United States Patent 9,808,530: Fidaxomicin Formulation Scope, Expiration, Orange Book Status, and Generic Risk
U.S. Patent No. 9,808,530 protects oral pharmaceutical compositions containing a tiacumicin B compound, including fidaxomicin, with xanthan gum in an amount that prevents foaming when the composition is dispersed in water. The patent is formulation-focused rather than compound-focused. Its principal commercial relevance is to dry fidaxomicin products that are reconstituted as aqueous suspensions or dispersed before administration.
The patent issued on November 7, 2017, from U.S. application publication 2013/0203692. The publicly available patent record identifies Astellas Pharma Europe B.V. as the applicant and assignee. The projected basic patent expiration is April 18, 2032, subject to any applicable patent-term adjustment. [1]
What does U.S. Patent 9,808,530 protect?
The patent protects a composition with four central elements:
- A tiacumicin B compound or a defined related form.
- Xanthan gum as an excipient.
- Xanthan gum present in an amount that prevents foaming in water.
- A pharmaceutical composition, with dependent claims covering fidaxomicin, oral administration, excipient combinations, and aqueous-suspension dosage forms.
The independent claim does not require fidaxomicin specifically. It covers a broader genus that includes:
- Tiacumicin B compounds.
- Analogues of tiacumicin B.
- Stereoisomers.
- Polymorphs.
- Pharmaceutically acceptable solvates.
Claim 9 narrows the analogues to dialkyltiacumicins and bromotiacumicins. Claim 2 separately identifies fidaxomicin as the active ingredient.
The claim uses the transitional term “comprising.” That language generally permits additional active ingredients and excipients unless another claim limitation is avoided. A product containing fidaxomicin, xanthan gum and additional formulation components can therefore fall within claim 1.
How are the claims structured?
| Claim |
Scope |
| 1 |
Composition containing a tiacumicin B compound or covered derivative and xanthan gum in an amount that prevents foaming in water |
| 2 |
Claim 1 where the active ingredient is fidaxomicin |
| 3 |
Claim 1 with microcrystalline cellulose or a sugar |
| 4 |
Claim 3 where the sugar is D-mannitol, erythritol, isomalt or trehalose |
| 5 |
Claim 1 with one or more disintegrants |
| 6 |
Claim 1 with sodium starch glycolate |
| 7 |
Claim 1 with partially pregelatinised starch |
| 8 |
Claim 1 as a dry powder, dry granulate or dispersible tablet for aqueous suspension |
| 9 |
Claim 1 where the analogue is a dialkyltiacumicin or bromotiacumicin |
| 10 |
Claim 1 where the composition is oral |
Claim 1 is the commercially important claim because it establishes the basic combination of active ingredient and xanthan gum. Claim 2 is particularly relevant to Dificid and any generic fidaxomicin product using the claimed formulation architecture.
Claims 3 through 8 create progressively narrower positions around common solid-dose excipients and reconstitution formats. Claims 6 and 7 are narrower than claim 5 because they identify specific disintegrants. Claim 8 targets products requiring dispersion in water, including dry oral suspensions and dispersible tablets.
What is the key limitation in claim 1?
The principal limiting language is the requirement that xanthan gum be present “in an amount to prevent foaming of the tiacumicin B compound in water.”
This is a functional limitation. The claim does not merely require any detectable quantity of xanthan gum. The amount must produce the specified anti-foaming result when the composition is placed in water.
A potential infringement analysis would therefore examine:
- The identity and concentration of xanthan gum.
- The composition’s behavior during reconstitution or dispersion.
- The meaning of “foaming” under the patent’s specification and test methods.
- Whether the claimed amount prevents foaming under relevant conditions.
- Whether the accused product is intended to form an aqueous suspension.
- Whether the product contains a tiacumicin B compound within the claim’s broad definition.
The limitation creates an evidentiary issue. A patent owner would likely need formulation records, analytical testing, technical expert evidence or product testing to establish that the accused xanthan gum concentration meets the functional requirement.
What formulations are protected by U.S. Patent 9,808,530?
The patent reaches several formulation categories.
Fidaxomicin dry powders
A dry powder containing fidaxomicin and xanthan gum may fall within claim 1 even if the product is not sold as a ready-to-use liquid. Claim 8 more specifically covers a dry powder intended for preparation of an aqueous suspension.
Dry granulates
A dry granulate containing fidaxomicin, xanthan gum and other excipients is within the express scope of claim 8 if it is intended to produce an aqueous suspension.
Dispersible tablets
A dispersible tablet is expressly covered by claim 8 when it is intended for aqueous suspension. A tablet that is swallowed intact without dispersion would present a more complex claim 8 analysis, although it could still implicate claims 1, 2 and 10 if the xanthan gum and functional anti-foaming limitations are met.
Oral fidaxomicin compositions
Claim 10 covers oral compositions. The claim does not require a particular dose, tablet strength, administration schedule, or indication. A fidaxomicin product used for Clostridioides difficile infection would be the principal commercial target.
Excipient combinations
The patent expressly contemplates formulations containing:
- Microcrystalline cellulose.
- D-mannitol.
- Erythritol.
- Isomalt.
- Trehalose.
- Sodium starch glycolate.
- Partially pregelatinised starch.
- Other disintegrants.
The use of one or more additional excipients does not avoid claim 1 because the claim is open-ended. It may, however, determine whether narrower claims 3 through 7 are also infringed.
When does U.S. Patent 9,808,530 expire?
The patent claims priority to an April 18, 2011 filing and issued from a PCT-derived application. On the basic twenty-year term calculation, the expected expiration date is April 18, 2032. The effective date can differ if the USPTO granted patent-term adjustment or if a terminal disclaimer applies. The patent record should be used for the final term calculation. [1]
This patent is not a compound patent covering fidaxomicin itself. Its value is tied to the formulation and dosage-form limitations. A competing product may avoid the patent by using a formulation that does not include xanthan gum or does not meet the anti-foaming limitation, subject to infringement under the doctrine of equivalents.
What is the FDA regulatory and Orange Book status?
Dificid, containing fidaxomicin, was approved by the FDA under NDA 201699 in 2011 for treatment of C. difficile-associated diarrhea in adults and, after a later label expansion, pediatric patients in specified age groups. [2]
The FDA Orange Book identifies patents associated with approved drug products and their listed uses. U.S. Patent 9,808,530 is associated with the Dificid patent estate as a formulation patent. Orange Book listing does not establish that every product containing fidaxomicin infringes the patent. It informs ANDA applicants of listed patents and may require a Paragraph IV certification if an applicant seeks approval before patent expiration. [3]
The FDA’s Orange Book framework distinguishes among:
- Drug-substance patents.
- Drug-product or formulation patents.
- Method-of-use patents.
Patent 9,808,530 is relevant primarily as a drug-product or formulation patent. It is not a method-of-use patent directed to treating C. difficile infection.
When does fidaxomicin lose exclusivity?
Fidaxomicin has multiple layers of protection, and the relevant dates differ.
| Protection |
Relevance |
| FDA approval exclusivity |
Regulatory exclusivity attached to the NDA and pediatric extensions, where applicable |
| Compound patents |
Protection for fidaxomicin or related antibiotic chemistry |
| Formulation patents |
Protection for specific compositions, including xanthan-gum formulations |
| Method-of-use patents |
Protection for particular dosing or treatment methods |
| Orphan or pediatric provisions |
Potential regulatory extensions depending on the approved indication and timing |
The 2032 date for U.S. Patent 9,808,530 does not necessarily represent the earliest date on which all fidaxomicin products could enter. A generic applicant may challenge individual patents through Paragraph IV certification, and approval may depend on the full Orange Book estate, regulatory exclusivity, litigation outcomes and settlement terms.
The patent also does not necessarily prevent a generic manufacturer from marketing a non-infringing fidaxomicin formulation after regulatory exclusivity ends. It is principally a barrier to products using the claimed xanthan-gum formulation structure.
How strong is the patent estate for this formulation?
The estate has meaningful commercial scope but is narrower than a compound patent.
Strengths
The patent’s strongest features are:
- Claim 1 covers a broad tiacumicin B genus.
- Fidaxomicin is expressly claimed in claim 2.
- The patent covers multiple dosage forms.
- The claims address a formulation problem tied to reconstitution behavior.
- The open-ended claim format permits additional excipients.
- The patent reaches dry powders, granulates and dispersible tablets.
A formulation patent can be commercially important when a branded product has a specific excipient profile and a generic applicant intends to replicate it closely.
Vulnerabilities
The principal validity and enforcement risks are:
- Obviousness based on known use of xanthan gum as a suspending or stabilizing agent.
- Lack of written description for the broad tiacumicin B genus.
- Enablement of all claimed xanthan-gum concentrations and all listed active forms.
- Indefiniteness or claim-construction disputes concerning “an amount to prevent foaming.”
- Prior-art disclosures of fidaxomicin formulations containing xanthan gum.
- Proof problems concerning the foaming result in an accused product.
The functional limitation can strengthen patentability if the anti-foaming result was unexpected and supported by comparative data. It can weaken enforcement if the patent lacks a reproducible test or if “prevent foaming” has no objective boundary.
What prior art is most relevant?
The relevant prior-art categories include:
- Earlier fidaxomicin and tiacumicin B compositions.
- Solid oral formulations containing binders, disintegrants and sugars.
- Xanthan gum as a suspending agent in aqueous pharmaceutical products.
- Anti-foaming excipients used with macrolide or fermentation-derived antibiotics.
- Dry powders and granulates reconstituted into oral suspensions.
- Formulation disclosures addressing poor wetting, aggregation or foaming.
A validity challenge would likely combine an earlier tiacumicin or fidaxomicin composition with formulation references teaching xanthan gum. The patent owner’s response would focus on whether the prior art identified the foaming problem and whether it would have motivated a skilled formulator to select the claimed xanthan gum amount.
Which companies could challenge the patent?
Potential challengers are manufacturers seeking an ANDA for generic fidaxomicin, including companies with established generic antibiotic and oral-solid-dose capabilities. A Paragraph IV challenger would need to address the entire listed patent estate, not only U.S. Patent 9,808,530.
Possible commercial strategies include:
- Filing an ANDA with a Paragraph IV certification.
- Filing with a Paragraph III certification and delaying approval until patent expiration.
- Developing a formulation without xanthan gum.
- Using a different viscosity modifier or suspension stabilizer.
- Using a dosage form that does not require aqueous dispersion.
- Seeking a non-infringement position based on failure to meet the anti-foaming limitation.
No published merits decision from the U.S. Court of Appeals for the Federal Circuit or a district court establishes a definitive construction of the claims of U.S. Patent 9,808,530. Publicly reported litigation involving a Paragraph IV challenge must be distinguished from patent listing and administrative patent records.
What generic launch risks exist?
Early launch
An early launch before April 2032 would carry substantial risk if the product contains xanthan gum at a concentration that prevents foaming and is sold as a dry powder, granulate or dispersible tablet for aqueous suspension.
At-risk launch
A manufacturer could launch before final resolution of patent litigation after receiving FDA approval. That strategy would expose the company to damages, injunctive relief and potential market disruption if the patent is upheld and found infringed.
Non-infringing formulation
The most direct design-around is to omit xanthan gum. Other options include:
- Replacing xanthan gum with another suspending agent.
- Selecting a concentration that does not satisfy the functional limitation.
- Using a non-aqueous dosage form.
- Selling an intact oral tablet that does not require aqueous suspension, if claims 1, 2 and 10 are also avoided.
- Altering the formulation architecture so that foaming does not occur for reasons unrelated to xanthan gum.
A design-around must account for dependent claims and the doctrine of equivalents. Changing the excipient may avoid literal infringement but still create litigation risk if the substitute performs substantially the same function in substantially the same way.
How does this patent compare with compound and method-of-use patents?
| Patent type |
Typical scope |
Relevance to fidaxomicin |
| Compound patent |
Active molecule or chemical class |
Broadest product-level protection |
| Formulation patent |
Composition, excipients, dosage form or release profile |
Protects specific commercial presentations |
| Method-of-use patent |
Treatment, dosing or patient population |
Can block labeled use but may not block all products |
| Manufacturing patent |
Process, purification or solid-state form |
Can create production barriers without covering every product |
U.S. Patent 9,808,530 is narrower than a fidaxomicin compound patent but may be more directly relevant to a generic product copied from the marketed formulation. Its value depends on the extent to which the reference product and proposed generic use xanthan gum and require dispersion in water.
Is there a licensing or settlement signal?
The patent record does not establish a publicly reported license or settlement specifically resolving U.S. Patent 9,808,530. A settlement involving other fidaxomicin patents would not automatically establish a license to this formulation patent. Any commercial agreement should be evaluated against the patent’s claims, Orange Book listing, geographic scope and permitted launch date.
What geographic coverage does the patent provide?
U.S. Patent 9,808,530 provides protection only in the United States. Parallel applications may exist in Europe and other jurisdictions based on the same priority family, but foreign claim scope, prosecution history, validity and expiration dates are jurisdiction-specific.
A global launch analysis therefore requires separate review of:
- European Patent Office family members.
- United Kingdom and other national validations.
- Canadian, Japanese and Australian counterparts.
- Local regulatory exclusivity.
- National litigation and settlement agreements.
- Differences in claim scope after prosecution.
Key Takeaways
- U.S. Patent 9,808,530 is a formulation patent centered on xanthan gum and anti-foaming performance.
- Claim 1 broadly covers tiacumicin B compounds and related forms combined with xanthan gum.
- Claim 2 directly targets fidaxomicin.
- Claim 8 covers dry powders, dry granulates and dispersible tablets for aqueous suspension.
- Claims 3 through 7 cover specific excipient combinations, including mannitol, trehalose, sodium starch glycolate and partially pregelatinised starch.
- The projected basic expiration date is April 18, 2032.
- The patent is relevant to the Dificid Orange Book estate but does not provide compound-level protection for every fidaxomicin product.
- The principal generic design-around is omission or replacement of xanthan gum, although the anti-foaming limitation and doctrine of equivalents remain material.
- The main validity risks are obviousness, enablement, written description and indefiniteness relating to the functional anti-foaming limitation.
- No published appellate or district-court merits decision establishes a controlling construction of these claims.
FAQs
Does U.S. Patent 9,808,530 cover all fidaxomicin tablets?
No. It covers fidaxomicin compositions only when the claim requirements are met, including xanthan gum in an amount that prevents foaming in water. A fidaxomicin product using a different formulation may avoid infringement.
Can a generic manufacturer use xanthan gum after 2032?
Yes, absent another unexpired patent, regulatory exclusivity or enforceable agreement. The 2032 date applies to this patent’s basic term, not necessarily to every patent covering fidaxomicin.
Does claim 8 require the product to be sold with water?
No. Claim 8 covers a dry powder, dry granulate or dispersible tablet intended for preparation of an aqueous suspension. The product can be sold in dry form.
Is xanthan gum itself patented by U.S. Patent 9,808,530?
No. The patent does not claim xanthan gum as a standalone substance. It claims pharmaceutical compositions containing xanthan gum with a tiacumicin B compound and the specified functional result.
Could a non-oral fidaxomicin product avoid the patent?
It may avoid claim 10, but non-oral administration alone would not necessarily avoid claim 1. The composition could still infringe the broader independent claim if it contains the claimed active ingredient, xanthan gum and the required anti-foaming property.
References
- United States Patent and Trademark Office. (2017). U.S. Patent No. 9,808,530, Pharmaceutical composition comprising a tiacumicin B compound.
- U.S. Food and Drug Administration. (2011). Dificid (fidaxomicin) prescribing information.
- U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book.
