US Patent 5,908,638: Scope, Claim Architecture, and US Patent Landscape for Conjugated Estrogen Matrix With Ethylcellulose Moisture Barrier
What is the core claimed invention in US 5,908,638?
US 5,908,638 claims an oral solid unit dosage form for hormonal treatment of peri-menopausal, menopausal, and post-menopausal disorders, built around three technical pillars:
- Powdered conjugated estrogen composition deposited on organic excipients (not inorganic excipients), with tightly controlled water content and a gel-former/non-gel-former organic excipient ratio.
- A moisture barrier coating applied to the solid unit dosage form using ethylcellulose (with a defined weight percent range).
- A downstream multi-hormone tablet architecture where additional hormones can be deposited after the moisture barrier coat, optionally bonded with polymeric films (including hydroxypropylmethylcellulose and ethylcellulose aqueous dispersions), and supported by defined polymer film solids, surfactants, and plasticizers.
The claim set is broad on indication class (perimenopausal through postmenopausal) and formulation modality (solid unit dosage capable of oral administration), while narrow on formulation mechanics: water thresholds, excipient taxonomy (organic excipients; “substantially free” of inorganic excipients), and specific coating materials (ethylcellulose moisture barrier; optional HPMC/ethylcellulose polymeric film to bind additional hormones).
How is claim scope structured across dependent claims?
Claims 1-7 establish the foundational composition and barrier system. Claims 8-20 extend into dosage form type and the ability to add other hormones, including multi-layer and film-bonded hormone deposition.
Claim 1: Baseline composition and moisture-barrier scaffold
Claim 1 defines a pharmaceutical composition in a solid unit dosage form suitable for oral administration for hormonal treatment. The composition comprises:
- Conjugated estrogens coated onto one or more organic excipients, forming a powdered conjugated estrogen composition.
- Powdered conjugated estrogen composition is substantially free of inorganic excipients.
- Organic excipients ratio:
- About 30% to 70% gel-forming organic excipient
- About 30% to 70% non-gel forming organic excipient
- By weight
- Water constraints:
- Less than about 2.5% free water by weight
- Greater than 2.5% total water by weight
- Solid unit dosage form is coated with a moisture barrier coating comprising:
This claim is the anchor for infringement analysis because it requires all listed constraints simultaneously: excipient classing (organic vs “substantially free” inorganic), gel/non-gel ratio, free/total water partitioning, and ethylcellulose as the moisture barrier coating material.
Claim 2-3: Specific gel-former family and mixtures
- Claim 2 narrows excipient selection:
- Organic excipients include a mixture of:
- one or more gel-forming hydroxyalkylalkylcelluloses
- and hydroxyalkyl cellulose
- Organic excipients make up more than about one third by weight of the solid unit dosage form.
- Claim 3 narrows further:
- Gel-forming organic excipients are a mixture of:
- one or more hydroxypropylmethylcelluloses
- and 0-33% methyl cellulose or other cellulose ether
These dependent claims are tighter and can be treated as “fallback” positions if broader cellulosic formulations are challenged.
Claim 4-6: Non-gel excipient requirements and estrogen identity
- Claim 4:
- Powdered conjugated estrogen composition further includes at least about 40% by weight of a non-gel forming organic excipient.
- Claim 5:
- Non-gel excipient selected from:
- lactose
- mannitol
- cellulose derivatives
- Claim 6:
- Conjugated estrogens are selected from:
- sodium sulfate esters of estrone
- equilin
- 17-α-dihydroequilin
- 17-β-dihydroequilin
- 17-α-estradiol
These dependencies lock both the non-gel bulking excipient and the estrogen chemical identity family.
Claim 7: Moisture barrier coating level
- Moisture barrier coating is 0.5% to 8.0% of total weight of the solid unit dosage form.
This is a quantitative boundary that matters for design-around: lower or higher ethylcellulose loading falls outside the explicit claim range (subject to doctrine-of-equivalents issues not addressed here).
What does the invention claim about tablet architecture and added hormones?
Claims 8-20 expand into a multi-hormone solid dosage concept, with sequence constraints: additional hormone is deposited after the moisture barrier coat.
Claim 8-10: Tablet embodiment and additional hormone selection
- Claim 8: solid unit dosage form is a tablet.
- Claim 9: further comprises at least one additional hormone deposited on the tablet after application of the moisture barrier coat.
- Claim 10: additional hormone is selected from:
- progesterone
- medroxyprogesterone
- medroxyprogesterone acetate
- testosterone
- methyltestosterone
- combinations
This creates a strong “product form” perimeter: the tablet must support added hormones that are applied post–moisture barrier.
Claim 11-12: Bonding mechanism and polymer film choice
- Claim 11: hormone is bonded to the tablet by a polymeric film.
- Claim 12: polymeric film selected from:
- hydroxypropylmethylcellulose
- ethylcellulose aqueous dispersion
This provides a clear list of polymeric film options to bind post-coated hormones.
Claim 13-14: Multi-coating and outer coating composition
- Claim 13: further comprises two or more coatings with one outer coating comprising a polymeric film and at least one additional hormone.
- Claim 14: hormone selection repeats the Claim 10 set.
Claim 15: Micronization
- Claim 15: additional hormone is micronized.
This is a formulation-dependent constraint that can materially narrow practical compliance.
Claim 16-18: Polymer film solids and surfactant system
- Claim 16: polymeric film contains about 10-30% solids by weight.
- Claim 17: polymeric film further comprises a surfactant.
- Claim 18: surfactant is selected from polyoxyethylene (20) sorbitan esters:
- polyoxyethylene (20) sorbitan monolaurate
- polyoxyethylene (20) sorbitan monopalmitate
- polyoxyethylene (20) sorbitan monostearate
- polyoxyethylene (20) sorbitan monooleate
- polyoxyethylene (20) sorbitan trioleate
Claim 19-20: Polymer film plasticizer options
- Claim 19: polymeric film further comprises a plasticizer.
- Claim 20: plasticizer is selected from:
- dibutyl sebacate
- triethyl citrate
Claim-by-claim “scope checklist” (what must be present)
The table below converts claim terms into engineering checkpoints for formulation and coating design.
| Element |
Claim anchor |
Required limitation(s) |
| Indication / patient population |
Claim 1 |
peri-menopausal, menopausal, post-menopausal disorders in a woman |
| Dosage form |
Claim 1 |
solid unit dosage form capable of oral administration |
| Conjugated estrogen |
Claim 1 |
conjugated estrogens coated onto one or more organic excipients |
| Excipient class |
Claim 1 |
powdered composition is substantially free of inorganic excipients |
| Excipient ratio |
Claim 1 |
30-70% gel-forming organic excipient; 30-70% non-gel forming organic excipient (by weight) |
| Water partition |
Claim 1 |
<2.5% free water; >2.5% total water (by weight) |
| Moisture barrier coating |
Claim 1,7 |
ethylcellulose; 0.5-8.0% of total dosage form weight |
| Gel-former identity (cellulose types) |
Claim 2-3 |
hydroxyalkylalkylcelluloses + hydroxyalkyl cellulose; gel-formers include hydroxypropylmethylcellulose and 0-33% methyl cellulose/other cellulose ether |
| Non-gel excipient amount |
Claim 4 |
at least ~40% by weight non-gel forming organic excipient |
| Non-gel identity |
Claim 5 |
lactose, mannitol, or cellulose derivatives |
| Estrogen identity |
Claim 6 |
sodium sulfate esters of estrone, equilin, 17-α-dihydroequilin, 17-β-dihydroequilin, 17-α-estradiol |
| Tablet embodiment |
Claim 8 |
solid unit dosage form is a tablet |
| Additional hormones |
Claim 9-14 |
additional hormone deposited after moisture barrier coat; optional multi-coat outer layer with polymeric film and additional hormone |
| Additional hormone set |
Claim 10,14 |
progesterone / medroxyprogesterone / medroxyprogesterone acetate / testosterone / methyltestosterone (+ combinations) |
| Hormone bonding mechanism |
Claim 11 |
polymeric film bonds hormone to tablet |
| Polymer film options |
Claim 12 |
hydroxypropylmethylcellulose or ethylcellulose aqueous dispersion |
| Micronization |
Claim 15 |
additional hormone is micronized |
| Polymer film solids |
Claim 16 |
10-30% solids by weight |
| Surfactant |
Claim 17-18 |
polyoxyethylene (20) sorbitan monoester/triesters listed |
| Plasticizer |
Claim 19-20 |
dibutyl sebacate or triethyl citrate |
Where are the likely infringement hot spots?
- Moisture barrier identity and loading: Claim 1 requires an ethylcellulose moisture barrier; Claim 7 defines 0.5-8.0% total weight. Any product using a different barrier polymer or outside the loading range targets a key limitation.
- Water partition requirements: The paired constraints (“<2.5% free water” and “>2.5% total water”) are unusually specific. Many manufacturing states can shift free vs total water content, so compliance hinges on how those are measured in the asserted product.
- “Substantially free of inorganic excipients”: Products using mineral fillers, pigments, or other inorganic excipient classes risk failing this element if they are material enough to breach “substantially free.”
- Post-barrier deposition sequence: Claim 9 requires additional hormones deposited after applying the moisture barrier coat. If the manufacturing sequence deposits hormones before the barrier or integrates the barrier into a different build order, the literal match can fail.
- Outer polymeric film system: Claim 11-12 specify polymer film materials (HPMC or ethylcellulose dispersion) bonding hormones. Claim 16-20 add solids %, surfactant selection, and plasticizer selection when the dependent path is asserted.
What is the likely design-around map?
Because the claim set is layered, the strongest design-around is to break a single “hard” element of Claim 1 (or Claim 7) rather than to tweak dependent parameters:
- Replace the moisture barrier material with a non-ethylcellulose barrier, or adjust barrier amount outside 0.5-8.0%.
- Alter the excipient system so it is not “substantially free of inorganic excipients.”
- Change free vs total water profile so at least one of Claim 1’s water thresholds is not met.
- Use a non-matching estrogen identity family (but note: Claim 6 is dependent on Claim 1).
- Avoid post-moisture-barrier hormone deposition architecture so Claim 9’s sequence element is not met.
For products that still aim to include additional hormones, further design-around lever points include the binder polymer (Claim 12) and the surfactant/plasticizer selections (Claims 17-20), but those matter only when the asserted claim chain reaches those dependents.
US patent landscape: what can be concluded from the provided record?
No bibliographic metadata, prosecution history, assignees, priority dates, expiration dates, related continuations, or cited/competing patents are included in the input. Without those facts, a complete US landscape cannot be produced from the provided claim text alone.
What can be stated from the claim text itself is the technical domain the patent occupies (oral solid unit peri/menopausal therapy; conjugated estrogen on mixed gel/non-gel organic excipient with defined water partition; ethylcellulose moisture barrier; optional additional progestin/androgen hormones applied as post-barrier deposits with polymeric film and defined excipient additives). Any landscape analysis that ranks competitors, maps blocking families, or identifies likely citation clusters requires external patent records not present here.
Per the constraints, no additional landscape mapping is provided.
Key Takeaways
- US 5,908,638 Claim 1 is a tightly constrained formulation and coating claim: conjugated estrogens coated on organic excipients (substantially inorganic-free), specific gel/non-gel ratios, a defined free vs total water profile, and an ethylcellulose moisture barrier coating.
- Claims 2-7 narrow excipient families (cellulose ether types, non-gel excipient identity) and quantify barrier level.
- Claims 8-20 add a tablet embodiment with post-barrier deposition of additional hormones, bound by a polymeric film (HPMC or ethylcellulose dispersion), with further constraints on film solids, surfactants (polyoxyethylene (20) sorbitan esters), and plasticizers (dibutyl sebacate or triethyl citrate).
- The practical infringement and design-around hinges most on: ethylcellulose barrier material and loading, water partition metrics, inorganic excipient absence, and the post-barrier deposition sequence.
FAQs
1) Does the patent require ethylcellulose as the moisture barrier only, or also in other polymeric layers?
Claim 1 requires ethylcellulose as the moisture barrier coating. Separately, Claim 12 allows ethylcellulose aqueous dispersion as the polymeric film that bonds additional hormones.
2) Are the water constraints optional in any dependent claim?
No. The water constraints are part of Claim 1’s core limitations and flow into all dependent claims.
3) Can the patent cover a formulation with no additional hormones?
Yes. Claims 8-20 add additional hormone deposition; Claim 1 itself covers conjugated estrogens with the ethylcellulose moisture barrier and the defined organic excipient and water constraints.
4) What additional hormones are explicitly covered?
Progesterone, medroxyprogesterone, medroxyprogesterone acetate, testosterone, methyltestosterone, and combinations (Claims 10 and 14).
5) What excipients are explicitly named as non-gel forming options?
Lactose, mannitol, and cellulose derivatives (Claim 5).
References
[1] United States Patent No. 5,908,638.
