In an ideal world, actual inventory counts would always match expected amounts. However, that is rarely the case and is particularly true when liquid controlled substances are dispensed to numerous patients by multiple individuals in a busy veterinary facility. Reconciliation challenges exist with every logging system regardless of whether you use manual logbooks, electronic logs or an automated dispensing unit.
Therefore, diligently identifying, investigating, resolving and reporting discrepancies in your practice’s controlled substance inventory within specific timeframes and without interrupting patient care is a battle that all veterinary professionals fight at some point. The responsibility can be exhausting, time-consuming, confusing and overwhelming, which is why the industry constantly seeks ways to improve the tracking of controlled substances. One answer is to weigh drugs.
Does weighing work? Are the weights reliable? Will doing it make the U.S. Drug Enforcement Administration look the other way? Let’s start by weighing the facts.
Government Protocols
Tracking controlled substances by weight is an ongoing debate in veterinary medicine. Federal guidelines for DEA practitioners do not specifically address the method. On the flip side, the DEA doesn’t discourage tracking by weight. The DEA doesn’t specify a particular way to track controlled substance usage but states that a practice’s logs must be accurate.
What else does the agency say about inventorying and tracking controlled substances? One requirement states that the inventory must be physically counted and include all controlled substances “on hand,” meaning in the possession of or under the control of the DEA registrant that ordered them.
The DEA mandates that practitioner registrants track controlled substance usage in dispensing logs. Some of the required information includes:
- The controlled substance’s name.
- Each finished form and the number of units or volume in each container. Is it a vial, ampule or bottle? Is it measured in milliliters or tablets?
- The date of manufacture, batch number or another identifier, possibly an expiration date or lot number.
- The activity performed, such as dispensing or administering.
In addition, when controlled substances are administered, DEA practitioner dispensing logs must include:
- The number of units or volume of each finished form dispensed.
- The name and address of the person to whom it was dispensed.
- The dispensing date.
- The name or initials of the person who dispensed or administered the controlled substance on behalf of the dispenser.
Whether you are dispensing, administering or both, you must keep a detailed record of all controlled substance usage.
What to Weigh
Generally, weighing is most effective when tracking containers of liquid controlled substances, while physical counts are best for tablets. From an accuracy and operational standpoint, counting tablets typically takes less time than weighing them.
Consistency is vital when weighing liquid controlled substances. That means weighing a container immediately upon receipt and before moving it unopened into back stock. Next, weigh the container once it’s opened and moved into active stock. Then, do it every time the controlled substance is extracted, and do a final weight during end-of-bottle counts.
When a controlled substance expires before its complete use, the container must be weighed and documented, removed from active stock, and placed in secure storage to await final destruction. Whether a container is active or expired, consistency matters if you use weight for tracking.
Remember that weight is best implemented as a supplemental method after tracking by quantity. Do not rely on weight alone.
Weighing the Pros and Cons
When performed correctly, weighing liquid controlled substances can improve accuracy. Doing it also helps identify manufacturer overfills and underfills.
Proper weighing:
- Improves log accuracy.
- Adds a verification layer.
- Reinforces checks and balances in inventory tracking.
- Allows the capture of manufacturer overfills and underfills, resulting in more accurate tracking from the time a bottle is opened.
Potential Issues
In addition to improving accuracy, weighing can identify problems when the numbers don’t compute correctly. Suppose you have several bottles of the same liquid controlled substance, all of which should be unopened. However, one has a missing seal or a removed tamper-resistant cap, and its weight differs from the other bottles. That finding might indicate the container was messed with.
I know of several times when controlled substances were siphoned from bottles using a tiny insulin syringe. The puncture hole was almost impossible to see with the naked eye. Sure enough, weighing revealed the tampered bottle weighed less than an unopened bottle. Laboratory testing confirmed that hydromorphone had been replaced with saline, which has a different weight.
Look for these potential issues:
- Is a tamper-resistant cap in place, or was it removed?
- Do expired controlled substances in the inventory show evidence of tampering, such as tears in the tape wrapped around the container when it was labeled expired?
- Does a previously weighed container look more or less full? If yes, compare the weights.
Accurate Scales
Have you ever gone to your doctor for a physical and spotted a sticker on the scale noting the date of the last calibration? Standardization is critical because an improperly balanced scale will not capture accurate weights.
Picking up and moving a scale in your practice might alter its calibration, as can gravity, temperature, uneven surfaces and overall maintenance. If you use a scale to track controlled substances, keep it in a dedicated location, calibrate it and conduct required maintenance.
Pharmacies, particularly compounders, use specific scales to measure and mix medications accurately. Every ingredient must be precisely tracked and weighed so that the end product isn’t compromised and is safe for consumption.
Remember that ensuring a scale’s accuracy doesn’t discount the importance of verifying the readings against the tracked dispensing quantities. Both sets of data should check out.
A Gray Area
There are no black-and-white answers for whether you should weigh controlled substances. It’s more about what works for you to ensure your logs are consistent, complete and accurate. That is where professional judgment comes in. If you continually see discrepancies and have reconciliation challenges, weighing is something to consider. As a best practice, weight is typically successful as a supplemental tracking system.
SHAKY NUMBERS
You might ask, “Why do I keep getting different weights when I place the same bottle on my gram scale?” The answer is that a scale is only as reliable as its balance, and numerous factors can come into play, ranging from gravity and temperature to uneven surfaces and maintenance. Receiving multiple weights for the same container is an indicator to recalibrate the scale.
WEIGHTS AND MEASURES
For those who need a math refresher, remember that a gram is a metric unit equalling the weight of one cubic centimeter (or milliliter) of water. When tracking controlled substances by weight, you should use a gram scale that measures to one one-hundredth of a gram (0.01g). That way, tiny amounts are calculated accurately and precisely.