Danger: Drontal/phenobarbital interaction

My cats were all treated at the same time with Drontal for roundworm and tapeworm because I rescued a kitten who was full of the parasites.

Tolly, who takes phenobarbital for seizures, had never had to be de wormed before.

The Drontal caused a phenobarbital overdose because both drugs are processed through the blood and liver the same way, and the Drontal (specifically the Pyrantel) prevented the phenobarbital from being processed, so it stayed in his blood and caused an over dose.

At about 4 pm yesterday Tolly actually came to me and told me something was wrong, when his symptoms first hit. He was disoriented, walking strangely (crouched, almost on his hocks), his eyes were sunken, pink rimmed with the third eyelid evident.

I wasted no time calling to find out who was on call and getting him there. After seeing the on-call vet she recommended that I call the ASPCA poison control number when I got home, to see if they could add anything to the treatment she had researched and prescribed. Which I did.

The poison control vet confirmed what the on-call vet though, and expanded on her recommendation, slightly.

The treatment was to keep him quiet, feed him as much as he would eat (he was ravenous, also a symptom of phenobarbital overdose) and give him 150 ml sub q to help flush his system.

Tolly is to all appearances completely recovered this morning, though I am not in such great shape. I wasn't able to break down yesterday I had to cope with the emergency. This morning I am a basket case with post traumatic reaction. Sobbing and shivering. Ugh.

I cannot think why I didn't check on drug interactions before giving him the Drontal, I ALWAYS check drug interactions with Tolly, and have since he first started the phenobarbital. So I really don't understand why this time I didn't. It's very strange.

Maybe it had to happen so we could warn other people.

ASPCA Animal Poison Control Center phone number

1-888-426-4435

Write it down and put it next to your phone, and/or put it on your cell phone.

I've had it taped to my wall for years. never had to use it before, but am glad it was there.

Wonderful wonderful vets staff this hot-line.

There is a fee of $65.

That's $65 I would be asking back from the vet.

It's not like the phenobarbital was a rare medication, so the vet should have been on the look out for that. You may want to make up a quick reference list of anything common it will interact with - I suggest people do this for any cat (or themselves) that has a daily must have med.

I hope the OD didn't do Tolly any lasting harm and that he's fine now.

From the day Tolly was first put on Phenobarbital I have never EVER before given him anything without checking for possible interactions first. Even hairball remedy and c.e.t. toothpaste went through an exhaustive research before I would use it on him.

So I had to think long and hard about why I did not do it for something as potentially toxic as prescription de-worming medicine.

My conclusion is, this happened to us because I am meant to spread the word. It happened to us, because I pay extremely close attention to anything odd about my cats and I am not the "wait and see" type.

We all have come across people who are reluctant to "waste" money at the vet, especially heaven forbid (said with deep sarcasm) paying an emergency fee.

Whatever runs the universe knew Tolly would not be in serious danger because I listened when he told he something was wrong and got him emergency care immediately.

So our job is to spread the word. And I will.

The emergency vet bill was $129 and the ASPCA poison control cost was $65 (which includes follow up consultation) I don't care about the money. I'm just glad he's okay and I can warn other people.

Originally Posted by otto

I don't care about the money. I'm just glad he's okay and I can warn other people.

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But your memory isn't 100% perfect, you may have a bad day, be stressed and in a hurry and not remember something. As for asking the vet for the money (credit), that's more to drive home that they need to catch these drug interactions. Tolly survived, someone elses pet may not.

Btw, I'm certainly not blaming you. Most of us give Drontal and flea treatments to our cats fairly often. It's so easy to get complacent about something so common and familiar.

Originally Posted by strange_wings

But your memory isn't 100% perfect, you may have a bad day, be stressed and in a hurry and not remember something. As for asking the vet for the money (credit), that's more to drive home that they need to catch these drug interactions. Tolly survived, someone elses pet may not.

Btw, I'm certainly not blaming you. Most of us give Drontal and flea treatments to our cats fairly often. It's so easy to get complacent about something so common and familiar.

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I had plenty of time to think about it. Two weeks in fact. This "mass drontal dosing" was planned well in advance, all cats were to be treated at the same time because of Queen Eva's roundworm infestation.

I had planned to do it today, because I never dose with a new med unless my vet is available to me. However I decided on yesterday instead, because I would be home all day to observe, it being a holiday.

It's a good thing I did, too. If I had dosed him today, I would not have been home when the reaction came. This is a long working day for me, I will be leaving shortly and will not be home until 10 PM. If I had dosed him today he would not have been taken care of in time.

I don't much believe in coincidence. This all happened the way it did for a reason. I may never know the reason, besides the need for putting the word out, perhaps my experience will save another animal's life that I will never hear about.

I have left a voice mail for my vet about what happened. I probably won't get to talk to her now as I am leaving the house soon and she is in surgery this morning, but I'm sure we can work things out. She obviously didn't know either. Either did the on-call vet, until she researched it.

Now lots of people will know. It's a good thing.

Wait, you're confusing me, now. I thought you were arguing against doing that for your cats and self in post #4.

And of course it wasn't coincidence, you're more cautious than to rely on luck.

Again, I hope Tolly's well now, and that your night doesn't go too slowly! I'm sure you'll be eager to check on him as soon as you get home.

Originally Posted by strange_wings

Wait, you're confusing me, now. I thought you were arguing against doing that for your cats and self in post #4.

And of course it wasn't coincidence, you're more cautious than to rely on luck.

Again, I hope Tolly's well now, and that your night doesn't go too slowly! I'm sure you'll be eager to check on him as soon as you get home.

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Oh no. I think it is terrific advice and I thank you for posting it. I was just saying that I always DO research interactions, and that's why it is so weird that I didn't with the Drontal. I love my vet but I don't rely on her to know everything, I always do my own research, and then discuss it with her.

Tolly is sleeping peacefully and I am trying not to hover. I am late leaving the house because I am hovering

I really do think this was meant to happen the way it did. Tolly is safe and I have a few more white hairs, and if it saves another pet's life, then it was worth it.

Thanks for your support. Not just in this thread, but always. You know.

Originally Posted by otto

I was just saying that I always DO research interactions, and that's why it is so weird that I didn't with the Drontal.

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I usually do too. The one time I didn't because I was too sick to I ended up with a drug interaction. The ER doc even looked up the medication I was on because he hadn't heard of it before - surely he would have seen it was a 2D6 inhibitor, yet he gave me a drug the metabolized on it. Pharmacy never caught it, either.

It's usually the one time you don't that something happens.


This also goes to show why people need to be careful with what they give their pets and don't do anything OTC unless you have your vet's blessing and have researched thoroughly. Something may be fine on it's own, but could cause a deadly interaction with something else.

I'm just glad Tolly is ok now, and we've all learned a valuable lesson.

Just a fyi : there are many vet med books similiar to the human pill books avail... I try to keep a updated one on hand...

Very scary honey. I'm glad everything is OK now

Thanks for your replies everyone. Tolly is doing much better. I haven't spoken to my own vet. She did return my call and left a message of her own. Hopefully we can talk tomorrow.

I want to clarify here that in no way do I hold my vet to blame for this misadventure. Vets are not gods, they can't know everything. She didn't know. The on-call vet and the poison control vet hadn't heard of it until they heard of Tolly.

I have since done some researching of my own and I have not been able to find any indication that the two drugs are contraindicated either, except for one thing. The on-call vet and the poison control vet did though, so they must have better ways than I to search.

I searched phenobarbital and Drontal, phenobarbital and pyrantel and phenobarbital and praziquantel. (the two ingredients in Drontal) Came up with nothing except that the effectiveness of the praziquantel (for tape worm) is greatly reduced. If Tolly has a tape worm, which is not what we were treating for, he can take a droncit. But I think Queen Eva's tapeworm was gone before she was integrated.

Back on topic, the fact remains that Tolly's symptoms were classic phenobarbital overdose symptoms. The symptoms came on 4 1/2 hours after he had the drontal, 5 1/2 hours (almost peak) after he had his phenobarbital.

The medications are put away. I split his pill fresh each morning so there is no way I forgot and dosed him twice.

He's been on this medicine a long time. He would have needed to get several extra doses to be so affected.

Anyway, I wanted to say this.

So..it happened. Maybe it's a rare reaction between the two. Maybe it's just never happened before that a pet on phenobarbital took drontal and had these symptoms. Or, if it DID happen, the pet's humans did not notice the symptoms, and the pet eventually was okay, after all. I don't know. But I am not holding my vet accountable. I'm sure she wants to know about this as much as anyone.

Gail

Good to know - with Lola being on Pheno.

Anti-parasitics are known inhibitors. In humans praziquantel inhibits CYP3A4, phenobarbital is both a substrate of this and an inducer. If metabolized much the same in cats, that's simply what happened.

I have just spoken to my vet. Bayer, maker of Drontal, has been unable to come up with any indication that Drontal could interfere with the phenobarbital metabolizing in a way that would cause an overdose of phenobarbital.

They did find that there is a very rare side affect where cats with compromised intestinal health will suffer some temporary ataxia, which includes trouble with the hind end while walking (Tolly was walking on his hocks) and disorientation, both of which Tolly exhibited..

Two weeks ago Tolly had a very serious illness involving several days of diarrhea and vomiting and inappetence brought on by an accumulation of fur in his digestive and intestinal tract. (not an uncommon illness, for him happens at least once a year)

It was my vet that told me to wait an extra week before using the drontal, because of that illness, which I did.

This actually does make sense, but his symptoms were more than just ataxia. I mean, he looked and acted really drugged with the red rimmed eyes sunken deep in his head.

So that's where we are. She is at a loss as to where the info diagnosing phenobarbital overdose came from that the on-call vet and the poison control vet came from, but she hopes to speak with both of them today.

Leave it to Tolly to have a rare reaction, eh?

He is fine and dandy this morning!

I will post with any new information when I get it.

Thanks for all your support.

So no one mentioned once that the drontal contains drugs that are inhibitors and Tolly already has liver issues that could greatly affect metabolization? That seems odd.

And drug interaction are only listed after enough people have reported them for studies to be done. If there's not been enough reported or no one wants to seriously investigate it those drug interactions can be missed even if they're obvious.

I'm currently looking up Advantage and itraconazole because those azoles inhibit quite a bit. But since you don't put advantage on a human it's unlikely to have been checked. (eta: looks like that's a no go. 3A4 isoform substrate on all the pesticides - potential for major problems. In case anyone wonders..)

Oh, I also found some slight mention that the pheno can interfere with pesticides, likely due to it inducing on some isozymes. You'll want to further check out that out.

Yes, it is strange. My vet will be talking to both the vets who diagnosed phenobarbital overdose due to interference from the Drontal, so that she can find their sources. I will keep this thread updated with any new news.