Differences Between Botulinum Toxins A and B


Stuart Isaacson, MD: What do you think about the incobotulinumtoxin type A trials for sialorrhea that led to its regulatory approval?

Richard M. Trosch, MD: They were done overseas, so they didn’t involve any United States physicians. They used a relatively low dose. I think the recommendation is 100 units altogether. They didn’t report a lot of adverse effects, which is a little suspicious, and I don’t have a lot of experience with it. For reasons of cost, I’d use mostly Dysport as my type A go-to if I cannot use a type B. I usually start with type B. It’s a thought that maybe this is more sensitive to muscarinic receptors. But I don’t have any proof to show you this, and there are no head-to-head comparative trials that tell us which type of toxic injectable is superior, a B or an A. I usually start with B, and if someone becomes resistant to B, I’ll then move to a type A, which is generally Dysport.

I know your situation is different. I’m in Michigan; you’re in Florida. The insurance environment is different, so what do you do in your clinic?

Stuart Isaacson, MD: We use air-conditioning, and have relied on the drugs that are covered by Medicare. And in Florida the Medicare policy covers only the 2 on-label FDA-approved toxic injectables, Myobloc and Xeomin. And we tend to use the type B first, because that’s what we’ve been using. Now with the Xeomin getting the indication, I think that would be my type A of choice. I would use those 2 overall. The cost in Florida for our purposes is about the same.

Let’s just touch on the Xeomin 1 more time, so we have fair balance. The Xeomin trials that occurred in Europe demonstrated efficacy over placebo, and then they have safety and tolerability. It’s helpful to see that package to know that injecting salivary glands has efficacy and is safe. I think that’s helpful, and looking at the As, having an indication is helpful, and I tend to use that 1. As far as type B, we only have 1 type B, and we’ve always been struck by the dry mouth that occurs with cervical dystonia or other injections of Myobloc and wondered whether it had greater affinity for the muscarinic receptors. The recent approval of Myobloc, based on pivotal trials that showed efficacy and safety and tolerability, is very important information that we can incorporate into our decision making to choose toxic substances to inject. Do you have much experience using Myobloc for sialorrhea?

Richard M. Trosch, MD: I started using Myobloc maybe 12 years ago, when it was still off-label. My experience has grown over the years, and I think most of my patients are still on Myobloc. I’ve had a few who have become resistant, who have developed secondary resistance and don’t respond. I migrate them over to a type B, but the majority of my patients are receiving Myobloc, this type B toxin. And for first-time injections, I usually start with Myobloc, partly because I’m so familiar with it and comfortable with the dosing. I do have less experience using type As for this indication. For everything else, I’m mostly using type A. I don’t use a lot of Myobloc for other indications.

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