I did alittle "quick" research from some other vets and there is nothing suggesting there is any less efficacy of enalapril to enacard. As a clinician the problem with online companies like 1800...is they are giving you medications at a low cost...but if you have a problem with that medication you go to your vet. So they are wanting the $$ from the sell but not the support of being your vet and dealing with the possible outcomes.
I would talk with your vet about getting enalapril. He can do his own research...via a network called www.vin.com that he is probably familiar with. It is a vet only network..but it has lots of information about using the generic form. You just need to communicate the desire for the less expensive medication and if he is using an online pharmacy, the generic should be available.
They both are equivalent...I use both enalapril and enacard. Why do I have both?? Because sometimes MERCK (enacard) has bulk discounts and I am able to purchase for less than normal. I do not have a problem with dispensing enalapril AT ALL..and I can find NO research suggesting that there is a difference.
Some other medications, the generic brands do not do as well...but Enacard/enalapril does not fall into that category.
You are welcome...good luck,