methods that achieve doses based on conversion ratios of 2.5:1 for onaBTXA:aboBTXA and 1:1 for onaBTXA:incoBTXA per 0.1 mL in a volume of 0.1 mL.1,3,5,6,17,18
As clinicians gain experience using the various BTXA products for both on- and off-label indications, they can refine their approaches for reconstitution. In addition, reconstitution methods could change, depending on a variety of factors, including injection sites, treatment goals, patient-specific characteristics (eg, previous response), and clinician experience. For example, when wanting to create a global relaxation effect, clinicians might choose to inject a higher total volume. Therefore, they are adding a higher volume of diluent to create a less concentrated solution. In contrast, when precise control of the affected area is particularly critical, less diluent would be added for reconstitution to produce a more concentrated solution that would deliver the total dose in a smaller volume.
Sterile preservative-free, 0.9%, normal saline is the recommended diluent for reconstitution of all BTXA products according to manufacturers’ directions.1,3,5,6 However, off-label use of bacteriostatic saline for reconstitution improves comfort with injection and can then enhance overall patient satisfaction.19
Dr Cohen: During my fellowship, Alastair Carruthers, MD, used to always say, “Dilution is for the convenience of the injector, whereas dose determines efficacy for the patient.” I think this concept holds true, specifically when injecting small muscle groups such as the glabellar complex. This is supported by the results of glabellar studies in which I participated. In one study, we reconstituted 300 U of aboBTXA with a volume of 1.5 or 2.5 mL of saline and treated patients with a total dose of 50 U.20 In an earlier study, we injected 20 U of onaBTXA and compared results when the 100-U vial was reconstituted with 1, 3, 5, or 10 mL of saline.21 Efficacy was the same in each study, regardless of BTXA concentration when the dose was kept constant.20,21
With convenience in mind, I use 1 mL of preserved saline to reconstitute a 300-U vial of aboBTXA. This approach results in a final concentration of 30 U/0.1 mL, which makes calculating the injection volume very easy with any given dose. When injecting larger muscle areas, such as the frontalis or platysma (and for hyperhidrosis), I double the reconstitution volume for all the neuromodulators I use in my practice.
Dr Aguilera: I choose my diluent volume for each product so that the total injection volume for a specific indication will be the same regardless of the product used. When reconstituting onaBTXA and incoBTXA, I add 2.0 mL of diluent to a 100-U vial. For aboBTXA, I add 2.5 mL to a 300-U vial. This approach eliminates performing mathematical calculations each time to determine volume.
Dr Kaufman: I usually add 2.0 mL of diluent to the 100-U onaBTXA vial and 300-U aboBTX vial and 1.5 or 1.6 mL of diluent to the 100-U incoBTXA vial. For varying reasons for certain procedures, however, I will double the diluent volume to create a less concentrated solution. For example, to avoid an unnatural-looking result, I might inject a hyperdiluted toxin into a very large forehead to achieve an even distribution of the drug without completely paralyzing the muscle. For new users, I recommend using the same volume of diluent for whatever product they are using because that will help mitigate confusion and avoid potential dosing errors when using different products.
Dr Yoelin: What is your advice to clinicians about choosing or switching among the BTXA products?
Dr Gold: I recommend focusing on the use of one product—it could be any of the 4 that are available—and then developing expertise with that one BTXA before adopting another product.
Dr Cohen: I agree that it is easier to start using just one product or perhaps 2. In reality, we now have 4 good products that are more similar than they are different.