. WHAT IS THIS MEDICINE AND WHAT IS IT USED
FOR?
Primidone is an anticonvulsant (anti-seizure) medicine belonging to the
barbiturate family. In the body, primidone is partially converted into
phenobarbital — a well-established anti-epileptic compound — and both primidone
and phenobarbital contribute to its anticonvulsant effect.
They work by enhancing the activity of GABA — the brain's main inhibitory
(calming) neurotransmitter — which reduces the abnormal electrical activity
responsible for seizures. Primidone is used for the treatment of epilepsy —
particularly for grand mal (tonic-clonic) seizures, focal (partial) seizures,
and complex partial seizures.
It is also used for essential tremor — an involuntary rhythmic shaking of
the hands or other body parts that is not caused by Parkinson's disease.
3. HOW TO TAKE THIS MEDICINE
Treatment is always started at a low dose and increased very slowly over
several weeks to minimise sedation and tolerance development. A typical
titration for adults: 50mg at night for days 1 to 3, then 100mg at night for
days 4 to 6, then 150mg at night for days 7 to 9, then 200mg at night, with
further increases as directed by your neurologist up to a usual maintenance
dose of 250mg to 500mg three times daily (750mg to 1500mg per day). For
essential tremor, lower doses are typically effective. Take with or without
food. Never stop primidone suddenly.
Primidone doses are expressed in terms of primidone — bear in mind that
it converts to phenobarbital in the body. Phenobarbital is itself an active
drug and its levels can be monitored in the blood if needed. When switching
between primidone and phenobarbital, the conversion ratio must be taken into
account by the prescribing neurologist.
⚠ PATIENT TIP: Starting primidone can cause
significant drowsiness, dizziness, and unsteadiness — particularly in the first
few weeks. This usually improves as your body adjusts, but avoid driving,
operating machinery, or activities requiring sharp alertness until you know how
the medicine affects you. Starting at night helps manage the initial sedation.
4. POSSIBLE SIDE EFFECTS
|
How Common? |
Side Effects |
|
Very Common at Start
(usually improves) |
Drowsiness and
sedation, dizziness, unsteadiness (ataxia — difficulty with co-ordination),
nausea — these are most pronounced in the first 1 to 2 weeks and typically
improve significantly as tolerance develops |
|
Common with Long-term
Use |
Fatigue, depression or
low mood, irritability, impaired memory or concentration, sexual dysfunction,
reduced libido, vitamin D deficiency and bone thinning (osteoporosis) with
long-term use, folate deficiency |
|
Serious — Tell Your
Doctor |
Severe skin reactions
— particularly Stevens-Johnson syndrome (painful blistering rash affecting
skin and mouth) — seek emergency care immediately if this develops. Signs of
liver problems: jaundice, dark urine, upper right tummy pain. Folate
deficiency — can cause megaloblastic anaemia (a type of anaemia from impaired
blood cell production). Signs of phenobarbital toxicity: extreme drowsiness,
slurred speech, confusion, poor coordination. |
5. WHO SHOULD NOT TAKE THIS MEDICINE
Primidone must not be used in patients with porphyria (a rare metabolic
disorder — primidone can trigger acute attacks). It is not recommended during
pregnancy without specialist guidance, as it may increase the risk of birth
defects.
Women who may become pregnant should discuss folic acid supplementation
and contraception with their neurologist before and during treatment.
Breastfeeding is generally not recommended — primidone and phenobarbital pass
into breast milk.
⚠ NEVER STOP SUDDENLY: Abrupt withdrawal of
primidone can trigger severe, potentially life-threatening seizures (status
epilepticus). If you need to stop for any reason, the dose must be reduced very
gradually over weeks to months under neurological supervision.
⚠ FOLATE AND BONE HEALTH: Long-term use of
primidone reduces folate (vitamin B9) and vitamin D levels. Your neurologist
may recommend folic acid supplements (especially if you might become pregnant)
and vitamin D supplementation. Bone density monitoring may also be needed with
very long-term treatment.
⚠ DRIVING: Primidone causes sedation and slows
reaction times, particularly when starting or adjusting the dose. Follow your
neurologist's and relevant licensing authority's guidance about driving. Do not
drive until you are confident the medicine is not affecting your alertness or
coordination.
6. MEDICINES THAT INTERACT WITH THIS TREATMENT
Primidone is a strong inducer of liver enzymes (CYP450) — it
significantly speeds up the breakdown of many other medicines, making them less
effective. This includes: oral contraceptives (the pill may become less
effective — additional contraception is needed), warfarin (anticoagulant effect
reduced — INR monitoring required), corticosteroids, certain antibiotics,
antifungals, and many other medicines.
Alcohol significantly enhances the sedative effects of primidone — avoid
alcohol during treatment. Other CNS depressants (sedatives, anxiolytics,
opioids) increase drowsiness. Valproate and other anti-epileptics may interact
— always inform your neurologist of all medicines.
7. HOW TO STORE THIS MEDICINE
Store below 25°C. Protect from light. Keep in original packaging. Keep
out of reach of children.
8. PRESCRIPTION REQUIREMENT
|
Field |
Details |
|
Status |
Prescription Only
Medicine (POM) — Specialist (neurology) prescription required for initiation;
may be managed long-term by GP |
9. GUIDANCE FOR PATIENTS & CAREGIVERS
Take your tablets exactly as prescribed — the dose is increased gradually
for a reason, so do not try to speed up the process. Start at night to help
manage the early drowsiness. Never stop taking primidone without speaking to
your neurologist first — sudden stopping can trigger life-threatening seizures.
If you use hormonal contraception (the pill, patch, or implant), speak to
your doctor as primidone can make it less effective. Avoid alcohol — it
significantly increases drowsiness. Attend regular blood tests as your
neurologist advises. If you are pregnant or planning a pregnancy, discuss with
your neurologist urgently — specialist guidance is essential.
10. PHARMACIST & PRESCRIBER NOTES
|
Field |
Details |
|
Clinical Dispensing
Notes |
Barbiturate
anticonvulsant — primidone is metabolised to phenobarbital (active) and
phenylethylmalonamide (PEMA). Titrate slowly — first-dose reaction
(drowsiness, dizziness, nausea) is significant; starting at night reduces
impact. Phenobarbital levels can be monitored as a surrogate. Strong CYP450
inducer: counsel on oral contraceptive failure (enzyme induction reduces
hormonal contraceptive plasma levels — additional or alternative
contraception required), warfarin (INR monitoring), corticosteroids, and all
co-prescribed CYP-metabolised medicines. Folate supplementation recommended
(particularly in women of childbearing age) — primidone reduces folate
levels. Vitamin D supplementation and bone density monitoring for long-term
users. Porphyria absolute contraindication. Pregnancy: teratogenic risk —
folic acid 5mg daily pre-conception and during pregnancy if treatment
continued; specialist obstetric-neurology co-management required. Never
withdraw abruptly — status epilepticus risk. |
11. FREQUENTLY ASKED QUESTIONS
Q: Why do I feel so drowsy when I first start?
Drowsiness, dizziness, and unsteadiness in the first 1 to 2 weeks are
very common and can be pronounced. This is why the dose is started very low and
increased very slowly — to give your body time to adjust. Starting the dose at
night helps many people manage the initial sedation. For most people, the
drowsiness fades significantly within 2 to 4 weeks.
Q: Why can't I stop taking it suddenly?
Primidone and the phenobarbital it converts into suppress the brain's
electrical excitability. Stopping suddenly removes this suppression abruptly,
which can trigger severe, prolonged seizures (status epilepticus) — a medical
emergency. Always taper the dose gradually, over weeks to months, under your
neurologist's guidance.
Q: Does it affect my bones?
Yes — long-term use of primidone reduces vitamin D levels, which can
weaken bones over time (osteoporosis). Your neurologist may recommend vitamin D
supplementation and, if you have been on primidone for many years, a bone
density scan (DEXA scan).
Q: Can I drink alcohol while taking primidone?
No — alcohol significantly intensifies the sedative effects of primidone,
causing extreme drowsiness, loss of coordination, and potentially dangerously
slow breathing. Avoid alcohol completely during treatment.
Q: Is this medicine also used for tremors?
Yes — primidone is effective for essential tremor (uncontrolled rhythmic
shaking of the hands, head, or voice not related to Parkinson's disease). For
tremor, lower doses are usually more effective than for epilepsy, and the same
careful dose titration applies.