Primidone 50 mg

Indications

Primidone is a prescription medicine used to control epilepsy, including generalised tonic-clonic seizures (grand mal) and focal (partial) seizures, either alone or with other anti-seizure medicines. It is also used to reduce essential tremor, a common condition that causes shaking of the hands, head or voice.

How It Works

In the body, Primidone is changed by the liver into two active substances, Phenobarbital and phenylethylmalonamide (PEMA). Together with Primidone itself, these calm over-active nerve signals in the brain, mainly by strengthening the effect of GABA, the brain's natural calming messenger, and by reducing the excitability of nerve cells. This makes seizures less likely and can reduce tremor.

Dosage and Administration

The dose is decided by the doctor and must be taken exactly as prescribed. Treatment is usually started with a small dose at bedtime and increased slowly over several weeks to reduce drowsiness and dizziness. The final dose differs from person to person and is usually split through the day. For tremor, lower doses are generally used.

• Take it at the same times each day, with or after food if it upsets your stomach.
• If you miss a dose, take it when you remember unless the next dose is due soon; do not take a double dose.
• Do not stop taking Primidone suddenly, as this can trigger seizures or withdrawal symptoms; the doctor will reduce the dose gradually.

Interactions

Primidone speeds up the liver's breakdown of many medicines, which can make them less effective. Tell your doctor about every medicine you use.

• Hormonal contraceptives (pill, implant, patch) may fail; a non-hormonal or other reliable method is needed.
• Effects of Warfarin, corticosteroids, some heart medicines, Doxycycline and many other drugs may be reduced.
• Other anti-seizure medicines such as Phenytoin, Carbamazepine, Valproate and Lamotrigine can change, or be changed by, Primidone levels.
• Alcohol, sleeping tablets, strong painkillers, antihistamines that cause drowsiness and other sedatives increase drowsiness and slow breathing.
• Folic acid and vitamin D levels may fall with long-term use.

Contraindications

• Allergy to Primidone or Phenobarbital.
• Acute porphyria, a rare inherited blood disorder.
• Severe breathing problems or severe liver or kidney disease, unless the doctor decides otherwise.

Side Effects

Drowsiness, dizziness, unsteadiness, nausea, tiredness and blurred or double vision are common, especially at the start; these often improve as the body adjusts. Other effects include loss of appetite, headache, mood changes, irritability or restlessness (especially in children and older people), skin rash, and, with long-term use, low folate levels causing anaemia, softening of the bones, and joint stiffness. Rarely, serious skin reactions, blood disorders or liver problems may occur. Like other anti-seizure medicines, a small number of people may have thoughts of self-harm.

Get urgent medical help if you have a widespread rash with blistering, peeling or mouth sores, fever with sore throat or unusual bruising, yellowing of the skin or eyes, extreme sleepiness or slow, shallow breathing, a seizure that does not stop, or thoughts of harming yourself.

Pregnancy and Lactation

Primidone may increase the risk of birth defects and can cause bleeding problems and withdrawal symptoms in the newborn. Women who could become pregnant should discuss this with their doctor before starting, use reliable contraception, and take folic acid as advised. Do not stop the medicine on your own if you become pregnant, because uncontrolled seizures are also dangerous; see your doctor promptly. The newborn may need vitamin K at birth. Primidone passes into breast milk and can make the baby sleepy and feed poorly; breastfeed only with your doctor's advice and watch the baby closely.

Precautions and Warnings

• Do not drive or operate machinery until you know how it affects you.
• Avoid alcohol while taking Primidone.
• Long-term use can lead to dependence; stopping must be gradual.
• Older people, children and those with liver, kidney or lung problems need closer monitoring.
• Your doctor may check blood counts, liver function and vitamin levels during long-term treatment.
• Tell family members to watch for changes in mood or behaviour.

Overdose

An overdose can cause deep sleepiness, confusion, unsteadiness, slow or shallow breathing, low blood pressure and coma, and can be life-threatening. Call emergency services or go to hospital straight away and take the pack with you.

Therapeutic Class

Anticonvulsant (barbiturate-related anti-seizure medicine).

Storage

Store below 30°C in a dry place, away from light and out of the reach of children.