Pharm- 15 Flashcards
What causes focal seizures to be focal?
Focal seizure, or partial seizure, is named for the focal nature (surprise) of where the brain is affected. Surround inhibition (same principle as eye inhibition) keeps the seizure location localized to one spot
How does focal seizures increase in strength to cause generalized seizurres?
GABA inhibition isnt strong enough
What i the key feature to distinguish focal seizures from generalized seizures?
The pt retains consciousness
What are the Sx to focal szrs in the frontal lobe?
a wave-like sensation in the head; in the temporal lobe, a feeling of déjà vu (glitch in the matrix)
What happens in a complex focal szr?
szr starts in 1 part –> spreads –> Sx’s spread accordingly.
What happens in secondary generalized szrs?
this type of seizure is bilateral due to spreading across the connections of the brain to the opposite hemisphere
What are the classical Sx of secondary generalized szrs?
loss of consciousness, and a tonic-clonic contraction of the body
What are the classical Sx of tonic-clonic (grand mal) szrs?
Loss of consciousness, and also as you would expect, intense contraction of both antagonist and agonist muscle groups.
What happens with the NMDA and AMPA receptors in the tonic phase?
They go super crazy
What happens to the AMPA and GABA receptors during the clonic phase?
They cycle back and forth,thats why u get jerky and spazzy
Where do absence szrs occur inth brain?
originate in a central location, and spreads to both hemispheres
What is the classical Sx of absence szrs?
characterized by a brief loss of consciousness
What is the mechanism to cause absence szrs?
T-type calcium channels, which are responsible for slow-wave sleep, so if they are activated, you just fall asleep right where you are. Somehow these calcium channels get activated inappropriately, leading to temporary loss of consciousness.
What are the 4 main mechanisms of anti-epileptic drugs (AEDs) to help wiht the Sx of szrs?
Drugs that increase Na+ channel inhibition
Drugs that inhibit calcium channels
Drugs that increase GABA mediated inhibition
Drugs that inhibit glutamate receptors
What is the mechanism to treat focal and general seizures?
treated via Na+ channel inactivation to stop channels, specifically channels that are cycling through open/closed states very quickly
What are the 4 drugs to treat local and secondary generalized seizures, which act on Na+ channels?
Phenytoin, Carbamazepine, Lamotrigine, and Valproic Acid
VPLC
What is the “use-dependent” mechanism of Phenytoin to treat szrs?
channels that are opened and closed at a high frequency, making them useless for slow, cyclical seizures such as Absence Seizures.
What % of phenytoin is bound to albumin in the blood?
95% bound to albumin
How is phenytoin metabolized in the body?
metabolized by the p450 hepatic system, and is an inducer of the p450 system (increases metabolism of fellow drugs metabolized by p450)
What is the T1/2 of phenytoin?
24 hour half life, because of its high albumin binding rate, if you give a patient too much, all of a sudden you may encounter very high levels of the drug in the plasma from virtually nothing before
What drug is an inducer of phenytoin?
Carbamezapine
What is an inhibitor of P450, causing the decreased metabolism of phenytoin?
Chloraamphenicol, Cimetidine, Disulfiram, Isoniazid
Phenytoin increases the metabolism of which drugs?
Oral contraceptives, quinidine, doxycycline, cyclosporine, methadone, levodopa
Why is carbamexapint pretty much the standard of choice for most patients that are also taking other drugs rather than phenytoin?
Linear metabolism
Why can Lamotrigine treat absence szrs better than phenytoin/carbamezapine?
due to its ability to affect High voltage Calcium channels
When do you use lacosamide?
Mechanism of action enhances slow inactivation of voltage gated sodium channels, and is another alternative to carbamazepine and phenytoin, especially for patients with drug-resistant epilepsy
Which tpye of Ca channels does ethosuximide block?
T-type calcium channels
What then does ethosuxamine treat>
absence szrs
Which type of Ca channels does valproic acid target?
blocks both T-type and High voltage calcium channels
Which Ca channels does gabapentin inhibit?
decreases release of excitatory neurotransmitter by inhibiting High Voltage calcium channels
Which Ca channels does pregabalin treat?
blocks High Voltage calcium channels
So in essence, blocking T-type Ca channels treats what type of szrs?
Petit mal (absence)
And then blocking high voltage Ca channels treats what type of szrs?
Generalized
What is the first line Tx drug for absence szrs?
ethosuxamide
Valproic acid can increase GABA-mediated inhibiton by increasing which enzyme?
glutamic acid decarboxylase, the enzyme that synthesizes GABA
Since valproic acid works on both T-type and high voltage-Ca channels, what types of szrs does it treeat?
Mixed
Why is gabapentin weird?
the drug’s oral availability (giggity) is unpredictable
Since pregabalin is more predictable than gabapentin, and inhibits high velocity Ca channels, what can it treat?
fibromyalgia and neuropathic pain
Vigabatrin- mech of action
inhibits GABA metabolism, so it enhances GABA activity – blocks the enzyme GABA transaminase.
Vigabeatrin- use
infantile spasms and refractory focal epilepsy
Vigabentin- adverse reactions
induces metabolism of carbamazepine, bad effects may include peripheral visual field defects
What are the main effects of benzos and barbs?
Benzodiazepines and barbiturates are GABA receptor helpers, and increase the effect GABA has on the receptors. They raise the action potential threshold by acting on GABA receptors, which open the Cl- channels
What are the 4 benzos for szrs?
Diazepam, Lorazepam, Midazolam, and Clonazepam (pampampamapmapamama)
Why is clonazepam unique, as far as what it targets?
it can inhibit T-type Calcium channels, helping stop absence seizures.
What is the main mechanism of barbituates?
These work on all the different GABA receptors, and keeps the Cl- channel open longer than normal via allosteric binding as well as weak agonist binding to the GABA receptor. For the reason of weak agonist binding, it can actually enhance T-type calcium channels and help start absence seizures.
What does phenobarbital treat?
partial seizures and tonic-clonic seizures
Why is felbamate no longer used regularly to treat seizures?
Felbamate was found to be linked to fatal aplastic anemia and liver failure. It is now only used for patients with refractory epilepsy
Rufinamide- mech of action
prolongs sodium channel inactivation, but it does so differently than the other drugs (phenytoin, carbamazepine) via a unknown MOA
Rufinimide- use
No serious side effects, and can be used in place of felbamate for refractory epilepsy. Main treatments include focal seizures and drop attacks in Lennox-Gastaut syndrome (childhood onset of frequent/refractory seizures).
