Antiseizure Drugs: Nursing Pharmacology Study Guide

Antiseizure Agents: Generic and Brand Names

• Drugs for generalized seizures
  • Hydantoins
    • ethotoin (Peganone)
    • fosphenytoin (Cerebyx)
    • phenytoin (Dilantin)
  • Barbiturates and barbiturate-like drugs
    • mephobarbital (Mebaral)
    • phenobarbital (Solfoton, Luminal)
    • primidone (Mysoline)
  • Benzodiazepines
    • clonazepam (Klonopin)
    • diazepam (Valium)
  • Succinimides
    • ethosuximide (Zarontin)
    • methsuximide (Celontin)
  • Others
    • acetazolamide (Diamox)
    • valproic acid (Depakene)
    • zonisamide (Zonegran)
• Drugs for partial seizures
  • carbamazepine (Tegretol, Atretol)
  • clorazepate (Tranxene)
  • gabapentin (Neurontin)

Disease Spotlight: Epilepsy

Epilepsy is a collection of syndromes, all marked by a sudden discharge of excessive electrical energy from nerve cells in the brain. This abnormal discharge produces a seizure. The nature of a seizure depends on which cells start the discharge and which neural pathways get stimulated. Seizures can be primary (no underlying cause) or secondary (from an external factor like head injury).

Status epilepticus is a state in which seizures recur rapidly with no recovery between them. It is potentially the most dangerous seizure presentation.

The International Classification of Seizures sorts seizures by symptoms and characteristics into two main categories.

Generalized Seizures

Massive electrical activity begins in one area of the brain and rapidly spreads to both hemispheres, usually with loss of consciousness. Five types:

• Tonic-clonic. Involuntary muscle contraction (tonic) followed by relaxation that looks like an aggressive spasm (clonic), loss of consciousness, then confusion and exhaustion in early recovery.
• Absence. An abrupt, brief (3-5 s) loss of consciousness, common in children (starting at age 3) and usually gone by puberty. Typically no muscle contractions.
• Myoclonic. Short, sporadic muscle contractions lasting several minutes. Relatively rare.
• Febrile. Self-limited seizures tied to very high fevers, usually tonic-clonic, most often in children.
• Jacksonian. Begins in one area of the brain and one part of the body, then spreads until a generalized tonic-clonic seizure develops.

Partial (Focal) Seizures

These originate in one area of the brain and do not spread. Two types:

• Simple partial. Occurs in a single area of the brain and may involve one muscle movement or sensory change.
• Complex partial. Appears in the late teens and involves a series of reactions or emotional changes plus complex sensory changes (hallucinations, mental distortion, personality changes, loss of consciousness, loss of social inhibition). Motor changes can include involuntary urination, chewing motions, and diarrhea.

Age-Group Considerations (All Antiseizure Classes)

These points apply across hydantoins, barbiturates, benzodiazepines, and succinimides:

• Children. More sensitive to the sedating effects, so monitor frequently and closely. These drugs can affect learning and social development. Give parents consistent support and education about the seizure disorder and the medications.
• Adults. Provide regular care and close monitoring for adverse effects, and encourage MedicAlert identification. Focus teaching on the disorder, lifestyle changes, medications, and handling stigma.
• Pregnancy and lactation. Use caution. Some agents are linked to fetal abnormalities in animal studies, and some are clearly tied to predictable congenital effects in humans. Encourage barrier contraception and alternative feeding methods. Do not stop an antiepileptic abruptly, since that can precipitate seizures and lead to anoxia.
• Older adults. More susceptible to adverse effects from impaired metabolism and excretion; doses may need reducing.

Drugs for Treating Generalized Seizures

These drugs work by blocking channels in the cell membrane or altering receptor sites, which stabilizes nerve membranes. Because they act on the whole nervous system, sedation is expected. The classes are hydantoins, barbiturates, barbiturate-like drugs, benzodiazepines, and succinimides. Succinimides and GABA-modulating drugs treat absence seizures.

Hydantoins

Therapeutic action. Stabilize CNS nerve membranes by reducing the excitability and hyperexcitability of ionic channels to stimulation. Slowing conduction through nerve pathways reduces the tonic-clonic, muscular, and emotional responses to stimulation.

Indications. Control of tonic-clonic and psychomotor seizures, seizure prevention during neurosurgery, and control of status epilepticus. They cause less sedation than other classes, making them the choice for patients who will not tolerate sedation and drowsiness. Their severe adverse effects, however, mean benzodiazepines have replaced them in many situations.

Contraindications and cautions. Allergy to hydantoins; pregnancy and lactation (possible harm to fetus or newborn); debilitated patients (may respond adversely to CNS depression); impaired hepatorenal function (interferes with metabolism and excretion); coma, depression, or psychoses (worsened by generalized CNS depression).

Adverse effects. CNS depression, confusion, drowsiness, lethargy, fatigue; CV arrhythmias and blood pressure changes; GI constipation, dry mouth, anorexia; GU urinary retention, loss of libido. Cellular toxicity shows up as severe liver toxicity, bone marrow suppression, gingival hyperplasia, and serious dermatological reactions (hirsutism, Stevens-Johnson syndrome).

Interactions. Alcohol (increased CNS depression); evening primrose (increased seizure risk); ginkgo (increased risk of serious adverse effects with phenytoin).

Barbiturates and Barbiturate-like Drugs

Therapeutic action. Inhibit impulse conduction in the ascending RAS, depress the cerebral cortex, alter cerebral function, and depress motor nerve input.

Indications. Control of tonic-clonic and psychomotor seizures, seizure prevention during neurosurgery, and control of status epilepticus. Like hydantoins, they stabilize CNS nerve membranes by acting directly on ionic channels to reduce excitability and hyperexcitability. Phenobarbital depresses the lower brainstem, cerebral cortex, and motor conduction. Mephobarbital treats tonic-clonic and absence seizures and also serves as an anxiolytic or hypnotic.

Contraindications and cautions. Same as hydantoins.

Adverse effects. CNS depression, confusion, drowsiness, lethargy, fatigue, sedation, hypnosis, anesthesia, deep coma; CV arrhythmias and blood pressure changes; GI constipation, dry mouth, anorexia; GU urinary retention, loss of libido; physical dependence, withdrawal, severe dermatological reactions. Mephobarbital is commonly tied to CNS and GI effects and can cause circulatory collapse and apnea, making it less desirable than other agents.

Interactions. Alcohol (increased CNS depression); ginkgo (increased risk of serious adverse effects).

Benzodiazepines

Therapeutic action. Potentiate GABA (the inhibitory neurotransmitter that stabilizes nerve cell membranes). They act mainly in the limbic system and RAS, so they also relax muscles and relieve anxiety without substantially affecting cortical function.

Indications. Adjunct treatment of status epilepticus and severe recurrent convulsive seizures, and management of epilepsy in patients who need intermittent use to control bouts of increased seizure activity. Also used to relieve anxiety before operative interventions.

Contraindications and cautions. Same as hydantoins.

Adverse effects. CNS depression, confusion, drowsiness, lethargy, fatigue; CV arrhythmias and blood pressure changes; GI constipation, dry mouth, anorexia; GU urinary retention, loss of libido; physical dependence and withdrawal.

Interactions. Alcohol (increased CNS depression).

Succinimides

Therapeutic action. Act in inhibitory neuronal systems and suppress the EEG pattern associated with absence seizures.

Indications. Most often used to treat absence seizures and reduce the frequency of attacks.

Contraindications and cautions. Same as hydantoins.

Adverse effects. CNS depression, drowsiness, fatigue, ataxia, insomnia, headache, blurred vision; GI decreased activity, nausea, vomiting, anorexia, weight loss, GI pain, constipation or diarrhea; direct chemical irritation of skin and bone marrow (bone marrow suppression, fatal pancytopenia, urticaria, alopecia, Stevens-Johnson syndrome). Ethosuximide has relatively few adverse effects compared with many antiseizure agents.

Interactions. Primidone (decreased primidone serum levels).

Drugs for Treating Partial Seizures

Partial seizures are either simple (single muscle or reaction) or complex (a series of reactions or emotional changes).

Therapeutic action. Stabilize nerve membranes by altering sodium and calcium channels or by boosting the activity of the inhibitory neurotransmitter GABA. Carbamazepine inhibits polysynaptic responses and blocks sodium channels to prevent repetitive action potentials; it is chemically related to TCAs. Clorazepate and felbamate potentiate GABA. Gabapentin blocks polysynaptic responses and, in certain situations, increases stimulus thresholds.

Indications. Carbamazepine, felbamate, and oxcarbazepine are used as monotherapy. The rest are adjunctive.

Contraindications and cautions. Allergy to antiseizure agents; bone marrow suppression (worsened by drug effects); severe hepatic dysfunction (interferes with metabolism); pregnancy (carbamazepine, clorazepate, and gabapentin shown dangerous to the fetus); renal stones (worsened by drug effects).

Adverse effects. CNS drowsiness, fatigue, weakness, confusion, headache, insomnia; respiratory upper respiratory infections; GI depression, nausea, vomiting, anorexia. Pregabalin is a category V controlled substance (can cause feelings of well-being and euphoria) and is also tied to CNS depression with somnolence, dizziness, and visual changes.

Interactions. Other CNS depressants and alcohol (increased CNS depression).

Pharmacokinetics

Drugs for Treating Generalized Seizures

Here are the characteristic interactions of hydantoins and the body in terms of absorption, distribution, metabolism, and excretion:

Drugs for Treating Generalized Seizures

Here are the characteristic interactions of barbiturates and barbiturate-like drugs and the body in terms of absorption, distribution, metabolism, and excretion:

Drugs for Treating Generalized Seizures

Here are the characteristic interactions of benzodiazepines and the body in terms of absorption, distribution, metabolism, and excretion:

Drugs for Treating Generalized Seizures

Here are the characteristic interactions of succinimides and the body in terms of absorption, distribution, metabolism, and excretion:

Drugs for Treating Partial Seizures

Here are the characteristic interactions of drugs used for treatment of partial seizures and the body in terms of absorption, distribution, metabolism, and excretion:

Nursing Considerations

Assessment. Screen for contraindications and cautions (drug allergy, diabetes, hepatorenal dysfunction, arrhythmias, hypotension). Characterize the seizures (onset, aura, duration, recovery) to determine type and set a baseline. Do a full physical (skin color and lesions, vital signs, orientation, affect, reflexes, bowel sounds, urine output). Monitor renal and liver function to gauge appropriateness and possible dose adjustment.

Nursing diagnoses. Acute discomfort related to GI, CNS, and GU effects; disturbed thought processes related to CNS effects; impaired skin integrity related to dermatological effects; risk for infection related to bone marrow suppression; risk for injury related to CNS effects and toxic drug levels.

Interventions. Monitor for adverse effects and provide supportive care. Watch CBC results to catch bone marrow suppression early. Stop the drug at any sign of hypersensitivity, liver dysfunction, or severe skin rash to limit the reaction. Provide comfort measures (positioning for dyskinesia, sugarless candy and ice chips for dry mouth, voiding before dosing for urinary hesitancy or retention) and safety measures (adequate lighting, raised side rails). Teach the patient.

Evaluation. Monitor response (fewer or no seizures) and adverse effects (CNS changes, GI depression, bone marrow suppression, severe dermatological reactions, liver toxicity). Confirm the patient can name the drug, its indication, and adverse effects, and check compliance.

Frequently Asked Questions

How do hydantoins like phenytoin stop seizures? They bind voltage-gated sodium channels in their inactive state and slow their recovery, which prolongs the refractory period and keeps neurons from firing at high frequency. That stabilizes the membrane and dampens the abnormal electrical activity driving the seizure (StatPearls).

Which drug class is first-line for status epilepticus? A benzodiazepine (IV lorazepam, midazolam, or diazepam) is the first-line choice. It reaches therapeutic CNS levels fast and potentiates GABA to abort ongoing seizure activity; second-line agents such as fosphenytoin, levetiracetam, or valproate follow if seizures persist (StatPearls).

Why should an antiepileptic never be stopped abruptly? Sudden withdrawal can precipitate seizures, including status epilepticus, with the risk of anoxia. Doses are tapered, and patients are taught not to skip or discontinue on their own.

What is the most dangerous seizure presentation? Status epilepticus, in which seizures recur rapidly with no recovery between them. It is a medical emergency because of the risk of hypoxia and permanent injury.

Why monitor the CBC during therapy? Several agents (hydantoins, succinimides, carbamazepine) can cause bone marrow suppression. Watching the CBC catches it early, and the drug is stopped at any sign of hypersensitivity, liver dysfunction, or a severe skin rash such as Stevens-Johnson syndrome.

Why is patient teaching about pregnancy important? Some antiseizure drugs are linked to congenital effects, so women of childbearing age are counseled on barrier contraception and alternative feeding. Because abrupt discontinuation is also dangerous, any change is made with the prescriber, not on the patient's own.