Troglitazone - Generic Drug Details

What are the generic sources for troglitazone and what is the scope of freedom to operate?

Troglitazone is the generic ingredient in two branded drugs marketed by Sankyo and Pfizer Pharms, and is included in two NDAs. Additional information is available in the individual branded drug profile pages.

Summary for troglitazone

US Patents:	0
Tradenames:	2
Applicants:	2
NDAs:	2
Raw Ingredient (Bulk) Api Vendors:	91
Clinical Trials:	16
DailyMed Link:	troglitazone at DailyMed

Recent Clinical Trials for troglitazone

Identify potential brand extensions & 505(b)(2) entrants

Sponsor	Phase
Instituto Nacional de Salud Publica, Mexico	Phase 3
Laboratorios Grossman, S.A.	Phase 3
Canadian Institutes of Health Research (CIHR)

See all troglitazone clinical trials

Anatomical Therapeutic Chemical (ATC) Classes for troglitazone

A10BG	Thiazolidinediones
A10B	BLOOD GLUCOSE LOWERING DRUGS, EXCL. INSULINS
A10	DRUGS USED IN DIABETES
A	Alimentary tract and metabolism

US Patents and Regulatory Information for troglitazone

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Exclusivity Expiration
Sankyo	PRELAY	troglitazone	TABLET;ORAL	020719-003	Aug 4, 1997		DISCN	No	No
Pfizer Pharms	REZULIN	troglitazone	TABLET;ORAL	020720-001	Jan 29, 1997		DISCN	No	No
Sankyo	PRELAY	troglitazone	TABLET;ORAL	020719-002	Jan 29, 1997		DISCN	No	No
Pfizer Pharms	REZULIN	troglitazone	TABLET;ORAL	020720-002	Jan 29, 1997		DISCN	No	No
Pfizer Pharms	REZULIN	troglitazone	TABLET;ORAL	020720-003	Aug 4, 1997		DISCN	No	No

Expired US Patents for troglitazone

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	Patent No.	Patent Expiration
Pfizer Pharms	REZULIN	troglitazone	TABLET;ORAL	020720-002	Jan 29, 1997
Pfizer Pharms	REZULIN	troglitazone	TABLET;ORAL	020720-002	Jan 29, 1997
Pfizer Pharms	REZULIN	troglitazone	TABLET;ORAL	020720-001	Jan 29, 1997
Sankyo	PRELAY	troglitazone	TABLET;ORAL	020719-002	Jan 29, 1997
Sankyo	PRELAY	troglitazone	TABLET;ORAL	020719-003	Aug 4, 1997

Troglitazone Market Dynamics, Financial Trajectory, Patent Position, and Withdrawal Analysis

Last updated: September 2, 2026

Troglitazone, marketed as Rezulin by Parke-Davis and Warner-Lambert, generated rapid commercial growth after its 1997 U.S. approval but lost its market within three years because of severe, sometimes fatal, liver toxicity. The FDA withdrew troglitazone on March 21, 2000, eliminating U.S. revenue despite substantial prescription demand. The product’s financial trajectory shows how a high-growth diabetes medicine can move from blockbuster expectations to liability-driven asset destruction when post-market safety risk is concentrated, difficult to predict, and not manageable through labeling controls.

What was troglitazone and how did the FDA regulate it?

Troglitazone was an oral thiazolidinedione antidiabetic drug that improved insulin sensitivity in patients with type 2 diabetes. Parke-Davis, then a Warner-Lambert company, received FDA approval for Rezulin on January 29, 1997, under New Drug Application 20-720.[1]

The FDA initially approved troglitazone with warnings concerning liver injury and required liver-function monitoring. The agency later strengthened the monitoring requirements as reports of serious hepatotoxicity accumulated. Troglitazone was withdrawn after evidence showed that routine monitoring did not reliably prevent acute liver failure.

Regulatory milestone	Date	Significance
FDA approval of Rezulin	January 29, 1997	U.S. launch authorization
Early post-market liver-safety warnings	1997-1998	Labeling and monitoring restrictions increased
FDA advisory and regulatory review	1999-2000	Risk-benefit profile deteriorated
U.S. withdrawal	March 21, 2000	Commercial sales ended in the United States
Post-withdrawal litigation and settlements	2000s	Financial exposure shifted from sales to liability

The FDA reported that troglitazone was associated with serious liver injury, including liver failure and deaths. The agency concluded that the risk could not be controlled adequately through continued marketing and monitoring.[2]

How did troglitazone sales develop before withdrawal?

Troglitazone initially benefited from several commercial factors:

• A large and growing type 2 diabetes population.
• A mechanism distinct from insulin and sulfonylureas.
• Demand for oral medicines that addressed insulin resistance.
• Promotion through the Warner-Lambert commercial organization.
• Limited initial competition within the thiazolidinedione class.

Prescription growth was rapid. By the late 1990s, troglitazone had been prescribed to more than one million patients in the United States, according to contemporaneous government assessments.[3]

Public sources report different figures for annual Rezulin sales because some estimates refer to gross product sales, while others refer to company-reported revenue, U.S. sales, or projected annualized sales. The available record supports the following trajectory:

Period	Market position	Financial interpretation
1997	Newly launched diabetes product	Initial commercialization and formulary expansion
1998	Rapid prescription growth	Product moved toward blockbuster scale
1999	High-volume use despite safety warnings	Revenue remained substantial while risk escalated
Early 2000	Sales disrupted by safety concerns	Prescribing fell before formal withdrawal
After March 2000	U.S. sales terminated	Revenue stream became zero in the U.S. market

Some contemporary accounts placed peak annual Rezulin sales near or above $1 billion, with certain estimates reaching approximately $2 billion. Those figures should be treated as market estimates rather than a single consistently reported audited revenue series. Warner-Lambert’s merger with Pfizer also complicated later product-level reporting because Rezulin financials were incorporated into a larger corporate reporting structure.

The key financial point is direction rather than a precise peak number: troglitazone progressed from rapid revenue expansion to a complete U.S. revenue shutdown in approximately three years.

What caused troglitazone’s market collapse?

Troglitazone’s commercial collapse resulted from idiosyncratic hepatotoxicity, not ordinary competitive erosion. The product’s liver risk had several market consequences:

1. Physicians became reluctant to initiate treatment.
2. Patients discontinued therapy or switched to alternatives.
3. Insurers and formularies had less incentive to retain the product.
4. Monitoring requirements increased prescribing friction.
5. Regulatory action removed the remaining commercial option.

The risk was especially damaging because severe liver injury could occur after treatment initiation and was not reliably prevented by the required liver-function testing. The FDA concluded that the drug’s benefit-risk profile was unfavorable even though the medicine was effective for glycemic control.[2]

Troglitazone also faced increasing competition from rosiglitazone, marketed as Avandia, and pioglitazone, marketed as Actos. Both entered the U.S. market in 1999. Their availability gave physicians substitute products within the same broad therapeutic category when concerns about troglitazone intensified.

How did troglitazone compare with Avandia and Actos?

Troglitazone, rosiglitazone, and pioglitazone were thiazolidinediones that acted through peroxisome proliferator-activated receptor gamma. The commercial difference was the safety profile and the timing of market entry.

Product	Active ingredient	U.S. approval	Commercial outcome
Rezulin	Troglitazone	1997	Withdrawn in 2000 for hepatotoxicity
Avandia	Rosiglitazone	1999	Continued commercialization, later subject to cardiovascular restrictions
Actos	Pioglitazone	1999	Continued commercialization, later subject to bladder-cancer litigation and labeling issues

Troglitazone’s early entry created a temporary advantage in physician familiarity and patient exposure. That advantage became a liability once the product’s safety signal emerged. Avandia and Actos captured treatment demand after troglitazone’s withdrawal, while the entire thiazolidinedione class later faced scrutiny concerning weight gain, edema, heart failure, cardiovascular risk, and other adverse events.

When did troglitazone lose exclusivity?

Troglitazone lost practical market exclusivity when the FDA withdrew Rezulin in March 2000. Patent or regulatory exclusivity dates became commercially irrelevant because the branded product was no longer available for ordinary U.S. prescribing.

The FDA’s original approval date indicates that any five-year new chemical entity exclusivity, if applicable to the approval, would have extended to approximately January 29, 2002. That period was overtaken by withdrawal. No commercially meaningful generic launch followed in the United States.

What patents protected troglitazone?

Troglitazone was protected primarily through compound and pharmaceutical-use patent rights associated with the thiazolidinedione class and the troglitazone molecule. The relevant commercial rights were held through the originator and licensing structure involving Sankyo and Parke-Davis or Warner-Lambert.

Patent protection did not create durable value after withdrawal. A generic manufacturer would have faced several obstacles:

• No active branded U.S. market after March 2000.
• Severe product-liability exposure.
• FDA safety concerns concerning reintroduction.
• Limited physician demand.
• Potential manufacturing and clinical requirements for a withdrawn drug.
• Little economic incentive to challenge remaining patent rights.

The Orange Book status of a withdrawn product is distinct from the status of an actively marketed reference drug. A discontinued listing does not create a realistic generic opportunity when the underlying reference product has been removed for safety reasons.

Were there Paragraph IV challenges to troglitazone?

There is no commercially significant public record of a successful Paragraph IV challenge leading to a U.S. troglitazone launch. The absence of a meaningful generic challenge is consistent with the product’s short commercial life and the FDA’s safety action.

Paragraph IV litigation generally creates value when a generic entrant expects a viable market after approval. Troglitazone lacked that economic profile after the hepatotoxicity signal became established. Even if patent barriers had been removed, an applicant would still have confronted FDA safety concerns and substantial liability risk.

What was troglitazone’s patent strength?

Troglitazone’s patent strength was commercially adequate during its launch period but strategically weak after withdrawal.

Patent-estate factor	Assessment
Compound protection	Important during early commercialization
Formulation protection	Secondary to the compound and regulatory position
Method-of-use protection	Limited practical value after safety withdrawal
Manufacturing know-how	Potential technical barrier, but not a meaningful commercial moat
Geographic coverage	Dependent on country-specific approvals and patent terms
Durability after withdrawal	Low
Generic-entry value	Minimal

The principal weakness was not necessarily expiration timing. It was the loss of an approvable, commercially attractive product. Patent rights protect exclusionary legal positions; they do not preserve value when a regulator removes the product from the market.

What formulation patents protected Rezulin?

Troglitazone was marketed as an oral tablet. Any formulation or dosage-form rights would have been subordinate to the safety profile of the active ingredient. A formulation patent could potentially protect excipients, dosage levels, release characteristics, or tablet composition, but it could not solve idiosyncratic liver toxicity associated with the active molecule.

The commercial value of formulation patents was therefore low. Unlike an extended-release product, injectable delivery system, or difficult-to-copy biologic formulation, Rezulin’s tablet form did not create a substantial technical barrier after the active ingredient’s safety problem became decisive.

What method-of-use patents covered troglitazone?

Troglitazone’s therapeutic use was the treatment of type 2 diabetes and related insulin-resistance conditions. Method-of-use rights may have covered specific patient populations, dosing approaches, or combination regimens, but such rights had little post-withdrawal value.

A method-of-use patent cannot overcome a regulator’s determination that the overall benefit-risk profile is unacceptable. It also cannot create durable revenue when physicians have safer substitutes and the product has been removed from the U.S. market.

Which companies were involved in troglitazone commercialization?

The main commercial participants were:

• Sankyo, the Japanese pharmaceutical company associated with troglitazone’s development and originator rights.
• Parke-Davis, the Warner-Lambert operating company that marketed Rezulin in the United States.
• Warner-Lambert, the parent company responsible for the broader commercial and legal position before its acquisition.
• Pfizer, which acquired Warner-Lambert in 2000 and inherited significant post-withdrawal litigation exposure.
• Generic manufacturers, which did not establish a meaningful U.S. commercial presence for troglitazone.

The licensing arrangement was commercially important because it distributed development, marketing, and legal exposure across companies. After withdrawal, those relationships became more relevant to liability allocation than to revenue generation.

What patent litigation and product-liability litigation affected troglitazone?

Troglitazone’s major legal exposure came from personal-injury and product-liability claims alleging that the companies failed to adequately warn about liver risks or acted too slowly in responding to adverse-event evidence.

The litigation profile included:

• Individual personal-injury claims.
• Wrongful-death claims.
• Multidistrict or coordinated litigation activity.
• Claims involving failure to warn and regulatory conduct.
• Settlement negotiations involving Warner-Lambert and Pfizer.
• Continuing legal expenses after the revenue stream had ended.

Public reporting in the mid-2000s described a settlement package of approximately $750 million involving thousands of Rezulin-related claims.[4] The amount reflects the financial impact of product liability rather than a continuing commercial dispute over patent validity.

The legal risk was asymmetric. A patent dispute could have delayed generic entry or produced a settlement tied to future market entry. Troglitazone litigation instead generated cash costs after the market had disappeared.

Did troglitazone have biosimilar risk?

No. Troglitazone was a chemically synthesized small-molecule drug, not a biologic. Biosimilar pathways under the Biologics Price Competition and Innovation Act were therefore irrelevant.

The relevant competitive threat was generic substitution under the abbreviated new drug application pathway. That threat never developed into a meaningful commercial event because of withdrawal, weak demand, and safety concerns.

What was the financial trajectory after FDA withdrawal?

The post-withdrawal trajectory had four stages:

Revenue destruction

U.S. Rezulin revenue ended after the March 21, 2000 withdrawal. Any residual inventory movement or non-U.S. activity did not restore the product’s U.S. commercial position.

Asset impairment

The product’s future cash flows were materially impaired. Commercial forecasts, sales-force investment, manufacturing activity, and marketing expenditure no longer supported a viable return on the asset.

Liability accumulation

Legal defense costs and settlement exposure continued after product revenue ceased. The economics shifted from operating profit to cash outflows associated with litigation, reserves, insurance, and corporate integration.

Strategic substitution

Demand moved to rosiglitazone, pioglitazone, insulin, metformin, sulfonylureas, and other diabetes treatments. The product’s withdrawal strengthened competitors with less immediate liver-toxicity concern.

What generic launch risks existed for troglitazone?

A generic launch would have faced unusually high risk:

Risk category	Effect on generic economics
Regulatory risk	Potential need for additional FDA scrutiny because of withdrawal history
Clinical risk	Reproduction of the hepatotoxicity concern
Liability risk	Exposure to failure-to-warn and patient-injury claims
Market risk	Weak physician and patient demand
Pricing risk	Limited market value after branded withdrawal
Manufacturing risk	Need to establish compliant supply for a discontinued product
Patent risk	Possible residual compound or use claims
Reimbursement risk	Formularies would favor available alternatives

The normal generic strategy of entering after patent expiration did not apply. Regulatory and liability barriers were more important than patent expiry.

How did troglitazone affect the diabetes-drug market?

Troglitazone changed the commercial and regulatory economics of diabetes drugs in several ways:

• Sponsors faced greater scrutiny of liver-safety signals during development.
• FDA post-market surveillance became more important for chronic-use medicines.
• Physicians became more sensitive to class-specific safety concerns.
• Competitors benefited from substitution but inherited greater monitoring expectations.
• Product-liability exposure became a larger factor in drug valuation.
• Regulators became less willing to rely solely on routine laboratory monitoring when severe adverse events were rare and unpredictable.

The event also showed that high prescription volume could increase, rather than reduce, commercial risk. Greater exposure expanded the number of patients potentially affected and increased the scale of litigation once a safety signal emerged.

What is the current FDA and commercial status of troglitazone?

Troglitazone is withdrawn from the U.S. market and is not an active FDA-approved commercial treatment for type 2 diabetes. Rezulin has no meaningful current U.S. revenue base, no active biosimilar market, and no realistic generic-entry opportunity.

Its residual value is historical and legal rather than commercial. The relevant assets are regulatory records, clinical-safety data, litigation precedent, and lessons for pharmacovigilance and pharmaceutical valuation.

Key Takeaways

• Troglitazone was FDA-approved in 1997 and withdrawn on March 21, 2000.
• Rezulin achieved rapid prescription growth and approached blockbuster-scale sales before withdrawal.
• Severe, unpredictable hepatotoxicity destroyed the product’s U.S. commercial value.
• Avandia and Actos became important substitutes after troglitazone exited the market.
• Patent protection became irrelevant once the FDA removed the product from commercial use.
• There was no meaningful U.S. Paragraph IV generic challenge or generic launch.
• Biosimilar competition did not apply because troglitazone was a small molecule.
• Post-withdrawal financial exposure came mainly from litigation and settlement costs.
• The case illustrates that regulatory and product-liability risks can overwhelm a strong early-market position.

FAQs About Troglitazone Market and Financial History

Why was Rezulin withdrawn from the market?

Rezulin was withdrawn because of severe liver toxicity, including cases of liver failure and death. The FDA determined that monitoring requirements did not adequately control the risk.[2]

Did Pfizer own troglitazone?

Pfizer acquired Warner-Lambert in 2000, shortly before or around the time of the U.S. withdrawal. Pfizer subsequently inherited substantial legal and financial exposure connected with Rezulin.

Was troglitazone ever approved outside the United States?

Troglitazone was developed and marketed in multiple jurisdictions, but regulatory treatment varied. Its international commercial position deteriorated as evidence of serious liver injury accumulated.

Did troglitazone make Warner-Lambert a blockbuster product?

Yes. Rezulin became a major commercial product for Warner-Lambert before withdrawal, although reported peak sales figures vary by source and accounting basis.

Could troglitazone return to the market?

A return would require a new regulatory strategy, extensive safety justification, and a commercially credible benefit-risk profile. The historical hepatotoxicity and availability of alternative diabetes treatments make a commercial reintroduction highly unlikely.

References

1. U.S. Food and Drug Administration. (1997). Rezulin (troglitazone) approval information, NDA 20-720. FDA.

2. U.S. Food and Drug Administration. (2000, March 21). FDA announces withdrawal of Rezulin. FDA.

3. U.S. General Accounting Office. (2000). Prescription drugs: FDA oversight of troglitazone and other drugs. U.S. Government Accountability Office.

4. Reuters. (2004). Pfizer agrees to settlement of Rezulin litigation. Reuters.

5. National Institute of Diabetes and Digestive and Kidney Diseases. (n.d.). Troglitazone. In LiverTox: Clinical and research information on drug-induced liver injury. National Institutes of Health.

6. U.S. Food and Drug Administration. (2000). Rezulin postmarketing safety information and labeling history. FDA.