PRIMIDONE Tablets Ref.[7908] Active ingredients: Primidone

Epilepsy

Treatment must always be planned on an individual basis. In many patients it will be possible to use Primidone alone, but in some, Primidone will need to be combined with other anticonvulsants or with supporting therapy.

Primidone is usually given twice daily and may be administered using either the 50 mg or 250 mg strength tablets.

Begin with 125 mg once daily late in the evening. Every 3 days increase the daily dosage by 125 mg until the patient is receiving 500 mg daily. Thereafter, every 3 days increase the daily dosage by 250 mg in adults or 125 mg in children under 9 years – until control is obtained or the maximum tolerated dosage is being given. This may be as much as 1.5 g a day in adults; 1 g a day in children.

Average daily maintenance doses:

The total daily dose is usually best divided and given in two equal amounts, one in the morning and the other in the evening. In certain patients, it may be considered advisable to give a larger dose when the seizures are more frequent. For instance: 1) if the attacks are nocturnal then all or most of the day’s dose may be given in the evening; 2) if the attacks are associated with some particular event such as menstruation, a slight increase in the appropriate dose is often beneficial.

Elderly patients

It is advisable to monitor elderly patients with reduced renal function who are receiving primidone.

Patients on other anticonvulsants

Where a patient’s attacks are not sufficiently well controlled with other anticonvulsants, or disturbing side effects have arisen, Primidone may be used to augment or replace existing treatment. First add Primidone to the current anticonvulsant treatment by the method of gradual introduction described previously. When a worthwhile effect has been achieved and the amount of Primidone being given has been built up to at least half the estimated requirement, withdrawal of the previous treatment can then be attempted. This should be done gradually over a period of 2 weeks, during which time it may be necessary to increase the Primidone dosage to maintain control.

Withdrawal of previous treatment should not be too rapid or status epilepticus may occur. Where phenobarbitone formed the major part of the previous treatment, however, both its withdrawal and Primidone substitution should be made earlier, so as to prevent excessive drowsiness from interfering with accurate assessment of the optimum dosage of Primidone.

Essential tremor

Initially a dose of 50 mg daily should be introduced. The daily dose should be increased gradually over a 2 to 3 week period until remission of symptoms or the highest dose tolerated up to a maximum of 750 mg daily.

Patients with essential tremor who have not previously been exposed to anticonvulsants, or other drugs known to induce increased hepatic enzyme activity, may experience acute symptoms of intolerance to Primidone, frequently characterised by vertigo, unsteadiness and nausea. It is, therefore, essential to start such patients at a low dosage (initially 50 mg daily) increasing very slowly up to the maximum tolerated dose or that which produces remission of tremor (up to 750mg daily).

Primidone is metabolised extensively to phenobarbitone and overdosage leads to varying degrees of CNS depression which, depending on the dose ingested, may include ataxia, loss of consciousness, respiratory depression and coma.

Crystalluria may occur in overdosage and could be used as a helpful diagnostic aid where primidone overdosage is suspected.

Depending on the severity of intoxication, therapy should include aspiration of stomach contents, administration of activated charcoal, administration of intravenous fluids, forced alkaline diuresis (striving for a urine pH of 8.0), and general supportive measures. In more life threatening circumstances, haemoperfusion (if the patient is hypotensive) or haemodialysis are effective.

There is no specific antidote.

Shelf life: 5 years.

Store below 25°C.

HDPE bottle containing 100 tablets, with a white HDPE, tamper-evident, child resistant push-on cap with a white LDPE liner.

No special requirements.