PTCB Guide to Anticonvulsants

Also called antiepileptic drugs, AEDs · suffix varied · updated August 6, 2026

What gets tested

• Matching brand to generic: Dilantin is phenytoin, Tegretol is carbamazepine, Depakote is divalproex, Lamictal is lamotrigine, Keppra is levetiracetam, Neurontin is gabapentin
• Which anticonvulsants are narrow therapeutic index drugs requiring monitoring
• The Stevens-Johnson syndrome rash warning with lamotrigine and carbamazepine, and the slow titration that reduces it
• That these drugs are not stopped abruptly
• That several are used for conditions other than epilepsy: nerve pain, migraine prevention, and bipolar disorder
• Pregnancy concerns, particularly with valproate

What is not tested

You do not need to classify seizure types, choose an agent, or interpret a specific serum level. What matters is brand and generic recognition, which drugs are narrow therapeutic index, the rash and abrupt-withdrawal warnings, and the counseling points. Strengths, dosage forms, routes, special handling, and duration of therapy fall under PTCE knowledge area 1.4, and the many extended-release and delayed-release forms in this class make dosage form accuracy a genuine safety issue.

Why anticonvulsants matter

Gabapentin is among the most dispensed medications in the United States, largely for nerve pain rather than epilepsy. Several drugs in this class are also narrow therapeutic index products where a substitution or a dosage form mix-up can cause real harm, which puts anticonvulsants squarely in the Patient Safety domain as well as the Medications domain.

Anticonvulsants at a glance

Mechanism of action

A seizure is a burst of excessive, synchronized electrical activity in the brain, so anticonvulsants work by making neurons harder to fire repeatedly. There are three main strategies and many drugs combine them. The first is blocking voltage-gated sodium channels in their inactivated state, which is what phenytoin, carbamazepine, oxcarbazepine, and lamotrigine largely do. Because the block preferentially affects neurons firing rapidly and repetitively, it suppresses seizure activity while leaving normal traffic relatively intact. The second is enhancing GABA, the brain's main inhibitory transmitter: barbiturates such as phenobarbital and benzodiazepines both hold the GABA-A chloride channel open longer, and valproate raises GABA levels by other routes. The third is reducing excitation, either by blocking calcium channels involved in transmitter release or by damping glutamate signalling, which is part of how topiramate and lamotrigine act. Levetiracetam is different again: it binds synaptic vesicle protein 2A, altering neurotransmitter release, and it has notably few drug interactions as a result. Gabapentin's name suggests a GABA mechanism but it does not actually act at GABA receptors; it binds a subunit of voltage-gated calcium channels, which is also why it works for nerve pain. Metabolism matters as much as mechanism here. Carbamazepine and phenytoin are strong enzyme inducers, so they speed the clearance of many other drugs including oral contraceptives, while valproate is an inhibitor that raises levels of others. Carbamazepine even induces its own metabolism over the first weeks of therapy, which is why its dose is adjusted after starting.

Common and important side effects

• Drowsiness, dizziness, unsteadiness, and blurred or double vision across the class
• Serious skin reactions including Stevens-Johnson syndrome and toxic epidermal necrolysis, most associated with lamotrigine and carbamazepine
• Gingival hyperplasia (gum overgrowth), hirsutism, and coarsening of facial features with long-term phenytoin
• Liver toxicity and pancreatitis with valproate, which carry boxed warnings
• Serious birth defects and reduced IQ in children exposed to valproate in the womb, also a boxed warning
• Low sodium (hyponatremia) with carbamazepine and oxcarbazepine
• Blood count suppression with carbamazepine, including rare aplastic anemia and agranulocytosis
• Weight loss, tingling in the hands and feet, word-finding difficulty, and kidney stones with topiramate
• A class warning for suicidal thoughts and behaviour across antiepileptic drugs

Key interactions

• Carbamazepine and phenytoin induce liver enzymes and reduce the effectiveness of oral contraceptives, warfarin, and many other drugs
• Valproate inhibits metabolism and roughly doubles lamotrigine levels, which is why lamotrigine is titrated even more slowly when the two are combined
• Carbamazepine and phenytoin can lower each other's levels and complicate combined therapy
• Antacids reduce the absorption of phenytoin and gabapentin, so doses are separated
• Alcohol and other sedatives add to drowsiness
• Enteral tube feeds bind phenytoin and reduce its absorption, so feeds are held around the dose

Patient counseling notes

• Never stop an anticonvulsant suddenly, even if seizures have stopped, because abrupt withdrawal can trigger a seizure or status epilepticus
• Report any new rash immediately, especially in the first weeks of lamotrigine or carbamazepine, because early rash can be the first sign of a life-threatening skin reaction
• Follow the lamotrigine starter pack exactly: the slow step-up is what reduces the risk of serious rash
• Attend blood tests as scheduled for phenytoin, carbamazepine, and valproate levels and blood counts
• Speak to the prescriber before becoming pregnant, particularly on valproate, which carries a high risk of birth defects
• Do not switch between brand and generic, or between immediate and extended-release forms, without the pharmacist's involvement
• Report unusual bruising, persistent fever or sore throat, yellowing of the skin, or severe abdominal pain

Practice questions

Work the Anticonvulsants questions below first, then widen out. Two skills carry most of the Medications domain, and each has its own quiz. The first is drug class identification: recognising which class a drug belongs to from its name or its stem, which is what the drug class identification quiz drills across every class. The second is brand and generic recall, because the exam switches between the two names freely and expects you to follow. Pair this guide with the brand and generic quiz until the brand and generic pairs in the table above come back without effort.

Related drug-class guides

Official sources

• MedlinePlus: Phenytoin
• MedlinePlus: Carbamazepine
• MedlinePlus: Valproic Acid
• MedlinePlus: Lamotrigine
• MedlinePlus: Levetiracetam
• MedlinePlus: Gabapentin
• ClinCalc DrugStats: Gabapentin (dispensing data)

PTCB Quiz Prep is an independent study resource, not affiliated with the Pharmacy Technician Certification Board. This guide is for exam preparation, not medical advice. Part of the PTCB Medications domain.