Anticonvulsant

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Anticonvulsant
Drug class
Class identifiers
Synonyms	Antiepileptic drugs, antiseizure drugs
Use	Epilepsy
Biological target	Brain

Anticonvulsants (also commonly known as antiepileptic drugs or as antiseizure drugs) are a diverse group of pharmacological agents used in the treatment of epileptic seizures. Anticonvulsants are also increasingly being used in the treatment of bipolar disorder and borderline personality disorder, since many seem to act as mood stabilizers, and for the treatment of neuropathic pain. Anticonvulsants suppress the excessive rapid firing of neurons during seizures. Anticonvulsants also prevent the spread of the seizure within the brain.

Conventional antiepileptic drugs may block sodium channels or enhance γ-aminobutyric acid (GABA) function. Several antiepileptic drugs have multiple or uncertain mechanisms of action. Next to the voltage-gated sodium channels and components of the GABA system, their targets include GABA_A receptors, the GAT-1 GABA transporter, and GABA transaminase. Additional targets include voltage-gated calcium channels, SV2A, and α2δ. By blocking sodium or calcium channels, antiepileptic drugs reduce the release of excitatory glutamate, whose release is considered to be elevated in epilepsy, but also that of GABA. This is probably a side effect or even the actual mechanism of action for some antiepileptic drugs, since GABA can itself, directly or indirectly, act proconvulsively. Another potential target of antiepileptic drugs is the peroxisome proliferator-activated receptor alpha. The drug class was the 5th-best-selling in the US in 2007.

Some anticonvulsants have shown antiepileptogenic effects in animal models of epilepsy. That is, they either prevent the development of epilepsy or can halt or reverse the progression of epilepsy. However, no drug has been shown in human trials to prevent epileptogenesis (the development of epilepsy in an individual at risk, such as after a head injury).

Terminology

Anticonvulsants are more accurately called antiepileptic drugs (abbreviated "AEDs"), and are often referred to as antiseizure drugs because they provide symptomatic treatment only and have not been demonstrated to alter the course of epilepsy.

Approval

The usual method of achieving approval for a drug is to show it is effective when compared against placebo, or that it is more effective than an existing drug. In monotherapy (where only one drug is taken) it is considered unethical by most to conduct a trial with placebo on a new drug of uncertain efficacy. This is because untreated epilepsy leaves the patient at significant risk of death. Therefore, almost all new epilepsy drugs are initially approved only as adjunctive (add-on) therapies. Patients whose epilepsy is currently uncontrolled by their medication (i.e., it is refractory to treatment) are selected to see if supplementing the medication with the new drug leads to an improvement in seizure control. Any reduction in the frequency of seizures is compared against a placebo. The lack of superiority over existing treatment, combined with lacking placebo-controlled trials, means that few modern drugs have earned FDA approval as initial monotherapy. In contrast, Europe only requires equivalence to existing treatments, and has approved many more. Despite their lack of FDA approval, the American Academy of Neurology and the American Epilepsy Society still recommend a number of these new drugs as initial monotherapy.

Drugs

In the following list, the dates in parentheses are the earliest approved use of the drug.

Aldehydes

Main article: Aldehyde

• Paraldehyde (1882). One of the earliest anticonvulsants. It is still used to treat status epilepticus, particularly where there are no resuscitation facilities.

Aromatic allylic alcohols

• Stiripentol (2001 – limited availability). Indicated for the treatment of Dravet syndrome.

Barbiturates

Barbiturates are drugs that act as central nervous system (CNS) depressants, and by virtue of this they produce a wide spectrum of effects, from mild sedation to anesthesia. The following are classified as anticonvulsants:

• Phenobarbital (1912). See also the related drug primidone.
• Methylphenobarbital (1935). Known as mephobarbital in the US. No longer marketed in the UK
• Barbexaclone (1982). Only available in some European countries.

Phenobarbital was the main anticonvulsant from 1912 until the development of phenytoin in 1938. Today, phenobarbital is rarely used to treat epilepsy in new patients since there are other effective drugs that are less sedating. Phenobarbital sodium injection can be used to stop acute convulsions or status epilepticus, but a benzodiazepine such as lorazepam, diazepam or midazolam is usually tried first. Other barbiturates only have an anticonvulsant effect at anaesthetic doses.

Benzodiazepines

The benzodiazepines are a class of drugs with hypnotic, anxiolytic, anticonvulsive, amnestic and muscle relaxant properties. Benzodiazepines act as a central nervous system depressant. The relative strength of each of these properties in any given benzodiazepine varies greatly and influences the indications for which it is prescribed. Long-term use can be problematic due to the development of tolerance to the anticonvulsant effects and dependency. Of the many drugs in this class, only a few are used to treat epilepsy:

• Clobazam (1979). Notably used on a short-term basis around menstruation in women with catamenial epilepsy.
• Clonazepam (1974).
• Clorazepate (1972).

The following benzodiazepines are used to treat status epilepticus:

• Diazepam (1963). Can be given rectally by trained care-givers.
• Midazolam (N/A). Increasingly being used as an alternative to diazepam. This water-soluble drug is squirted into the side of the mouth but not swallowed. It is rapidly absorbed by the buccal mucosa.
• Lorazepam (1972). Given by injection in hospital.

Nitrazepam, temazepam, and especially nimetazepam are powerful anticonvulsant agents, however their use is rare due to an increased incidence of side effects and strong sedative and motor-impairing properties.

Bromides

• Potassium bromide (1857). The earliest effective treatment for epilepsy. There would not be a better drug until phenobarbital in 1912. It is still used as an anticonvulsant for dogs and cats.

Carbamates

• Felbamate (1993). This effective anticonvulsant has had its usage severely restricted due to rare but life-threatening side effects.

Carboxamides

Carbamazepine

The following are carboxamides:

• Carbamazepine (1963). A popular anticonvulsant that is available in generic formulations.
• Oxcarbazepine (1990). A derivative of carbamazepine that has similar efficacy but is better tolerated and is also available generically.
• Eslicarbazepine acetate (2009)

Fatty acids

The following are fatty-acids:

• The valproates — valproic acid, sodium valproate, and divalproex sodium (1967).
• Vigabatrin (1989).
• Progabide (1987)
• Tiagabine (1996).

Vigabatrin and progabide are also analogs of GABA.

Fructose derivatives

• Topiramate (1995).

GABA analogs

• Gabapentin (1993).
• Pregabalin (2004).
• Vigabatrin (1989).
• Progabide (1987).

Hydantoins

The following are hydantoins:

• Ethotoin (1957).
• Phenytoin (1938).
• Mephenytoin
• Fosphenytoin (1996).

Oxazolidinediones

The following are oxazolidinediones:

• Paramethadione
• Trimethadione (1946).
• Ethadione

Propionates

• Beclamide

Pyrimidinediones

• Primidone (1952).

Pyrrolidines

• Brivaracetam
• Etiracetam
• Levetiracetam (1999).
• Seletracetam

Succinimides

The following are succinimides:

• Ethosuximide (1955).
• Phensuximide
• Mesuximide

Sulfonamides

• Acetazolamide (1953).
• Sultiame
• Methazolamide
• Zonisamide (2000).

Triazines

• Lamotrigine (1990).

Ureas

• Pheneturide
• Phenacemide

Valproylamides

• Valpromide
• Valnoctamide

Other

• Perampanel
• Stiripentol
• Pyridoxine (1939)

Non-pharmaceutical anticonvulsants

Sometimes, ketogenic diet or vagus nerve stimulation are described as "anticonvulsant" therapies as well. However they do not work as well as the anticonvulsant drugs

Treatment guidelines

According to guidelines by the American Academy of Neurology and American Epilepsy Society, mainly based on a major article review in 2004, patients with newly diagnosed epilepsy who require treatment can be initiated on standard anticonvulsants such as carbamazepine, phenytoin, valproic acid/valproate semisodium, phenobarbital, or on the newer anticonvulsants gabapentin, lamotrigine, oxcarbazepine or topiramate. The choice of anticonvulsants depends on individual patient characteristics. Both newer and older drugs are generally equally effective in new onset epilepsy. The newer drugs tend to have fewer side effects. For newly diagnosed partial or mixed seizures, there is evidence for using gabapentin, lamotrigine, oxcarbazepine or topiramate as monotherapy. Lamotrigine can be included in the options for children with newly diagnosed absence seizures.

History

The first anticonvulsant was bromide, suggested in 1857 by the British gynecologist Charles Locock who used it to treat women with "hysterical epilepsy" (probably catamenial epilepsy). Bromides are effective against epilepsy, and also cause impotence, which is not related to its anti-epileptic effects. Bromide also suffered from the way it affected behaviour, introducing the idea of the 'epileptic personality' which was actually a result of medication. Phenobarbital was first used in 1912 for both its sedative and antiepileptic properties. By the 1930s, the development of animal models in epilepsy research led to the development of phenytoin by Tracy Putnam and H. Houston Merritt, which had the distinct advantage of treating epileptic seizures with less sedation.^[35] By the 1970s, a National Institutes of Health initiative, the Anticonvulsant Screening Program, headed by J. Kiffin Penry, served as a mechanism for drawing the interest and abilities of pharmaceutical companies in the development of new anticonvulsant medications.

Marketing approval history

The following table lists anticonvulsant drugs together with the date their marketing was approved in the US, UK and France. Data for the UK and France are incomplete. In recent years, the European Medicines Agency has approved drugs throughout the European Union. Some of the drugs are no longer marketed.

Drug	Brand	US	UK	France
acetazolamide	Diamox	27 July 1953	1988
carbamazepine	Tegretol	15 July 1974	1965	1963
clobazam	Frisium		1979
clonazepam	Klonopin/Rivotril	4 June 1975	1974
diazepam	Valium	15 November 1963
divalproex sodium	Depakote	10 March 1983
eslicarbazepine		Data needed
ethosuximide	Zarontin	2 November 1960	1955	1962
ethotoin	Peganone	22 April 1957
felbamate	Felbatol	29 July 1993
fosphenytoin	Cerebyx	5 August 1996
gabapentin	Neurontin	30 December 1993	May 1993	October 1994
lamotrigine	Lamictal	27 December 1994	October 1991	May 1995
lacosamide	Vimpat	28 October 2008
levetiracetam	Keppra	30 November 1999	29 September 2000	29 September 2000
mephenytoin	Mesantoin	23 October 1946
metharbital	Gemonil	1952
methsuximide	Celontin	8 February 1957
methazolamide	Neptazane	26 January 1959
oxcarbazepine	Trileptal	14 January 2000	2000
phenobarbital			1912	1920
phenytoin	Dilantin/Epanutin	1938	1938	1941
phensuximide	Milontin	1953
pregabalin	Lyrica	30 December 2004	6 July 2004	6 July 2004
primidone	Mysoline	8 March 1954	1952	1953
sodium valproate	Epilim		December 1977	June 1967
stiripentol	Diacomit		5 December 2001	5 December 2001
tiagabine	Gabitril	30 September 1997	1998	November 1997
topiramate	Topamax	24 December 1996	1995
trimethadione	Tridione	25 January 1946
valproic acid	Depakene/Convulex	28 February 1978	1993
vigabatrin	Sabril	21 August 2009	1989
zonisamide	Zonegran	27 March 2000	10 March 2005	10 March 2005

Pregnancy

During pregnancy, the metabolism of several anticonvulsants is affected. There may be an increase in the clearance and resultant decrease in the blood concentration of lamotrigine, phenytoin, and to a lesser extent carbamazepine, and possibly decreases the level of levetiracetam and the active oxcarbazepine metabolite, the monohydroxy derivative. Therefore, these drugs should be monitored during use in pregnancy.

Many of the common used medications, such as valproate, phenytoin, carbamazepine, phenobarbitol, gabapentin have been reported to cause increased risk of birth defects. Among anticonvulsants, levetiracetam and lamotrigine seem to carry the lowest risk of causing birth defects. The risk of untreated epilepsy is believed to be greater than the risk of adverse effects caused by these medications, necessitating continuation of antiepileptic treatment.

Valproic acid, and its derivatives such as sodium valproate and divalproex sodium, causes cognitive deficit in the child, with an increased dose causing decreased intelligence quotient. On the other hand, evidence is conflicting for carbamazepine regarding any increased risk of congenital physical anomalies or neurodevelopmental disorders by intrauterine exposure. Similarly, children exposed lamotrigine or phenytoin in the womb do not seem to differ in their skills compared to those who were exposed to carbamazepine.

There is inadequate evidence to determine if newborns of women with epilepsy taking anticonvulsants have a substantially increased risk of hemorrhagic disease of the newborn.

Regarding breastfeeding, some anticonvulsants probably pass into breast milk in clinically significant amounts, including primidone and levetiracetam. On the other hand, valproate, phenobarbital, phenytoin, and carbamazepine probably are not transferred into breast milk in clinically important amounts.

In animal models, several anticonvulsant drugs have been demonstrated to induce neuronal apoptosis in the developing brain.