Pharmacology: AntiConvulsants, AntiEpileptics, Benzos

[AnthonyM83]

I sat in on a short paramedic prep lecture on pharmacology today.

Lecturer was discussing the difference between anticonvulsants, antiepileptics, and benzodiazepines. I just want to run what I remember by you guys, since I didn't have the chance to take notes.

Anticonvulsants work at the muscular level. Doesn't much matter what the cause of the seizure is. If a seizure is in progress these work best, because once it starts it's harder to control that brain activity with antiepileptics. They work by blocking sodium channels. Examples: Klonopin and phenobarbitol?

Antiepileptics work in the brain. They're good for preventing seizures, but not for intervening with in-progress seizures. They're used more to prevent seizures in those with seizure disorders. They work by blocking Chloride channels. Examples: carbamazepine/Tegretol and phenytoin/Dilantin

Benzodiazepenes can also be used to prevent/stop seizures, though apparently not as good as an anticonvulsant if seizure in-progress. Also used for anxiety. Examples: diazepam/Valium and lorazepam/Ativan

Is this how you guys classify the drugs too? Am I recalling the lecture correctly?

[Mateo_1387]

I never really categorized them like that, but I guess it works.

The anticonvulsants you mention, Klonopin and Phenobarbital, I do not think is accurate in that they work at the site of the muscle. Klonopin is a benzodiazepine, and Phenobarbital works in the brain, not directly on the muscles. They both act on Gama Aminobutyric Acid (GABA). A drug that would work directly on the muscles would be paralytics such as Vecuronium, or Succinylcholine.

Tegretol works primarily on calcium channels, but does affect sodium channels, GABA receptors, adenosine receptors, and increases serotonin and other neurotransmitters. Dilantin on the other hand works primarily on sodium channels.

Benzodiazepines are primarily known to work on GABA, though Valium can be used for muscle relaxation. Benzodiazepines are used to treat seizures as they occur because the quickly increase the effects of GABA.

[logos]

I think the distinction they were trying to make with their classification, Anti-epileptics (AEDs) vs anti-convulsants, was with regard to timing and frequency of the medication's use. That is, one is used to stop seizures, the other to prevent them. If you find that distinction helpful, I would try to think of it as a practical distinction, not a pharmacologic distinction. For example there were in the past substantial numbers of epileptics controlled on daily phenobarbital.

The barbiturates (of which phenobarbital is a member) and benzodiazepines (lorazepam (ativan), diazepam (valium), etc, etc) are drugs that bind to GABAergic (meaning activated by the neurotransmitter GABA) chloride channels. They cause these channels to OPEN, allowing negatively charged chloride ions into the neuron and thus hyperpolarising it (making it resistant to firing). They are centrally acting (meaning act on the brain, as do all "muscle relaxants" sold for orthopedic pain...surprise!). These drugs are generally used, in the context of seizures, to stop the seizure because they are rapid acting and can be delivered via a number of routes (rectal valium for example can be given to parents of epileptic children for emergency use).

There are some subtle differences between benzos, which are commonly used, and barbiturates, which are only rarely utilized since the advent of the benzos, in their mechanism of action. The only clinically relevant difference that I can think of is in their toxicity profile. Benzos are generally considered safe in overdose (when given alone), while barbiturates can lead to life threatening respiratory depression relatively easily.

I suggest reading something like the wikipedia article on benzos: http://en.wikipedia.org/wiki/Benzodiazepines

The other classes of drugs are generally known as the AEDs, they all act on ion channels. Different drugs block different channels, but the principle is that by blocking ion channels, one prevents the propigation of an action potential down the axon of the neuron. The levels of these drugs are often quite finicky and can be affected by other drugs the patient is placed on by increasing or decreasing their metabolism by the liver. Another important point to keep in mind is that these drugs may have effects on the heart by blocking cardiac ion channels.

wiki AEDs : http://en.wikipedia.org/wiki/Antiepileptic

Epilepsy has a very specific definition. It is a term that often is misused. The key is that it must be RECURRENT seizures. The epilepsy wiki article gives not only some decent info on epilepsy, but talks about the different types of seizures. Not all seizures are the "tonic-clonic" variety that we commonly think of as seizures.

[AnthonyM83]

Thanks both of you.

Logos glad to see you posting more. I was reviewing a few of your posts, just yesterday.

I think they were trying to make the distinction on which drugs suppress impulse to contract muscles and which contract muscles themselves. By what method do common paralytics works? Muscarinic receptors?

I know the lecturer told me they had a lot of fire fighters in the class, so he was trying not to get too complex and just give big ideas(apologies for any FF's on here...the ones in my area don't much care about this stuff).

[Mateo_1387]

They work on Nicotinic receptor sites.

[logos]

They work on Nicotinic receptor sites.

Yes. Nicotinic acetylcholine receptors located in a very particular place, the neuromuscular junction.

NMJ: http://en.wikipedia.org/wiki/Neuromuscular_junction

Paralytics: http://en.wikipedia.org/wiki/Neuromuscular-blocking_drugs

Important concepts:

http://en.wikipedia.org/wiki/Receptor_theory

Receptor agonsim vs antagonism is very important in basic pharmacology.

[Just Plain Ruff]

Thanks both of you.

Logos glad to see you posting more. I was reviewing a few of your posts, just yesterday.

I think they were trying to make the distinction on which drugs suppress impulse to contract muscles and which contract muscles themselves. By what method do common paralytics works? Muscarinic receptors?

I know the lecturer told me they had a lot of fire fighters in the class, so he was trying not to get too complex and just give big ideas(apologies for any FF's on here...the ones in my area don't much care about this stuff).

So they used small words then?

[ccmedoc]

Just a heads up.......wikipedia is NOT a reference.. 8)

--just sayin'

[logos]

Just a heads up.......wikipedia is NOT a reference.. 8)

--just sayin'

Haha. I love wikipedia.

Its about the quickest drug/medical reference out there when you just want to know the basics. For drugs it has what I want: the structure, the alternate names, the class, and the mechanism. Same for disease, it lists the name(s) of the disorder, its symptoms, its pathogenesis, and the very basics of its treatment. For a quick overview or a quick review of something you will recognize, it is absolutely great. On the otherhand, I agree with some of the skepticism and would never trust the specifics, like a reccomended dosage for example (thats what epocrates is for!). I admit to finding only a few mistakes about the details of the science that would be easy for a lay person to make, which I corrected.

And its pretty accurate: http://news.bbc.co.uk/1/hi/technology/4530930.stm