Chapter 36: Seizure Disorders – Antiepileptic Drug Therapy

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Welcome to the Deep Dive.

We're here to cut through the dense stuff and give you the clinical essentials.

Today, it's a really big topic for advanced practice, seizure disorders, and specifically the pharmacotherapy.

It gets complex fast.

It really does.

The number of drugs, the warnings.

It's a lot.

Yeah.

So maybe start with the basics.

What is epilepsy?

It's not just having one seizure.

It's actually a complex neurologic disorder.

The key is recurrent, unprovoked seizure activity.

Okay.

Recurrent and unprovoked.

That's important.

Yeah.

Affects nearly three million people here in the U .S.

It's often ranked fourth among common neurologic disorders.

So that single seizure presentation, that doesn't automatically equal epilepsy.

Generally, no.

Unless, and this is the key exception, you find some kind of brain abnormality that makes future seizures highly likely.

Got it.

And it all comes down to brain chemistry, right?

That electrical balance going wrong.

Exactly.

Normally, neurons communicate through this really precise balance of positive and negative ions.

It's very controlled.

But a

chaos breaking out.

Pretty much.

Yeah.

A massive abnormal firing.

Lots of neurons all going off at once, totally out of sync.

The chemical balance just tips way over towards excitation.

And the main players there are.

You've got your excitatory neurotransmitters, primarily glutamate and aspiricate.

They're pushing the go signal.

And then there's the main inhibitory one,

GABA, gamma, aminobutyric acid, trying to put on the brakes.

So in a seizure, it's like the accelerator is floored and the brakes fail.

Too much glutamate, not enough GABA action.

That's a good way to put it.

And where that imbalance starts,

that dictates how we classify it, which then guides treatment.

Right.

Classification.

We use the ILA system now, don't we?

The International League Against Epilepsy.

Yes, that's the standard.

It classifies seizures based on where they start the onset.

So focal onset, generalized onset, and unknown onset.

Though you still hear the older terms floating around in practice sometimes.

Oh, definitely.

You'll still hear petit mal for what we now call absent seizures and grand mal for toniclonic.

But for accurate documentation and treatment planning, you really need the ILAE terms.

Okay.

Let's really nail the difference between focal and generalized because that seems critical for picking the right drug.

Absolutely critical.

Focal onset means it starts in one specific area, maybe one part of the brain.

And the person might stay aware.

Or not.

Exactly.

Awareness can be preserved or it can be impaired.

Impaired awareness used to be called complex partial seizure.

Okay.

And generalized onset.

That's different.

It involves both sides of the brain, both hemispheres, right from the very beginning.

Which means?

Immediate impact on consciousness.

Usually an early and complete loss of consciousness because the whole network is involved right away.

Let's picture the main generalized types.

Absent seizures.

Those are the brief ones.

Yeah.

Often non -motor.

Yeah.

The person might just have a blank stare, maybe for five, 10 seconds.

It can be subtle.

And the key clinical pearl there is no confusion afterwards.

Exactly.

No postical confusion.

They usually snap right back to normal awareness.

Very different from other types.

Like the tonic clonic seizure.

The one most people think of as grand mal.

Right.

That's the dramatic one.

Abrupt loss of consciousness.

Then that stiffening phase, the tonic part, with sharp muscle contractions.

Followed by the jerking, the clonic phase.

Yes.

And afterwards there's that significant postictal period.

Profoundly depressed consciousness, confusion, exhaustion.

It can last for hours sometimes.

So we have the history, maybe an eyewitness account.

How do we actually diagnose and look for causes?

Well, a history and a good physical exam are always step one.

Non -negotiable.

But the gold standard test is still the EEG, the electroencephalogram.

It shows the brainwave activity, those abnormal voltage spikes.

And imaging to look for structural problems.

CT or MRI.

We're looking for lesions, tumors, scarring, anything structural.

MRI is generally preferred, especially in kids.

It's better for seeing subtle things.

Like medial temporal sclerosis.

Exactly.

That subtle scarring in the temporal lobe that MRI can pick up, which is highly epileptogenics.

CT might miss it.

In adults, either CT or MRI might be used depending on the situation.

Okay, diagnosis is clear.

Now the big question.

When do we actually start medication?

Generally, the rule of thumb is after two or more unprovoked seizures.

But there are exceptions.

Yes.

You'd start therapy after just one seizure if there are significant risk factors pointing towards recurrence.

Such as?

Things like finding a structural lesion on the MRI, seeing clear abnormalities on the EEG, or even a strong family history of epilepsy.

In those cases, the risk is high enough to warrant starting treatment sooner.

Alright, let's talk treatment goals.

It's not just about stopping the seizures, is it?

There's more to it.

Oh, definitely.

The primary goal is complete seizure control, yes.

But, and this is a huge but, it has to be done while limiting side effects.

The real aim is improving the patient's overall quality of life.

If they're seizure -free but miserable from side effects, that's not success.

And the approach usually starts with monotherapy.

One drug first.

Yes, absolutely.

Monotherapy first.

Why the strong preference?

I imagine it's tempting to add drugs if the first one isn't working perfectly.

It is tempting, but monotherapy has major advantages.

Think about compliance.

It's much simpler for the patient to take one drug correctly.

And lack of compliance is honestly the most common reason for treatment failure.

Okay, better compliance.

What else?

Easier toxicity management.

If a side effect pops up, you know which drug is causing it.

With multiple drugs, it gets much harder to figure out the culprit.

So if that first drug doesn't work, you don't just add another one on top?

Ideally, no.

The recommended step is to replace the first drug with a different first -line agent.

Try another single drug before you jump to polytherapy.

Because polytherapy using two or more drugs increases risks.

Significantly.

More complexity, way more potential for drug interactions, and a higher burden of chronic side effects.

You only go there if you really have to, after failing multiple single agents.

Okay, standard treatment.

But what about the worst case scenario?

Status epilepticus.

That's a true emergency.

Absolutely life -threatening.

Status epilepticus, or SE, we need to define that clearly.

It's continuous seizure activity that lasts longer than five minutes.

Or it can be recurrent seizures where the person doesn't fully recover consciousness in between.

Five minutes?

That's not very long.

Time is critical.

Every second counts.

There's usually a protocol often visualized like in figure 36 .2 from the source material.

It's time sensitive.

Let's walk through that timeline verbally, the first few minutes.

Right.

Phase one, stabilization.

Zero five minutes.

This is all about the ABCs.

Airway, breathing, circulation, get 5e access established, basic supportive care.

Then quickly moving into actual treatment.

Yes.

Phase two, initial therapy.

Five, 20 minutes.

This is where you need to stop the seizure fast.

But the diazepines are the first choice here.

Like lorazepam.

Lorazepam is often preferred.

4e is ideal, but IM or even rectal administration works if you can't get IV access quickly.

Midazolam IM is another common option, diazepam too.

And the big caution with benzos, always respiratory depression, right?

That's the main one.

Especially if you need repeat doses.

You have to be ready to support their breathing.

Okay, so the benzo might stop the initial seizing, but what if it doesn't fully resolve it or we need longer -term control?

Then you move to phase three, second therapy phase, 20 to 40 minutes.

This is about initiating a definitive longer -acting anti -epileptic drug, an AED.

This isn't just aborting the seizure.

It's about preventing recurrence.

And the options here are drugs -like.

Common choices include IV finitoin or its pro -drug phosphinitoin, levotiracetam, valproic acid, even phenobarbital in some cases.

The goal is to get definitive control established, ideally within about 60 minutes, to minimize the risk of permanent brain injury.

Okay, that's the emergency handled.

Now let's dive into some of those key maintenance AEDs, starting with the real classic finitoin and phosphinitoin.

Right, the high dantoins.

Finitoin is, well, a workhorse.

Been around a long time.

Its main mechanism is blocking sodium channels.

It stabilizes those neuronal membranes, decreases that rapid influx of sodium ions that drives the seizure firing.

Technically, it blocks post -antipotentiation.

And phosphinitoin is just a version that's easier to give IV.

Essentially, yes, a pro -drug.

Gets converted rapidly to finitoin in the body.

It's less irritating to veins and can be given faster intramuscularly if needed.

Now, finitoin, this is where kinetics get really, really important.

It's not straightforward dosing, is it?

Not at all.

This is probably the biggest clinical pearl for finitoin.

It has non -linear kinetics, often called Michaelis -Menten kinetics.

Meaning?

Meaning the enzymes that break down get saturated easily.

Once you reach that saturation point, even a tiny increase in the dose can cause a disproportionately massive jump in the serum concentration.

So a small dose adjustment could push someone from therapeutic straight into toxic levels.

Exactly.

The therapeutic window is narrow and this saturation kinetic makes it incredibly easy to overshoot.

Missed doses followed by catch -up doses are also really dangerous.

Wow.

Okay, so dosing requires care.

Loading dose.

Yes, you typically need a loading dose to get levels up quickly, usually around 15 to 20 milligrams per kilogram.

But the IV infusion rate is critical too.

You mentioned that black box warning.

Extremely critical.

The absolute maximum rate for IV finitoin is 50 milligrams per minute and you had to cut that in half 25 milligrams per minute for patients with cardiac issues or the elderly.

Why so slow?

Because rapid IV infusion can cause severe cardiovascular problems, hypotension, arrhythmias, even cardiovascular collapse.

That's the black box warning.

Phospho -finitoin can be given faster, which is one of its advantages.

And monitoring.

We look at total and free levels.

Yes.

Total therapeutic range is typically 10 to 20 micrograms per milliliter.

But finitoin is highly protein -bound, mostly to albumin.

So the free level of the unbound drug that's actually active is also important.

That range is usually 1 to 2 .5 micrograms per milliliter.

What happens if someone has low albumin, like an older adult or someone malnourished?

That's a huge risk factor.

If albumin is low, there's less protein for the drug to bind to.

That means a higher fraction of the drug is free and active.

So the total level might look okay, maybe 15, but the free level could be toxic.

Precisely.

You have to adjust the dose or at least interpret the levels very carefully in patients with hypoalbuminemia.

Standard equations exist to estimate the corrected level.

And the side effects.

There are some well -known chronic ones.

There are.

Chronic use can lead to things like gingival hyperplasia, overgrowth of the gums, and hirsutism, excess hair growth.

These really impact quality of life.

And concentration -related toxicity.

What signs should you look for?

Those correlate pretty well with serum levels.

The stagmas that involuntary eye movement often starts showing up when levels get above 20.

Ataxia, like trouble walking and coordinating movements, usually kicks in above 30.

Confusion and lethargy occur at even higher levels.

Okay, that's finny -toin.

Let's shift gears to another major player.

Carbamazepine.

Also a sodium channel blocker.

Yes, similar mechanism, limiting that sodium influx.

Carbamazepine is a first -line choice for focal -onset seizures and also for generalized conoclonic seizures.

But it has its own kinetic work, right?

Something called autoinduction.

That's the one.

Carbamazepine induces its own metabolism.

It literally speeds up the enzymes that break it down.

So the dose you start with becomes less effective over time.

Exactly.

When you first start it, the metabolism is slower.

But over the first, say, three to five days, it starts inducing those liver enzymes, mainly CYP3A4.

This process continues and usually stabilizes after about three to four weeks.

Meaning you need to monitor levels closely at the beginning.

Absolutely.

You often need to increase the dose during those first few weeks to maintain therapeutic levels as the drug starts chewing itself up faster.

What was a good level in week one might be subtherapeutic by week four.

And carbamazepine has some really serious black box warnings, too.

It does.

Two major ones.

First, potentially fatal dermatologic reactions.

Stevens -Johnson syndrome, SJS, and toxic epidermal necrolysis, TEN.

This risk is strongly linked to specific genetic marker, the HLAB1502 allele.

Which is more common in certain populations.

Yes, particularly in people of Asian ancestry.

Because of this strong link, screening for HLAB1502 is mandatory before starting carbamazepine in these patients.

It's a key example of pharmacogenetics in action.

And the second black box warning.

That involves potential bone marrow suppression specifically, a plastic anemia, and a granulocytosis.

They're rare, but serious.

So baseline and periodic blood counts are recommended.

What about oxcarbazepine?

It's related, often used maybe because it avoids the autoinduction.

Right.

Oxcarbazepine is a keto analogue.

It also blocks sodium channels.

It doesn't have the same autoinduction issue, which simplifies dosing.

But it has its own things to watch for.

There's about a 25, 30 % chance of cross reactivity if someone had a hypersensitivity reaction to carbamazepine.

And something about sodium levels.

Yes, a significant risk of clinically significant hyponatremia, low sodium.

It's more common with oxcarbazepine than carbamazepine, especially in older adults.

Needs monitoring.

Okay, moving on to a really broad spectrum agent.

Valproic acid or dValprox?

Valprox is, yeah, a powerhouse.

It works for a wide range of seizure types, focal, generalized, tonic, clonic.

And it's particularly good for many generalized epilepsies, including absent seizures.

Often first line there.

Its mechanism is different though, right?

More GABA related.

Yes, it seems to work through multiple mechanisms.

But a key one is increasing the availability of GABA and enhancing its inhibitory action.

It might also affect sodium and calcium channels.

But valproic acid, it comes with some of the heaviest warnings in the book.

Three black dogs warnings.

It does.

And they are critical to know.

First,

hepato toxicity, liver failure.

The risk is highest in young children, especially under two years old, and particularly those on multiple AEDs.

Second warning.

Pancreatitis.

It can be severe, even fatal, and can occur at any time during therapy, even years later.

Abdominal pain, nausea, vomiting need immediate evaluation.

And the third, hugely important for counseling.

Teratogenicity.

Valproic acid is a major human teratogen.

It's pregnancy category DX.

It significantly increases the risk of major congenital malformations, especially neural tube defects like spina bifida if taken during the first trimester.

So it should be avoided in pregnancy, especially early pregnancy, whenever possible.

Absolutely.

And in women of childbearing potential who could become pregnant, it should only be used if other medications aren't effective and with very clear counseling about the risks and the need for effective contraception.

You also mentioned a really specific dangerous drug interaction with valpro.

Yes, the carbapenem interaction.

This is crucial.

If you give a patient who is stable on valproic acid an antibiotic from the carbapenem class, like merapenem or imapenem,

it causes a rapid and dramatic drop in valpro levels.

We're talking potentially a 60 -70 % decrease within 24 hours.

Which could lead to?

Breakthrough seizures or even status epilepticus.

This combination should generally be avoided if at all possible.

If it's absolutely necessary, you need extremely close monitoring and likely supplemental valpro dosing.

Okay, let's quickly touch on a few other key drugs for pure absent seizures, the classic patimel.

The drug of choice there is ethosuximide.

It's very specific for absent seizures and generally well tolerated compared to valpro.

What about lamotrigine?

That's used quite a bit.

Lamotrigine is another broad spectrum option used for focal and generalized seizures and also in Lennox -Gastell syndrome.

It works mainly on sodium channels, but possibly others too.

But it has its own serious skin reaction risk.

Yes, it also carries a black box warning for serious rashes, including SJS10.

The risk is highest with rapid doeth escalation, especially when starting.

Or if it's given concurrently with valproic acid, which slows lamotrigine metabolism.

So slow titration is absolutely essential.

And liviteracetam or kepra, you mentioned it's popular for adding on.

Why?

Liviteracetam's big advantage is its pharmacokinetic profile.

It's primarily cleared by the kidneys and doesn't rely heavily on liver enzymes for metabolism.

Meaning fewer drug interactions.

Exactly.

That makes it much easier to add to complex regimens without worrying as much about messing up the levels of other AEDs.

It's generally well tolerated, although mood changes or irritability can sometimes occur.

Are there newer agents with significant warnings we should highlight?

Yes, a couple stand out.

PeremPenel has a black box warning for serious, potentially life -threatening neuropsychiatric events.

Things like aggression, hostility, homicidal ideation needs careful monitoring.

Wow.

And vigabatrin.

Vigabatrin is highly effective for certain seizure types like infantile spasms, but it's restricted through a special REM -S program.

That's because of its black box warning.

It can cause permanent vision loss, specifically bilateral concentric visual field constriction.

Patients need baseline and regular follow -up vision testing.

It's a significant risk -benefit discussion.

It really highlights that even newer drugs aren't free from serious risks.

Okay, let's bring this back to specific patient groups.

Geriatric patients.

Key considerations for older adults are decreased kidney and liver function, which affects drug clearance.

Lower starting doses and slower titration are generally needed.

And remember the albumin issue we discussed with phenytoin.

Lower albumin is common in older adults, increasing the free fraction of highly protein -bound drugs and raising toxicity risk.

So start low, go slow is really the mantra.

Definitely.

What about women of childbearing age?

We touched on Velproat, but other issues?

Beyond the teratogenicity of Velproat, polytherapy in general is associated with higher risks in pregnancy.

So trying to achieve monotherapy before conception is ideal.

Also, several AEDs can actually decrease the effectiveness of hormonal contraceptives, like birth control pills.

Which ones?

Enzyme -inducing AEDs like phenytoin, carbamazepine, phenobarbital, oxcarbazepine, and topiramate at higher doses can speed up the metabolism of estrogen and progestin.

Lamotrigina can also interact.

So relying solely on hormonal methods might lead to unplanned pregnancy.

It could.

Patients need counseling about this interaction and discussion of more reliable contraceptive methods, like IUDs or barrier methods, or potentially adjusting the hormonal contraception itself.

You mentioned pharmacogenetics with carbamazepine and HLA -B59202.

That feels like a really concrete example of personalized medicine.

It absolutely is.

Knowing to test patients of Asian ancestry before starting that specific drug to avoid a potentially fatal reaction?

That's tailoring therapy based on individual genetic risk.

It's where the field is heading.

Before we wrap up, any key patient education points?

Lifestyle first aid.

Yes.

Lifestyle factors are huge.

Patients should understand that things like significant sleep deprivation and excessive alcohol intake can lower their seizure threshold and provoke seizures.

Consistency is key.

And first aid for a tonic -clonic seizure.

What should bystanders do?

The main things are safety and airway protection.

Ease the person to the floor.

Clear the area around them of hard or sharp objects.

Turn them gently onto their side, the semi -brown or recovery position, to help keep the airway clear and prevent aspiration if they vomit.

And definitely don't put anything in their mouth.

Absolutely not.

Don't try to restrain them forcefully either.

Just protect them from injury.

Time the seizure if possible.

And stay with them until they're fully awake and aware.

Call for emergency help if the seizure lasts more than 5 minutes, if they have trouble breathing afterwards, or if they get injured.

Okay, this has been a really comprehensive deep dive.

We've hit the ILA classification, the importance of starting with monotherapy, the emergency management of SCE, and those critical details about specific drugs, phenytoin's non -linear kinetics, carbamazepine's auto -induction and HLA testing, valpro's major warnings,

levichathetam's cleaner interaction profile.

It really underscores that managing epilepsy requires knowing these details inside and out.

It does.

And while we focus a lot on things like serum drug levels, especially for drugs like phenytoin, that number isn't the whole story.

Right.

So maybe a final thought for our listeners, especially those advanced practice students heading into managing these patients.

Considering all this complexity, the goal of seizure freedom, the challenges of monotherapy, the risks of polytherapy and side effects,

what do you think is the most critical measure of success for an AED regimen?

Beyond just getting that serum level in range, what truly tells you if the treatment is working for the patient?

Is it just counting seizures?

Or is it about their daily functioning, their mood, their ability to work or study, freedom from those chronic side effects like fatigue or cognitive slowing?

Thinking about that bigger picture of quality of life.

Exactly.

How does the treatment impact their life overall?

That's often the real challenge and the true measure of successful pharmacotherapy and epilepsy.

Something to really think about as you manage these patients.