Additional thoughts on the use of gravimetrics for I.V. compounding

Several months ago I wrote about my thoughts on using gravimetrics for I.V. compounding. At the time I wasn’t convinced of the utility, but my thoughts on the matter have changed. Over the past several months I’ve had the opportunity to dig deeper and mull over my thoughts on the matter.

There was a session at ASHP Midyear back in December titled New and Emerging Strategies for Minimizing Errors in I.V. Preparation: Focus on Safety and Workflow Efficiency. The presentation covered several topics, but one thing that caught my attention was data presented on error rates for the preparation of compounded sterile products (CSPs)¹ and the benefits of using gravimetrics in the process. I was skeptical about some of the numbers that were presented. Data is only as good as how it was collected, what it’s compare against, and how it’s presented. One should always question the data, especially when it runs contrary to previously held beliefs.

Since ASHP Midyear I have devoted a fair amount of my free time looking at gravimetrics and how it’s applied to the compounding process. Unfortunately the use of gravimetrics for CSP preparation isn’t popular in the United States, and is rarely seen outside of inclusion in IV room robots. A fact that has made it difficult to review the process in a real-world situation.

However, it came to my attention that the world-renowned MD Anderson Cancer Center in Houston, Texas has been utilizing gravimetrics for CSP preparation for years. Earlier this week I had an opportunity to visit MD Anderson and spend some time in their I.V. room.

While in the pharmacy I.V. room at MD Anderson I witnessed pharmacy technicians prepare several chemotherapy doses using a system of bar code scanning and gravimetrics. Bar code scanning was used to verify correct ingredients, while gravimetrics was used to verify that appropriate quantities of each ingredient was drawn and added to the final dose container.

As a practicing pharmacist I never had the opportunity to use gravimetrics. Instead I always used volumetrics²Â to verify the quantity of ingredients added to a CSP. It was strange to observe a process that relied on the weight of an ingredient instead of the volume.

Here are some thoughts after observing gravimetrics in a working pharmacy environment:

1. Is gravimetrics a viable option in CSP preparation? Yes, it has a place in pharmacy I.V. rooms. In my mind it fits better in certain situations than others.
2. Is gravimetrics slower than other methods of CSP preparation? Yes and no. It depends on your process. No matter how fast you do something, inserting additional steps into a process will slow it down. However, this applies to any process.
3. Is gravimetrics more accurate than volumetrics? Unfortunately there’s no good answer here. Technically speaking tolerance is better with gravimetrics, but is the difference clinically significant? Not likely.
4. Does gravimetrics replace the need for a pharmacist to verify the contents – drug and volume – of a CSP? Ha! I have an opinion on this one, but I think I’ll keep it to myself for now.
5. Should you evaluate gravimetrics for inclusion in your CSP preparation process? That’s a personal choice, but yes I think you should. As I said in #1 above, I think it fits in certain situations.

Overall I was quite impressed with the entire workflow in the I.V. room at MD Anderson. Their use of gravimetrics during CSP preparation works well for them and gave me a real sense of how it may fit into pharmacy operations.

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1. While not explicitly defined in USP <797>, a CSP can be loosely defined as a sterile drug product prepared via compounding, i.e. a medication prepared in the “I.V. room” under a hood.
2. Using syringes to measure the volume of ingredients, i.e. drawing the ingredient up in a syringe before shooting it into a bag