• Clinical science

Anticonvulsant drugs

Summary

Anticonvulsant drugs are classified as either first-generation (classic) agents or second-generation agents. Second-generation anticonvulsants are usually better tolerated and have a broader therapeutic range than classic anticonvulsant drugs. The choice of drug is guided by the type of seizure. First-line treatment for focal seizures includes, e.g., lamotrigine or levetiracetam, while valproate is used for generalized seizures. While all anticonvulsants have dose-dependent side effects on the central nervous system (e.g., somnolence, nausea), select agents also have other side effects (e.g., gingival hyperplasia caused by phenytoin). Anticonvulsants are also used for pain management (e.g., carbamazepine or gabapentin) and as mood stabilizers in bipolar disorders (valproate).

For more information on the treatment of generalized seizures, see treatment of epileptic seizures.

Overview

Anticonvulsant drugs inhibit neural activity (↓ neural excitation, ↑ neural inhibition) and increase the seizure threshold by interacting with specific receptors and ion channels.

Overview of anticonvulsant drugs
Classification Agent Indication Mechanism of action Side effects

First-generation (classic) anticonvulsants

Valproate

  • Inhibits GABA transaminase GABA → decreased neuronal excitability
  • Inactivates Na+ channels

Carbamazepine

  • Inactivates Na+ channels

Ethosuximide

  • Inhibition of voltage-gated calcium channels (T-type) in neurons of the thalamus

Phenytoin, fosphenytoin

  • Inactivation of Na+ channels
  • Zero-order elimination (i.e., constant rate of drug eliminated)
Phenobarbital
  • Cardiorespiratory depression
  • Tolerance and dependence
  • Sedation
  • Induces cytochrome P-450
Benzodiazepine
  • Sedation and dependence (see benzodiazepines)
  • Tolerance
  • Respiratory depression
Second-generation (newer) anticonvulsants

Lamotrigine

  • Inhibition of voltage-gated Na+channels → glutamate release
Levetiracetam
  • Not fully understood
  • Blockage of SV2A receptor → GABA and/or glutamate release modulation and inhibition of voltage-gated Ca2+ channels
  • Lethargy, fatigue
  • Nausea
  • Headache
  • Psychiatric symptoms (e.g., personality changes)
Gabapentin
  • Inhibition of presynaptic P/Q-type Ca2+ channels via action on the α2δ-subunit → Ca2+ intracellular flow → glutamate release [2]
  • Does not bind to GABA receptors despite being a GABA analog
Pregabalin (tentative FDA approval)
Vigabatrin
  • Inhibits GABA transaminase irreversibly → GABA
  • Irreversible vision loss

Topiramate

  • Blockage of voltage-gated Na+
    channels
  • GABA
  • Glaucoma
  • Weight loss
  • Kidney stones
  • Cognitive dysfunction (e.g., decreased verbal fluency, cognitive speed, and working memory)
  • Sedation
Tiagabine
  • Focal seizures, with or without impairment of consciousness (adjunctive therapy)

You can use the following to remember the features of PHENYTOIN: cytochrome P-450 interaction, Hirsutism, Enlarged gums (gingival hyperplasia), Nystagmus, Yellow-browning of skin (melasma), Teratogenicity, Osteomalacia, Interacts with folate, Neuropathy

To remember that the most important side effects of ethoSUXimide are Steven-Johnson syndrome, fatigue, headache, ABdominal upset, and ALLErGies (e.g., urticaria), think of “It sucks that Steven's FATher has given everyone a headache with his ABsurd ALLEGorizations.”

To remember a crucial side effect of vigabatrin, think of “Vision goes away by accident.”

To remember that phenobarbital is first-line treatment for neonates, think of “Phenobarbital is phenomenal for treating babies.”

To remember that the most common side effects of topiramate are speech impairment, weight loss (light), cognitive impairment, sedation, and kidney stones, think of “It leaves you speechless how lightly the cog railway travels through sediments and stones to the top.”

References:[3][2]

Additional considerations

  • Monotherapy should always be the first-line treatment: increase the dosage of the drug to the therapeutic range before initiating combination therapy
  • Combination therapy: drugs from different classes and/or with different pharmacologic modes of action for refractory seizures [4]
  • For more detailed approaches to seizure treatment and epilepsy, see treatment of epileptic seizures.

References:[3][4]

Special patient groups

Pregnancy and breastfeeding

  • Classic anticonvulsants (especially carbamazepine and sodium valproate!) should be avoided if possible → teratogenic effects
  • Newer anticonvulsants: lack of medical data and trials during pregnancy
  • The choice of treatment depends on the type of seizure and which substance enables optimal control of seizures.
  • Approach
    • Optimize seizure control prior to conception.
    • Avoid multiple therapies.
    • Administer the drug at the lowest dose that controls seizures.
    • Monitor plasma drug levels regularly.

References:[3]

  • 1. Glauser T, Shinnar S, Gloss D, et al. Evidence-Based Guideline: Treatment of Convulsive Status Epilepticus in Children and Adults: Report of the Guideline Committee of the American Epilepsy Society. Epilepsy Currents. 2016; 16(1): pp. 48–61. doi: 10.5698/1535-7597-16.1.48.
  • 2. Katzung B,Trevor A. Basic and Clinical Pharmacology. McGraw-Hill Education; 2014.
  • 3. Le T, Bhushan V, Sochat M, Chavda Y. First Aid for the USMLE Step 1 2017. McGraw-Hill Education; 2017.
  • 4. Schmidt D, Schachter SC. Drug treatment of epilepsy in adults. BMJ. 2014; 348(feb28 2): pp. g254–g254. doi: 10.1136/bmj.g254.
  • Herold G. Internal Medicine. Cologne, Germany: Herold G; 2014.
  • Karow T, Lang-Roth R. Allgemeine und Spezielle Pharmakologie und Toxikologie. Dr. med. Thomas Karow (2012 und 2013); 2010.
  • Lüllmann H, Mohr K, Wehling M. Pharmakologie und Toxikologie. Thieme Verlag (2002); 2003.
  • Karow T, Lang-Roth R. Pharmakologie und Toxikologie. ; 2012.
last updated 08/10/2020
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