When do the SINEQUAN patents expire, and when will SINEQUAN go generic?

Subscribe to access the full database, or Start Trial
Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Exclusivity Expiration
Pfizer	SINEQUAN	doxepin hydrochloride	CAPSULE;ORAL	016798-003	Approved Prior to Jan 1, 1982		DISCN	Yes	No	⤷ Start Trial	⤷ Start Trial				⤷ Start Trial
Pfizer	SINEQUAN	doxepin hydrochloride	CONCENTRATE;ORAL	017516-001	Approved Prior to Jan 1, 1982		DISCN	Yes	No	⤷ Start Trial	⤷ Start Trial				⤷ Start Trial
Pfizer	SINEQUAN	doxepin hydrochloride	CAPSULE;ORAL	016798-006	Approved Prior to Jan 1, 1982		DISCN	Yes	No	⤷ 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 17, 2026

SINEQUAN (doxepin hydrochloride; listed for oral use) is a long-established branded antidepressant with limited visibility of near-term, high-value patent-led exclusivity. The investment profile is driven by (1) whether any enforceable composition, method-of-use, or formulation patents remain in key jurisdictions, (2) Orange Book status and any Hatch-Waxman exclusivity blocks to generic entry, (3) historical supply stability and margin structure in older antidepressants, and (4) risk from established generics and cost containment. For investors, the “fundamentals” question reduces to durability of branded differentiation versus the practical inevitability of generic market share.

What patents protect SINEQUAN (doxepin HCl) and how strong is the patent estate?

Featured snippet answer: For SINEQUAN, core patent protection typically concentrates in older compositions and use claims; investable upside depends on whether any late-expiring or secondary patents (formulation, dosing regimen, polymorphs, salts, crystal forms, manufacturing) remain in-force for the specific marketed strength and dosage form.

Composition, salt, and basic drug-identity claims: likely legacy coverage

Doxepin HCl is a tricyclic antidepressant with a long commercial history. In practical investment terms, the “first-in-class” identity risks are usually low for current branded doxepin: the active ingredient has been widely available as generic decades earlier in multiple markets.

Secondary patents that can still matter for cash flows

Even when the core API patent has expired, residual branded value can come from:

Formulation patents (bioavailability, dissolution profiles, controlled release vs immediate release).
Manufacturing/process patents (scale-up, impurity limits, solvent systems, crystallization conditions).
Method-of-use patents (specific indications or dosing regimens).
Switching or continuation patents tied to specific dosage forms/strengths.

For SINEQUAN, the investment lens is narrow: if Orange Book does not show unexpired listings for the specific NDC(s) supporting current branded sales, the branded premium has limited legal durability.

Geographic reality check

For investment decisions, enforceability outside the US is often less relevant unless:

royalties or licensing arrangements are structured internationally, or
litigation is active in multiple jurisdictions.

Given doxepin’s age and generic penetration, the highest analytical weight usually goes to US market access constraints.

What is the Orange Book status of SINEQUAN (doxepin HCl) and are there unexpired exclusivities?

Featured snippet answer: The key investment variable is whether the FDA Orange Book lists unexpired patents or exclusivities tied to SINEQUAN’s specific drug product/NDC. If patent listings are expired and exclusivities are exhausted, generic entry pressure is structurally high.

What investors should look for in Orange Book listings

For SINEQUAN’s branded product, the decisive fields are:

Patent numbers listed for the specific NDC
Patent expiration dates
Exclusivity type (12-year, 7-year, pediatric, orphan, marketing exclusivity) tied to the NDA/BLA
Whether a competitor filed a Paragraph IV certification against any listed patent

Why this drives valuation

If Orange Book listings show:

No unexpired patents for the branded NDC: branded market share erosion continues.
Unexpired patents with strong remaining life: branded cash flows can be partially protected; higher willingness to pay for the franchise is rational.
Unexpired exclusivities: can slow AB-rated generic competition.

When does SINEQUAN lose exclusivity and what are the patent expiration timelines investors should model?

Featured snippet answer: Model two timelines: (1) patent expiration for Orange Book-listed patents tied to the branded NDC and (2) any remaining statutory or pediatric exclusivity windows. Commercial “peak protection” ends at the first actionable date that removes legal barriers to a generic launch.

How to build an exclusivity-to-revenue model (practical)

Use a three-stage timeline:

Current period: branded remains protected only if Orange Book prevents generic approvals.
Approaching expiry: expect generic applicant behavior to intensify (ANDA filings; litigation).
Post-expiry: generic approvals and label switches drive price and gross margin compression.

Investment implication for older, generic-prone drugs

For legacy antidepressants like doxepin, most of the value is already “spent” in historical exclusivity. The model should assume:

declining branded share post-expiry
margin compression as generics gain volume
limited near-term upside unless a late-formulation or life-cycle patent is still active and enforceable against specific generic products.

What generic entry risks exist for SINEQUAN under Hatch-Waxman, including Paragraph IV challenges?

Featured snippet answer: Generic entry risk is highest when at least one Orange Book-listed patent is close to expiry or already expired and when generic applicants can file and win quickly on validity/non-infringement.

Paragraph IV as the driver of “surprise” entry

For investment-grade risk assessment, track:

Whether any ANDA applicants filed Paragraph IV certifications
Whether the branded holder litigated and the case outcome timeline
Whether a 30-month stay delayed generic launch
Whether a settlement triggered authorized generic timing

Settlement agreements can move the generic date

Even after an expiry date, actual launch can be altered by:

“Agreement to settle” terms
authorized generic production rights
court-entered consent judgments

For older drugs, settlements are less likely to be value-destructive than for newer biologics, but the impact can still be material to near-term branded pricing.

What patent litigation affects SINEQUAN and how do case outcomes impact generic launch timing?

Featured snippet answer: Litigation outcomes determine whether a generic faces an injunction risk, a launch delay via stay, or a “fast entry” path. Case outcomes are critical for modeling volume timing and gross margin pressure.

What to map in litigation analysis

For each relevant case, build:

branded NDA holder and patent list
asserted patents and claims
filing dates of ANDA and Paragraph IV
court decisions (validity, infringement, construction)
settlement dates and authorized launch terms

Practical investment expectation

With long-known APIs like doxepin, litigation may be sparse in recent years, but if there is continued branded listing for a particular formulation strength, litigation can reappear as generic launches target those specific claims.

How does SINEQUAN compare with other doxepin products and competing tricyclic antidepressants on market access and margin?

Featured snippet answer: Investment upside for SINEQUAN is usually constrained by generic availability and therapeutic class price pressure. Relative value depends on whether SINEQUAN has specific dosing strengths, patient adherence advantages, or any protected formulation attribute.

Within-tricyclic class: pricing compression is typical

Tricyclic antidepressants compete on:

acquisition cost and pharmacy formulary position
payer tiering
generic substitutions at the pharmacy counter

This typically pressures branded gross margins unless SINEQUAN has a structural advantage (protected formulation, payer contracting, or supply reliability).

Differentiation that can still matter for investors

Even when patents fade, branded holders sometimes maintain a premium via:

preferred formulary placement
adverse event experience with certain generics leading to prescriber preference (rare and not reliably modelable)
supply continuity that reduces stockout risks

These are commercial levers, not legal exclusivity levers.

What formulations are protected by SINEQUAN patents and do dosage strengths have different IP risk?

Featured snippet answer: Formulation and strength-specific patent listings can create uneven risk across the product line. A generic can enter one strength while another remains blocked if different patents cover different strengths/NDCs.

Typical formulation patent categories to check

Bioequivalence-related formulation improvements (rare as a remaining driver once generics are present)
Controlled-release vs immediate-release (if SINEQUAN is immediate release, controlled-release-specific patents would be separate)
Hard capsule/tablet engineering (if any)
Stability and impurity specs that are tied to manufacturing methods

Dosage-strength segmentation and revenue risk

If Orange Book shows different listed patents by strength:

model generic entry timing per strength
apply weighted-average revenue loss across strengths based on historical sales mix

What is the FDA regulatory status of SINEQUAN (NDA/ANDAs) and what does that imply for future approvals?

Featured snippet answer: FDA status matters mainly through whether the branded product is tied to an NDA with active listed patents or exclusivity and whether ANDAs exist that can launch upon legal clearance.

What investors should infer from regulatory structure

If multiple AB-rated generics exist, the branded product’s incremental legal protection is usually limited.
If newer ANDAs are actively filed, the market expects future price competition pressure.
If no active ANDA contest is present, the risk may be slower but still structural with aging exclusivity.

Which companies are positioned to challenge SINEQUAN and what does their ANDA posture signal?

Featured snippet answer: The identity of ANDA challengers and their certification patterns are leading indicators for launch timing and potential settlements.

How to interpret ANDA challenger behavior

Multiple challengers suggest higher likelihood of entry once a barrier clears.
Consistent Paragraph IV patterns across years signal coordinated strategy to force settlements or win litigation.
Rapid amendments or repeated filings can precede a “market entry wave.”

For investment work, this becomes a monitor-and-update item rather than a one-time static diligence task.

What are the revenue exposure scenarios for SINEQUAN across time and what margins are at risk?

Featured snippet answer: Revenue exposure is dominated by generic substitution speed after legal clearance. In older oral generics, a base case assumes branded share erodes quickly post-entry, with gross margin decline following price competition.

Three scenario framework (for modeling)

Base case (slow entry): limited competition wave; branded share declines gradually.
Upside (delayed entry): legal blocks or litigation delays; branded preserves premium longer.
Downside (fast entry): quick generic ramp; branded share collapses and payer switching accelerates.

Margin and working capital considerations

For an older branded drug:

gross margin compression typically occurs without parallel increases in R&D costs
inventory and supply planning become a key operational variable ahead of generic launch

How strong is the overall patent and regulatory defensibility of SINEQUAN versus generic alternatives?

Featured snippet answer: For SINEQUAN, defensibility is likely limited to any remaining Orange Book-listed patents tied to the specific branded NDC. Without current unexpired listings, generic entry risk is structurally high.

Defensibility scorecard investors can use

Unexpired Orange Book patents? (yes/no, and earliest date)
Unexpired exclusivity? (yes/no)
Active Paragraph IV landscape? (none/low/moderate/high)
Litigation history in last 5–10 years? (active/quiet)
Formulation/NDC-specific patent coverage? (broad/narrow)
Likelihood of settlement-led delay? (low/medium/high)

For legacy doxepin branded products, the score typically hinges on whether any narrow, still-valid patent listing exists for the exact strength NDC.

Key Takeaways

SINEQUAN’s investment profile is driven by legal status tied to specific Orange Book listings for its NDCs, not by a novel MOA thesis.
The decisive valuation variable is unexpired patent or exclusivity coverage that can block generic entry and preserve branded margin.
For older oral antidepressants like doxepin, structural generic pressure dominates unless a still-enforceable, product-specific patent exists.
Generic entry risk under Hatch-Waxman (Paragraph IV, litigation stays, settlements) controls the timing of revenue compression.
Best-in-class diligence for investment use focuses on NDC-specific patent expiry dates, any active ANDA challenge activity, and past litigation/settlement patterns.

FAQs

How do NDC-specific Orange Book patent listings change generic entry timing for SINEQUAN strengths?
What role do 30-month Hatch-Waxman stays and settlement agreements play in delaying generic launches for older antidepressants like doxepin?
How can formulation patents (if any) be distinguished from method-of-use patents when assessing SINEQUAN’s remaining defensibility?
What commercial indicators (payer formulary status, substitution patterns, wholesale behavior) best forecast branded doxepin margin erosion after generic entry?
How does SINEQUAN’s competitive positioning versus other tricyclic antidepressants affect its ability to sustain branded share during generic price competition?

References

FDA. Orange Book: Approved Drug Products with Therapeutic Equivalence Evaluations. U.S. Food and Drug Administration.
FDA. Hatch-Waxman Amendments Overview (21 U.S.C. § 355(j) and related provisions). U.S. Food and Drug Administration.

US Patents:	0
Applicants:	1
NDAs:	2

AI Deep Research

Questions you can ask:

Summary for SINEQUAN