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Medication Spray During Vial Access

The Role of Pressure and Air

Published research has documented how vial pressurization can contribute to medication spray, aerosolization, medication loss, and occupational exposure.

Damea Alexander
Founder & CEO, Alexander International Innovations | Nurse | Inventor
Published August 2026

Why This Matters

Anyone who routinely prepares medications from vials may have seen it: a needle is withdrawn from a vial and a small amount of liquid suddenly sprays from the puncture site.

Sometimes the event is obvious. Sometimes it is only a few droplets. And sometimes it may be small enough to go largely unnoticed.

It can be tempting to dismiss the event as a minor inconvenience of medication preparation. Published guidance, however, identifies the underlying mechanism as an important medication-handling and occupational-safety issue.

The problem is pressure.

A medication vial is a closed container. When air or liquid is introduced, removed, or exchanged, the pressure inside that container can change. If pressure inside the vial becomes greater than the surrounding atmospheric pressure, that pressure seeks a pathway to escape.

The puncture created in the vial’s elastomeric closure can provide one.

And medication can leave with it.

Evidence Reviewed

ASHP Guidelines on Handling Hazardous Drugs

Power LA, Coyne JW.ASHP Guidelines on Handling Hazardous Drugs. American Journal of Health-System Pharmacy. 2018;75(24):1996–2031.

The American Society of Health-System Pharmacists specifically addresses vial pressure during medication preparation. ASHP advises that pressurizing hazardous-drug vials should be avoided because excessive pressure can cause medication to escape around the needle, through the puncture site, or through an imperfect seal and become aerosolized in the work area.

View Original Publication → https://academic.oup.com/ajhp/article/75/24/1996/5248544

OSHA — Controlling Occupational Exposure to Hazardous Drugs

The Occupational Safety and Health Administration similarly identifies vial pressurization as a potential source of drug escape. OSHA guidance warns that pressurization can place stress on the vial septum and allow hazardous drug material to aerosolize and escape.

View OSHA Guidance → https://www.osha.gov/hazardous-drugs/controlling-occex

Together, these sources establish an important point:

Pressure-driven medication escape from vials is a recognized physical and occupational-safety phenomenon.

Understanding What Happens Inside the Vial

A medication vial contains two major internal spaces: the liquid medication and the headspace, or gas-filled space above the liquid.

The pressure within that headspace is not necessarily equal to atmospheric pressure outside the vial.

Introducing air into the vial can increase internal pressure. Removing medication without replacing sufficient volume can decrease internal pressure. Repeated manipulation can change the pressure relationship again.

The elastomeric stopper normally maintains the vial as a closed container. Inserting a needle temporarily creates a pathway through that barrier.

During needle withdrawal and immediately following removal, the puncture pathway can provide a transient route between the vial interior and the surrounding environment. If pressure inside the vial is greater than atmospheric pressure while that pathway is available, the pressure gradient favors movement outward.

Gas can escape. If liquid medication is present at or near that pathway, medication can be expelled with it.

The result may appear as droplets, spray, mist, or aerosolized material.

The amount released can depend on multiple variables, including the magnitude of the pressure difference, vial orientation, medication characteristics, needle size, puncture characteristics, and provider technique.

But the underlying principle is straightforward:

When a pathway exists, pressure moves from an area of higher pressure toward an area of lower pressure.

In Plain Language

Think of the vial as a small closed container.

If there is more pressure inside than outside, that pressure wants to escape.

The needle puncture provides a pathway.

When the needle comes out, air can escape through that pathway—and liquid medication can come with it.

That is the spray clinicians sometimes see when accessing medication vials.

Why Medication Spray Matters

For hazardous medications, occupational exposure is an obvious concern. ASHP, OSHA, and NIOSH have all addressed the importance of reducing healthcare-worker exposure to hazardous drugs.

But the underlying physical phenomenon is not exclusive to hazardous medications.

Pressure is pressure.

The reason hazardous-drug literature discusses spray so explicitly is that the potential consequences of exposure make containment particularly important. The same fundamental pressure mechanics can exist when other medications are prepared from sealed vials.

That broadens the issue.

Even when occupational toxicity is not the primary concern, visible medication leaving the vial represents something else:

Medication loss.

Medication that lands on a work surface, glove, vial exterior, or surrounding area is medication that is no longer available for administration.

With inexpensive medications, a small amount may seem inconsequential. With expensive medications, biologics, controlled substances, medications supplied in limited quantities, or drugs requiring precise dose accountability, the significance can be very different.

A small spray event may occur in a fraction of a second.

But the medication leaving the vial is real.

Technique Matters—But Technique Varies

Traditional medication-preparation techniques attempt to manage vial pressure.

ASHP’s hazardous-drug guidance, for example, describes exchanging air and liquid in controlled amounts and maintaining slight negative pressure during certain vial manipulations.

That approach makes physical sense.

If positive pressure contributes to outward spray, reducing positive pressure reduces the driving force behind it.

But it also highlights another issue:

Pressure management depends on technique.

Different clinicians may introduce different amounts of air. They may withdraw medication at different rates, use different syringe sizes, position the vial differently, or compensate for pressure differently.

Even experienced clinicians are still performing a manual pressure-balancing process.

That introduces provider-to-provider variability into a process governed by basic physical forces.

For Alexander International Innovations, this led to a different question:

Instead of relying entirely on clinicians to manage pressure consistently, can the system itself make pressure management more consistent?

The AII Perspective

AII’s investigation of medication spray grew from direct observation of the phenomenon during vial access.

Repeated observations demonstrated visible spray following needle withdrawal under conventional vial-access conditions. AII subsequently documented the phenomenon using slow motion video, making an event that can occur in a fraction of a second much easier to observe.

The observation aligned closely with the mechanism described in published guidance:

Vial pressure can drive medication outward when a pathway becomes available.

That raised an engineering question:

What if vial pressure could be managed without relying entirely on the clinician to manually balance air and liquid?

I2F — Improved Fluid Flow — was developed to change how air and pressure are managed during medication preparation.

By providing a filtered pathway for air movement, I2F changes the pressure dynamics within the vial.

The objective is straightforward:

Reduce the pressure differential capable of driving medication outward during vial access.

Under the conditions evaluated, AII has repeatedly observed visible medication spray during conventional vial access and a substantial reduction in visible spray when I2F is used.

The difference has also been documented through comparative video observation.

Seeing the Difference

Comparative observation of medication spray following vial access. AII has repeatedly documented a substantial reduction in visible spray when I2F is used under the conditions evaluated.

Spray can occur extremely quickly during routine medication preparation. A clinician may recognize the phenomenon without ever having had an opportunity to examine the event closely.

Video comparison allows the event to be slowed, repeated, and directly compared.

More importantly, it allows the reader to see the phenomenon rather than simply read a description of it.

Why Standardization Matters

The objective of I2F is not simply to compensate for poor technique.

Experienced clinicians can—and routinely do—use pressure-management techniques during vial access.

The larger issue is variability.

When pressure management depends primarily on individual technique, the result can vary with the person performing the procedure.

An engineering approach addresses the problem differently.

Instead of requiring every provider to reproduce exactly the same pressure-management technique every time, the system itself can help create more consistent physical conditions.

Training attempts to control variability in human behavior.

Engineering attempts to reduce how much the process depends on that variability in the first place.

Both have value.

But they address different parts of the problem.

What We Know—and What Comes Next

Published evidence and direct observation provide a strong foundation for understanding medication spray during vial access. The next opportunity is to quantify the phenomenon more precisely.

What Published Evidence Establishes

Published ASHP guidance recognizes vial pressurization as a mechanism capable of causing medication to spray or escape from a vial and become aerosolized.

OSHA similarly recognizes vial pressurization as a mechanism by which hazardous drug material can aerosolize and escape.

Occupational contamination and exposure to hazardous medications are well-documented concerns in healthcare environments.

Together, this evidence establishes the physical and occupational relevance of pressure-driven medication escape during vial access.

What AII Has Demonstrated

AII has repeatedly observed and video-documented visible medication spray following conventional vial access under the conditions evaluated.

AII has also repeatedly demonstrated a substantial reduction in visible spray when I2F is incorporated into comparable procedures.

These observations support the underlying engineering rationale: changing the way air and pressure are managed within the vial can change the visible spray behavior observed during access.

Where the Research Goes Next

The evidence reviewed above establishes an important foundation: pressure-driven medication escape from vials is a recognized physical phenomenon, and published guidance has long addressed its relevance to medication handling and occupational exposure.

AII’s observations build on that foundation. Under the conditions evaluated, AII has repeatedly observed and video-documented visible medication spray during conventional vial access and a substantial reduction in visible spray when I2F is incorporated into comparable procedures.

The next step is not simply to ask whether the phenomenon occurs. The next step is to characterize it more precisely.

Controlled research can quantify the amount of medication expelled during spray events, measure pressure changes within the vial, evaluate the influence of vial size and medication characteristics, examine provider-to-provider variability, and quantify the magnitude of spray reduction achieved when pressure is managed differently.

These studies can move the science from documented mechanism and repeatable observation to quantitative characterization—helping determine how much medication is expelled, under what conditions spray is most likely to occur, and how effectively it can be reduced.

A Small Event Worth Examining

Medication spray can happen in a fraction of a second.

That may be one reason it receives relatively little attention outside hazardous-drug handling.

But the mechanism is straightforward.

A vial contains medication, gas, and pressure. Manipulating that vial changes the relationship between them. When internal pressure exceeds external pressure and a pathway becomes available, material can move outward.

Published guidance has long recognized this problem when the medication involved poses an occupational hazard.

AII’s observations suggest there is value in examining the same phenomenon more broadly.

Medication escaping from a vial can represent occupational exposure, environmental contamination, medication loss, and variability in medication preparation.

That leads to a simple question:

Can we manage the air and pressure before the medication has an opportunity to escape?

For AII, that question helped shape the development of I2F.

It also represents another example of why seemingly small details in medication preparation deserve closer examination.

Every Drop Matters.

References

Power LA, Coyne JW. ASHP Guidelines on Handling Hazardous Drugs. American Journal of Health-System Pharmacy. 2018;75(24):1996–2031. doi:10.2146/ajhp180564.
View ASHP publication

Occupational Safety and Health Administration. Hazardous Drugs — Controlling Occupational Exposure to Hazardous Drugs.
View OSHA guidance

National Institute for Occupational Safety and Health. Antineoplastic Agents — Healthcare Workers.
View NIOSH resource

Human-Use Status: I2F has not been cleared or approved by the U.S. Food and Drug Administration for human clinical use and is not currently available for human use in the United States. References to potential human applications reflect scientific discussion and areas for future research; they should not be interpreted as established claims of safety, effectiveness, or clinical performance.

About the Author

Damea Alexander
Founder & CEO, Alexander International Innovations | Nurse | Inventor

Damea Alexander is the founder and CEO of Alexander International Innovations and the inventor behind I2F. His work focuses on identifying overlooked sources of variability, medication waste, and inefficiency in medication preparation and delivery and developing practical engineering approaches to address them.