Pharmacology of Antiepileptic Drugs

1. Stabilizing Neurons: Maintaining electrolyte balance to prevent erratic firing.
2. Decreasing Hyperexcitability: Suppressing the transmission of impulses from one nerve to the next.
3. Controlling Impulse Spread: Decreasing the spread of excessive nerve impulses so they fire in a controlled, unified manner.

Acute vs. Maintenance Therapy

It is a common clinical error to attempt to use maintenance medications to stop an active seizure. Maintenance drugs are for long-term prevention, whereas acute management requires specific agents.

Acute Seizure Management: Benzodiazepines

Benzodiazepines are the first-line drugs for acute seizures or the treatment of status epilepticus. They work by depressing activity in the brainstem and limbic system. Common examples include:

• Lorazepam (Ativan®): 1–2 mg IV every 5–10 minutes as needed.
• Diazepam (Valium®): 5–10 mg IV every 5–10 minutes as needed.
• Midazolam (Versed®): Used as a sedative/anesthetic during invasive procedures or to induce coma in the ICU.

Maintenance Antiepileptic Agents

Once the acute phase is managed, patients are transitioned to maintenance therapy.

1. Phenytoin (Dilantin®) Phenytoin is a widely used maintenance drug but requires strict administration protocols. It is highly protein-bound and is a potent hepatic enzyme inducer (CYP450).

• Administration: Must be given via slow IV infusion in Normal Saline (NS) only. It is alkaline and highly irritating; failing to flush the vein with NS post-infusion can cause local tissue sloughing and thrombophlebitis.
• Side Effects: Gingival hypertrophy (gum overgrowth), "Dilantin facies," osteoporosis, and teratogenicity (Pregnancy Category D).

2. Carbamazepine (Tegretol®) and Valproic Acid (Depakote®)

• Carbamazepine: Chemically similar to TCAs; it inactivates Na channels and acts as a GABA agonist. It is a strong hepatic enzyme inducer and may worsen myoclonic or absence seizures.
• Valproic Acid: A broad-spectrum agent used for absence, myoclonic, and resistant seizures. It blocks Na channels and inhibits GABA transaminases.
• Drug Interaction Warning: Avoid using Carbamazepine and Valproic acid together, as they can cause toxicity in one another.

3. Barbiturates (Phenobarbital) Used specifically for status epilepticus, phenobarbital increases GABA receptor activity. It is a Schedule IV drug and can interfere with REM sleep.

4. Newer Classes of AEDs Newer agents often have different side effect profiles and are used for specific seizure types:

• Gabapentin (Neurontin®): For refractory partial seizures; structurally similar to GABA.
• Lamotrigine (Lamictal®): For simple and complex partial seizures. Warning: Must avoid Valproic acid with Lamotrigine due to the risk of dermatological emergencies like Stevens-Johnson syndrome or DRESS.
• Levetiracetam (Keppra®), Topiramate (Topamax®), and Pregabalin (Lyrica®): Other modern options for seizure management.

Nursing Implications and Patient Care

Nursing management for patients with epilepsy spans from acute emergency response to long-term lifestyle education.

Priority Actions During a Seizure

When a patient begins a seizure, the nurse must act immediately to ensure safety:

1. Protect the head and call for help.
2. Time the seizure (seconds/minutes).
3. Administer 100% oxygen via non-rebreather mask at 15 LPM.
4. Prepare for IV access: Ensure large-bore IV access is available for emergency benzodiazepines (Lorazepam or Diazepam).

Long-term Management and Monitoring

• Therapeutic Drug Monitoring: Because many AEDs have a narrow therapeutic index, serum drug levels must be monitored to prevent toxicity.
• Medication Adherence: Patients must take oral agents at the same time each day to maintain steady-state levels. Extended-release forms should never be crushed or chewed.
• Lifestyle Education:
  • Patients should keep a seizure journal to track occurrences, descriptions, and side effects.
  • A medical alert tag should always be worn.
  • Do not discontinue AEDs abruptly, as this can cause rebound or recurrent seizures.
  • Driving may be restricted until drug levels stabilize and a physician provides clearance.

Exam Tip: Documentation When documenting a seizure event, always include: the time it started, duration, events leading up to the seizure, activity during the seizure, the resolution (whether it was drug-induced or spontaneous), and any injuries incurred.

Assessment and Evaluation

Nurses must perform baseline assessments, including liver function studies, CBC, and pregnancy tests (Beta HCG), due to the hepatotoxicity and teratogenic nature of many AEDs.

The success of therapy is evaluated by the decrease or absence of seizure activity and the patient's ability to perform activities of daily living (ADLs) despite potential CNS depression side effects.