Anti Epileptics

Question 1

Classification of anti epileptic drugs

Answer 1

BBICHSO

1) barbiturates- phenobarbitone
2) Benzodiazepines- diazepam, lorazepam, clonazepam, clobazam
3) iminostilbenes- carbamazepine, oxcarbazine
4) carboxylic acid derivatives- sodium valproate
5) hydantoins- phenytoin, fosphenytoin
6) succinamide-
7) others- levityracetam, lacosamide, lamotrigine, gabapentin, vigabatrin, zonisamide

Question 2

MOA of anti epileptic drugs on Na+ channels

Answer 2

1. Binds to the voltage dependant sodium channels
2. Prevents further entry of Na+ into the neurons
3. Stabilises the neuronal membrane
4. Inhibits the generation of repetitive action potentials
5. Thereby preventing/ reducing spread of seizure discharges

Question 3

MOA of anti epileptics on GABA

Answer 3

1. ⬆️ GABA activity
2. ⬆️ chloride conductance into the neuron (IPSP)
3. Hyper polarisation
4. Reducing neuronal excitability
5. Anti epileptic effect

Question 4

MOA of phenytoin

Answer 4

1. Delays recovery of Na+ channels from inactivated state
   => ⬇️ neuronal excitability
   => Inh. Frequency of firing

*at high conc. phenytoin Inh. Calcium ion influx into the neuron
~> ⬇️ glutamate levels, ⬆️ response to GABA

Question 5

phenytoin- PK, use

Answer 5

PK:
1. Highly bound to plasma proteins
2. Almost completely metabolised in the liver- hydroxylation & glucuronide conjugation
3. Repeated administration- causes enzyme induction
~> ⬆️ the rate of metabolism of co administered drugs
4. Plasma conc. increases markedly with slight increase in dose => toxicity

Use:
GTC seizures
Partial seizures
Trigeminal & other neuralgias 
Status epilepticus

Question 6

Phenytoin A/E

Answer 6

H’s

1. Hypertrophy & hyperplasia of gums
2. Hypersensitivity reactions- including rashes, neutropenia, Hepatic necrosis
3. Hisutism
4. Hyperglycaemia
5. Hypocalcemia
6. Foetal Hydantoin syndrome
7. Ostomalacia
8. Megaloblastic anaemia

⬆️ conc.

1. CNS: vestibulocerebellar syndrome- vertigo, ataxia, tremor, headache
2. CVS: hypotension, cardiac arrhythmias
3. GIT: nausea, vomiting, dyspepsia