrombocytopenia, hyperglycemia and diabetic ketoacidosis, and erythema multiforme in patients receiving cranial radiotherapy (EMPACT syndrome). The EMPACT reports matter in oncology settings involving the brain.
For drug interactions, the only entry is pharmacological (target: Nav1.2 / SCN2A) and is not a drug-drug interaction. Please refer to the package insert for formal warnings, contraindications and interactions.
Conclusion and Next Steps
Decision: Hold
Rationale: The prediction for trigeminal nerve neoplasm rests on model score alone (L5). There are no trials, the literature does not address tumours, and no antineoplastic mechanism is known. The product is also no longer licensed in New Zealand.
Other predicted indications in the data (all Hold unless noted):
- Trigeminal neuralgia (L3, "Research Question"): The most plausible repurposing direction. Phenytoin shares the sodium channel mechanism of carbamazepine, the first-line therapy. Retrospective data support IV phenytoin for acute exacerbations (a 144-case cohort and another retrospective cohort), but guidelines treat it as non-first-line, and evidence for it is weak with no RCTs.
- Reflex and stimulus-induced seizures (micturition-induced, thinking, audiogenic, eating, orgasm-induced, startle, reading): These are subtypes within the existing epilepsy indication, so they are not true repurposing. Support is mostly preclinical or case-report level.
- Beta-ketothiolase deficiency (L5): No mechanistic link; likely a graph artefact.
To proceed, the following is needed:
- A package insert for phenytoin (Medsafe warnings and contraindications are missing, which blocks safety screening)
- Mechanism of action data from DrugBank
- For trigeminal neuralgia: a focused evidence review or a trial comparing phenytoin (especially IV for acute crises) with standard therapy, plus a decision on whether a licensed product could be re-supplied in New Zealand
- For trigeminal nerve neoplasm: preclinical or clinical evidence of antitumour activity, otherwise this indication should be deprioritised
Disclaimer
This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.