My 17 month old chihuahua has been on Iverhart Max (6 to 12 lbs.) and doing fine with it. At her last vet visit, she weighed in at 12.3 pounds and the vet now wants to change her to the 12 to 25 lb. dosage. First, I think the scale was off by half a pound -- it read 0.5 when no dog was on it. Second, she's had bad reactions to to both the lepto and bordatella vaccines, and I've decided not to have her vaccinated again (she's never exposed). She's also had allergies that seemed to disappear when I removed all grain from her diet (switched to grain-free super-premium dry). She is not obese, she is CKC and not the tiny AKC apple-dome head type.

My question is would the lower dose of heartworm medicine be sufficient? I am very hesitant to give more than necessary in view of her other sensitivities. (More is NOT always better... ) Some evidence would be helpful as well, as the vet seems insistent on the higher dose citing that overdose is not likely. "Not likely" doesn't put me at ease since it is also "not likely" that dogs react so badly to vaccines or grains.

Thanks in advance!
A concerned and vigilant pet owner.

Where do you live? Because heartworm is more of a problem in some areas. I see no reason to increase the dose for up to 25lbs. Especially if she is pregnant or you plan to breed her. If he gives you the larger pill just break it in half if the dog is only 12lbs.