Vigabatrin dosage and dose calculator

Vigabatrin is dosed twice a day. For infantile spasms, the dose is based on weight: it starts at 50 mg/kg/day and can rise to 150 mg/kg/day. For refractory complex partial seizures, adults take a fixed dose and children 2 to 16 years old take a weight-based dose.^1,2 The calculator below shows the label's starting and maximum doses in milligrams and in millilitres for each form.

Vigabatrin dose calculator

Shows the FDA label’s starting and maximum dose. It does not replace the prescriber’s instructions. Nothing you enter leaves your browser.

ConditionInfantile spasms (1 month–2 years)Refractory complex partial seizures (2 years and up)FormReady-to-use liquid (Vigafyde, 100 mg/mL)Powder sachets, mixed (50 mg/mL)

Weight

kglb

Enter a weight to see the label dose.

Infantile spasms (1 month to 2 years)

• Start: 50 mg/kg/day, as 25 mg/kg twice a day.
• Increase: by 25 to 50 mg/kg/day every 3 days if needed.
• Maximum: 150 mg/kg/day, as 75 mg/kg twice a day.¹

In the main US trial, babies on high doses (100 to 148 mg/kg/day) responded more often than babies on low doses.³ Most babies who respond do so within the first week or two, so the label advises stopping vigabatrin if it has not clearly helped within 2 to 4 weeks.^2,4

The same mg dose is a different volume in each form:

From the FDA dosing tables for Vigafyde and Sabril powder.^1,5

Refractory complex partial seizures

Adults and children 17 and older

Start at 500 mg twice a day (1,000 mg per day). Increase by 500 mg per day each week. The recommended dose is 1,500 mg twice a day (3,000 mg per day). In the dose-finding trial, 6,000 mg per day worked no better than 3,000 mg and caused more side effects.^2,6

Children 2 to 16 years

Split into two doses a day. From the Sabril label.²

Many of these doses (for example 175 mg twice a day) cannot be made from whole or half 500 mg tablets, so children are often given the powder for oral solution. The ready-to-use liquid is not labeled for these seizures.¹ If vigabatrin has not clearly helped within 3 months, the label advises stopping it.²

Kidney function

Vigabatrin leaves the body mostly unchanged in the urine, so reduced kidney function raises blood levels.⁷ For patients 2 years and older, the label lowers the dose by 25% when creatinine clearance is 50 to 80 mL/min, by 50% at 30 to 50 mL/min, and by 75% at 10 to 30 mL/min. There is no dosing information for infants with kidney impairment.² The calculator does not make this adjustment.

Switching between forms

The ready-to-use liquid (100 mg/mL) is twice as concentrated as mixed powder (50 mg/mL). When a baby switches, the number of mL changes even though the dose in mg stays the same. The Vigafyde label specifically warns prescribers, pharmacists and caregivers to confirm the new volume.¹ Ask for it in writing, and use a syringe sized for the new dose.⁸ See liquid vs powder.

Giving each dose

• Use the oral syringe from the pharmacy, never a kitchen spoon.^1,9
• Vigabatrin can be given with or without food.¹
• The ready-to-use liquid can go through a G-tube; flush with water afterward.¹
• For powder, follow the mixing steps every time and throw away what is left.⁵

Stopping vigabatrin

Do not stop vigabatrin suddenly; that can bring on seizures. The dose is tapered. In the infantile spasms study it was lowered by 25 to 50 mg/kg every 3 to 4 days.¹ Vision is checked again 3 to 6 months after the last dose.¹