By: David O’Connell, BSc (Hons), Director of Scientific Affairs, PCI Pharma Services
The newest generation of small-molecule therapies bring containment needs well beyond those of conventional HPAPIs. What does this mean for the pharma lexicon – and the pharma landscape?
For decades, “high potency” has served as the industry’s sweeping term to define active pharmaceutical ingredients (APIs) requiring specialized handling, exacting engineering controls and risk-based containment. The acronym “HPAPI” has become a mainstay of everything from regulatory language and internal production guidelines to infrastructure manuals and outsourced service offerings. And yet, as the potency landscape continues to evolve, this designation increasingly fails to capture the above-and-beyond demands of next-generation molecules.
A burgeoning subset of small-molecule therapies – including targeted protein degraders (TPDs) like PROTACs, SERDs and molecular glues, and certain antibody-drug conjugate (ADC) payloads – now exhibit substantially greater potency, narrower therapeutic indices and more complex toxicology than the legacy compounds comprising the original HPAPI category. Their behaviors and requirements often extend far beyond the purviews of traditional high-potent facilities, forcing both pharma companies and contract development and manufacturing organizations (CDMOs) to rethink or even reinvent risk management protocols.
Amid this shift, a newer term has surfaced: ultra-high potency. Though neither formally recognized by regulators nor universally used, the phrase aptly reflects a practical need to distinguish compounds occupying the uppermost rungs on the potency ladder.
The underlying point is clear: pharmacological science has outgrown current designations and categories. And as therapies evolve, so must their classifications – officially recognized or not.
Term Limits: The Constraints of Existing Pharma Phraseology
Despite its ubiquity, “HPAPI” has no harmonized global definition. When classifying potency, most organizations operate under long-established markers: for example, therapeutic doses at or below 1 mg/day, occupational exposure limits (OELs) at or below 10 μg/m³, and toxicological profiles where even minor exposure deviations can cause harm.
Approximately 30-50% of new small molecules now fall under this broad HPAPI umbrella. Such an inclusive view is problematic, as it groups together compounds with wildly different hazard profiles. For instance, a cytotoxic drug with an OEL of around 5 μg/m³ may sit in the same category as a TPD requiring sub-microgram-level containment.
While formal OELs for many emerging modalities are not yet widely published, their catalytic mechanisms, very low therapeutic doses and evolving safety profiles suggest a need for much tighter containment than conventional high-potent compounds. Their exposure limits, mechanism-driven toxicity and operational parameters differ materially – yet the terminology does not.
The result is a vocabulary that no longer reflects reality. As more assets enter the highest potency bands, the lack of distinction between “highly potent” and “ultra-highly potent” compounds creates ambiguity that affects risk assessment, facility selection and program planning.
Three key industry developments in particular have accelerated this challenge:
A more sophisticated therapy pipeline. Precision oncology, TPDs, molecular glues and other mechanism-driven modalities have introduced potency levels beyond what many legacy HPAPI facilities were designed to handle.
Heightened outsourcing complexity. CDMOs increasingly receive early-stage assets with extreme potency profiles, often before comprehensive toxicology is available. In such scenarios, a sponsor generally defaults to the only familiar term available – HPAPI – only to subsequently discover that the compound requires substantially tighter containment.
Ambiguous capability differentiation. While many CDMOs can safely handle Occupational Exposure Bands (OEB) 3-4, far fewer can operate confidently at OEB 5-6. Without clearer language, sponsors struggle to distinguish between routine high-potent support and facilities equipped for the uppermost potency bands.
Loftier Lexicon: Where “Ultra-High Potency” Applies
“Ultra-high potency” has gained traction as a functional way to identify molecules assigned to the upper limits of occupational exposure banding, typically OEB 5-6, where expected OELs fall below 1 μg/m³ and, in some cases, into the 0.1–0.01 μg/m³ range. While the term lacks official recognition, in practice it is certainly no understatement: from the earliest stages, an “ultra-high potency” designation shapes formulation decisions, containment strategy and program feasibility.
Crucially, what distinguishes these molecules is not merely their potency but also the nature of their biological activity. Many induce protein degradation or multi-pathway signaling, making off-target effects less predictable and necessitating more conservative occupational protection strategies. In addition, their ultra-low therapeutic doses narrow manufacturing tolerances and increase the consequences of cross-contamination; this prompts the need for highly sensitive analytical methods, enhanced cleaning strategies and stricter segregation.
In short, the term has emerged because these compounds exceed the assumptions embedded in the traditional HPAPI label. For biotechnology companies and other early-stage innovators, discovering that a molecule sits in this “upper tier” has immediate implications. These include:
Earlier, more exacting technical planning. Ultra-potent assets require pristine, multilayered high-containment manufacturing. Many HPAPI-labeled sites were designed and constructed to accommodate mid-range potency and, as a result, lack the rigid-wall isolators, closed transfers, engineered airflow and segregation required for sub-microgram OELs. Unfortunately, such containment shortcomings often become evident only upon detailed risk assessments.
Elevated analytical demands. With ultra-high potency products, cleaning validation, environmental monitoring and residue analysis must operate at significantly lower detection limits. Achieving this requires state-of-the-art analytical solutions, highly sensitive methods and specialized expertise; notably, such attributes often are necessary earlier than a sponsor anticipates.
Narrower process windows and increased cost. Ultra-high potency molecules frequently require micro-batches, bespoke or miniaturized equipment, and a greater degree of automation to maintain containment and ensure dose uniformity. The combination of strict containment, analytical sensitivity and reduced operational flexibility increases complexity and cost, particularly for smaller organizations.
Higher regulatory and reputational stakes. A containment failure involving an ultra-potent compound can have serious consequences. Developers must understand a CDMO’s OEB assignment process, containment verification history and environmental monitoring performance before selecting a partner.
Speaking the Same Language: What “Ultra-High Potency” Means for CDMOs
For outsourcing partners, this emerging designation underscores a widening capabilities gap. To truly be considered worthy of handling ultra-high potency applications, CDMOs must pass muster across four critical categories:
Capabilities transparency. Simply stating HPAPI capability is no longer sufficient. Savvy sponsors now demand clarity concerning precisely which OEB bands a facility can support, how containment levels have been verified, and how often they are retested.
Robust, validated infrastructure. Facilities handling ultra-potent assets require isolators tested to extremely low OELs, integrated and automated material transfers, engineered containment systems and continuous particulate monitoring – all backed by rigorous maintenance and periodic reverification.
Advanced analytical infrastructure. Operating at ultra-high potency levels demands analytical methods with exceptionally low limits of detection, as well as the expertise to develop and validate such protocols.
Specialized workforce and culture. Extreme potency handling requires disciplined training, deep understanding of toxicology, and a culture in which deviation-free execution is the norm. This expertise remains rare, and is decisive.
Considering these high hurdles, CDMOs capable of supporting early-stage work, scale-up and clinical supply at validated OEB 5-6 levels will play an increasingly central role as the global drug development pipeline continues to shift toward ultra-highly potent products.
Whether or not “ultra-high potency” eventually becomes an officially recognized category, the facts on the ground – or in this case, on the facility floor – remain unchanged. While words matter, actions matter more. Lifesaving therapies aren’t developed and manufactured in regulatory rulebooks, internal protocol documents, or any other literature. They are produced in pharmaceutical facilities, by pioneering development experts and the partners that serve them.
In other words, words are just… well, words. It’s what we as an industry do with them that matters. To that end, the essence of “ultra-high potency” is a clear, consistent acknowledgement that traditional HPAPI designations no longer captures the full potency spectrum. Used carefully and correctly, it helps distinguish between classical high-potent APIs and molecules demanding significantly more advanced containment. Understanding these delineations will guide sponsors toward partners capable of safely managing ultra-high potency assets.
As modern drug development continues to push into the uppermost potency bands, a more nuanced vocabulary helps the industry align expectations, assess risk and make informed decisions. The emergence of “ultra-high potency” is best understood not as unnecessary or trendy terminology, but as a reflection of scientific progress – and, consequently, a prompt for clearer, more precise conversations about potency, risk and the future of advanced small-molecule manufacturing.
About the Author
David O’Connell, BSc (Hons) is Director of Scientific Affairs for PCI Pharma Services, a leading CDMO providing integrated end-to-end drug development, manufacturing and packaging capabilities that increase products’ speed to market and opportunities for commercial success. In his current role, O’Connell aids clients with formulation development, technical transfer and scale-up of solid oral, oral liquid and semi-solid products for clinical trials and/or commercialization.