Anti-Convulsants
INTENDED
LEARNING OBJECTIVES
At the end of this
lecture, student will be able to:
• Distinguish between convulsions and epilepsy
• Differentiate the types of epilepsy
• Define anti convulsants/antiepileptics
• Categorize the various anticonvulsants/antiepileptics according
to their structure
• Outline the synthesis of some anticonvulsants
• Recognize the specific uses of the different anticonvulsants
Introduction of Anticonvulsants/Antiepileptics
• Convulsions are involuntary spasms or a series of jerking of
the muscles
– It can be experimentally produced by certain chemicals
– Eg. PTZ (pentylene tetrazole)
• Epilepsy is a disease that occurs due to central nervous
system (CNS) disorder, which is characterized by seizures and convulsions or
abnormal body movements with the loss of consciousness.
Three principle types of epilepsy are found.
They are as follows:
• Grandmal: In
which the seizures
last from 2
to 5 min,
being characterized by a sudden loss of consciousness, tonic and clonic convulsions
of all muscles associated with urinary incontinence.
• Petitmal: The seizures last from 5 to 30 sec, being
characterized by brief attacks of unconsciousness, usually occur in children at
the age of 4 to 8 years.
• Psychomotor seizures: Characterized by attacks without convulsions
and lasts from 2 to 3 min.
Anticonvulsants
• Antiepileptic/anticonvulsants:
A medication used to control (prevent) seizures
(convulsions) or stop an ongoing series of seizures.
• They prevent, stop, or lessen the excessive electric
activity in the brain
Anticonvulsants
Mechanism of action:
The anticonvulsant therapy mediated by the drugs is through
different aspects of neurotransmission inhibition in the brain:
• By inhibiting sodium channels (phenytoin).
• By inhibiting gamma amino butyric acid (GABA) transaminase
enzyme (vigabatrin).
• By inhibition of T-type calcium currents (ethosuximide,
valproate).
• By GABA agonistic activity (benzodiazepine).
Classification
of Anticonvulsants
• BARBITURATES
– PHENOBARBITONE
– METHABARBITONE
• HYDANTOINS
– PHENYTOIN
– MEPHENYTOIN
– ETHOTOIN
• OXAZOLIDINE DIONES
– TRIMETHADIONE
– PARAMETHADIONE
• SUCCINIMIDES
– PHENSUXIMIDE
– METHSUXIMIDE
– ETHOSUXIMIDE
• UREA AND MONOACYL
UREAS
– PHENACETAMIDE
– CARBAMAZEPINE
• BENZODIAZEPINES
– CLONAZEPAM
• MICELLENEOUS
– PRIMIDONE
– VALPROIC ACID
– GABAPENTIN
– FELBAMATE
I.
Barbiturates
• Most of the barbiturates are sedatives and hypnotics. Only
a few of them show anticonvulsant characters.
• Three important barbiturates that show anticonvulsant
properties are the following:
SAR of
Barbiturates
1. Optimum activity is observed when the substitution at C-5
is phenyl.
2. The 5, 5’-diphenyl derivative have less activity than
phenobarbitone.
3. N1and N3 substituents in some cases resulted in an increase
in activity
BARBITURATES
Classification
• PHENOBARBITONE
• METHABARBITONE
PHENOBARBITAL
INN, USAN, PHENOBARBITONE BAN
Chemically it is 5-ethyl-5-phenyl-1H, 3H, 5H-pyrimidine-2,
4, 6-trione
• Phenobarbitone sodium is hygroscopic, bitter taste, water
soluble, odorless, white crystalline powder.
Medicinal
Uses
• It is used both as sedative
and hypnotic.
• It is the drug of choice in the treatment of grandma and
petitmal epilepsy
• It is useful in nervous and related tension states.
• An overdose of it can result in coma, severe respiratory
depression,
Methabarbital
Chemically it is
5,5-diethyl-1-methyl-1,3-diazinane-2,4,6-trione/
5,5-Diethyl-1-methyl-2,4,6(1H,3H,5H)-pyrimidinetrione
It is a barbiturate anticonvulsant, used in the treatment of
epilepsy
II.
Hydantoins
• Hydantoins are cyclic monoacylureas.
• They possess imidazoline-2, 4-dione heterocyclic system
• The hydantoins are close structural relatives of
barbituric acid, differing due to the lack of C-6 oxo group.
• The lack of this carbonyl group decreases the acidity. So
it is a weaker acid than that of barbiturates
SAR OF
HYDANTOIN
• 5-phenyl or other aromatic substitution is essential for activity
• Alkyl substituent at position 5 may contribute to sedation
• 1,3-disubstituted hydantoins, exhibit activity against
chemically induced convulsion, while it remains ineffective against electric
shock induced convulsion
Phenytoin:
• Phenytoin occurs as phenytoin sodium, chemically phenytoin
is 5,5′-diphenylhydantoin.
Properties:
Phenytoin occurs as white, crystalline powder, slightly
hygroscopic, soluble in water and in alcohol, practically insoluble in ether
and in methylene chloride.
Medicinal uses:
• Phenytoin is used alone or in combination with
phenobarbital in the treatment of grand mal and psychomotor epilepsy
• It is also used in the treatment of other types of
convulsions
Phenytoin Synthesis
Mephenytoin:
• Mephenytoin is a hydantoin derivative. Chemically it is
5-ethyl-3-methyl 5-phenylhydantoin.
Properties:
Mephenytoin is water insoluble, colorless crystalline solid.
It forms a water soluble sodium salt which has an alkaline reaction.
Medicinal uses:
• It was introduced as a sedative-hypnotic and
anticonvulsant under the name Nirvanol, but it was withdrawn because of
toxicity.
Ethotoin
INN, USAN, BAN,:
• Ethotoin is a hydantoin anticonvulsant with anti-epileptic
activity.
Chemically it is 3-ethyl-5-phenylimidazolidine-2,4-dione
Medicinal uses:
• An antiepileptic, it is less toxic than phenytoin but also
less effective.
• Used in the treatment of Grandmal epilepsy
• It has a role as an anticonvulsant
III.
Oxazolidinediones
• Replacement of the -NH group at position 1 of the
hydantoin systems with oxygen atom yields the oxazolidine- 2,4-dione system
• Trimethadione is only clinically used
SAR OF
OXAZOLIDINE DIONES
• Replacement of the -NH group at position 1 of the hydantoin
system with an oxygen atom yields the oxazolidine-2,4-dione system
• 3,5,5-Trimethadione (tridione) was the first drug
introduced specifically for treating absence seizures.
• The nature of the substituent on C-5 is important,
example, lower alkyl substituents towards antipetitmal activity while acyl
substituents towards antigrandmal activity
• The N-alkyl substituent does not alter or afford the
activity since all the clinically used agents from this class undergo N-dealkylation
in metabolism.
Trimethadione:
Trimethadione is an oxazolidinedione derivative. Chemically
it is 3, 5,5-trimethyloxazolidine-2,4-dione
Properties:
Trimethadione is colourless or almost colourless crystals,
soluble in water,very soluble in alcohol and in ether. It should be protected
from light.
Medicinal uses:
• Used in the treatment of absence seizures
Paramethadione
Chemically it is 5-ethyl-3, 5-dimethyl oxazolidine-2,
4-dione.
Structurally it is very closely related to trimethadione
Properties:
Paramethadione is available as clear, colourless liquid. It
is partially miscible with water. It should be stored in a well-closed
container.
Medicinal uses:
• Used in the treatment of absence seizures
IV. SUCCINIMIDES
• Due to the inherent high-level of toxicity attributed by the
oxazolidinediones in prolonged therapy as anticonvulsants
• A vigorous attempt was made to replace them with better
effective and less toxic drugs.
• Three members of this class of compounds were introduced between
early fifties to late fifties, namely; Phensuximide, Methsuximide and
Ethosuximide.
All of them gained with acceptance for the treatment of
petit mal seizures specifically
SAR of
Succinimides
• The activity of antiepileptic agents, such as the oxazolidine
2,4-dione with substituted succinamides (CH2 replace O) was logical choice for
synthesis and evaluation.
• N-demethylation occurs to yield the putative active
metabolite.
• Both phensuximide and the N-demethyl metabolite are
inactivated by p-hydroxylation and conjugation.
PHENSUXIMIDE
(Milontin)
• Phensuximide is a 2,5-pyrrolidinedione derivative
• Chemically it is N-methyl- 2-phenylsuccinimide
Properties: It is
a crystalline solid, soluble in water and freely soluble in ethanol.
Medicinal Uses:
It is used in the treatment of petitmal epilepsy
Methsuximide:
(Celontin)
Chemically it is 2-ethyl-2-methylsuccinimide.
Methsuximide is a 2,5-pyrrolidinedione derivative
Properties: It is
a crystalline solid, soluble in water and freely soluble in ethanol.
Medicinal Uses:
• More active than Phensuximide
• It is used in the treatment of petitmal epilepsy
ETHOSUXIMIDE:
(Zarontin)
Chemically it is 2-ethyl-2-methylsuccinimide.
ethosuximide is a 2,5-pyrrolidinedione derivative
Properties: It is
a white or an almost white powder or waxy solid.
Freely soluble in water, ethanol, and methylene chloride.
Medicinal Uses:
• It is used in the treatment of petitmal epilepsy
ETHOSUXIMIDE
SYNTHESIS
V. UREA AND
MONOACYL UREAS
• PHENACETAMIDE
• CARBAMAZEPINE
General chemical
structure of an urea
General chemical
structure of an acylurea
PHENACETAMIDE
:(Phenurone)
Properties: It is
available as crystalline, slightly water soluble solid
Medicinal uses:
Phenacemide is used as an anticonvulsant drug
CARBAMAZEPINE:
(Tegretol, Zen, Zeptol)
Properties: It is
a white or almost white crystalline powder and it shows polymorphism, slightly soluble
in water, freely soluble in methylene chloride, but sparingly soluble in
acetone and ethanol
Medicinal Uses:
• Carbamazepine, a urea derivative, is a broad spectrum antiseizure
agent, but is toxic
• Used to treat partial seizures and grandmal seizures
CARBAMAZEPINE
Synthesis
VI.
BENZODIAZEPINES
CLONAZEPAM:
Clonazepam is 5-(2-chlorophenyl)-3-dihydro-7-nitro-2H-1,4- benzodialzepin-2-one
Properties:
Clonazepam is slightly yellowish, crystalline powder, practically insoluble in
water, slightly soluble in alcohol and in methanol, very slightly soluble in
ether. It melts at about 239°C.
Medicinal Uses:
Clonazepam is used in the treatment of grand mal epilepsy
VII. MICELLENEOUS:
• PRIMIDONE
• VALPROIC ACID
• GABAPENTIN
• FELBAMATE
PRIMIDONE:
• Primidone is an antiepileptic agent related to
barbiturates
• Primidone is a diketone derived from hexahydropyrimidine chemically
it is 5-ethyl-2, 3-dihydro-5-phenyl-4, 6-(1H, 5H)-pyrimidine dione.
Properties: A
white or almost white, crystalline powder, very slightly soluble in water, slightly
soluble in alcohol, practically insoluble in ether.
Medicinal Uses:
Primidone is an antiepileptic agent used to control grandmal
and psychomotorseizures.
VALPROIC
ACID:
• Valproic acid was discovered as an anticonvulsant in 1963,
and it was approved by the FDA for seizures in 1978.
• Valporic acid is 2-propylpentanoic acid. It is available
as sodium valproate.
• Valproic acid is not chemically related to other
anticonvulsants.
Properties:
Sodium valproate is hygroscopic, white, crystalline powder.
• It is freely soluble in water and should be stored in an
airtight container.
Medicinal Uses:
• Used for different types of seizures
• Absence seizures (petit mal seizures), generalized tonic-clonic
seizures, complex partial seizures, and myoclonic seizures.
• Sodium valproate may be effective against myoclonic and
atonic seizures in young children
• considered as the agent of choice.
• Used for treating bipolar mania and migraine headaches
Gabapentin
(Gabantin, Gaba, Rejuron)
• It is a GABA analogues
Properties: It is
a colourless, crystalline substance, soluble in water.
Medicinal uses:
• It has been endorsed as an effective drug for the
management of neuropathic pain.
• Used to treat partial seizures
Felbamate:
(MedPointe)
• Felbamate is a dicarbamate derivative anticonvulsant chemically
it is (3-carbamoyloxy-2-phenylpropyl) carbamate
Medicinal uses:
• An anticonvulsant used in the treatment of epilepsy.
• It is used to treat partial seizures
SUMMARY
• Epilepsy is a disorder characterized by dysfunction due to
excessive neuronal discharge and usually associated with some alteration of
consciousness
• Antiepileptic is a medication used to control (prevent)
seizures (convulsions) or stop an ongoing series of seizures.
• They prevent, stop, or lessen the excessive electric
activity in the brain
• Classification of anticonvulsant agents
• Drug profiles of some anticonvulsant agents
• Synthesis of some antiepileptics have been outlined.
• Although the drugs are effective antiepileptics, they have
numerous side effects. Thus, there is a need for better anti-epileptic drugs.