First I should say that this review is for Merck and not for Pets Drug Mart. (who are fantastic, BTW) I've been using the pen for 4 years now and have gone through 3 of them and about to purchase my 4th. Merck claims that they are good for 3000 doses; you'll be lucky to get half of that. When I contacted them, they said that "We only guarantee items purchased through a vet and not online." Nice cop out, the greedy jerks. Seeing as it is the only pen that is compatible with 40iu insulin, I'm stuck paying for a new 'kit' every year (of course Merck doesn't make a pen only available to purcha$e) If you can find another pen, I suggest you use that instead of this garbage. (and preferably not from Merck). I will add that the dosing is correct as my dogs blood sugar is perfect so, they get points for that. Anyway, while the dosing is correct, the pen itself is not long lasting whatsoever. I'd suggest looking into a pen intended for human use.

My dog has been on novalin n and for two years I used a nova pen so when I went back to caninsulin I thought the pen should be just as good. Unfortunately my dogs blood glucose skyrocketed so so I tried a syrnge and magically her numbers were back on target. So either the pen was faulty or just not made well. I cant recommend the pen under these circumstances but if Merck exchange for another, then I will try it because I have three boxes of pen needles that are now if no use to us.