Drug interactions
Amobarbital + Fosphenytoin
Severity: Moderate
Amobarbital and Fosphenytoin: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Barbiturates can alter phenytoin concentrations unpredictably, since they may induce its metabolism but can also compete for it. Seizure control may worsen or phenytoin toxicity may occur, and CNS depression is additive.
What this interaction means in plain words
Amobarbital and Fosphenytoin can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Amobarbital belongs to Central Nervous System; Fosphenytoin belongs to Central Nervous System.
Why it happens
Enzyme induction (CYP2C9/2C19) and possible competitive metabolism alter phenytoin clearance, with additive CNS depression.
What to do
Monitor total or free phenytoin levels when amobarbital is started or stopped and adjust the fosphenytoin dose accordingly. Watch for sedation and loss of seizure control.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Amobarbital
- Amobarbital + Calcium / magnesium / potassium / sodium oxybates Contraindicated
- Amobarbital + Doravirine Contraindicated
- Amobarbital + Elbasvir / grazoprevir Contraindicated
- Amobarbital + Isavuconazonium Contraindicated
- Amobarbital + Isocarboxazid Contraindicated
- Amobarbital + Lonafarnib Contraindicated
Other interactions of Fosphenytoin
- Dronedarone + Fosphenytoin Contraindicated
- Fosphenytoin + Ledipasvir-sofosbuvir Contraindicated
- Fosphenytoin + Lorlatinib Contraindicated
- Fosphenytoin + Lurasidone Contraindicated
- Fosphenytoin + Ranolazine Contraindicated
- Fosphenytoin + Sofosbuvir-velpatasvir-voxilaprevir Contraindicated
Frequently asked questions
Can I take Amobarbital with Fosphenytoin?
MediHelp rates the interaction as moderate. Amobarbital and Fosphenytoin can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Barbiturates can alter phenytoin concentrations unpredictably, since they may induce its metabolism but can also compete for it. Seizure control may worsen or phenytoin toxicity may occur, and CNS depression is additive.
How serious is the interaction between Amobarbital and Fosphenytoin?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor total or free phenytoin levels when amobarbital is started or stopped and adjust the fosphenytoin dose accordingly. Watch for sedation and loss of seizure control.
What other medicines interact with Amobarbital?
MediHelp also lists interactions of Amobarbital with, for example, Calcium / magnesium / potassium / sodium oxybates, Doravirine, Elbasvir / grazoprevir. The full list is on the Amobarbital page.
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