Anticonvulsants IBrian J. Piper, Ph.D., M.S.

piperbj@husson.edu

February 6, 2013

Objectives

• At the end of this lecture, pharmacy students should be able to:– describe the overall neurochemistry of seizures

(AED targets).– list the procedures to induce seizures.– contrast by PD and AE the different 1st generation

AED.

Epidemiology of Epilepsy• 200K new cases/year• Age: 20: 1%; 75: 3%• Minorities > Caucasians• Developing (2) : Developed (1)

Condition %mental retardation 26stroke 22Cerebral palsy 13Alzheimer’s Disease 10

http://www.epilepsyfoundation.org/aboutepilepsy/whatisepilepsy/statistics.cfmNgugi et al. (2011). Neurology, 77, 1005-1012

Seizure Classification

• Partial (focal): origin of seizure is localized– simple partial: consciousness maintained– complex partial: consciousness lost

• Generalized: origin of seizure is distributed– tonic-clonic (grand malg): • tonic: continuous muscle contraction• clonic: rapid contraction & relaxation

– absence (petit malp): brief loss of consciousness

g(0:40 to 1:20) Skip Ad: http://www.youtube.com/watch?v=MRZY2a2jnuwp(0:35 to 1:10) Skip Ad: http://www.youtube.com/watch?v=DruJDZVO7Ko

Normal CNS Function

Hyperexcitability reflects both increased excitation and decreased inhibition

glutamateaspartate

ExcitationInhibition

GABA

ComparisonGlutamate

• Ionotropic– NMDA– AMPA– kainate

• Metabotropic– mGluR1– mGluR2– mGluR3– mGluR4– mGluR5– mGluR6– mGluR7– mGluR8

GABA• Ionotropic

– GABAA

• Metabotropic– GABAB

AMPA: α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid

GABA

Overall Incidence of Convulsive Disorders: Increased frequency at extremes of age (Rochester, MN 1935-84)

Hauser, W. A. et al. (1995). Epilepsia, 34(3), 453-458.

300

250

200

150

100

50

0

0 20 40 60 80 100

AlcoholOther provokedEpilepsySingle

Total

Age

Inci

denc

e Pe

r 100

,000

Pati

ent Y

ears

White (2005). American Epilepsy Proceedings.

***

**

->->

*

GABA Biosynthesis & Breakdown(so many drug targets)

• GAD: glutamic acid decarboxylase converts glutamate to GABA

• VGAT: vesicular GABA transporter• GAT-1, GAT-2: membrane GABA

transporter found on neurons & astrocytes

• GAT-3: membrane GABA transporter found on astrocytes

• GABA-T: GABA Aminotransferase, begins conversion of GABA to succinic semialdehyde (SSA)

Meyer & Quezner (2008). Psychopharmacology, Chapter 7.

GABAA & Adult Brain

GABA Neuron

<- Cl- pool

Vm : membrane potentialcotransporter: transports ions against concentration gradient

White, H. S. & Rho, J. M. (2010). Mechanisms of AED, p. 67.

Mechanisms of Action: GABA-ergic AEDs

History of AEDs• 1857: Sir Charles Locock reports on KBr for hysterical epilepsy• 1912: Alfred Hauptmann’s sleep problems lead to phenobarbital• 1938: Maximal electroshock seizure (epilepsy?) model used to identify phenytoin

Brodie, M. J. (2010). Seizure, 19, 650-665; Castel-Branco et al. (2009). Meth Find Clin Exp Pharma, 31(2), 101-106.

1) Apply electrode to cornea2) Apply current3) Rate tonic-clonic behavior4) Repeat 1-3 with drug

Phenytoin (1938)

• History: less sedative than phenobarbital

• MOA: decreased recovery of voltage gated Na+ channels from inactivation

• PK: 3A4 inducer• Adverse Events: lethargy

(transient), gingival hyperplasia

Goodwin & Gillman (2011). p. 588.Sharma & Dasroy (2000). NEJM, 342, 325.

Phenytoin & Category D

• ↓ growth• Facial Abnormalities– nasal hypoplasia– maxilla hypoplasia– flat philtrum

• ↓ IQ (variable)• ↓ K+

Howe et al. (1995). American Journal of Medical Genetics, 58, 238-248.

AED Syndrome?

Pentylenetetrazol (1938)• MOA: GABA antagonist

Brevard et al. (2006). Epilepsia, 47(4), 745-754.

fMRI shows thalamus activation 4 s before PTZ seizure.EEG

Valproate (1962)

• History: Pierre Eymard is using pentylenetetrazol to induce convulsions with valproate as solvent/vehicle.

• Uses: different seizure types• MOA: ?, ↑GABA, ↓ aspartate

Stahl (2008).Essential Psychopharm, p. 678.

Valproate: Category D

• 2% risk of spina bifida• ↓ Cmax• folic acid supplementation

Perukka, E. (2002). CNS Drugs, 16(10), 695-714.

Status Epilecticus (SE)

• continuous, unremitting seizure lasting > 5 min

• convulsive > non-convulsive • mortality = 20%• medical emergency

Trinka et al. (2012). Epilepsia, 53(4), 127-138.

Lorazepam (1977)

• MOA: GABAA α1,2,3,5

• Dose: 2 mg/ml per min x 2• Adverse Effects: heavy sedation, especially

with alcohol• t1/2 : 12 hours

SummaryMOA Concern

phenobarbital GABAA

Cl- channel durationsedation

phenytoin voltage gatedNa+ channels

Category D

lorazepam GABAA α1,2,3,5

Cl- channel frequencyaddiction (Schedule IV)

valproate ↑ GABA (?) Category D

GABAA & Neonatal Brain

Vm : membrane potentialcotransporter: transports ions against concentration gradient

White, H. S. & Rho, J. M. (2010). Mechanisms of AED, p. 67.

GABA Neuron

<- Cl- pool

Brodie, M. J. (2010). Seizure, 19, 650-665.

Summary

• MES and PTZ have been used to identify many AED.

• Pharmacotherapy for epilepsy is complex and polypharmacy is common.

Self-Test

• Match the AED on the left with the potential adverse effect.– valproic acid– phenytoin– phenobarbital