Topical drug products can look promising in early development and still encounter serious performance issues later in the program. For sponsors developing creams, ointments, gels, lotions, foams, sprays, or transdermal products, those issues can be especially frustrating because they are not always obvious at the beginning. A formulation may appear acceptable at the bench, meet early expectations, and even move into stability or clinical planning before deeper problems begin to appear.
For CPL, these challenges are familiar because topical and semi-solid products have been the company’s focus for decades. Underperformance is rarely caused by one isolated issue. More often, it reflects a combination of formulation design, material behavior, process assumptions, patient usability, and stability concerns that were not fully understood early enough in development.
When Efficacy Depends on More Than the API
One of the most common reasons topical products underperform is that the drug is not being delivered effectively from the formulation. Even when the active pharmaceutical ingredient is appropriate for the indication, the formulation matrix must support the right drug release, skin penetration, and thermodynamic activity. If the API is not released from the cream, ointment, or gel in a meaningful and consistent way, the product may fail to deliver the expected clinical benefit.
This is why topical formulation cannot be treated as a simple exercise in combining an API with acceptable excipients. The formulation itself plays a direct role in performance. The vehicle must be chosen and optimized based on where the drug needs to act or targeted site of action, how it behaves chemically, how it interacts with excipients, and how it moves through or into the skin.
For products targeting conditions such as atopic dermatitis, psoriasis, acne, or localized pain, the site of action matters. A formulation intended to reach the dermis may require a different vehicle strategy than one designed for a more superficial epidermal target. Without that understanding, a product may look correct on paper but fail to perform in practice.
The Patient Experience Can Make or Break a Topical Product
Topical products also depend heavily on patient compliance. A formulation can be scientifically sound and still struggle commercially or clinically if patients do not want to use it.
If a product is too greasy, sticky, oily, stiff, gritty, difficult to spread, or unpleasant on the skin, patients may apply it inconsistently or avoid using it altogether. That can make a product appear less effective, even when the API and basic formulation concept are reasonable.
This is especially important for chronic skin conditions, where patients may need to apply a product repeatedly over a long period of time. An ointment that feels heavy or does not spread well may create adherence issues. A cream with poor texture may cause patients to stop using it. A product that is difficult to squeeze from the tube may create a problem before it ever reaches the skin.
For CPL, topical performance includes both technical performance and practical usability. The product must release the drug, remain stable, scale properly, and feel acceptable enough for patients to actually use it as intended.
Stability Issues Often Appear Later Than Sponsors Expect
Another common source of underperformance is stability. Some products behave well during early development but begin to change over time. These changes may appear during accelerated stability studies, long-term stability, clinical supply storage, or later commercial planning.
A topical product may experience viscosity loss, phase separation, changes in texture, differences in rheological behavior, API degradation, impurity formation, or altered release profile. For creams and other emulsions, instability can be especially challenging because the formulation depends on a carefully balanced relationship between oil phase, aqueous phase, emulsifiers, thickeners, and processing conditions.
A product may appear stable at the lab scale but behave differently after months of storage or after scale-up. Sponsors that rush development timelines may not give the formulation enough time to demonstrate whether it is truly robust. That risk can become costly when problems appear after clinical plans, regulatory discussions, or manufacturing commitments are already underway.
Why Creams and Ointments Can Be Especially Challenging
While topical dosage forms all have unique challenges, creams and ointments are often among the most complex. Creams are emulsions, which means two different phases must be brought together and maintained in a stable, uniform structure. If the emulsifier system is not properly selected, if the oil and water phases are not balanced, or if the manufacturing process is not optimized, the product can lose stability over time.
Microscopic structure matters. If oil globules are not uniform, if the internal phase is poorly distributed, or if the cohesive network is weak, the product may eventually separate or fail to deliver the drug consistently. These issues may not be obvious from appearance alone.
Ointments bring a different set of challenges. They may be too stiff, too greasy, too difficult to apply, or too dependent on small changes in excipient grade or processing conditions. A product that appears ideal from a drug solubility or stability standpoint may still fail because it is not functional for patients or clinical sites.
Material Variability Can Undermine a Formulation
Critical material attributes are another major source of hidden risk. Many excipients used in topical products have broad supplier specifications. A thickener, for example, may technically meet the vendor’s specification while still behaving differently from batch to batch.
During early development, a sponsor may only test one portion of that material range simply because other lots are unavailable. The formulation may perform well with that specific material lot, but later fail when a commercial or clinical batch uses material at the lower or higher end of the supplier’s specification.
Similarly, the physical form of the API present in the dosage form should be carefully evaluated. Dispersed versus solubilized, as well as the polymorphic form affect the drug release and therapeutic efficacy.
This is where Quality by design becomes important. If the formulation is not challenged against the realistic variability of its raw materials, sponsors may not know whether it is truly robust. A batch may pass once or twice because the material attributes happen to align, but later fail when the same approved material behaves differently.
Process Assumptions Can Create Scale-Up Problems
Topical products are also highly sensitive to processing parameters. Mixing time, temperature control, order of addition, homogenization, cooling rate, vacuum, and equipment selection can all affect the final product.
A process that works at the bench may not be practical or reproducible at commercial scale. A twenty-hour mixing step may be manageable in a small lab batch, but it is not a realistic commercial manufacturing strategy. If process and unit operations are not considered early, a product may reach Phase II or clinical supply planning before sponsors discover that the original process cannot scale.
This is why CPL views formulation and process development as connected from the beginning. A topical product should not simply work in the lab. It should be designed with future scale-up in mind.
Generic Topicals Face Additional Bioequivalence Challenges
For generic topical products, underperformance may also appear as a bioequivalence failure. These products often need to match a reference product not only in qualitative (Q1) and quantitative composition (Q2), but also in microstructure and performance (Q3).
Small differences in excipient levels, globule size, rheological behavior, or drug release can create meaningful differences in IVRT, IVPT, or other performance testing. On paper, two products may appear similar. In practice, their internal structure and release behavior may not match closely enough to support the regulatory pathway.
This is one reason topical generics can be so technically demanding. Matching the ingredients is only part of the challenge. Sponsors also need to understand how those ingredients behave together, how the process affects the drug product quality, and how the final dosage form performs.
The Earlier the Problem Is Found, the Easier It Is to Solve
Sponsors often discover underperformance at different stages. Some identify issues during formulation development or early stability. Others do not see problems until six-month accelerated stability, eighteen-month long-term stability, clinical supply preparation, or even after toxicology work has already been completed.
The later the issue appears, the more complicated the solution becomes. Reformulation after clinical, toxicology, or regulatory milestones can force sponsors to repeat work, revise documentation, or justify changes to the agency. In some cases, a formulation change may require additional testing that could have been avoided with a more complete development strategy upfront.
For CPL, the message is straightforward: topical reformulation is possible, but prevention is always better than rescue. Sponsors should involve experienced topical formulation experts as early as possible, particularly when the product involves complex excipients, multiple APIs, an emulsion system, challenging stability expectations, or a specific skin delivery target.
Building Better Topicals Starts With Better Questions
Underperforming topical products are often the result of questions that were not asked early enough. Is the API dissolved or dispersed and stable in this vehicle? Does the product release the drug appropriately? Is the formulation aesthetically acceptable? Are the excipients compatible? Has the process been challenged for scale-up? Has raw material variability been considered? Does the product match the intended QTPP?
These questions are central to CPL’s approach. With decades of experience focused on semi-solids and liquids, CPL helps sponsors look beyond the surface of a formulation and understand the technical details that determine whether a topical product can succeed.
For sponsors facing an underperforming topical drug product, the first step is not simply to change an excipient or adjust a process. It is to understand why the product is underperforming in the first place. Once that root cause is understood, reformulation can become a targeted strategy rather than a costly reset.