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Discussion Starter · #3 ·
"2.1.1 Absorption, distribution and excretion

Oxfendazole, fenbendazole and febantel are three metabolically
related anthelmintics. Fenbendazole and oxfendazole are
metabolically interconvertible, and febendazole is a prodrug of them
both.
Oxfendazole and fenbendazole both undergo further metabolic
oxidation and carbamate hydrolysis."

There you go, maybe that will clear things up. :wink:
 
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No. I understand what that means. Do you? Are you suggesting that Oxfenbendazole has identical effects as fenbendazole? Or are you suggesting that Oxfenbendazole is "commonly advocated for frogs?"

Once again, who is suggesting this?
 

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Discussion Starter · #5 ·
David, I posted this as a resource so that others can use it as a reference for greater understanding. If you want to read this paper, feel free.
 

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Discussion Starter · #6 ·
By the way a prodrug is a precursor to another drug. So, essentially, a prodrug is metabolically converted into a drug. Therefore, fenbendazole is metabolically converted into oxfendazole. The chemical ratio of prodrug to drug varies with species and prodrug, but general side effects of a prodrug can usually be determined from a resultant drug's effects. because the prodrug is converted into a drug.

Yes, I took biochemistry.
 
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Oh, I have read the paper you posted. It is Yugoslavian research of an American drug. I understand what the paper says. Your original statement was misleading at best, and I just wanted to make certain 1) people didn't believe that oxfenbendazole was commonly prescribed for amphibians, or 2) if some vet was doing this, I would just want to know who so we could discuss it.

If you have any worrys about any side effects of fenbendazole or oxfenbendazole, please bring them up here so we can discuss it and everyone can benefit from the disussion.

Interestingly enough, oxfenbendazole is a very safe dewormer that is FDA approved for cattle - even though cattle are the most adversely effected species. The LD50 is over 100 mg/kg, which means that a cow will need to eat more than 1/10th its body weight of pure drug to have a 50% chance of dying. When you take into account that the drug is only 22% of the powder, that means the cow would have to eat 1/2 of its body weight in powdered drug to have even a 50% chance of dying. Then realize that they mix this powder in water and the cow would need to drink more than its own body weight of liquid before reaching that 50% chance of death. Cows weigh thousands of pounds, Cows don't drink thousands of pounds of water each day. And remember that cows are the MOST ADVERSELY EFFECTED SPECIES IN THIS STUDY.
 

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Discussion Starter · #8 ·
What is your source for your LD50 statistics, and what was the species tested? Note that the LD50 varies widely from species to species.

Regardless, it is apparent from this study (and others from DVM/PhD's I have talked to) that fenbendazole causes bone marrow suppression and can cause some liver damage when used long term.
 
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2.2.1 Acute studies

Table 1. Acute studies on oxfendazole


Species Sex Vehicle LD50 Reference
(mg/kg b.w.)


Mouse M&F distilled water > 6400 Hallesy, 1973

Rat M&F distilled water > 6400 Hallesy, 1973b
Chester & Bidlack,
1987a

Chester & Bidlack,
1987b

Dog F gelatine capsule > 1600 Hallesy, 1973c

Sheep F water > 250 Braemer & Bidlack,
suspension 1976

Cattle M&F water purified > 112.5 Bidlack, 1977

The graph in your link makes it much easier to understand.
 
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Homer wrote, "Regardless, it is apparent from this study (and others from DVM/PhD's I have talked to) that fenbendazole causes bone marrow suppression and can cause some liver damage when used long term."

Actually this study did not look at fenbendazole, and every drug has some side effects at some dose. Asprin causes much much more bone marrow supression and liver damage than fenbendazole. Asprin also causes cartilage damage and gastric ulcers. Asprin is much more harmful and deadly than fenbendazole, but we use asprin all the time and many doctors recommend a daily dose of asprin.

What exactly do you mean by "apparent?"
 

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Discussion Starter · #12 ·
Dr. Frye said:
Oh, I have read the paper you posted. It is Yugoslavian research of an American drug. I understand what the paper says. Your original statement was misleading at best, and I just wanted to make certain 1) people didn't believe that oxfenbendazole was commonly prescribed for amphibians, or 2) if some vet was doing this, I would just want to know who so we could discuss it.

If you have any worrys about any side effects of fenbendazole or oxfenbendazole, please bring them up here so we can discuss it and everyone can benefit from the disussion.

Interestingly enough, oxfenbendazole is a very safe dewormer that is FDA approved for cattle - even though cattle are the most adversely effected species. The LD50 is over 100 mg/kg, which means that a cow will need to eat more than 1/10th its body weight of pure drug to have a 50% chance of dying. When you take into account that the drug is only 22% of the powder, that means the cow would have to eat 1/2 of its body weight in powdered drug to have even a 50% chance of dying. Then realize that they mix this powder in water and the cow would need to drink more than its own body weight of liquid before reaching that 50% chance of death. Cows weigh thousands of pounds, Cows don't drink thousands of pounds of water each day. And remember that cows are the MOST ADVERSELY EFFECTED SPECIES IN THIS STUDY.
Yes, David, I read the article. That's why I am perplexed by your LD50 analysis. First, the LD50 for cattle in the study was found to be 112.5 mg/Kg body weight.

That means that for every kilogram of bodyweight, it takes 112.5 milligrams of oxfendazole (not oxfenbendazole) to kill 50% of the cattle. Let's do the math on the percent weight here:

112.5 mg = .1125 grams

1Kg = 1000 grams

Therefore, .1125 grams ofendazole per 1000 grams of body weight of cattle will kill the cattle. That is not 10% of the cattle body weight, that is .01125 % --three orders of magnitude difference there between your calculation and the true LD50 calculation (1000 times off).

Plus, let's remember that we are talking about the effects on mammals here, which varies widely between species. Without actual lab data on its effects on darts, let alone on different species of darts, don't you think that there are going to be varying LD50 levels for different darts? It seems to me that arguing the safety or toxicity of a drug n amphibia based on its widely varying toxicity in mammals should give pause for concern. I thought you were giving me some new data from elsewhere.
 
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Homer, you are correct. In my haste, I made a decimal place error. I keep forgetting how sensitive these cows are to their own medicine. According to Amphibian Medicine and Captive Husbandry the recommended dose for amphibians is greater than the LD50 for cows. The dose for fenbendazole in amphibians is 100mg-200mg/kg.

24.7 Anthelmenitics
"Fenbendazole is effective in reducing or eliminating many nematode infections in amphibians. Fenbendazole (100 mg/kg PO q 7-10 days) is used often for prophylaxis during quarentine or as therapy for confirmed gastrointestinal nematodiasis in amphibians. Granular fenbendazole may be used to dust insects for administration to small amphibians, but this modality renders it impractical to quantify the amount of drug ingested by an amphibian. NO ADVERSE REACTIONS HAVE BEEN NOTED AT THIS DOSAGE. In resistant cases, fenbendazole may be administered at a lower dose on a more frequent basis to effect a cure (e.g., 50 mg/kg PO q 24 hours for 3-5 days, repeated every 2-3 weeks).

Page 317 under Pharmacotherapeutics

It seems like Doctors Kevin Wright and Brent Whitaker missed the "apparent" problems with fenbendazole. :wink:
 

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Discussion Starter · #14 ·
Dr. Frye said:
Homer wrote, "Regardless, it is apparent from this study (and others from DVM/PhD's I have talked to) that fenbendazole causes bone marrow suppression and can cause some liver damage when used long term."

Actually this study did not look at fenbendazole, and every drug has some side effects at some dose. Asprin causes much much more bone marrow supression and liver damage than fenbendazole. Asprin also causes cartilage damage and gastric ulcers. Asprin is much more harmful and deadly than fenbendazole, but we use asprin all the time and many doctors recommend a daily dose of asprin.

What exactly do you mean by "apparent?"
David,

I thought you said you knew what a prodrug was. If you administer fenbendazole to an animal, you will get oxfendazole in vivo (in the animal). Therefore, you can extrapolate potential side effects of fenbendazole from an oxfendazole study. You are correct that they won't be at the same dosage because it is not a 1:1 ratio of fenbendazole being broken down into oxfendazole. Actually, it is widely held that oxfendazole is the active form of fenbendazole.

I will continue to post links to sites so that others can make an informed judgment as to what treatments they think are appropriate for their animals. However, I am not going to continue to explain the chemistry behind the science to you or correct your gross dosage miscalculations. In fact, I am now placing you on my ignore list.

By the way, who is recommending the use of Aspirin for dart frogs?
 

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drugs

Ok, lets bring a little layman logic to this. Drugs are typically meant to cure one ailing organism by killing a smaller one (parasite, bacteria, fungus). What we are doing by medicating is giving small doses of poison, large enough to kill the invader, but typically small enough to not significantly disrupt the host.

Expecting absolutely no side effect from this process is not very realistic.

Fenbendazole is used preventatively, but not to such a degree where one would see it being a harm to the animal they are treating. So, bringing an unnecessary light to the harmful effects of this drug might be creating an unnecessary concern of those that aren't as biochemically gifted.

I think the ultimate take home message is that use these drugs cautiously. Don't over medicate. Consult with a doctor when you have questions, and don't look at drugs as a cure all.
 

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good advice

Getting a 2nd opinion is always a good idea. We have had fecals misdiagnosed before, so it is always a good idea to get the 2nd opinion.

I think the most important thing, is whoever is doing the fecals (you, a friend, or a vet) need to know how to operate a microscope, proper procedures and materials to perform floats, stains, etc, and resources to identify what they have seen. A camera integrated with the microscope is an awesome benefit as well.

If anyone is interested, I will be happy to provide anyone with the name and number for our vet. He charges $10 per fecal and performs two tests on each speciman. 1. a float and 2. a stain.

Thanks,

Melis




idea said:
and always get a second opinion =)
 
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Melissa,
It is important to know exactly what you are looking at, what you have found. Leave the fecals to a Vet, for $10 you can not afford to pass it up. Do you know how many different Coccidia there are alone? Knowing what you have found is THE most important part of a fecal exam, there are just too many critters out there for the average Joe to be making definitive guesses at what is in their fecals.

Rich
 
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Re: good advice

melissa68 said:
If anyone is interested, I will be happy to provide anyone with the name and number for our vet. He charges $10 per fecal and performs two tests on each speciman.
idea said:
and always get a second opinion =)
dont think that she does these by herself, looks like she is offering a vet referal to me..... :wink:
 
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