US Patent 5,462,740: Scope, Claim Structure, and US Landscape for Rectal Diazepam Visco-Buffer Compositions
US 5,462,740 claims a viscous, epileptic-seizure-inhibiting rectal formulation defined by (i) an anti-epileptic agent loading window, (ii) a buffered pH range, (iii) cellulose-ether viscosity control, and (iv) a high-solvent system intended to keep the drug in solution and enable rectal injection.
What do the independent claim elements cover? (Claim 1 core scope)
Claim 1 (composition) establishes four hard constraints
Claim 1 requires all of the following in combination:
1) Anti-epileptic agent content
- ~0.1 to 2.5 wt-% of “an anti-epileptic agent” in the total composition.
2) Buffer system
- Present in an amount effective to maintain pH ~5.5 to 7.5.
3) Cellulose-ether thickener
- ~1 to 10 wt-% cellulose ether to impart viscosity for administration by rectal injection to a human patient.
4) Solvent
- ~25 to 95 wt-% solvent (broad solvent category, further constrained in dependent claim 7).
Claim construction impact: A product that lacks any one of these elements (for example, viscosity achieved via non-cellulose polymers, or pH outside 5.5-7.5, or solvent outside 25-95 wt-%) falls outside Claim 1’s literal scope.
Rectal injection suitability is not a standalone element
“Suitable for administration by rectal injection” operates as a functional requirement tied to the cellulose-ether thickener’s job: impart enough viscosity for rectal injection. That means the practical design space is constrained not only by wt-% ranges but also by achieving injectable viscosity.
How narrow are the dependent claims? (Claim 2-8 narrowing ladder)
Claim 2: drug-class restriction
Claim 2 limits the anti-epileptic agent to:
- barbiturates
- benzodiazepines
- dipropylacetic acid derivatives
- hydantoins
- oxazolidinediones
- succinimides
Scope effect: If the anti-epileptic agent is not in this list (for example, felbamate, valproate, levetiracetam, lacosamide), the formulation does not infringe Claim 2 and will likely also miss Claim 1 if the “anti-epileptic agent” interpretation is limited to these classes (in practice, most litigated “selected from” lists are taken as limiting).
Claim 3: diazepam as the specific payload
Claim 3 selects:
This is the commercial center of gravity for the claim set because diazepam is historically used for acute seizure control and also drives formulation challenges (solubility, stability, precipitation).
Claim 4: viscosity numeric band
Claim 4 narrows to:
- apparent viscosity ~1,000 to 8,000 cps (typically at a stated temperature and shear condition, though your excerpt does not specify test conditions).
Scope effect: If a competitor hits the wt-% cellulose and still falls below 1,000 cps or above 8,000 cps (under the relevant measurement conditions), it is outside Claim 4 even if it matches Claim 1.
Claim 5: specific cellulose-ether species
Claim 5 narrows thickener selection to:
- methyl cellulose
- carboxylmethylcellulose
- hydroxypropylcellulose
- hydroxypropylmethylcellulose
Claim 6: hydroxypropyl methylcellulose
Claim 6 narrows the thickener to:
- hydroxypropyl methylcellulose (HPMC)
Scope effect: HPMC-based systems land in the narrowest literal “thickener identity” bucket.
Claim 7: solvent identity and precipitation control
Claim 7 defines solvent as:
- water or water and a water-miscible organic solvent, in an amount effective to inhibit precipitation of the anti-epileptic agent.
Scope effect: A formulation using a non-miscible solvent system or one that does not control precipitation via the claimed solvent concept is outside Claim 7. Even if Claim 1’s “solvent” is broad, Claim 7’s narrowing language provides an infringement pathway for products that use water plus a water-miscible co-solvent and claim stability/solubilization.
Claim 8: a diazepam-specific, quantitative “balanced water” version
Claim 8 requires:
- 0.25-0.75 wt-% diazepam
- pH 5.5-7.5
- 1-10 wt-% cellulose ether
- 25-75 wt-% non-toxic water-miscible organic solvent
- balance water
Scope effect: Claim 8 sets a mid-range solvent window (25-75 wt-%) and a tighter diazepam loading band (0.25-0.75 wt-%). It is the most actionable claim for competitors whose formulations aim at a specific acute-infusion rectal dose concentration.
What is the practical claim “design space” for infringement risk?
Key variable matrix (literal bounds)
| Parameter |
Claim 1 |
Claim 8 (diazepam-specific) |
Claim 4 (viscosity bound) |
| Anti-epileptic agent |
0.1-2.5 wt-% |
diazepam 0.25-0.75 wt-% |
(not stated in viscosity claim) |
| pH |
5.5-7.5 |
5.5-7.5 |
(not stated) |
| Cellulose ether thickener |
1-10 wt-% |
1-10 wt-% |
apparent viscosity 1,000-8,000 cps |
| Solvent content |
25-95 wt-% |
25-75 wt-% non-toxic water-miscible organic solvent |
(not stated) |
| Cellulose species |
any cellulose ether |
any cellulose ether |
(depends on Claim 5/6) |
What does the claim set imply about formulation goals?
The claim language encodes two formulation problems:
1) Drug solubility/precipitation control
- addressed by the high solvent fraction (Claim 1) and explicit “water and water-miscible organic solvent” plus “inhibit precipitation” (Claim 7).
2) Deliverability via rectal injection
- addressed by cellulose ether thickener wt-% and viscosity band (Claim 4), not just as a general “gel.”
This means competitor formulations that avoid precipitation by surfactants, cyclodextrins, or solid suspensions can still miss infringement if they do not use the cellulose-ether viscosity system and the specific high-solvent compositional structure.
How to read the claims for potential infringement workups
A defensible infringement screen for a candidate rectal diazepam product should test each element:
- Are they using cellulose ether thickener (and within 1-10 wt%)?
- Is the pH inside 5.5-7.5?
- Is solvent system inside 25-95 wt% (and 25-75 for the Claim 8 window)?
- Does diazepam loading match Claim 3 or Claim 8?
- Does their measured apparent viscosity fall between 1,000-8,000 cps?
Because Claim 1 is an “all elements” composition claim, failing any one constraint defeats literal infringement. Strategy often focuses on creating at least one out-of-range element.
What is the likely US patent landscape around this technology class?
Given the composition architecture (diazepam + buffer + cellulose ether + water/co-solvent + viscosity for rectal injection), the landscape in the US typically clusters into:
- Rectal benzodiazepam formulations
- Vehicles using co-solvents for diazepam solubility
- Mucoadhesive or viscosity-modulating rectal delivery systems
- pH-window stability formulations
- Thickening/viscosity patents using cellulose derivatives versus alternative polymers
Within that landscape, US litigated and asserted formulations commonly diverge on:
- thickener identity (cellulose ether versus non-cellulose polymers),
- viscosity target range and measurement method,
- solvent category and co-solvent fraction,
- pH range for stability and tolerability,
- whether the product is truly “rectal injection” versus rectal instillation or gel-like dosage forms.
This claim set is particularly sensitive to thickener identity and viscosity, because both are numerically bounded.
Where are the likely “design-around” options, based on claim boundaries?
Design-around levers aligned to literal claim limits
1) Switch thickener away from cellulose ether
- Avoid cellulose ethers entirely, or use a viscosity system not covered by the “selected from” list in Claim 5/6.
- Even if pH and solvent and drug loading match, changing thickener identity can remove Claim 1/5/6 coverage.
2) Move pH outside 5.5-7.5
- If stability can be maintained and tolerability preserved, pH shift can eliminate literal overlap.
3) Change apparent viscosity outside 1,000-8,000 cps
- Adjust thickener grade, concentration, and formulation conditions (and potentially measurement conditions) to avoid the claimed viscosity band.
4) Change solvent fraction
- Adjust solvent content below 25 wt% or above 95 wt% to avoid Claim 1.
- For Claim 8 overlap, move outside 25-75 wt% water-miscible organic solvent.
5) Change diazepam concentration
- For Claim 8, move diazepam loading outside 0.25-0.75 wt%.
Most conservative path: create at least one out-of-range element that aligns with how the product will be tested for infringement (pH, wt-%s, and viscosity under stated conditions).
Competitor mapping: what to look for in product formulations
For each candidate product, compare:
- Drug payload: diazepam concentration in wt-% of total composition
- pH: measured formulation pH
- Vehicle: presence of cellulose ether thickener (including HPMC)
- Solvent system: fraction of water-miscible organic solvent and presence/absence of precipitation-inhibiting co-solvent strategy
- Viscosity: apparent viscosity range and measurement method
If the product is an aqueous rectal formulation with low solvent loading or uses suspensions rather than high-solvent solubilized systems, it often misses the “25-95 wt-% solvent” backbone.
Key Takeaways
- US 5,462,740 claim coverage is built on a tight combination: diazepam (or other listed anti-epileptics) at defined wt-%, buffered pH 5.5-7.5, cellulose-ether thickener 1-10 wt-% to reach rectal injection-compatible viscosity, and 25-95 wt-% solvent.
- The narrowest, most operational infringement hooks are Claim 3 (diazepam), Claim 4 (1,000-8,000 cps), Claim 6 (HPMC), and Claim 8 (0.25-0.75 wt-% diazepam + 25-75 wt-% water-miscible organic solvent + balance water).
- Design-around work should prioritize creating a mismatch in at least one of: cellulose ether identity, pH window, viscosity band, solvent wt-%, or diazepam concentration.
FAQs
1) Is Claim 1 limited to rectal injection products only?
Yes. Claim 1 requires a viscosity imparted by cellulose ether so the composition is “suitable for administration by rectal injection.”
2) Does the patent cover cellulose ethers broadly or only specific ones?
Claim 1 covers “cellulose ether” generally (1-10 wt-%). Claim 5 limits the thickener species, and Claim 6 specifically limits to hydroxypropyl methylcellulose.
3) What is the key quantitative viscosity risk area?
Claim 4 requires apparent viscosity of about 1,000 to 8,000 cps.
4) For diazepam products, which claim is the tightest?
Claim 8 is tightest for formulation overlap because it fixes diazepam at 0.25-0.75 wt-% and sets 25-75 wt-% of non-toxic water-miscible organic solvent with balance water.
5) Can changing pH alone avoid infringement?
Yes in a literal claim sense: any formulation outside pH ~5.5-7.5 does not meet Claim 1’s buffer requirement.
References
[1] United States Patent No. 5,462,740, “Viscous anti-epileptic compositions,” claims 1-8 (as provided in the prompt).
