Bromethalin is becoming one of the more common active ingredients seen in rodenticides, but the ASPCA Animal Poison Control Center notes that many veterinarians are nervous about treating it.
Some of this apprehension comes from the fact that there is no antidote or truly effective treatment for bromethalin, and many are unaware of key details about the toxin.
Keep reading for the basics you need to know when a patient has ingested bromethalin.
Identification & Dosage Calculation
You cannot treat correctly if you do not know the active ingredient. Have the pet's owner bring in packaging the bait came in (not one that looks similar to what they think they bought six years ago!)
Going by appearance of the bait itself is also risky. Since companies do not change the appearance of the bait for identification purposes, many different types of bait can match the same description. Make sure you get the right info when you take the patient’s history.
Most bromethalin-containing baits are 0.01%, but be sure to read that label, as some come in 0.025% concentrations. If it is a 0.01% concentration then there will be 2.84 mg of bromethalin in one ounce of bait.
Most of us are used to dealing with anticoagulants; it generally does not take a lot of an anticoagulant to cause problems in our patients, and luckily there is an effective antidote.
Bromethalin is different, since there is no effective antidote and even therapeutic measures can be lacking, but compared to anticoagulants it does take more bromethalin bait to be a problem in dogs.
APCC recommends starting decontamination procedures for dogs exposed to 0.1 mg/kg and 0.05 mg/kg in cats. It is not likely that CNS signs will be seen at these doses – but since there is no antidote for bromethalin, and we have seen pets ingest more bait than the owners thought, we tend to be conservative.
To give you an idea of what a 0.1 mg/kg dose in a dog may look like, a 30-pound dog would have to ingest a half-ounce, or a 60-ound dog one ounce. Most bait blocks tend to weigh one-half to one ounce, but there are blocks that weigh up to four ounces – another reason that getting original packaging is so important!
Decontamination & Treatment
Most owners realize that rat and mouse bait should not be ingested by their pets, furthermore, most baits have a delay in onset of symptoms. Therefore, many times pets will arrive at the clinic when there is still time to prevent symptoms.
Emesis and activated charcoal are at this time the only therapies known to prevent toxicity from bromethalin (we will discuss lipid emulsion therapy shortly). If you want to be a toxicology rock star use this handy chart – we use it every day to treat bromethalin cases.
When giving activated charcoal to bromethalin cases, it is important to monitor sodium levels and the hydration status of your patient. Unfortunately, signs of hypernatremia from activated charcoal and signs of bromethalin toxicosis look very similar, but treatment and prognosis for them are very different.
The first thing to remember with bromethalin is that not all cases that develop signs from bromethalin are going to die. Some lower doses of bromethalin can cause symptoms like ataxia, lethargy and hind limb weakness that may eventually resolve.
So when do you worry about the signs potentially being lethal? High doses, rapid onset of signs, signs that are progressive, or initial signs that are severe (tremors, seizures) are all poor prognostic factors. Historically, treatment is aimed at lowering CSF pressure and decrease swelling of the nerves. Mannitol, corticosteriods and diuretics in addition to symptomatic measures have been mainstays of therapy.
The problem with these drugs is that once they are stopped symptoms come back – and they’re not good reaching the main site of action of bromethalin, which is inside the myelin sheathes of nerves.
Lipid emulsion therapy’s efficacy with bromethalin is unknown. We get asked a lot about using lipids for a lot of different toxins, but seeing that bromethalin can be found in the fat, it is a common one we are asked about.
Another issue is that since onset of signs can be delayed with bromethalin, we do not know when the best time may be to use it (as part of the decontamination procedures vs. once signs have started).
If you are considering using lipid emulsion therapy with bromethalin toxicity, there are a few things to keep in mind.
Still follow guidelines for standard decontamination. If it is a severe dose (>0.75 mg/kg), still give your doses of activated charcoal and induce emesis if timing is appropriate.
If you are giving it once signs have developed, remember many of your antiepileptics are also fat soluble.