Basic Information:
Always select the smallest syringe size that will contain the dose needed. This is always the best way to predict accuracy during compounding.
Although when not possible, we want to use a syringe volume where at least 50% of the total fill capacity of a syringe will be used (Example: At least 5 mL in a 10 mL syringe) this gives +/- 5% error in measurement (which is within acceptable USP range).
However, the absolute smallest volume measurable is 20% in order to stay within the allowable +/-10% tolerance limit of USP. For example, pulling up 2 mL using a 10 mL syringe will deliver a dose that is within +/- 10% accuracy.
Bulk Anticipatory Compounding:
For bulk anticipatory compounding it is customary to use one larger syringe to deliver multiple doses to different bags in a batched lot. For example, during compounding of vancomycin 1500 mg, often a 60 mL syringe will be used to deliver 15 mL of vancomycin to each bag. This is an acceptable scenario since 15 mL (dose) is 25% of a 60 mL syringe. Exceptions to this would be chemotherapy, NICU, and narrow therapeutic drugs where we would want to use the smallest syringe possible.
The following chart shows the minimum deliverable amounts compared to syringe size for best accuracy. As an example, to batch a drug that requires 5 mL into each bag, the compounder must choose the appropriate syringe size for accuracy (up to and including a 20 mL syringe). Using a 30 mL syringe would not be appropriate since the absolute minimum measurable volume for accuracy is 6 mL for the 30 mL syringe.
Note: Again, the most accurate measurement is to use the smallest syringe size. As syringe volume increase so does accuracy. The chart above is for Bulk Anticipatory Compounding. Remember, smallest syringe size must always be used for chemotherapy, NICU, and narrow therapeutic drugs.
Measuring In Between Calibration Markings of a Syringe:
Although not 100% accurate and dependent on the compounder's acuity, it is an acceptable practice to measure half measurements (e.g., 7.5 mL). However, it is not acceptable to measure any other volumes between (e.g., 7.25 mL or 7.75 mL). If these volumes are required, two syringes should be used: a 10 mL syringe to measure 7 mL and a 1 mL syringe to measure 0.25 mL or 0.75 mL respectively. For chemotherapy, NICU, and narrow therapeutic drugs, it's always best to use the two-needle/syringe method.
Needle/Syringe Hub Volume (Dead Space):
Next, consider the "dead space" of the needle and syringe hub (refer to "Needle Volume and Compounding Accuracy" for a review or better understanding of this topic).
If needle volume and syringe hub are concerns (usually for chemotherapy, NICU, and narrow therapeutic drugs), use a new needle/syringe combination for each step in the compounding process. For example, after reconstitution, since diluent will be left in the needle/syringe, use a new syringe/needle for best accuracy when pulling up the deliverable dose.
Also, it’s important to understand and use the dry needle/wet needle concept illustrated in the mentioned document "Needle Volume and Compounding Accuracy" (https://smilstead5.wixsite.com/website-5/post/compounding-process-needle-volume-and-compounding-accuracy-important-to-have-detailed-sops).
Exceptions: (There are always exceptions in medicine)
In some cases, doses smaller than 0.2 mL (in a 1 mL syringe) are required, such as in NICU and eye injections, which often require smaller volumes. This is where dilutions come into play. Compounding a dilution increases the accuracy of the dose being pulled up. Therefore, if a volume less than 0.2 mL is required, consider a dilution to increase the accuracy of the deliverable dose.
Pharmacist (BCSCP) and the founder of Soigner Solutions (Soigner Universal, LLC). Collectively, Steve has over 20 years experience in sterile compounding of non-hazardous and hazardous preparations (including non-sterile to sterile using API). He is also experienced in non-sterile compounding and has fully developed and implemented all-inclusive compounding programs including USP <800> hazardous drug programs since the release of <800> in 2016. Steve received his Doctor of Pharmacy degree from McWhorter School of Pharmacy and holds two other degrees from Samford University and Université Sorbonne.
Thank you for visiting my site. For more information please visit www.SoignerSolutions.com or email me directly at smilstead@SoignerUniversal.com
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