CLINICAL TRIALS PROFILE FOR PHENYTOIN

505(b)(2) Clinical Trials for phenytoin

This table shows clinical trials for potential 505(b)(2) applications. See the next table for all clinical trials

Trial Type	Trial ID	Title	Status	Sponsor	Phase	Start Date	Summary
OTC	NCT00011063 ↗	Effect of Ginkgo Biloba on Phenytoin Elimination	Completed	National Institutes of Health Clinical Center (CC)	Phase 1	2001-02-01	This study will examine how the herbal remedy ginkgo biloba may affect the body's elimination of other medicines. Many people take ginkgo biloba to improve memory, mental alertness and overall feeling of well being. Since this product is considered a food supplement and not a drug, it is not subject to the rigorous pre-market testing required for prescription and over-the-counter (OTC) drugs. As a result, information has not been collected on possible interactions between ginkgo biloba and other medications. This study will look at how ginkgo biloba affects the elimination of phenytoin-a medication used to treat patients with seizures. Normal healthy volunteers 21 years of age or older may be eligible for this 40-day study. Candidates will provide a medical history and undergo a physical examination and routine blood tests. Women of childbearing age must use a reliable form of birth control other than oral contraceptives ("the pill"). For at least 2 weeks before the study and throughout its duration, study participants may not have any of the following: 1) medications that can affect platelet function (e.g., aspirin, Motrin, Advil, Nuprin, ibuprofen, etc.); 2) alcoholic beverages; 3) grapefruit and grapefruit juice; and 4) all medications except those given by study personnel. On day 1 of the study, subjects take one 500-mg dose of phenytoin at 8:00 A.M.. On an empty stomach. (Subjects fast the night before taking the phenytoin and are allowed to eat breakfast 2 hours after the dose). Blood samples are drawn just before dosing and again at 0.5, 1, 1.5, 2, 4, 6, 8, 10, 12, 24, 32, 48, 72 and 96 hours after the dose. Blood drawn on this first study day is collected through a catheter (small plastic tube) placed in a vein to avoid multiple needlesticks. After the 12-hour sample is collected, the subject goes home and then returns to the clinic for the remaining blood draws, which are taken by direct needlestick. When the blood sampling is completed, subjects begin ginkgo therapy. The NIH Clinical Center provides participants a supply of 60-mg capsules of ginkgo to take twice a day (at 8 A.M. and 8 P.M..) for 4 weeks. At the end of the 4 weeks, subjects are given a second dose of phenytoin as described above and repeat the blood sampling procedure. Subjects continue taking ginkgo during this second phenytoin study.

All Clinical Trials for phenytoin

Trial ID	Title	Status	Sponsor	Phase	Start Date	Summary
NCT00000285 ↗	Effects of Phenytoin on Cocaine Use in Humans - 2	Completed	University of Minnesota	Phase 1	1996-05-01	The purpose of this study is to determine the effects of phenytoin on the self-administration of smoked cocaine.
NCT00000285 ↗	Effects of Phenytoin on Cocaine Use in Humans - 2	Completed	University of Minnesota - Clinical and Translational Science Institute	Phase 1	1996-05-01	The purpose of this study is to determine the effects of phenytoin on the self-administration of smoked cocaine.
NCT00000285 ↗	Effects of Phenytoin on Cocaine Use in Humans - 2	Completed	National Institute on Drug Abuse (NIDA)	Phase 1	1996-05-01	The purpose of this study is to determine the effects of phenytoin on the self-administration of smoked cocaine.
NCT00004403 ↗	Randomized Study of Albendazole in Patients With Epilepsy Due to Neurocysticercosis	Completed	Johns Hopkins University	N/A	2000-05-01	OBJECTIVES: I. Determine the effect of antiparasitic treatment with albendazole on the severity and duration of epilepsy due to neurocysticercosis. II. Determine the effect of a short course of albendazole on Taenia solium cysts present in the brain. III. Determine the natural regression of cerebral T. solium cysts in patients given placebo and their response to treatment at the end of the study.
NCT00004817 ↗	Phase III Double Blind Trial of Valproate Sodium for Prophylaxis of Post Traumatic Seizures	Completed	Harborview Injury Prevention and Research Center	Phase 3	1991-02-01	OBJECTIVES: I. Determine whether treating head injured patients with valproate sodium will reduce the risk of developing seizures as a result of the head injury. II. Determine the safety of valproate, the appropriate dose, and the effect valproate may have on the recovery of the brain's ability to compute numbers, solve problems, remember information, and control the movement of limbs after head injury.
NCT00004817 ↗	Phase III Double Blind Trial of Valproate Sodium for Prophylaxis of Post Traumatic Seizures	Completed	National Institute of Neurological Disorders and Stroke (NINDS)	Phase 3	1991-02-01	OBJECTIVES: I. Determine whether treating head injured patients with valproate sodium will reduce the risk of developing seizures as a result of the head injury. II. Determine the safety of valproate, the appropriate dose, and the effect valproate may have on the recovery of the brain's ability to compute numbers, solve problems, remember information, and control the movement of limbs after head injury.
NCT00006025 ↗	Temozolomide Plus Irinotecan in Treating Patients With Recurrent Malignant Glioma	Completed	National Cancer Institute (NCI)	Phase 1	2001-01-05	RATIONALE: Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Combining more than one drug may kill more tumor cells. PURPOSE: Phase I/II trial to study the effectiveness of temozolomide plus irinotecan in treating patients who have recurrent malignant glioma.

Clinical Trial Conditions for phenytoin

Condition Name

Condition Name for phenytoin
Intervention	Trials
Epilepsy	23
Healthy	13
Seizures	8
Epilepsies, Partial	5

Condition MeSH

Condition MeSH for phenytoin
Intervention	Trials
Epilepsy	26
Seizures	16
Status Epilepticus	12
Epilepsies, Partial	6

Clinical Trial Locations for phenytoin

Trials by Country

Trials by Country for phenytoin
Location	Trials
United States	138
India	8
Egypt	8
Israel	6
Spain	6

Trials by US State

Trials by US State for phenytoin
Location	Trials
New York	11
Texas	10
Maryland	10
California	8
Arizona	7

Clinical Trial Progress for phenytoin

Clinical Trial Phase

Clinical Trial Phase for phenytoin
Clinical Trial Phase	Trials
PHASE4	7
PHASE3	1
PHASE2	5

Clinical Trial Status

Clinical Trial Status for phenytoin
Clinical Trial Phase	Trials
Completed	73
RECRUITING	19
Unknown status	17

Clinical Trial Sponsors for phenytoin

Sponsor Name

Sponsor Name for phenytoin
Sponsor	Trials
National Cancer Institute (NCI)	6
Johnson & Johnson Pharmaceutical Research & Development, L.L.C.	6
Emory University	5

Sponsor Type

Sponsor Type for phenytoin
Sponsor	Trials
Other	227
Industry	53
NIH	14

Phenytoin Clinical Trials Update, Market Analysis, and Projection

Last updated: April 27, 2026

What is phenytoin’s clinical development status?

Phenytoin is an established, off-patent small-molecule antiepileptic drug. Clinical trial activity in the core indication is dominated by: (1) generic bioequivalence studies, (2) formulation optimization (e.g., extended-release, different salt forms), and (3) comparative pharmacokinetic work rather than novel mechanism-of-action epilepsy efficacy trials.

Implication for “clinical trials update”
Across major registries, phenytoin does not show a pattern of large, late-stage (Phase 3) new-molecular-entity programs typical of active proprietary pipeline assets. The most visible trial entries tend to be label-preserving studies: pharmacokinetics, bioequivalence, or short-duration comparative studies tied to product approvals and switching.

Where does phenytoin sit in the evidence base for efficacy and safety?

Phenytoin remains widely used for focal-to-bilateral tonic-clonic seizures and various seizure types based on decades of clinical evidence and guideline inclusion, with well-characterized safety risks tied to exposure and interactions.

Key clinical risk framing that persists in modern prescribing and monitoring:

• Narrow therapeutic index driving plasma level monitoring in many jurisdictions.
• Nonlinear (Michaelis-Menten-like) kinetics at higher concentrations, increasing the risk of dose-related toxicity.
• Drug-drug interactions via hepatic enzyme induction and metabolic effects.
• Adverse effects that are dose- and level-linked (neurologic toxicity, gingival changes, rash).

Are there any meaningful new clinical programs in registries?

Published and registry-level visibility for phenytoin is concentrated in studies that support generic and formulation switching rather than new clinical endpoints. In practice, this means the “update” cycle for phenytoin tracks manufacturing scale, product availability, and regional regulatory refresh rather than innovation-driven trial outcomes.

Data note: a registry-by-registry, trial-by-trial extraction is required to quantify counts by phase and completion status. That extraction is not possible from the information available in this prompt.

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What does the market look like today?

Phenytoin is a mature, low-to-mid value, high-volume legacy antiepileptic marketed globally. Market structure is typically characterized by:

• Multiple generics across immediate-release and extended-release formats.
• Low brand premium versus newer antiepileptics in many markets.
• Price pressure driven by generic competition.
• Continued uptake driven by physician familiarity, cost sensitivity, and therapeutic role in acute and chronic seizure management.

Market demand drivers

1. Epilepsy prevalence supports steady underlying demand for antiepileptic therapies.
2. Clinical inertia and experience: phenytoin is entrenched in protocols for specific seizure contexts, including status epilepticus pathways in some healthcare systems.
3. Cost-based formulary placement: in many countries, older generics remain default options on national or payer formularies.

Market constraints

• Switching to newer antiseizure medicines where payer policies allow.
• Safety monitoring burden: narrow therapeutic index can reduce preference in some settings, pushing prescribers toward alternatives.
• Substitution dynamics: pharmacies and PBMs may swap products within the same molecule class if the price gap changes.

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How big is the phenytoin market and what is it growing at?

A precise market size and CAGR cannot be computed from this prompt alone because it requires:

• a specific geography scope (global vs. region),
• a specific market definition (phenytoin active ingredient vs. formulations vs. units vs. dollars),
• and an identified set of market research sources.

Actionable alternative for investment/R&D planning: treat phenytoin as a cash-flow, low innovation-risk segment where value capture is more dependent on:

• supply chain reliability,
• packaging and dosing form differentiation,
• and regulatory continuity than on new clinical efficacy breakthroughs.

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What projections are realistic for pricing and volumes?

Given generic dominance, the dominant economics typically follow these patterns:

• Volumes: relatively stable with modest fluctuation tied to seizure epidemiology and payer formularies. In markets with strong cost control, volumes can be resilient.
• Unit prices: pressured by generic competition and procurement cycles, usually trending toward low single-digit annual declines (sometimes flat) rather than sustained growth.
• Revenue mix: shift between immediate-release and extended-release can occur based on tolerability and clinician preference, but molecule-level total revenue generally tracks cost competition.

Projection framework (typical for mature generics):

• Base case: low CAGR in revenue, with share moving among manufacturers via procurement.
• Downside: margin compression from additional generic entrants or price renegotiations.
• Upside: procurement exclusivity, stable sourcing, or continued inclusion in status epilepticus and emergency seizure pathways.

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Where is value created for phenytoin today?

Value creation for established off-patent drugs focuses on product and operational factors:

Formulation and product differentiation

• Immediate-release vs extended-release targeting different dosing convenience and tolerability.
• Salt/form factors designed to improve manufacturability and patient adherence.
• Bioequivalence reliability to prevent switching disruptions.

Operational and regulatory execution

• Maintain consistent manufacturing, dissolution profiles, and stability.
• Avoid supply interruptions that can prompt switches to alternative agents.

Competitive positioning

• Win formularies through procurement pricing and service reliability.
• Minimize pharmacy disruption costs by ensuring uninterrupted supply.

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What about intellectual property?

Phenytoin is well beyond primary patent coverage in most markets. Competitive differentiation is generally not built on new patents for the core active ingredient. Where IP exists, it is usually:

• formulation/process specific,
• method-of-use (in limited cases),
• or secondary patents tied to particular dosage forms or manufacturing routes.

A credible IP map requires jurisdiction-specific patent family extraction and is not possible within the constraints of this prompt.

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Business implications for R&D

Phenytoin does not present the typical profile for innovation-led clinical investment. The highest-probability paths are:

• formulation re-engineering aimed at patient adherence and reduced adverse effects in real-world dosing.
• comparative PK/BE packages that support fast market entry or market share capture.
• therapeutic protocol support in acute care settings where consistent supply and dosing accuracy matter.

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Key Takeaways

• Phenytoin is mature and off-patent, with clinical trial activity dominated by bioequivalence and formulation support rather than novel Phase 3 efficacy programs.
• Market demand is steady due to entrenched clinical use and payer cost pressure favoring generics.
• Revenue growth is likely limited by generic price competition; value capture depends more on manufacturing reliability, procurement execution, and product reliability than on clinical innovation.
• Investment and R&D strategies should prioritize dosing form reliability, BE execution, and supply continuity over new clinical mechanism development.

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FAQs

1) What phase of clinical trials is phenytoin mostly associated with today?

Most visible activity is associated with bioequivalence and formulation support studies, not new mechanism Phase 3 development.

2) Is phenytoin still prescribed for epilepsy?

Yes. It remains used where clinicians and formularies rely on established efficacy and cost-effective generic availability.

3) What drives phenytoin market share among manufacturers?

Procurement pricing, reliable supply, and product form availability (e.g., immediate-release vs extended-release), along with BE and regulatory continuity.

4) Is phenytoin a growth market?

It is typically not a high-growth innovation market; growth tends to track incremental volume stability, while pricing is constrained by generic competition.

5) What is the main clinical risk that affects adoption?

Dose-related toxicity risk due to a narrow therapeutic index and nonlinear pharmacokinetics, plus drug-drug interactions.

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References

[1] U.S. National Library of Medicine. ClinicalTrials.gov. “Phenytoin” search results. https://clinicaltrials.gov/
[2] European Medicines Agency. EPAR and assessment materials for phenytoin-containing products (by submission history). https://www.ema.europa.eu/
[3] FDA. Drug approvals and safety communications related to phenytoin products and labeling. https://www.fda.gov/