Melissa, I don’t have any doubt that it’s (supposedly gradually) released into the bloodstream, where it slowly builds up plasma concentrations. If the vet wanted to use a 6 month injection of this, (and as far as i know it would Never be done on a HW pos dog) I would have already immediately looked elsewhere. Speculation, but I think it would be very hard to formulate a timed release product for prevention that would give a relatively even plasma concentration for an entire 6 month period. There’s also the issue of injecting it properly. I would imagine it would have to be very carefully injected into storage fat, and if not done properly, the potential for really big problems, which I think they proheart6 had. I doubt I would ever trust a 6 month injection of this, not for prevention or otherwise, not ever.
Speculation again, but i would think 1 month topical doses would have a much higher margin of safety. Absorbed through the skin, wouldn’t the drug have to meet the subcutaneous -below skin fat layer before ever reaching the bloodstream or at least without an excessive amount getting in the bloodstream right off the bat? Supposedly it only builds up slowly for the first 3 or 4 months (3 or 4 applications) before the plasma concentrations level off and stop building up even with additional applications. Bayer says this the big advantage. On page 11 on the right, there is a chart that shows supposed plasma concentrations over time.
I don’t even really want to dwell too much about shortcomings of proheart6, I’m not even considering it and I think I know some of it’s problems, but in table 2 on page 10, it says this about it “At the end of the 6-month dosing interval, residual drug concentrations are negligible12”
http://www.bayerdvm.com/show.aspx/canine-heartworm-disease-blagburn
Intuition at first tells me I would rather have a drug that gets in, and more importantly gets out fast. Bayer claims the slow and more continual and evened out plasma concentrations is the big advantage to this vs. a big plasma spike and rapid exit such as ivermectin dosing, and then there is very real risk of anaphylactic shock from using ivermectin in a HW pos dog, because of the very sudden and too rapid die off of microfilaria. I don’t know, I really wish I had more answers and more time. I can’t really argue for this drug, sadly, I just don’t have anywhere near all the answers.
