[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Antiseizure medicines](https://durgical.com/en/pharmacology/classes/antiseizure-medicines/) › Primidone

# Primidone

## Antiseizure medicines?

Antiseizure medicines

An old antiseizure medicine that the body turns into phenobarbital. Today it is used mostly for essential tremor and some epilepsies.

Updated Nov 1, 2026

## Quick facts

**Group**
[Antiseizure medicines](https://durgical.com/en/pharmacology/classes/antiseizure-medicines/)

**Target**
GABA-A receptor (through its metabolite phenobarbital)

**Used for**
Essential tremor

**Key effects**
Excessive tiredness · Poor coordination · Nausea

**Monitor**
Seizure or tremor control · Mood and suicidal thoughts

**ATC**
N03AA03

No doses: the clinician sets them by the current guideline.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## Mechanism of action

◎**GABA-A receptor (through its metabolite phenobarbital)**Primidone

ⓘ The figure shows phenobarbital, the main active metabolite of primidone, bound to the human GABA-A receptor (α1β2γ2) with GABA.

**Target in 3D:** GABA-A receptor (through its metabolite phenobarbital). PDB structure 6X3W (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/6X3W) · Drag to rotate · pinch to zoom

Primidone is a deoxy analogue of phenobarbital. The liver converts it into two active metabolites, phenobarbital and phenylethylmalonamide (PEMA); primidone and both metabolites have antiseizure effects. Much of its effect comes from phenobarbital, which prolongs the opening of GABA-A chloride channels. The exact mechanism of primidone itself is not fully understood.

- Primidone is absorbed and reaches the liver
- It is converted into phenobarbital and PEMA
- Phenobarbital strengthens GABA-A inhibition
- Fewer seizures and less tremor

## Indications

- Focal and generalized tonic-clonic seizures (largely replaced by newer medicines) [Epilepsy and seizures →](https://durgical.com/en/conditions/epilepsy-and-seizures/)
- Essential tremor (with propranolol, a first-line option) [Essential tremor →](https://durgical.com/en/conditions/essential-tremor/)

## Adverse effects

### Common

- Excessive tiredness, drowsiness and dizziness
- Poor coordination
- Nausea, vomiting and loss of appetite
- Double vision and involuntary eye movements (nystagmus)
- Decreased sexual ability

### Serious (rare, important)

- Rash
- Suicidal thoughts or behaviour, as with all antiseizure medicines
- Worse seizures if it is stopped suddenly

## Contraindications

- Porphyria
- Allergy to primidone or phenobarbital

## Key interactions

**Alcohol and other sedatives**
More drowsiness and slower reactions

**Medicines broken down by CYP3A4**
Primidone (like phenobarbital) induces CYP3A4 and can lower their levels

## What is monitored

- Phenobarbital blood levels during dose changes
- Seizure or tremor control
- Mood and suicidal thoughts
- Laboratory tests ordered at follow-up

## Administration and safety

- Oral tablets, usually several times a day
- Started low and raised slowly
- Never stopped suddenly: it is tapered to avoid withdrawal seizures
- When switching from another antiseizure medicine, one is lowered while the other is raised over weeks

## Pregnancy and breastfeeding

Its safety in pregnancy is not established and it shares the risks of phenobarbital; the decision is made with the treating team, and the medicine passes into breast milk.

## Nursing care

- Check alertness, gait and fall risk, especially in older adults
- Ask about porphyria and phenobarbital allergy before the first dose
- Teach that drowsiness is common and that alcohol makes it worse
- Watch for mood changes and suicidal thoughts and tell the family what to look for
- If breastfeeding, watch the baby for drowsiness and poor weight gain

## Pharmacokinetics

**Absorption**
Completely absorbed by mouth

**Metabolism**
In the liver, to phenobarbital and PEMA (both active)

**Half-life**
Primidone itself is short-lived; phenobarbital stays much longer and builds up slowly

## Memory aid

«PRIMIdone is phenobarbital's PRIMEr»: the liver turns it into phenobarbital plus PEMA.

## Test yourself

Think of the answer, then tap the question to see it.

## What are the two active metabolites of primidone?

Phenobarbital and phenylethylmalonamide (PEMA).

## Besides epilepsy, which movement disorder is primidone a first-line treatment for?

Essential tremor (propranolol is the other first-line option).

## Which inherited metabolic disease contraindicates primidone?

Porphyria.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/primidone/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## Connections

## Related drugs 4

- [Phenobarbital](https://durgical.com/en/pharmacology/phenobarbital/)
- [Propranolol](https://durgical.com/en/pharmacology/propranolol/)
- [Carbamazepine](https://durgical.com/en/pharmacology/carbamazepine/)
- [Valproic acid](https://durgical.com/en/pharmacology/valproic-acid/)

## Related conditions 2

- [Epilepsy and seizures](https://durgical.com/en/conditions/epilepsy-and-seizures/)
- [Essential tremor](https://durgical.com/en/conditions/essential-tremor/)

[← Back to the class: Antiseizure medicines](https://durgical.com/en/pharmacology/classes/antiseizure-medicines/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Primidone: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682023.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=N03AA03) (WHO Collaborating Centre for Drug Statistics Methodology, 2026); [RCSB PDB - 6X3W: Human GABAA receptor alpha1-beta2-gamma2 subtype in complex with GABA plus phenobarbital](https://www.rcsb.org/structure/6X3W) (RCSB Protein Data Bank, 2026).

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Representative model, for educational purposes only.

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