Acetazolamide, Sulthiame and Newer Antiepileptics

Acetazolamide

Not commonly used for treatment of epilepsy. Only effect is due to acidosis produced, being more effective in petit mal epilepsy.

Sulthiame

Derivative of sulphonamide. Weak antiepileptic effect mainly due to enzyme inhibiting property. It inhibits metabolism of other antiepileptic drugs, so their action increases, thus can be used in combination.

Vigabatrin, Lamotrigine, GABA pentin, Topiramate, Tiagabine and Zonisamide are newer drugs, which are 2^nd line drugs, used only when patient does not respond to 1^st line drugs. They have four properties:

Always given as 2^nd line and in combination with other antiepileptic drugs, when patient is not responding. In rare conditions may be used alone
Have wide range of activity, so used in all types of epilepsy
Have minimal plasma protein binding, having less drug interactions.
Do not have enzyme inducing or inhibiting property so have less drug interactions.

Vigabatrin

Half life 6-8 hours.

Mechanism of Action

Acts by inhibiting GABA transaminase enzyme (responsible for metabolism of GABA) inhibiting it non-competitively.

Uses

Broad spectrum –all types of epilepsy, mostly used in patients with seizures and infantile spasms.

Adverse effects

Can cause visual field defects on prolonged administration. So uses are declining.

Dose

Start at low dose of 500 mg, which may be increased up to 1500 mg.

Lamotrigine

Mechanism of Action

As wide range spectrum, can cause

sodium channel blockage
blocks calcium T channels

Pharmacokinetics

Mainly metabolized in liver. Longer half life of 24 hours.

Uses

All types of epilepsy.

Adverse effects

CNS –in children can cause severe rash, which may even lead to death.

Avoided by giving drug in low doses, 100-300 mg in divided doses.

GABA Pentin

Mechanism of Action

Interferes with GABA metabolism, synthesis, release and reuptake. Exact mechanism is not known.

Pharmacokinetics

Excreted in urine. Half life is 6-8 hours.

Uses

In all types of epilepsy.

Partial seizures, infantile spams. Also used in neuralgias or neuropathic pains.

Dose

1.8-4.8 g. Start at low dose

Adverse effects

CNS- drowsiness and sedation

Topiramate

Mechanism of Action

blocks sodium channels directly
blocks calcium T channels
GABA mediated effects – increase in GABA
Inhibitory effects on excitatory neurotransmitters.

Mostly excreted unchanged in urine. Half life is 24-30 hours, thus having a longer half life.

Broad spectrum, so used in all types of epilepsy.

Adverse effects

On prolonged use, increased incidence of urinary calculi or urinary stones.

Advised to take excess of water.

Dose 50-600 mg, start at lower dose.

Taigabine

Mechanism of Action

Mainly by inhibiting the uptake of GABA, increasing the concentration of GABA in brain or in synapses.

Drug is mainly oxidized in liver. About 75% of drug is excreted in faeces. 25% in urine.

Half life is 6-8 hours.

Uses broad range activity

Adverse Effects depression in certain patients.

Dose in range of 16-56 mg. start at lower dose.

Zonisamide

Mechanism of Action

Same on sodium channels and GABA.

Has longer half life of about 1-3 days.

Used in all types of epilepsy.

Dose is 100-600 mg. start at lower dose.

Paraldehyde

Sedative hypnotic not used now, as is an older drug. It is used in patients suffering from head injury as has least respiratory depressant effect.

Now more safer benzodiazepines have been produced (diazepam). Only used in certain cases of status epilepticus.