When will the patents on ZARONTIN expire, and when will generic ZARONTIN be available?

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Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Exclusivity Expiration
Parke Davis	ZARONTIN	ethosuximide	CAPSULE;ORAL	012380-001	Approved Prior to Jan 1, 1982	AB	RX	Yes	Yes	⤷ Start Trial	⤷ Start Trial				⤷ Start Trial
Parke-davis	ZARONTIN	ethosuximide	SYRUP;ORAL	080258-001	Approved Prior to Jan 1, 1982	AA	RX	Yes	Yes	⤷ Start Trial	⤷ Start Trial				⤷ Start Trial
>Applicant	>Tradename	>Generic Name	>Dosage	>NDA	>Approval Date	>TE	>Type	>RLD	>RS	>Patent No.	>Patent Expiration	>Product	>Substance	>Delist Req.	>Exclusivity Expiration

Last updated: July 29, 2026

Zarontin (Ethosuximide) Investment Scenario and Patent-Driven Fundamentals

Zarontin (ethosuximide) is an established, off-patent antiepileptic for absence seizures. From an investment fundamentals perspective, the core driver is not near-term pipeline upside but chronic, commoditized demand under generic competition risk, with revenue exposure shaped by (1) Orange Book exclusivity and formulation IP that can delay or deter generic entry, (2) any active Hatch-Waxman or state-level patent litigation affecting specific NDCs, and (3) payer contracting and manufacturing capacity rather than R&D cadence.

What is Zarontin (ethosuximide) and what demand fundamentals matter for investors?

Core product profile

Drug: ethosuximide
Indication: absence seizures (often childhood absence epilepsy)
Therapeutic category: antiepileptic drug (AED)
Market structure: mature AED market with significant generic penetration (ethosuximide has long been available)

Demand drivers

Persistent but modest incidence-driven demand: absence seizures are a distinct epilepsy phenotype with limited population size compared with broader AED markets.
High dosing continuity: ethosuximide therapy typically runs long-term while seizures persist or until remission, supporting repeat prescription flows rather than episodic demand.
Substitution intensity: when branded exclusivity is expired and formulation IP is weak, bios and physician preference are usually secondary to acquisition cost and contracting.

Investor implications

The commercial base case is typically stable volume with pricing pressure. Returns tend to come from securing market share via supply reliability, contracting discipline, and niche formulation benefits (if any IP remains).

What is the Orange Book status of Zarontin (ethosuximide) and how does it affect generic timing?

Featured-snippet answer

Zarontin’s investability is constrained by generic availability dynamics. The main near-term questions are whether any listed patents or exclusivities still block certain dosage strengths, release profiles, or manufacturing changes for specific NDCs.

What to check in practice (deal and litigation gating items)

Orange Book active listings for:
- specific dosage forms (capsules/tablets; if multiple strengths exist, each NDC can have separate listed patents)
- method-of-manufacture or formulation patents
- pediatric exclusivity, 180-day exclusivity triggers (Paragraph IV), and unexpired exclusivity periods
Whether the branded product still has:
- active, enforceable patents tied to the marketed dosage strength
- a recent FDA approval that re-starts exclusivity windows (rare for long-established drugs but possible through supplemental approvals)

Why this matters for investment scenarios

If no Orange Book protections remain for the relevant NDCs, a generic launch can happen quickly at FDA acceptance, and branded pricing becomes purely market-driven.
If patents remain, investors must underwrite:
- expected entry timing
- probability-weighted litigation outcomes
- settlement terms that can preserve brand economics for a defined period

(Note: the analysis above is structured for how the Orange Book gate controls generic timing; specific Orange Book listings, expiration dates, and NDC mapping are required for an exact calendar forecast.)

When does ethosuximide lose exclusivity and how fast could generic entry ramp?

Exclusivity pathways that affect launch timing

For small-molecule AEDs, generic entry timing is typically governed by:

Patent expiration (listed patents)
FDA exclusivities (pediatric exclusivity, new clinical investigations, orphan exclusivity if applicable, though unlikely for ethosuximide)
Hatch-Waxman Paragraph IV certifications and any 180-day exclusivity

Generic ramp mechanics

Once allowed to enter, generics usually capture share quickly due to:
- therapeutic interchange
- pharmacy benefit manager preference based on net cost
- payer protocols in chronic epilepsy

Investment scenario logic

Base case: ongoing generic share expansion, with Zarontin brand increasingly limited to:
- shortfall coverage if supply is constrained
- patients stabilized on brand who do not switch
Upside case: any residual formulation/manufacturing IP can slow full substitution for particular NDCs or strengths.
Downside case: a Paragraph IV-driven entry wave compresses branded pricing and forces volume decline.

(To provide exact “loss of exclusivity” dates and 180-day triggers, Orange Book active and expired listing data tied to Zarontin NDCs is required.)

What patents protect ethosuximide (Zarontin) and how strong is the patent estate?

Patent estate typical for long-established small molecules

For older AEDs, enforceable IP that still matters today usually clusters around:

formulation (granulation, excipient composition, dissolution profile)
manufacturing method (process parameters, impurities control)
packaged dosage technologies (shell composition, coatings, stability improvements)
specific salts or polymorphs (less common for ethosuximide, which is typically a single active form)

How to assess “strength” for investment

A defensible patent estate for a marketed small molecule generally has at least one of:

Remaining term that overlaps with current generic entry risk
Specific claim scope that is difficult to design around
Litigation history indicating willingness and capability to enforce

Commercial linkage

If claims cover the commercially critical release/dissolution behavior for absorption, generics may need costly reformulation.
If claims are broad to composition or method steps, design-around probability drops.

(Exact patent numbers, claims, assignees, and remaining term are necessary for a true strength rating. Without Orange Book and patent-to-NDC mapping for Zarontin, only a framework can be provided.)

What formulation and method-of-use patents affect Zarontin’s competitive risk?

Formulation patents: where barriers actually show up

In chronic epilepsy products, formulation patents matter when they:

affect bioavailability variability or dissolution rate
stabilize an active to meet shelf-life and impurity specs
target patient tolerability (GI effects can drive adherence)

Method-of-use patents: usually less relevant for AED generics

Method-of-use patents can be harder to enforce against generics because:

standard labeling becomes controlling
off-label use does not prevent generic approval

Investment relevance

If only method-of-use IP remains, generic substitution can still proceed.
If formulation or manufacturing IP remains, generics face higher compliance or design-around cost.

Are there any Paragraph IV challenges or patent litigation affecting ZARONTIN?

What to look for

FDA Paragraph IV notifications tied to ethosuximide NDCs
docketed litigations in federal court:
- Hatch-Waxman case filings, Markman outcomes, injunction or settlement rulings
Settlement terms:
- “no-AG” agreements
- “first filer” 180-day exclusivity preservation
- licensed launch date carveouts by strength or NDC

Why this drives investment

Paragraph IV events are the fastest route to revenue compression. They also create:

predictable near-term supply ramp risk
legal cost drag
potential settlement cash flows or license revenue if the brand holder participates

(Litigation and Paragraph IV event specifics cannot be reliably enumerated here without docket and FDA notification records tied to Zarontin NDCs.)

What FDA status does Zarontin have and do pathway or labeling changes change economics?

Regulatory status that matters for branded vs generic

For established generics and legacy brand products:

The original NDA/BLA approval year does not matter as much as:
- current labeling content
- strength and dosage form availability
- any newly approved manufacturing changes that keep certain NDCs distinct

Labeling and dosing stability

If dosing instructions are stable and standards for bioequivalence are straightforward, generics gain ease of entry once legal barriers clear.
If specific strengths have unique manufacturing controls, substitution can be slower.

(Exact FDA approval history and labeling revisions require dossier and regulatory data beyond this prompt.)

Which companies compete with Zarontin and how does their market positioning affect pricing?

Competitive landscape characteristics

Ethosuximide is typically competed on:

net pricing through wholesaler and PBM contracts
distribution reliability (chronic therapy requires continuous supply)
internal formularies and therapeutic interchange policies

Investment implications

A company that controls manufacturing yields can capture share even in mature generics.
Brand holders are typically not a cost leader once generic parity is reached unless they control a protected NDC set.

(Specific competitor NDCs and market share require current Orange Book and pharmacy pricing datasets.)

What generic entry risks exist for Zarontin by dosage strength and NDC?

Risk model by strength

For many legacy drugs, risk is strength-specific:

Patent coverage may attach to one strength NDC with remaining term
Generics may launch only the strengths that are legally cleared
Pricing declines can be non-uniform until full multi-strength substitution occurs

Key underwrite points

Whether all strengths face the same legal clearance date
Supply timing risk for first and second wave entrants
Contracted inventory cycles that buffer near-term price effects

(A strength-by-strength legal risk table requires the Orange Book listing by NDC.)

How does Zarontin compare with alternative AEDs for absence seizures in payer and prescriber dynamics?

Substitution pressure

Absence seizures can be treated with other AEDs depending on patient profile and clinician preference. Competitive pressure can reduce ethosuximide share even when generic pricing is favorable.

Investor view

If ethosuximide faces therapeutic substitution, generic price erosion may translate to volume erosion faster.
If it remains preferred for tolerability or efficacy, volume may stabilize and pricing pressure becomes the primary negative variable.

(Comparative positioning requires current clinical guideline and formulary data.)

What manufacturing and IP barriers could delay a full commoditization outcome?

IP-adjacent barriers

Even when patents expire, generics can be delayed by:

FDA chemistry and manufacturing controls compliance
impurity profile validation
stability and shelf-life controls
scale-up bottlenecks

Investment implication

A supply-constrained competitive environment can temporarily support pricing above pure commoditization.
Investors should underwrite manufacturing continuity risk and procurement resilience rather than patent-led exclusivity alone.

What are the most likely investment scenarios for Zarontin (ethosuximide)?

Scenario 1: Base case (continued commoditization)

No enforceable patent barriers for relevant NDCs or exclusivity windows are already exhausted.
Generic share continues expanding.
Brand revenue declines with periodic pricing resets.

Scenario 2: Patent-persisted protection for selected NDCs

Specific strengths retain formulation or manufacturing IP coverage.
Generics launch later for those strengths.
Brand declines slower and remains stronger in protected strengths.

Scenario 3: Litigation/Paragraph IV settlement preserves a launch date

Brand holder settles with a first-filer, delaying entry.
Settlement terms may include payment and launch carveouts.
Net outcome is a defined period of pricing relief before full generic penetration.

Scenario 4: Supply or quality disruptions create temporary pricing support

Manufacturing failures or QA issues reduce generic supply.
Brand share increases or pricing holds temporarily.
Risk: short duration unless systemic supply constraints persist.

Key data table investors should build (patent and exclusivity calendar model)

Element	What to map to Zarontin	Why it drives valuation
Orange Book active patents by NDC	Listed patents and expiration dates	Legal barrier to entry by strength
Exclusivity (if any)	Pediatric and other FDA exclusivity periods	Delay independent of patents
Paragraph IV history	Certifications and 180-day eligibility	Controls first entrant economics
Litigation status	Dockets, rulings, injunctions, settlements	Probability-weighted entry dates
FDA approvals	Supplemental changes affecting NDCs	Re-segment market protection
Competitor NDC launch waves	Which strengths each generic files	Non-uniform pricing and margin impacts

(The table is the required modeling scaffold; exact populated fields require Orange Book and litigation records for Zarontin.)

Key Takeaways

Zarontin (ethosuximide) is a mature AED with investment fundamentals dominated by generic substitution dynamics and NDC-level legal/exclusivity status rather than near-term R&D upside.
The most material upside or downside comes from whether any Orange Book-listed patents or exclusivities still block specific strengths and whether Paragraph IV challenges or settlements delay entry.
Commercial outcomes hinge on payer contracting, supply reliability, and strength-by-strength competitive timing, not broad therapeutic growth.

FAQs

Which ZARONTIN NDCs face the highest generic entry risk based on Orange Book listings?
How do Paragraph IV settlements typically impact ethosuximide launch dates and pricing?
Do formulation patents on ethosuximide meaningfully delay generic substitution versus method-of-use patents?
What manufacturing or FDA CMC issues most often delay generic launches for older small-molecule AEDs?
How does formulary positioning of ethosuximide versus alternative absence-seizure AEDs affect long-term volume durability?

References

FDA. Orange Book: Approved Drug Products with Therapeutic Equivalence Evaluations. (Accessed via FDA Orange Book database).
FDA. Hatch-Waxman Amendments and Paragraph IV certification framework. (FDA guidance and statutory basis).
U.S. Patent and Trademark Office (USPTO). Patent search and assignment records.

US Patents:	0
Applicants:	2
NDAs:	2

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Summary for ZARONTIN