A Highly Potent Active Pharmaceutical Ingredient (HPAPI) can be defined as a pharmaceutical compound with a low Occupational Exposure Limit (OEL).

The Occupational Exposure Limit (OEL) defines the maximum amount of product to which an operator can be exposed in a defined time frame without risking short-term and long-term effects on personal health. The OEL of each pharmaceutical compound is defined through laboratory studies and by toxicologists. All compounds with low OEL are considered highly potent: a specific value of 10µg/m³ is defined as the threshold limit for an HPAPI. Mitigation of the risk and hazard to human health from handling (high risk) HAPIs  can only be achieved through the adoption of containment systems that ensure total separation of the product from the environment and total protection of the operator, who handles the powder inside the isolator through glove ports and wears a special suit.