Anticonvulsants

Anticonvulsants

INTRODUCTION

Anticonvulsants are drugs that are used to arrest convulsions or seizures caused in epilepsy. The term epilepsy, based on the Greek word epilambian (meaning to seize), has been first mentioned by Hippocrates. 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.

Approximately 1% of world’s population has epilepsy, the second most common neurological disorder after stroke. Up to 1990, approximately 16 antiseizure drugs were available and 13 of them can be classified into five similar chemical groups, that is, barbiturates, hydantoins, oxazolidinediones, succinamides, and acetyl ureas. These groups have a common and similar heterocyclic ring structure with a variety of substituents for the drugs with this basic structure; the substituents on this heterocyclic ring determine the pharmacological class, either antimaximal electro shock or antipentylenetetrazole. The remaining drugs, carbamezpine, valproic acid, and benzodiazepines, are structurally dissimilar and the newer drugs used are felbamate, gabapentin, lamotrigine, oxcarbazepine, tigabatrine, topiramate, vigabatrin, and levetiracetam. The anticonvulsant therapy mediated by these 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).

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.

The ideal antiepileptic drug should completely suppress seizures in doses that do not cause sedation or other undecided CNS toxicity. It should be well tolerated and highly effective against various types of seizures and devoid of undesirable side effects on vital organs and functions.