A closed system transfer device, or CSTD, is a piece of medical equipment designed to prevent hazardous drugs from escaping into the air or onto surfaces during preparation and administration. These devices are primarily used in hospitals and pharmacies where staff handle chemotherapy drugs and other medications that can cause harm through skin contact, inhalation, or accidental spills. By mechanically sealing the drug transfer process, CSTDs protect nurses, pharmacists, and technicians from repeated low-level exposure to toxic compounds.
Why CSTDs Exist
Dozens of drugs used in healthcare settings, particularly chemotherapy agents, are classified as hazardous. The CDC maintains a regularly updated list of these drugs, most recently revised in 2024. Workplace exposure to these medications, even in tiny amounts over time, has been linked to skin rashes, infertility, spontaneous abortions, congenital malformations, and possibly leukemia and other cancers. These risks affect anyone who regularly handles the drugs: pharmacists who mix them, nurses who hang IV bags, and technicians who transport or dispose of them.
Before CSTDs became standard, healthcare workers relied on safety cabinets, gloves, gowns, and careful technique to minimize exposure. Those measures help, but they can’t fully prevent drug particles or vapors from reaching the worker during the moment a syringe connects to a vial or an IV bag gets spiked. That brief, repeated point of transfer is exactly what CSTDs are engineered to seal off.
How a CSTD Works
A typical CSTD is a set of interlocking plastic components that replace the standard needle-and-syringe approach to moving liquid drugs between containers. The system usually includes a vial adaptor (which locks onto the drug vial with a spike or plastic connector and clips that grip the vial’s neck), a matching syringe attachment, and sometimes a bag spike for connecting to an IV bag. Once attached, these components create a sealed pathway so the drug can be drawn up, transferred, and administered without any opening to the outside environment.
CSTDs use one of two design approaches to achieve that seal. The first is a physical barrier: the device is mechanically closed at every connection point, so no liquid, aerosol, or vapor can cross the boundary between the drug and the surrounding air. The second approach uses air-cleaning technology, typically a filter that scrubs drug particles from any air that exits the system during pressure equalization.
This distinction matters more than it might seem. A physical-barrier CSTD blocks everything, liquid and vapor alike, because there is simply no opening. An air-cleaning CSTD lets filtered air pass through, which works well for drugs that only produce liquid droplets or aerosols. But for drugs that generate vapor (molecules in gas form), filtration can be unreliable. The effectiveness of a filter depends on the specific chemical properties of the drug it contacts, meaning an air-cleaning device that contains one drug’s vapor may not contain another’s. For drugs with known or uncertain vapor-generating potential, physical-barrier designs offer more consistent protection.
Proven Reduction in Contamination
Studies measuring surface contamination in pharmacies show meaningful reductions when CSTDs replace traditional transfer methods. A comparative study from China tested contamination levels at multiple locations in the compounding area, including countertops, air-intake vents, door handles, and the glass interior of the safety cabinet. For cyclophosphamide, a widely used chemotherapy drug, contamination dropped between 23% and 68% depending on the surface measured. For cytarabine, another common agent, reductions ranged from 12% to 70%.
The protective effect extended to workers’ personal equipment as well. Contamination on pharmacists’ masks decreased by roughly 48% for cyclophosphamide and 18% for cytarabine. Glove contamination fell by about 50% and 42%, respectively. These aren’t perfect numbers, which is why CSTDs are considered one layer of protection rather than a replacement for gloves, gowns, and ventilated safety cabinets.
When CSTDs Are Required
In the United States, the key regulatory standard is USP Chapter 800, which governs how healthcare facilities handle hazardous drugs. Its requirements draw a clear line between two activities: compounding (mixing or preparing a drug) and administration (giving it to a patient).
For administration of antineoplastic (cancer-fighting) hazardous drugs, CSTDs are mandatory when the dosage form allows it. Some drug formulations, such as certain tablets or topical preparations, simply aren’t compatible with a transfer device, but for injectable drugs, there is no exception. For compounding, the language is slightly different: CSTDs “should” be used when the dosage form allows, but they must not be used as a substitute for a ventilated safety cabinet. In other words, during preparation you still need the cabinet, and the CSTD works inside it as an added layer of containment.
The FDA classifies CSTDs as Class 2 medical devices under the product description “closed antineoplastic and hazardous drug reconstitution and transfer system.” This means manufacturers must meet specific performance and safety standards before their devices can be marketed, including compliance with international sharps-injury protection requirements.
Components of a Typical System
While designs vary by manufacturer, most CSTDs share a few core components:
- Vial adaptor: Attaches to the drug vial, usually with a spike that punctures the rubber stopper and locking clips that grip the vial’s neck. This replaces the traditional method of inserting a bare needle through the stopper.
- Syringe connector: A port on the distal end of the vial adaptor that interfaces with a matching syringe attachment, allowing you to draw up drug without exposing any liquid or vapor to the air.
- IV bag spike or line connector: Used to transfer the prepared drug into an IV bag or connect directly to a patient’s IV line, maintaining the sealed pathway from vial to patient.
It is worth noting that vial adaptors sold separately (outside a full CSTD system) may eliminate needle use but are not necessarily designed to prevent vapor or aerosol exposure. A true CSTD is an integrated system where every connection point is sealed, not just needle-free.
Limitations to Understand
CSTDs reduce exposure, but they do not eliminate it entirely. Surface contamination studies consistently show improvement, not perfection. Drug residue can still appear on surrounding surfaces, likely from moments before or after the CSTD is engaged, such as wiping a vial or disconnecting a line.
The vapor question remains one of the most important practical limitations. NIOSH has been working on a unified testing protocol that can evaluate both physical-barrier and air-cleaning CSTDs under the same conditions. Until that standard is finalized, healthcare facilities choosing between device types need to consider which drugs they handle most frequently and whether those drugs are known to produce vapors. For drugs with uncertain vapor profiles, physical-barrier devices are the more conservative choice.
CSTDs also add cost and complexity to the drug preparation workflow. Each transfer requires specific compatible components, and not every drug vial or container is designed to interface smoothly with every CSTD brand. Compatibility between the drug’s packaging and the device’s connectors is a real-world concern that facilities evaluate before adopting a system.