Patent 4,921,843 (US): Scope and Claim Landscape for Daily Estrogen-Progestin Contraception Regimens and 24-Unit Oral Delivery Systems
US 4,921,843 claims a contraceptive method and an oral “drug delivery system” that implements a specific cycle-based estrogen start (Day 2 to Day 7) followed by progestin-only or combined progestin dosing through Day 28. The claims are tightly anchored to (i) menstrual-cycle day ranges, (ii) estrogenic-compound dose equivalents in the 17-alpha-ethinyl estradiol (EE) activity range of about 0.01 to about 0.04 mg, (iii) progestin “follow-up” dosing through Day 28, and (iv) in the system claims, a pack structure of at least 24 separate daily units with a fixed count split between “initial” and “follow-up” dosage units.
What matters for freedom-to-operate (FTO) and generic entry risk is that the asserted claim set is drafted in two layers: (a) method claims that can be infringed by prescribing/using the claimed regimen, and (b) product/pack-structure delivery claims that can be infringed by manufacturing or marketing a packaging/dosing unit structure that matches the claimed unit counts and sequence behavior.
What is US Patent 4,921,843 and what does it claim?
Answer: US 4,921,843 claims (1) a contraception method with a specific menstrual-cycle schedule and estrogen-progestin dosing sequence, and (2) an oral drug delivery system structured as at least 24 daily dosage units with “initial” estrogen-only units followed by “follow-up” progestin (or estrogen+progestin) units.
Key claim buckets
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Method of contraception (Claims 1–17)
- Estrogenic compound administered daily from about Day 2 to about Day 7 (Day 1 is first day of menses).
- Estrogen administered as sole contraceptively active ingredient, at daily dosage equivalent to about 0.01 to about 0.04 mg of 17-alpha-ethinyl estradiol activity.
- Followed by at least one follow-up composition daily through Day 28 containing a contraceptively effective daily dosage of a progestin (progestin alone or with estrogen, depending on subclaims).
- Multiple variants: specific estrogen identity (EE, mestranol, 17-beta-estradiol), specific progestins (norethindrone, D-norgestrel, specific oxime, 19-nor-17-hydroxy progesterone ester), and specific dosing-sequence patterns across multiple follow-up compositions (Claims 13, 16, plus dependent specifics).
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Drug delivery system (Claims 18–28)
- At least 24 separate oral daily dosage units.
- At least four initial dosage units containing the same estrogenic-compound daily dosage as the sole contraceptively active ingredient.
- Followed by twenty-one follow-up dosage units each containing a contraceptively effective daily dosage of a progestin.
- Product-pack structure variants for how progestin dosing and estrogen/progestin pairing differ across follow-up groups (Claims 21–23).
- Dependent claims specify estrogen and progestin identities (EE, mestranol, 17-beta-estradiol; norethindrone, D-norgestrel).
What are the exact claim elements for the contraception method in US 4,921,843?
Answer: The method claims require a day-specific regimen: estrogen-only dosing for a defined initial window (Day 2–Day 7), then daily progestin-containing follow-up through Day 28 at contraceptively effective doses, with the estrogen dose defined by an EE-equivalent activity range.
Claim 1: core method architecture (independent claim)
Claim 1 can be broken into enforceable limitations:
Dependent method claim scope: what flips the infringement analysis
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Progestin composition form
- Claim 2: follow-up composition contains progestin as sole contraceptively active ingredient.
- Claim 3: follow-up composition comprises estrogenic compound + progestin.
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Estrogen identity specificity
- Claim 4: estrogenic compound is ethinyl estradiol (EE).
- Claim 5: mestranol
- Claim 6: 17-beta-estradiol
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Progestin identity specificity
- Claim 7: norethindrone daily dose about 0.5 mg to about 1.0 mg
- Claim 8: D-norgestrel
- Claim 9: D-17-beta-acetoxy-13-beta-ethyl-17-alpha-ethinyl-gon-4-en-3-one oxime
- Claim 10: “a 19-nor-17-hydroxy progesterone ester”
- Claim 11: EE + norethindrone
- Claim 12: mestranol + D-norgestrel
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Multi-follow-up dosing patterns
- Claim 13: plural follow-up compositions in sequence where:
- estrogenic compound daily dosage is substantially the same across follow-up compositions
- progestin dosage increases across successive follow-up compositions
- Claim 16: plural follow-up compositions in sequence where:
- estrogenic compound daily dosage is substantially the same across follow-up compositions
- progestin dosage first increases to a higher value then decreases back to the first progestin dosage
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Numeric anchor points
- Claim 15: EE daily dosage about 0.035 mg
- Claim 17: EE daily dosage 0.035 mg
What the claims imply structurally
- The regimen is essentially a sequenced combined regimen with an initial estrogen-only phase followed by progestin-only or estrogen-progestin follow-up phase.
- The estrogen constraint is not only identity, but an EE-equivalent estrogenic activity range (0.01–0.04 mg). This makes design-around difficult for competitors using another estrogen salt/ester with comparable estrogenic activity, depending on how “equivalent in estrogenic activity” is construed.
What are the exact claim elements for the drug delivery system in US 4,921,843?
Answer: The system claims require an oral pack with a minimum unit count and a dosing sequence split: at least four initial estrogen-only units at a uniform estrogen daily dose, followed by 21 follow-up daily progestin-containing units.
Claim 18: independent delivery system claim
- Oral delivery system
- “constituted by at least 24 separate daily dosage units”
- at least four initial dosage units
- each contains the same contraceptively effective daily dosage of an estrogenic compound
- estrogen is the sole contraceptively active ingredient in those initial units
- “followed by twenty-one follow-up dosage units”
- each contains a contraceptively effective daily dosage of a progestin
Dependent system claims: structural permutations
- Claim 19: follow-up units each contain substantially the same daily dosage of a progestin.
- Claim 20: follow-up units each contain substantially the same daily dosage of estrogenic compound and a progestin (so follow-up can be combined, not just progestin-only).
- Claim 21: two follow-up groups:
- first group of 10 units: each contains a first effective daily dosage of estrogenic compound and a progestin
- second group of 11 units: each contains a follow-up effective daily dosage of a progestin and an estrogenic compound
(This permits a step-change across the 10/11 split.)
- Claim 22: three consecutive groups of about seven units each:
- each group contains estrogenic compound and progestin at substantially the same weight ratio within the group
- but weight ratios differ across consecutively administered groups
- Claim 23: weight ratio in group 1 equals group 3 (symmetry across first and third groups).
Dependent identity anchors
- Claim 24–26: initial estrogen identity can be EE, mestranol, or 17-beta-estradiol.
- Claim 27–28: progestin can be norethindrone or D-norgestrel.
What makes the system claims potent
Pack structure can be “read” on manufacturing and commercialization: a marketer can infringe even if the method is not explicitly taught, because delivering the claimed dosage-unit sequence can map to the delivery-system claim. The unit counts (at least 24, with “initial” at least 4 and “follow-up” at 21) are bright-line constraints.
How do claim variations (progestin-only vs combined follow-up) expand or narrow infringement risk?
Answer: Claims 1–3 and 18–20 determine whether a competitor must match progestin-only follow-up dosing or whether combined estrogen-progestin follow-up dosing also falls within scope.
Method claim pathway
- If a competitor’s regimen uses progestin-only after Day 7, it can fall within Claim 2 (if other elements match).
- If a competitor’s regimen keeps estrogen present during follow-up through Day 28, it can fall within Claim 3.
System claim pathway
- Claim 18 frames follow-up units as containing progestin; it does not explicitly require estrogen to be absent from follow-up units.
- Claim 19 locks in a “uniform progestin dose” profile if the follow-up progestin dosage is the same across all 21 units.
- Claim 20 locks in the “uniform estrogen+progestin dose” profile if both components remain substantially the same across follow-up units.
Net effect: A competitor using estrogen-progestin combined follow-up is still within the system claim set, provided the pack structure and identity constraints in dependent claims are met (or the independent claim scope is matched).
What estrogen and progestin identities are explicitly covered?
Answer: The claims explicitly cover EE, mestranol, and 17-beta-estradiol as estrogenic compounds, and (at least) norethindrone and D-norgestrel as progestins, plus additional specific progestins described by chemical identifiers.
Estrogenic compounds
- Ethinyl estradiol (Claim 4, 11, 14, 15, 17, 24)
- Mestranol (Claim 5, 12, 24–26)
- 17-beta-estradiol (Claim 6, 24–26)
Progestins
- Norethindrone (Claims 7, 11, 27)
- with an explicit dosage range: about 0.5 mg to about 1.0 mg daily (Claim 7)
- D-norgestrel (Claims 8, 12, 28)
- Specific oxime progestin (Claim 9)
- 19-nor-17-hydroxy progesterone ester class (Claim 10)
What dosing patterns across multiple follow-up compositions are claimed?
Answer: The independent method claim (Claim 1) only requires “at least one” follow-up composition. Claims 13 and 16 impose additional sequencing patterns in multi-composition regimens, and the system claims impose additional group-based dose ratio patterns.
Method multi-composition sequencing
- Claim 13: progestin dosage increases across successive follow-up compositions; estrogen dose stays substantially constant across those follow-up compositions.
- Claim 16: progestin dose increases then decreases back to the initial follow-up value; estrogen dose stays substantially constant across follow-up compositions.
These sequencing limitations matter most when a competitor uses “phasic” follow-up with multiple distinct progestin doses rather than a single constant-dose progestin phase.
Delivery system phasic group sequencing
- Claim 21: stepwise change with a 10-unit first group and 11-unit second group.
- Claim 22: three groups of about seven units, with weight ratios differing by group while each group maintains a substantially constant ratio.
- Claim 23: ratio symmetry: first and third groups share substantially the same weight ratio.
When does the claimed regimen start and when does it end?
Answer: The estrogen-only phase starts “about Day 2” and ends “about Day 7.” Progestin-containing follow-up runs “daily through Day 28.”
Timing implications
- The “about” language provides some flexibility around Day boundaries, but the claim still anchors to a menstrual-cycle day framework.
- The follow-up window extends to a 28-day cycle end, which is consistent with many oral contraceptive pack conventions.
How strong is the patent estate for US 4,921,843 claims based on the claim drafting approach?
Answer: On claim scope, strength is high where competitors must match a combination of (i) day-based dosing, (ii) EE-equivalent estrogen activity range, and (iii) unit-count pack structure. Strength is narrower where competitors can deviate on estrogen dose-equivalence, switch estrogen identities, change unit count or split, or change the dosing-window structure away from Day 2–7 and through Day 28.
Scope anchors that are harder to design around
- EE-equivalent estrogen activity range (0.01–0.04 mg EE activity)
Competitors using estrogenic compounds (including non-EE esters/salts) may still be pulled into the claim depending on activity equivalence.
- Day 2–Day 7 estrogen-only initial window
Competitors with different initiation (e.g., starting Day 1 or later) or different phase structure could avoid the method claims.
- Pack structure: “at least 24” daily units and “at least four” estrogen-only initial units followed by “21” follow-up units
Deviating the unit split or total unit count is a clean design-around if the product strategy allows.
Narrowing features
- Dependent claims impose identity and dosing-range constraints (e.g., norethindrone daily dose 0.5–1.0 mg; EE daily dose 0.035 mg; specific progestin identities).
- Phasic subgroup claims impose specific numeric groupings (10/11 or ~7/7/7) and ratio relationships (group 1 equals group 3).
What US generic entry risks does this patent create for oral contraceptive products?
Answer: The largest generic risk is to products whose dosing schedule maps to the same estrogen start window and follow-up through Day 28 and whose pack structure matches the claimed minimum unit counts and phase split.
Risk zones by product architecture
- Same regimen schedule
- Day 2–7 estrogen-only, followed by progestin-containing dosing through Day 28
- plus estrogen daily dose within the EE-equivalent band
- Same pack unit split
- at least 4 estrogen-only units then 21 follow-up units within a ≥24 unit daily pack
- Same phasic dose sequencing
- if using multiple follow-up compositions with increasing/decreasing progestin patterns, risk expands into Claims 13 and 16
- if using phasic weight-ratio group sequencing across the 21 units, risk expands into Claims 22 and 23
How does US 4,921,843 compare with typical fixed-dose combined oral contraceptive (COC) structures?
Answer: The patent is structured around a phased schedule with an estrogen-only start and a follow-up progestin phase (and, in system claims, pack unit splits and weight-ratio grouping). It is therefore more aligned with “phasic” or sequenced regimens than with simple monophasic COCs where both estrogen and progestin doses are constant across active days.
Practical infringement mapping
- Monophasic COCs (constant estrogen+progestin from early cycle days) are less likely to match the “estrogen-only” initial window and could be design-arounds for method claim scope.
- Phasic regimens with estrogen-only early units and progestin-focused late units align more closely with the claimed sequence.
Key Takeaways
- US 4,921,843 claims two enforcement vectors: a method tied to Day 2–Day 7 estrogen-only dosing and progestin through Day 28, and a product delivery system tied to ≥24 daily units with ≥4 initial estrogen-only units followed by 21 follow-up progestin units.
- The estrogen constraint is the EE-equivalent activity range 0.01 to 0.04 mg and the claims explicitly cover EE, mestranol, and 17-beta-estradiol.
- The risk to competitors increases when products use (i) a similar phase timing, (ii) estrogen activity within the claimed EE-equivalent range, and (iii) pack unit counts and follow-up grouping that match the claimed 10/11 or ~7/7/7 structure and weight-ratio symmetry where applicable.
- Dependent claims add “hard” numeric and identity limits (e.g., norethindrone 0.5–1.0 mg and EE 0.035 mg) that can narrow infringement for products that deviate on dose selection.
FAQs
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Does US 4,921,843 require progestin dosing to be progestin-only after Day 7?
No. Claim 1 requires progestin in follow-up. Dependent Claim 2 specifies progestin-only follow-up; dependent Claim 3 permits combined estrogen-progestin follow-up.
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What estrogen dose range is built into the method claim?
The initial estrogen-only daily dosage is defined as EE-equivalent estrogenic activity of about 0.01 to 0.04 mg of 17-alpha-ethinyl estradiol.
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What pack structure does the delivery system claim require?
At least 24 daily dosage units, with at least four initial estrogen-only units, followed by 21 follow-up units containing progestin.
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Are phasic follow-up regimens covered?
Yes. Method dependent Claims 13 and 16 claim specific progestin dosing patterns across multiple follow-up compositions; system dependent Claims 21–23 claim specific unit-grouping and weight-ratio behaviors.
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Which progestins are explicitly named in dependent claims?
Norethindrone, D-norgestrel, a specific oxime progestin, and a class of 19-nor-17-hydroxy progesterone esters.
References
- United States Patent 4,921,843.
