What Makes a Compound High Potency?
The term high potency active pharmaceutical ingredient (HPAPI) refers to any compound with significant biological activity at very low doses, typically below 1 milligram per day in humans, or with occupational exposure limits in the microgram per cubic metre range. The category includes cytotoxic oncology agents, hormonal compounds, certain immunosuppressants, and novel targeted therapies with high receptor affinity.
The manufacturing challenge with HPAPIs is not the chemistry itself, which may be no more complex than for conventional APIs, but the containment required to protect operators and the environment from exposure to a compound that causes harm at extremely low concentrations. The engineering controls, facility design, and operational procedures needed to handle HPAPIs safely are substantially different from those applicable to conventional pharmaceutical manufacturing, and they must be in place before any GMP manufacturing campaign begins.
The Occupational Exposure Banding Framework
Occupational exposure banding (OEB) is the standard industry framework for classifying the hazard of a pharmaceutical compound based on its potency, toxicology profile, and pharmacological activity, and for defining the corresponding engineering controls required for safe handling. The ISPE guide to risk-based manufacture of pharmaceutical products and guidance from the American Industrial Hygiene Association (AIHA) provide frameworks for OEB classification. Most CDMOs use a five-band or six-band system, with Band 4 and Band 5 requiring the most stringent containment.
| OEB Band | OEL Range (8-hour TWA) | Typical Compound Types | Required Containment Level |
| OEB 1 | Greater than 1 mg/m3 | Conventional APIs with low hazard | Standard pharmaceutical engineering controls |
| OEB 2 | 0.1 to 1 mg/m3 | APIs with moderate potency | Local exhaust ventilation; PPE |
| OEB 3 | 0.01 to 0.1 mg/m3 | Potent APIs; some hormones | Closed or semi-closed processing; enhanced PPE |
| OEB 4 | 0.001 to 0.01 mg/m3 (1 to 10 micrograms/m3) | Cytotoxics; HPAPIs; most ADC payloads | Containment isolators or RABS; dedicated facilities or rigorous decontamination |
| OEB 5 | Below 0.001 mg/m3 (below 1 microgram/m3) | Genotoxic compounds; highly potent cytotoxics; TCDD-like compounds | Dedicated facility; full containment isolators; continuous air monitoring; stringent decontamination validation |
OEL ranges above represent typical band definitions and may vary between organisations and classification systems. Compound-specific OELs should always be established by qualified industrial hygienists.
Engineering Controls: The Hierarchy of Protection
The occupational health principle of the hierarchy of controls applies directly to HPAPI manufacturing. Elimination and substitution are rarely options for an API that is the entire point of the product. Substitution with a less hazardous alternative may be possible at the discovery stage but not at the development stage. Engineering controls, specifically containment technology, are therefore the primary means of protecting operators.
Closed Handling Systems
At OEB 3 and lower OEB 4, closed handling systems including contained transfer systems and split butterfly valves allow material to be transferred between vessels and equipment without operator exposure. These systems are widely used in pharmaceutical manufacturing for potent materials and do not require a dedicated facility.
Containment Isolators
For OEB 4 and OEB 5 compounds, manufacturing operations must be conducted inside containment isolators: sealed enclosures with integrated glove ports that allow operators to manipulate materials inside without direct contact. Isolators maintain negative pressure relative to the surrounding environment, ensuring that any leak is inward rather than outward. Decontamination of the isolator between campaigns is typically achieved using hydrogen peroxide vapour or other validated decontamination agents.
Facility Design
At the highest potency levels, dedicated facilities with separate HVAC systems, airlocks, and personnel decontamination facilities are required. The facility must be validated to demonstrate that decontamination procedures achieve adequate removal of the compound from surfaces and that the HVAC system prevents cross-contamination with less potent products. Continuous environmental monitoring for HPAPI compounds in work area air is standard practice at OEB 4 and 5.
Process Design for HPAPI Manufacturing
Containment is not only about the physical infrastructure. The manufacturing process itself must be designed to minimise the number of open handling steps, reduce the generation of dust and aerosols, and simplify the decontamination requirements. Process design considerations for HPAPI manufacturing include using wet granulation rather than dry granulation where the API is amenable, minimising the number of charging and discharging operations, and using in-line or at-line analytical methods that do not require sample removal from the contained environment.
Ardena’s HPAPI Manufacturing Capability at Pamplona
Ardena’s Pamplona (Idifarma) facility in Spain provides OEB 3, 4, and 5 manufacturing capability for high potency API and drug product development and GMP manufacturing. The site is equipped with containment isolators for handling at the highest potency levels, dedicated HPAPI suites with appropriate HVAC segregation, and validated decontamination procedures.
Pamplona’s HPAPI capability supports both drug substance synthesis and drug product manufacturing for oral solid and injectable dosage forms, covering the full manufacturing chain for oncology compounds, ADC payloads, and other high-potency molecules from pre-GMP development through to clinical batch supply.
