Evaluation of anti epileptic drugs practical

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Introduction

• A Seizure (from the Latin

• is a paroxysmal event due to abnormal, excessive, hyper synchronous discharges from an aggregate of central nervous system (CNS) neurons.

• Epilepsy describes a condition in which a person has seizures due to a chronic, underlying process.

• Incidence ~0.3–0.5%• Prevalence 5–10 persons per 1000.

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Historical Aspects

• Over the centuries the epilepsy is known as “the

falling sickness”, “the sacred disease”, “St. Johns

disease”.

• Among the famous who suffered from epilepsy

were Julius Caeser, Alexander the great &

Napolean Bonapart.

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• Hippocrates was the first person to dispel the myth of epilepsy, as not being caused by devils and spirits.

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• John Jackson:.

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Classification Of Seizures

A) Partial • Simple• Complex• Secondary generalized

B) Primary Generalized• Absence• Tonic-clonic• Tonic• MyoclonicC) Unclassified• Neonatal• Infantile Spasms

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Experimental methods for evaluating antiepileptic drugs

1)Electroconvulsion method.

2)Chemically induced convulsion method

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In vitro models

• Hippocampal slices model

• Electric recording from isolated brain cells

• GABA receptor binding assays

• Exitatory aminoacid receptor binding assays

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Disadvantages of in vitro study

• Serve as initial screening for drug discovery

• Not give proper idea about pharmacokinetics and pharmacodynamics or PK-PD interaction of compound in living animals.

• Not possible to study compensatory changes that occur in body when drug is given.

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Electroconvulsion method:

• 1)Maximum Electroshock Seizures(M.E.S.)

• Model of grand mal epilepsy

• End point : Tonic Hind Limb Extension

• The agents screened through this model considered an antiepileptic drugs if it corrects or suppresses Tonic Hind Limb Extension

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• Maximum current of such voltage is applied as to induce convulsions in all the tested animals (rats, mice).

• A well characterized course of convulsion,

• (a short latent period, followed by a tonic extensor tonus and then by a phase of clonic convulsion)

• The drugs effective in the test alter the seizure pattern by suppressing the tonic phase of convulsions. Such drugs are potentially useful in Grand mal epilepsy(Generalized Tonic Clonic Seizures)

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• Materials and methods:• Animal :Rat /Mouse

: 150-250 gm• Drugs :Phenytoin (20-30mg/kg,i.p./po) ,

: Phenobarbitone sodium, 15 mg/kg i.p.:Diazepam (3-4mg/kg i.p.)

• Instrument:• Electro convulsiometer:• Rat:150 mA ,50 Hz for 0.2 sec• Mouse:12 mA ,50 Hz for 0.2 sec

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convulsiometer

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Tonic Hind Limb Extension

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• Methods:• Step 1:• Weight the animals and mark properly• Divide animals into 3 group• They are given stimulus with ear electrode.• Phases of convulsions are recorded in each mouse• The drugs are injected • Step 2:• Group 1: Isotonic saline• Group 2: Phenytoin sodium, 30 mg/kg i.p.• Group 3: Phenobarbitone sodium, 15 mg/kg i.p.

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• After 1 hour animals are given electroconvulsions• Observations are noted • Record whether ‘THLE’ Present /Absent

• Step 3:• Observe the animal after MES• Calculate percentage protection

• Percentage protection =No. of animals with THLE absent /total no. animal ×100

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M.E.S.(Maximum Electroshock Seizure)

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Group no Latent period (sec) Extensor tonus(sec) Clonicconvulsions(sec)

Before After Before After Before After

A 1 2 3 8 8 10 10

A 2 2 3 8 10 10 12

B 1 2 2 8 ------- 10 11

B 2 3 3 12 -------- 10 12

C 1 3 3 8 -------- 10 10

C 2 3 3 12 -------- 14 12

Minimal Electroshock seizure Threshold: (MET)• Measurement of minimal strength of current

required to elicit electroconvulsion.2) Hyponatremic Electroshock seizure Threshold

(HET)• animals injected with isomolar glucose solution

(10 ml/100 gm body wt.). • This induces hyponatremia and lowers the M.E.T. • Drugs elevate the threshold used in grandmal

epilepsy .

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3) Psychomotor Seizures

• Mice are subjected to unidirectional current pulses

• animal becomes stunned and shows automatism lasting for 15-20 sec.

• Drugs inhibiting the effect of current in this test are potentially useful in Psychomotor seizures.

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4) Kindling model of epilepsy:A model for human focal epilepsy is that produced

in animals by “kindling”. This consists of delivery of brief localized trains of

electrical stimuli to an area of the brain, repeatedly, at about 24 hour intervals.

After a time, generalized motor seizures are regularly elicited during such electrical stimulation.

Useful in partial simple/complex seizure

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Chemically induced convulsion:

• A threshold dose of a suitable convulsant (e.g. Leptazole, Strychnine) is injected in mice or rats.

• This induces clonic type of convulsions.

• Some of the anticonvulsants (ethosuccimide, sodium valproate) prevent these convulsions. Such drugs may be potentially useful in Petitmal epilepsy (Absence Seizures).

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(B) Chemical method:-

• Two mice (D1, D2) are selected.

• One is injected with antiepileptic drug (sodium valproate) and

• other is kept as control.

• Then both mice are injected with leptazoleand observations are noted.

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Chemical method:

Convulsant Antiepileptic No. of animal showing convulsions

No. of animalsshowing protection from convulsions

Drug and dose Drug and dose

Leptazole(70 mg/kg i.p)

Normal Saline 1 nil

Leptazole(70 mg/kg i.p)

Sodium Valporate40 mg/kg i.p.

nil 1

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Assignment

a) Define epilepsy.

b) Classify epilepsy.

c) Enumerate experimental methods for evaluation of anticonvulsant.

d) Enlist one drug of choice each for common type of epilepsy.

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Selection Of Anti-epileptic Drug

• Primary GTC: Phenytoin

• Partial: Carbamazepine

• Absence: Ethosuxamide

• Myoclonic seizure: Valporic acid

• Drug resistant seizures: Lamotrigine

• Febrile convulsions: Diazepam

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Classification Of Seizures

A) Partial • Simple• Complex• Secondary generalized

B) Primary Generalized• Absence• Tonic-clonic• Tonic • MyoclonicC) Unclassified• Neonatal• Infantile Spasms

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