Just Scut'n along

[MDT]

Yeah, pretty much what VH said...

From an antigenicity standpoint, the Wyeth product utilized the entire antibody, and this was derived from hyperimmunizing horses. Imagine a molecule that looks like the letter "Y". That's what the molecule looks like. So this whole thing was injected and circulating in your blood stream. Your own immune system is really good at recognizing things that "don't belong", especially foreign proteins. So, upon seeing this circulating letter Y, in a lot of folks, that triggered an immune response (which manifests in wheezing, swelling, hives, hypotension, and cardiovascular collapse, which leads to you dying from anaphylaxis). This was a relatively common occurrence, but severity was variable, and clearly, was a life saving product. So you had to use it with care.

The ovine products (sheep derived) are made similarly, only that letter "Y" is chopped into pieces, for CroFab, 3 pieces (imagine cutting the Y into \, |, / ) and Anavip is carved into 2 pieces (thing of a V and | ). So they seprate and keep the "slanty" parts and get rid of the "stick" portion. Getting rid of the "stick" portion seems to significantly reduce the antigenicity of the antivenom. So, the result is a much cleaner product.

CroFab is made with 4 US pit viper species. AnaVip made with 2 SA species. I have not reviewed any pharmacokinetic data, and in full disclosure, I have not had an opportunity to use Anavip.

I do understand that the circulating level of each product is different. In my mind (again, not having read any kinetic data), it would seem that the US specific compound would be more effective in the US (each venom being genetically/molecularly different). Also, the relative cost...CroFab was the first guy out there. They can "name their price" so-to-speak. Now that there is some (apparently good) competition, CroFab will adjust prices and hopefully, everyone will be a little more sane.

As far as administering the med, that is a good question. Seriously...I don't get it. Maybe because of the reputation that the Wyeth product had? We give thrombolytics (clot busters like tPA) in the ED on a relatively common basis. This is pretty tricky stuff, in that it basically stops your ability to clot your blood. We give medications to paralyze people before we intubate them. Nothing like taking an awake, talking patient and removing all muscular control and stopping their breathing, only to insert an endotracheal tube into them and we breath for them. That is a pucker time for sure. We give all kinds of really gnarly stuff and don't bat an eye, because we know that's part of taking care of a particular disease process. So it's not like we aren't familiar with giving tricky stuff. But when it comes to antivenom, it seems like the medical community wets their collective pants.

Oh well, not sure if this answered your question, but I tried to hit the high points...