Four BTXA products are commercially available in the United States with approval for cosmetic use, but they vary in their approved indications (Table 1).1-6 Listed in order of date of first approval for cosmetic use are the products onabotulinumtoxinA (onaBTXA), abobotulinumtoxinA (aboBTXA), incobotulinumtoxinA (incoBTXA), and prabotulinumtoxinA-xvfs (praBTXA).
The BTXA products are all derived from Clostridium botulinum type A, which produces a protein complex containing the core neurotoxin, BTXA, with ≥ 1 nontoxic accessory (or neurotoxin-associated) protein (NAP).7,8 The core neurotoxin has a molecular weight of approximately 150 kDa and is responsible for the therapeutic action of the BTXA product. The total molecular weight of the available BTXA products varies given differences in NAP content. NAPs can be removed during the manufacturing process and are absent in incoBTXA.5 Although NAPs are present in the other BTXA products, they dissociate from the core protein when saline is added to the vial for reconstitution.9 NAPs are believed to protect the core protein against harsh environments such as the gut and intestinal tract, and they aid in the movement of BTXA across epithelial barriers.10 Whether NAPs have an effect on clinical outcomes is still unknown and quite controversial.
Conversion Ratios/Dose Equivalence
In real-world practice, clinicians might vary their injection of each BTXA product, as well as among BTXA products, at different anatomic sites to achieve optimal results for individual patients. The potency units of the different BTXA products are not interchangeable.2,11 The potency of each product is determined using the manufacturer’s proprietary assay and reference standard. Therefore, potency units are specific to each product.2,11 Because the potencies of BTXA products cannot be directly compared, there are no universally accepted conversion ratios for making dose-equivalence comparisons among products.2 Published reports suggest that the conversion ratio for aboBTXA:onaBTXA is between 2:1 and 3:1 and that for incoBTXA:onaBTXA is between 1:1 and 1.25:1; these ratios are frequently used in clinical practice.11-15