When you think of seizures and epilepsy, you think of electrical activity. With drug therapy we’re trying to stabilize this abnormal area and/or take a normal area adjacent to it and stabilize it further so the abnormal electrical activity can’t travel further so the person doesn’t have a seizure. We’re also going to raise the threshold of stimulation and activate inhibitory pathways.
Phenytoin (Dilantin) – p.o.
- Generalized non-convulsive seizures (petit mal; when there’s absolutely no movement other than maybe their eye lids.)
- Febrile seizures (fever associated with children; unfortunately every time they have a fever they may have a seizure. The good news is though the children outgrow it.)
- Generalized convulsive seizures (grand mal)
- Seizures following withdrawal of short acting barbiturates.
- Hyperplasia of gums. As long as a person practices good oral hygiene, this will not happen, but if a person does not practice good oral hygiene, the gums will overgrow to the point where you can’t see the teeth anymore.
- Dermatitis (rash)
- Hirsuitism (abnormal growth of hair where you don’t want it grown)
- GI Upset
- Sedation. Usually within a few days or week of getting balanced with the drug the sedation goes away.
Phenytoin is one of those unique drugs where a person can easily get toxic with the drug. It doesn’t take much to go from therapeutic to extremely toxic. One of the earliest tests we could do is a test for nystagmus. Tell the patient, without moving your head, follow my finger with your eyes. If they have nystagmus their eyes are going to be bouncing. That’s an early indication that they’re toxic and we need to look at their blood levels.
Interactions: Instead of a drug/drug interaction, this time it’s a food/drug interaction. Phenytoin tends to partially block the absorption of folic acid and once the levels of folic acid are down for some time the person becomes anemic, so most patients given this drug are given extra folic acid supplementation.
Phenytoin is also available in injectable use for IV use. In intravenous use, we’re talking about giving an intravenous push. We draw it in a syringe, and we just shoot it into a patients veins but you have to be very careful how you shoot it in the patient. Phenytoin is in liquid form but this product is not water soluble. If you look at the manufacturers package insert it says don’t mix it in any IV solution. If you normally mix it into the IV solution, it’s usually saline (0.9% sodium chloride) or dextrose (5% dextrose). If you mix this in either one, the crystals will grow right there in front of your eyes and one thing you’ll be told in nursing is to not inject crystals into a patients veins. If you mix it into sodium chloride, you won’t see crystals but the manufacturers don’t recommend it. So that puts you in a dilemma if the doctor says hang it up in an IV. So do you go with the literature or follow the doctors orders? You have to go with your hospital IV policy. Every hospital has one.
Phenytoin is soluble in propylene glycol. So there is a warning: When you shoot this in a persons veins, it cannot be faster than 1cc/minute, so with phenytoin that means 50mg a minute. If the patient is having status epilepticus, you have to give them a loading dose and usually this loading dose contains 20cc’s. That would take 20 minutes while the patient is convulsing.
Primidone (Mysoline) – p.o.
Primidone is known as a pro drug because it is metabolized to something else. Primidone is converted to phenobarbital. Phenobarbital takes a long time to take effect and the chance of abuse is low. Primidone takes even longer to take effect and has virtually no chance for abuse.
- Febrile seizures
- Convulsant seizures
- Barbiturate withdrawal seizures (because it’s like phenobarbital but because it needs to be metabolized into it, it’s a little more gentle)
Barbiturate Properties: The main side effect is sedation.
The drug interaction issue is hepatic induction which stimulates metabolism of other agents including other anticonvulsant agents so the dosage of the other drugs may need to be increased.
Ethosuximide (Zarontin) – p.o.
Therapeutic Use: Mainly with children that have general non-convulsant seizures (petit mal).
Side Effects include sedation, headache, dizziness.
Divalproex (Depakote) – p.o.
- Febrile Seizures
- Non-convulsant seizures
- Convulsant Seizures
Side Effect: Sedation
Clonazepam (Klonopin) – p.o.
Always used as adjunct therapy only
Tolerance develops to therapeutic properties
Diazepam (Valium) or Lorazepam (Ativan) – inj.
Intravenous use for status epilepticus
Carbamazepine (Tegretol) – p.o.
Therapeutic Use: Partial Seizures and Neurologic Pain
Toxicity: Bone marrow depression
- Fosphenytoin: intravenous administration of phenytoin
- Gabapentin (Neurontin) – p.o. – Adjunct therapy for partial seizures and neurologic pain
- Felbamate (Felbatol) – p.o.
- Lamotrigine (Lamictal) – p.o.