Vigabatrin

MECHANISM OF ACTION:

Vigabatrin inhibits gamma amino butyric acid transaminase (GABA-T), which destroys GABA, an inhibitory neurotransmitter. Vigabatrin is structurally similar to GABA but contains an additional vinyl group. This permits vigabatrin to operate as a GABA - T substrate, liberating GABA from the synaptic left. The concentration of GABA in the brain rises, which helps to stop seizure activity. Vigabatrin inhibits GABA-T, hence preventing neuronal uptake of GABA and stimulating its release into the synapse. Vigabatrin boosts the activity of glutamine, an inhibitory neurotransmitter, which increases its anticonvulsant efficacy.

PHARMACOKINETICS:

Absorption: Absorption occurs after oral administration. The peak plasma concentrations are achieved in approximately 1 hour.

Distribution: Vigabatrin doesn’t bind to plasma proteins and is widely distributed. The drug exhibits negligible plasma protein binding.

Metabolism: Vigabatrin is a mild inducer of CYP2C9, undergoes minimal hepatic metabolism, and is primarily excreted unchanged through the kidneys.

Excretion: Approximately 95% of vigabatrin is excreted unchanged in the urine.

PHARMACODYNAMICS:

Vigabatrin enhances gamma-aminobutyric acid function in the CNS. By increasing brain concentrations of this inhibitory neurotransmitter, the drug appears to decrease the propagation of abnormal hypersynchronous discharges, thereby reducing seizure activity.

DOSAGE AND ADMINISTRATION:

The dosage prescribed for each patient can differ based on the patient’s condition, body weight, and others.

For adults of age 17 and older the recommended dose starts at 1000mg/day (500mg twice daily). Increases total daily dose weekly to 500mg/day, then the recommended dose is 3000mg/day (1500 mg twice daily).

for pediatric patients, which is typically adjusted based on their body weight and individual response. The specifics of this guideline would depend on the medication in question, but the general approach you mentioned—administering two divided doses with weekly adjustments—suggests a carefully tailored approach to treatment.

• If the body eight is between 10 – 15 g The starting dose is 50 mg and the maintenance dose is 1050mg
• If the body weight is between 15 – 20kg, the starting recommended dose is 450mg and the maintenance dose is 1300mg.
• If the body weight is between 20 – 25 kg, the dose starts with 500mg and the maintenance dose is 1500mg.
• If the body weight is 25 – 60 kg, the dose starts with 500mg and the maintenance dose is 2000mg.

DRUG INTERACTIONS:

Before taking vigabatrin it is required to discuss with the health care provider if the patient is undergoing treatment for any other medications. Because some medications when interacting with vigabatrin can cause adverse effects. Below are mentioned few drugs that should be avoided with vigabatrin.

• Retinotoxic drugs – Chloroquine, hydroxychloroquine, phenothiazines, thioridazine, orlistat.
• Antihistamines – Cetirizine, diphenhydramine
• Anxiety medicines – Alprazolam, clonazepam, diazepam, zolpidem
• Muscle relaxants – Codeine

FOOD INTERACTIONS:

Vigabatrin can be taken with or without food but should be taken with plain water. Vigabatrin oral solution powder should be mixed only with plain water.

CONTRAINDICATIONS:

It is not recommended for use in patients who are hypersensitive to any of its ingredients and is also contraindicated during pregnancy and lactation.

ADVERSE EFFECTS:

• Joint pains
• Blurred vision
• Severe menstrual cramps
• Irritability
• Weight gain
• Memory problems 
• Pain, burning, or tingling in the hands or feet.
• Constipation
• Diarrhea
• Heartburn
• Fever

OVERDOSE:

Overdosage of vigabatrin can cause some toxic effects like

• Drowsiness
• Loss of consciousness