List of Excipients in Branded Drug IMIPRAMINE PAMOATE

Company	Tradename	Ingredient	NDC	Excipient	Potential Generic Entry
STAT RX USA LLC	IMIPRAMINE PAMOATE	imipramine pamoate	16590-963	D&C RED NO. 28
STAT RX USA LLC	IMIPRAMINE PAMOATE	imipramine pamoate	16590-963	FD&C BLUE NO. 1
STAT RX USA LLC	IMIPRAMINE PAMOATE	imipramine pamoate	16590-963	FD&C YELLOW NO. 6

Generic Drugs Containing IMIPRAMINE PAMOATE

Company	Ingredient	NDC	Excipient
Hikma Pharmaceuticals USA Inc	imipramine pamoate	0054-0273	FD&C BLUE NO. 1
Hikma Pharmaceuticals USA Inc	imipramine pamoate	0054-0273	FD&C RED NO. 40
Hikma Pharmaceuticals USA Inc	imipramine pamoate	0054-0273	FD&C YELLOW NO. 6

What are the Most Frequently-Used Excipients in IMIPRAMINE PAMOATE?

# Of NDCs	Excipient
4	FD&C BLUE NO. 1
4	FD&C RED NO. 40
4	FD&C YELLOW NO. 6

Imipramine Pamoate Excipient Strategy and Commercial Opportunities

Last updated: August 20, 2026

Imipramine pamoate is a mature tricyclic antidepressant with limited patent protection and a small, largely generic market. Commercial value is concentrated in reliable supply, differentiated dosage forms, improved swallowability, dose flexibility, and regulatory execution rather than in blocking intellectual property. Its pamoate salt creates formulation opportunities because it has lower aqueous solubility than imipramine hydrochloride, but it also increases dissolution, bioequivalence, and manufacturing risk.

What is the commercial status of imipramine pamoate?

Imipramine pamoate is the pamoate salt of imipramine, marketed historically as an oral capsule for depression. Imipramine hydrochloride is more commonly associated with immediate-release tablets and oral solutions. Both products deliver the same active moiety but are not automatically interchangeable because the salt form, dosage form, strength expression, dissolution profile, and labeling differ.[1]

Attribute	Imipramine pamoate
Active moiety	Imipramine
Drug class	Tricyclic antidepressant
Historical brand	Tofranil-PM
Dosage form	Oral capsule
Typical labeled strengths	75 mg, 100 mg, 125 mg, and 150 mg imipramine pamoate capsules
Primary indication	Depression
Regulatory pathway for generic products	ANDA, subject to reference-product and bioequivalence requirements
Patent position	Historical composition and product patents are expected to be expired
Regulatory exclusivity	No meaningful new-drug exclusivity remains
Biosimilar exposure	None; this is a small-molecule drug
Main commercial barriers	Supply continuity, reference-product availability, dissolution performance, and limited market size

The product has mature clinical use and low generic barriers from a patent perspective. The remaining barriers are technical and commercial. A manufacturer must establish a reproducible capsule product, demonstrate bioequivalence, maintain a compliant supply chain, and compete in a market where annual demand is likely modest relative to newer antidepressants.

What patents protect imipramine pamoate?

Imipramine pamoate is unlikely to have meaningful unexpired composition-of-matter protection in the United States. Imipramine was developed and commercialized decades ago, and the relevant original patents would have expired long ago under modern patent-term rules.

The likely IP position is:

IP category	Current commercial relevance
Imipramine base composition patent	Expired
Imipramine pamoate salt patent	Historical protection, expected expired
Original capsule product patent	Expected expired
Method-of-use patent for depression	Expected expired
Formulation patent covering a modern excipient system	No established blocking estate identified
Manufacturing-process patent	Potentially relevant only if a supplier develops a proprietary process
Trademark protection	Brand-specific and separate from active pharmaceutical ingredient protection

The practical opportunity is therefore an open generic market rather than a license-driven market. A new entrant would generally compete through an ANDA if it matches the reference product and can meet FDA quality and bioequivalence requirements.[2]

What is the Orange Book status of imipramine pamoate?

The Orange Book remains the controlling source for current listed drug products, therapeutic-equivalence evaluations, and any active patent or exclusivity information.[2] Imipramine pamoate should be assessed against the specific reference-listed drug and dosage form because the pamoate capsule and imipramine hydrochloride tablet products are distinct products.

A commercial diligence review should distinguish:

• Whether an active reference-listed drug remains marketed.
• Whether the reference product has an Orange Book therapeutic-equivalence listing.
• Whether any patent or exclusivity entry remains associated with the product.
• Whether a proposed generic can use the relevant reference product for an ANDA.
• Whether the applicant would need a 505(b)(2) pathway because of formulation, dosage form, or reference-product limitations.

A new formulation that materially changes release, route, indication, or clinical performance may fall outside a conventional ANDA strategy.

When does imipramine pamoate lose exclusivity?

Imipramine pamoate lost meaningful market exclusivity decades ago. The original small-molecule exclusivity period and any conventional patent protection have expired. Current commercial entry is therefore not constrained by a known orphan, pediatric, or new-chemical-entity exclusivity period.

There is no biosimilar pathway because imipramine pamoate is a chemically synthesized small molecule. Competitors would enter as generic drugs, reformulated products, or 505(b)(2) products rather than biosimilars.

Paragraph IV risk is correspondingly limited. A new ANDA applicant could file a Paragraph IV certification only if an active patent were listed against the relevant reference product. For a mature imipramine pamoate product, the more probable certifications would be Paragraph I, II, or III, depending on whether the reference product has current patent information and whether any listed patent remains unexpired.[3]

How does the pamoate salt affect excipient selection?

The pamoate counterion is the central formulation issue. Pamoate salts are generally selected to reduce solubility and can alter dissolution, precipitation, particle behavior, and absorption relative to more soluble salts. The excipient system must support dose uniformity and capsule stability without creating an overly slow or variable release profile.

Solubility and dissolution

The formulation should be designed around the measured intrinsic dissolution behavior of the specific imipramine pamoate API lot. Key variables include:

• API particle-size distribution.
• Crystal form and crystallinity.
• Salt stoichiometry.
• Water content.
• Milling and agglomeration.
• Wetting and dispersion in gastrointestinal media.
• Capsule disintegration.
• Excipient-driven precipitation or adsorption.

Suitable excipient categories may include lactose, microcrystalline cellulose, starch, pregelatinized starch, dibasic calcium phosphate, colloidal silicon dioxide, magnesium stearate, and sodium lauryl sulfate. The final selection must be based on compatibility and dissolution data rather than on the excipient’s generic function.

A small amount of a wetting agent may improve reproducibility if the API is hydrophobic, but excessive surfactant can change dissolution too sharply and create stability or capsule-shell interactions. Hydrophilic fillers can improve dispersion, while hydrophobic lubricants can delay wetting if overused.

Capsule-shell strategy

Hard gelatin capsules are the most natural dosage form for an immediate-release pamoate product. The manufacturer should evaluate:

• Gelatin versus hypromellose shells.
• Shell moisture transfer.
• Brittleness and cracking.
• Cross-linking risk.
• Colorant compatibility.
• Light protection.
• Printing and identification requirements.
• Storage under high humidity and temperature.

Hypromellose capsules may offer supply-chain and vegetarian-labeling advantages, but a shell substitution can change disintegration and dissolution. The capsule shell should be treated as part of the drug product, not as a neutral packaging component.

Lubrication and flow

Imipramine pamoate blends may have poor flow because of low bulk density, electrostatic behavior, or fine API particles. Colloidal silicon dioxide can improve flow and reduce weight variation. Magnesium stearate can improve ejection and processing but may impair wetting when used at high levels or with excessive blending time.

A robust process should control:

1. API deagglomeration.
2. Geometric dilution.
3. Lubricant addition time.
4. Blend uniformity.
5. Encapsulation speed.
6. Fill-weight variation.
7. Dissolution after scale-up.

Direct compression may be attractive for cost reasons, but dry granulation or roller compaction may be preferable if the API has poor flow or segregation risk. Wet granulation introduces water and drying variables that may be unnecessary for a low-dose or highly potent product unless the formulation needs improved density and flow.

What formulations are protected by imipramine pamoate patents?

No modern formulation patent estate is broadly associated with imipramine pamoate as a commercial barrier. The principal opportunity is to create a differentiated formulation that earns regulatory and market value through performance, convenience, or supply advantages.

Potential formulation concepts include:

Formulation concept	Commercial rationale	Main risk
Conventional immediate-release capsule	Lowest development and regulatory complexity	Weak differentiation
Smaller capsule with optimized density	Improved swallowing and manufacturing efficiency	Fill-weight and content-uniformity risk
Sprinkle capsule	Administration to selected patients who cannot swallow capsules	Food-effect and labeling requirements
Modified-release capsule	Reduced dosing frequency and smoother exposure	505(b)(2) or clinical bridging risk
Oral liquid or suspension	Pediatric and geriatric dose flexibility	Chemical, microbial, and palatability challenges
Multiparticulate capsule	Tunable release and dose flexibility	Higher manufacturing complexity
Taste-masked liquid	Improved adherence for patients unable to swallow	Salt taste, stability, and preservative burden
Combination product	Potential adherence or symptom-management rationale	Combination-product and clinical-development burden

A conventional immediate-release generic is the most realistic near-term product. Modified-release, liquid, or sprinkle products have greater differentiation but require more extensive development and may not qualify for the simplest ANDA route.

Which excipients offer the strongest commercial opportunity?

The strongest opportunity is not a single novel excipient. It is a controlled excipient platform that solves a documented product problem while preserving rapid and reproducible dissolution.

High-value excipient functions

Wetting and dispersion

Surfactants or wetting agents can reduce dissolution variability caused by hydrophobic API particles. The commercial value is highest when the reference product has inconsistent dissolution or when API particle-size variability affects performance.

Flow and dose uniformity

Colloidal silicon dioxide, selected cellulose grades, and optimized granular carriers can reduce segregation and encapsulation variability. This is especially relevant for high-strength capsules where fill weight and density change across strengths.

Lubrication control

A low-level lubricant system can improve manufacturing without creating a dissolution penalty. Lubricant concentration and blending time should be established as critical process parameters.

Moisture management

Moisture-barrier excipients, low-moisture fillers, and appropriate capsule-shell selection can improve shelf life. Packaging may deliver more value than a novel excipient, particularly in humid markets.

Palatability

For a liquid, taste masking would be a central development issue. Imipramine products can present bitterness and local irritation concerns. Ion exchange resins, polymeric coatings, sweeteners, and flavor systems could support a liquid product, but each increases regulatory and stability complexity.

What FDA regulatory pathway applies to new imipramine pamoate products?

A conventional immediate-release capsule that matches the reference product would generally target an ANDA under section 505(j) of the Federal Food, Drug, and Cosmetic Act. The applicant would need pharmaceutical equivalence, bioequivalence, chemistry, manufacturing, and controls data.[3]

A product with a new release profile, new route, materially different dosage form, or new clinical positioning may require a 505(b)(2) application. That pathway could support differentiated products such as:

• Once-daily modified-release capsules.
• Oral suspensions.
• Sprinkle formulations.
• New dosage strengths.
• Products designed for specific administration populations.

The regulatory value of a 505(b)(2) product depends on whether the formulation solves a clinically relevant problem. A merely cosmetic excipient change is unlikely to justify a premium.

What generic entry risks exist for imipramine pamoate?

Patent litigation risk is low relative to newer branded products. The main entry risks are operational and regulatory.

Technical risks

• Failure to match reference-product dissolution.
• Inadequate capsule disintegration.
• API segregation during blending.
• Strength-dependent bioequivalence performance.
• Stability loss under humidity.
• Variable pamoate particle size.
• Inconsistent salt formation or residual solvent profile.
• Packaging-related moisture uptake.

Commercial risks

• Small addressable market.
• Limited reimbursement premium.
• Few distributors willing to carry a low-volume product.
• Price erosion after multiple ANDA approvals.
• Dependence on a single API or capsule supplier.
• Low inventory turns and expiry exposure.
• Reference-product discontinuation or limited availability.

A differentiated product can reduce price competition, but the development cost must remain proportionate to the market. The most defensible position is usually a reliable, multi-strength product with strong supply continuity and a documented formulation advantage.

How does imipramine pamoate compare with imipramine hydrochloride?

Factor	Imipramine pamoate	Imipramine hydrochloride
Salt behavior	Lower-solubility pamoate form	More soluble hydrochloride form
Common historical dosage form	Capsule	Tablet and oral solution
Formulation emphasis	Wetting, dispersion, dissolution control	Dose uniformity, liquid stability, tablet performance
Differentiation potential	Modified release, sprinkle, capsule engineering	Liquid, tablet, and release-profile differentiation
Generic competition	Mature and limited	Broader historical product presence
Development risk	Salt-specific dissolution and capsule performance	Salt-specific stability and dosage-form performance
Substitution	Not automatically interchangeable by salt and dosage form	Not automatically interchangeable with pamoate

A company with imipramine hydrochloride capabilities could leverage existing analytical and manufacturing knowledge, but it should not assume direct product equivalence. The pamoate salt requires independent control of dissolution, solid-state properties, and bioequivalence.

What licensing deals and manufacturing barriers affect the market?

No major current licensing structure is inherent to imipramine pamoate. The active ingredient is a mature generic API, and commercial arrangements are more likely to involve:

• API supply agreements.
• Contract encapsulation.
• Private-label distribution.
• Regional marketing rights.
• Technology transfer for modified-release systems.
• Dual-source packaging and manufacturing.

Manufacturing barriers are manageable but can be material for a low-volume product. API qualification is the main supply risk. A supplier should be assessed for salt consistency, impurity control, particle-size control, residual solvents, genotoxic impurity management, and change-control discipline.

A dual-source strategy is commercially valuable because a single manufacturing interruption can remove a mature product from the market. Smaller generic products may have fewer qualified suppliers, creating an opportunity for a dependable entrant even without formulation novelty.

What is the revenue opportunity for imipramine pamoate?

The addressable market is limited by the declining use of tricyclic antidepressants, competition from SSRIs and SNRIs, and the availability of imipramine hydrochloride products. Revenue potential is therefore more likely to come from niche supply and differentiated positioning than from broad market expansion.

The most viable commercial models are:

1. A low-cost generic capsule with three or four strengths.
2. A supply-continuity product for distributors and institutional buyers.
3. A smaller or easier-to-swallow capsule.
4. A sprinkle or liquid product for patients with administration barriers.
5. A modified-release product if clinical and regulatory economics support development.
6. Regional licensing where existing manufacturers lack a pamoate product.

A standard ANDA may have the shortest path to revenue but the weakest margin profile. A 505(b)(2) formulation may command better pricing but carries higher development, clinical, and regulatory risk.

How strong is the patent estate for imipramine pamoate?

The patent estate is weak as a blocking asset and potentially useful only as a platform for new formulation claims. A new applicant could seek protection for:

• Specific excipient ratios.
• Particle-size ranges.
• Controlled-release coatings.
• Multiparticulate systems.
• Improved dissolution profiles.
• Moisture-stabilized capsule compositions.
• Sprinkle administration.
• Palatable liquid compositions.
• Manufacturing processes that produce defined solid-state properties.

Such claims would need to satisfy novelty, nonobviousness, written-description, enablement, and utility requirements. Broad claims covering imipramine pamoate with routine pharmaceutical excipients would face substantial obviousness risk.

Key Takeaways

• Imipramine pamoate is a mature small-molecule product with no meaningful original patent or exclusivity barrier.
• The commercial opportunity is generic supply, formulation differentiation, and reliable availability.
• Pamoate’s lower solubility makes wetting, particle-size control, dissolution, and capsule disintegration central development priorities.
• A conventional immediate-release capsule is the lowest-risk product strategy.
• Sprinkle, liquid, multiparticulate, and modified-release products offer greater differentiation but may require 505(b)(2) development.
• No biosimilar pathway applies.
• Paragraph IV litigation risk is likely limited unless a current Orange Book-listed patent exists for the specific reference product.
• Supply continuity, API qualification, and distributor access may matter more than patent exclusivity.
• New formulation patents would need narrow, data-supported claims because broad excipient combinations are vulnerable to obviousness challenges.

FAQs

Can imipramine pamoate be formulated as an oral liquid?

Yes, but the product would require control of solubility, taste, chemical stability, microbial quality, preservative performance, and dose uniformity. A suspension may be more practical than a true solution because of the pamoate salt’s limited aqueous solubility.

Is imipramine pamoate interchangeable with imipramine hydrochloride?

No. The salt forms and dosage forms differ. Therapeutic interchangeability depends on the specific FDA-approved product and its therapeutic-equivalence designation.

What is the most defensible commercial formulation for imipramine pamoate?

A multi-strength immediate-release capsule with reproducible dissolution, strong humidity stability, and dependable supply is the most defensible low-risk strategy. A modified-release or sprinkle product has more differentiation but higher regulatory risk.

Can a novel excipient create new exclusivity for imipramine pamoate?

A novel excipient alone does not guarantee exclusivity. Protection would generally depend on patentable formulation claims, regulatory approval, and evidence that the composition provides a non-obvious technical or clinical benefit.

Is imipramine pamoate suitable for a 505(b)(2) product?

It may be suitable where the product introduces a materially different dosage form, release profile, route, or administration method. The commercial case is strongest when the change addresses swallowing, dosing frequency, palatability, or adherence.

References

1. U.S. Food and Drug Administration. (2023). Imipramine pamoate capsule prescribing information. DailyMed.

2. U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. Orange Book.

3. U.S. Food and Drug Administration. (2020). Guidance for industry: ANDAs for certain highly variable drugs. Center for Drug Evaluation and Research.

4. United States Pharmacopeia. (2024). United States Pharmacopeia and National Formulary: Imipramine hydrochloride and related monographs. U.S. Pharmacopeial Convention.