Vigabatrin (Sabril)

Vigabatrin is an antiepileptic drug used in treating a particular type of seizure in adults and children over ten when other medications have not worked. It is also used to treat babies with infantile spasms. Vigabatrin should be used with caution as it may affect the mental health of those taking it.

Vigabatrin brand names

Vigabatrin is available under the brand names Sabril and Vigadrone. ^[1]

What is vigabatrin prescribed for?

Vigabatrin is most commonly used to treat patients with refractory complex partial seizures (a type of epilepsy) or infantile spasms when other medications have not achieved satisfactory control. However, it may also be used off-label for other conditions, such migraines or neuropathic pain. Vigabatrin is generally well-tolerated, but the most common side effects include fatigue, weight gain, and dizziness. Less common side effects include vision problems and mood changes.

In the United States, vigabatrin has been approved to be used as adjunctive therapy with other anticonvulstant medications since 2009. ^[2]

How does vigabatrin work?

Vigabatrin is a medication that is typically used to treat complex partial seizures. It belongs to a class of drugs called anticonvulsants, which work by reducing the abnormal electrical activity in the brain that leads to seizures. This calming effect is achieved by increasing the levels of gamma-aminobutyric acid or GABA, an inhibitory neurotransmitter (chemical messenger).

Increasing the levels of GABA in the central nervous system is achieved by blocking the action of an enzyme called GABA-transaminase (GABA-T), which normally breaks down GABA when it is no longer needed.^[3]

This helps to decrease the number and severity of complex partial seizures. Vigabatrin is typically used as part of a combination seizure treatment plan and may be used alone or with other medications. While vigabatrin may help to control the condition, it does not cure it. Thus, the patient needs to keep taking medicine even if they feel well and the seizures have subsided. The drug should not be stopped unless under a doctor’s supervision; stopping a seizure medicine can result in status epilepticus, a condition where seizures start that will not stop.^[4]

How is vigabatrin usually taken?

Vigabatrin is available as a tablet or a powder that needs to be mixed with water to make an oral solution. The dose is usually twice daily and can be taken with or without food. It is best to take vigabatrin at approximately the same time of day.

Dosage is based on the severity of the condition and the response achieved and will thus vary between patients. The doctor will direct the patient to start on a lower daily dose and gradually increase it at weekly intervals, as this gradual increase lowers the chance of getting side effects. The amount will then be adjusted according to the reaction and response until the doctor finds the best dose where treatment controls seizures and side effects are minimized.

The medicine’s dose should not be altered without specific instructions and supervision by your healthcare provider and should also not be stopped abruptly. However, if you feel that the seizures have increased in number or intensity, you should tell your doctor; vigabatrin can make certain types of seizures worse.^[5]

The oral powder packet contains 500mg of vigabatrin. The contents should be mixed with water, and the dose should be measured using the supplied oral syringe. Using the syringe provided rather than a kitchen spoon is essential, as the former provides a more accurate dosage. The dose should be taken immediately after mixing, so it should not be pre-mixed for future use. Any unused medication should be discarded.

To use the oral powder, empty the contents of the packet into a clean cup and dissolve it with 10 milliliters (mL) of room temperature or cold water. Do not use hot water. The resulting liquid should be free of particles and colorless. Do not take it if the solution is not clear.

For infantile spasms in babies aged one to twenty-four months of age, the dose is based on body weight and will be determined by your doctor. The initial dose for an infant or child is 50 milligrams per kilogram of body weight, divided into two daily doses. The dose is then adjusted according to response but will generally not be more than 150 mg per kilogram per day.

The dose is calculated for children between 2 and 16 according to body weight.

• Less than 10 kg: dose needs to be determined by the doctor.
• 10-15 kg: at first, 175 mg is given two times daily, gradually increasing, usually up to 1050 mg per day.
• 15-20 kg: at first, 225 mg is given two times daily, gradually increasing, usually up to 1300 mg per day.
• 20-25 kg: at first, 250 mg is given two times daily, gradually increasing, usually up to 1500 mg per day.
• 25-60 kg: at first, 250 mg is given two times daily, gradually increasing, usually up to 2000 mg per day.

The oral tablet is available in 500mg doses and can be taken with or without food.

The dosage for children over 17 who weigh more than 60 kg, and adults: at first 500 mg given two times daily, gradually increased usually up to 3000 mg per day.^[6]

How long does vigabatrin stay in your system?

The elimination half-life of vigabatrin is between 5.7 (in infants) to 9.5 hours (in children 10-16 years) and 10.5 hours (in adults). It is not significantly metabolized and is eliminated through the kidneys. This means that in infants, less than 3% of the drug will be in the system after two days, and in adults, the elimination will take slightly longer.^[7]

Vigabatrin side effects

Like with other antiepileptic drugs, vigabatrin can cause serious side effects; including the risk of suicidal thoughts and actions, permanent vision loss, and MRI changes in babies with infantile spasms.

Vision loss can happen in anyone taking vigabatrin. This includes loss of peripheral vision that can result in tunnel vision (only being able to see things directly in front of you). Due to this and other possible severe side effects, vigabatrin is only used in patients who do not respond well to other treatments. Alert your doctor immediately if you or your child experience changes in vision. For example, your child may become more clumsy than usual and bump into things.

This vision loss is not reversible and should be seen immediately. Regular vision tests are crucial during treatment with vigabatrin. However, conducting vision tests in infants and young children is challenging. Risk increases with higher doses of vigabatrin in patients and a more extended treatment period.

The risk of suicidal thoughts or actions occurs in about 1 in 500 people taking vigabatrin. You should contact a healthcare provider straight away if you experience or observe any of the following:

• New or worsening depression
• Panic attacks
• Trouble sleeping
• Thoughts of suicide or dying
• New or worse irritability, agitation, or restlessness
• Unusual increase in activity/talking
• Increased aggression, violence, or anger
• Impulsive behavior
• Other remarkable changes in mood or behavior

Vigabatrin/Sabril side effects can include sleepiness and tiredness. In addition, infants may have a more challenging time feeding and may be irritable when this happens. Infants also experience swelling in the lungs’ bronchial tubes and ear infections.

Other serious side effects in adults are anemia (low red blood cell count), nerve issues such as tingling or numbness in the toes or feet, and swelling.

The most common side effects in children and adults are blurred vision, tremors, tiredness, sleepiness, dizziness, and lack of coordination. In addition, the most common side effect seen in children up to 16 years is weight gain.^[8]

Other side effects that could occur due to vigabatrin are:

• Weakness
• Uncontrollable shaking
• Fever
• Diarrhea
• Nausea and vomiting
• Constipation
• Heartburn
• Stomach pain
• Tingling, burning, or pain in hands and feet
• Memory problems
• Confusion
• Joint or muscle pain
• Painful menstrual cramps

Seek immediate medical attention in case of the following:

• Fast heartbeat
• Pale skin
• Itching and hives
• Confusion
• Tiredness
• Difficulty breathing

Even if severe side effects are suspected, vigabatrin should always be tapered under medical supervision. Suddenly stopping the medication can result in severe seizures (epileptic fits).

Vigabatrin precautions

You should seek medical advice if you suffer from any of these conditions before starting vigabatrin:

• Suicidal tendencies
• Visual acuity / vision loss [major potential hazard]
• Neurotoxicity
• Peripheral neuropathy

Also, inform your medical professional if you are planning on becoming pregnant, are pregnant, or breastfeeding. Vigabatrin can pass into breast milk in small amounts, and could harm your baby. 

Since vigabatrin may cause sleepiness and drowsiness, exercise caution when using machinery or driving, especially until you know how this medicine affects you. Always stay attentive to any change in your or the patient’s mental health.

Vigabatrin interactions

Inform your doctor and pharmacist about any other medicines you or your child take, including all prescription medications, over-the-counter preparations, vitamins and minerals, or herbal supplements. Any of these may interact with vigabatrin and cause side effects. There are no known food interactions with vigabatrin, so unless your doctor alerts you, you should your usual diet.

Vigabatrin interacts with phenytoin, and the phenytoin dose may need to be adjusted. In addition, if taken with clonazepam, this increases the risk of clonazepam-associated side effects. 

Other medications that cause moderate interactions are levetiracetam (Keppra), lithium, pregabalin (Lyrica), valproate sodium, and cetirizine (Zyrtec).^[9]

Vigabatrin storage

Vigabatrin or Sabril tablets and powder should be stored in the container they came in, closed tightly and kept out of reach of children or pets. In addition, they should be kept at room temperature, away from excess heat, moisture, and light.

Do not flush any unwanted medication down the toilet. Instead, ask your pharmacist about proper disposal or local Drug Take Back Day.^[10]

What to do if you overdose on vigabatrin

Symptoms of overdose with vigabatrin include drowsiness and loss of consciousness. Call the poison control helpline if you know or suspect an overdose has occurred. Call emergency services if the patient has collapsed, has trouble breathing, has a seizure, or is not responsive.

Overdose can lead to severe side effects, including permanent loss of vision.^[11]