Last week’s feline renal failure patient came in feeling especially under the weather. I’d been monitoring her progress for about eight months and was impressed by her improving blood values and overall condition. Though her kidneys weren’t getting any younger, Zoe’s owner was doing a great job. That is, until the pharmacist over at the big box superstore threw a wrench in the works.

Here’s the story …

On this visit, Zoe was depressed and hadn’t eaten for over 24 hours. She’d been vomiting too. Now, Zoe had had little events like this during the course of her illness but they’d quickly resolved with the help of a little yellow pill called mirtazapine. It helped stimulate her appetite and made her feel peppier almost immediately. This time, however, things had gone the opposite way.

It’s a good thing Zoe’s owner doesn’t take a wait-and-see attitude. She’s learned that renal disease is nothing to mess with. So when Zoe woke up still feeling crappy she’d brought her right over.

After a lengthy conversation, a complete physical and comprehensive labwork, we were still mystified. Maybe there’s something new going on here, we mused. (She is fifteen, after all.) That’s when the light bulb clicked. Zoe’s owner had an idea. It was then that she told be aboutthe new shape of the medication …

Turns out the pharmacy had given her a different drug –– a different shape of drug, anyway. It was still small and yellow, for sure, but this one was round, not oval-shaped. Could that make any difference, she asked?

After examining the pill and looking it up online (thank you, drugs.com) it was clear that the pharmacy had given her the wrong medication. It was 7.5 mg, just like the mirtazapine was supposed to be (it even said 7.5 right there on the tablet), but it was decidedly not mirtazapine.

Unfortunately, this was meloxicam, not mirtazapine. Which is a very bad thing indeed. Let me count the ways:

7.5 mg of meloxicam is an appropriate dose for a 150-pound mastiff, not a seven-pound cat.
Meloxicam is only approved for cats as a one-time injectable dose for post-operative pain.
This drug is an NSAID, a class of drugs well known for their potential renal side-effects.
Meloxicam is expressly contraindicated in the case of renal compromise.

In other words, I can’t think of a worse pharmacy mistake. Well … maybe I can, but I’ve never personally treated a patient who experienced one more more potentially catastrophic.

Most of the pharmacy mistakes I’ve seen are related to improper dosing, most of which owners are quick to identify if they’ve used these medications before. I’ve also heard about dogs dying from xylitol poisoning after receiving certain elixirs formulated to appeal to pediatric patients (for example, Pfizer’s Neurontin® is a big no-no). But I’d never seen an honest mistake like this one.

This was an honest mistake, of course. No one wants to make this kind of life-threatening professional error –– especially not a sleep-deprived Costco pharmacist with two jobs, a new baby at home, an under-the-water mortgage, and $100K in student loans to pay off. And to his credit, the pharmacist in this instance did not shirk his responsibility or fail to offer a straight-up apology. The company would also pay any costs involved in treatment, of course.

Good thing we didn’t have to test the limits of that last promise. (After all, dialysis is expensive.) As it turns out, Zoe’s kidneys did not decompensated and die. In fact, they never even registered a blip in her typical level of function. And once we got the right drug back up and running, Zoe responded the way she always had –– chirpily, and with gusto.

So what happened? Not so sure, though her owner suspects that the half-tablet she administered might’ve proved more bitter than the usual one (it is a bitter pill!) and, as such, could’ve been spit out somewhere in the house, never to be seen again.

Lucky break, right?

The question remains, however, as to how such a medical error could’ve been made. How do pharmacists reach for one drug and grab another? What policies and procedures are in place to make sure these things don’t happen with regularity?

To be sure, pharmacies have a lot of practices and checklists in place to minimize problems, including placing an alert sticker on the side of a bottle whenever the manufacturer of a drug has changed. (No sticker should trigger an alert for you should you come across a drug that looks different than usual.) It also includes greater vigilance in the case where drugs of the same size (in mg) might be confused for one another –– especially when a mixup might prove fatal.

It’s a pharmacy safety issue, for sure. To me, however, this error speaks more of the unique problems veterinarians and their patients confront when they employ human pharmacies. After all, this particular mistake is way less likely to have happened in a veterinary pharmacy. Here’s why:

Veterinary pharmacists are always on the lookout for mistakes related to species-specific and size-related problems. As such, meloxicam and mirtazapine’s identical 7.5 mg size would likely put veterinary pharmacists and pharmacy technicians on notice. Moreover, drugs like meloxicam (and other NSAIDs, which are at high risk of side effects), adverse drug interactions and dosing mistakes in animal medicine (in part as a result of their ubiquity), tend to be more greatly scrutinized as a whole.

There are plenty more reasons why veterinary pharmacies are a great choice over human ones, including a) their greater knowledge of bad drug interactions, b) common adverse reactions, c) which drugs are absolute no-nos, d) what kinds of alerts might be useful to you as a pet owner, and e) which additives can potentially render a medication toxic. (Here's an article that details some more risks.)

But that doesn’t mean you can’t use a human pharmacy. You just have to be smart about it if you do. In fact, it might just be a good idea to keep an up-to-date veterinary drug resource on hand (consider this one). I also recommend you look up your pills online to be sure they’re what the pharmacy says they are.

Right now you might be thinking that I’m just trying to scare you. That I’m like one of those veterinarians that has a beef (legitimate or otherwise) with losing all that in-house drug income to outside pharmacies. But that’s far from the truth. In fact, I’m a big proponent of all kinds of veterinary pharmacies. Not only should my track record on this subject convince you, but the fact that my own hospital’s website redirects my clients to an Internet pharmacy will readily prove my allegiance to consumer freedom.

Want to know more about this topic? Here are some online drug tips from the FDA. While I’m at it, here are some things you should know, as a pet owner, when it comes to sourcing drugs (including getting a written prescription from your veterinarian).

-Dr. Patty Khuly