primidone: clinical use

Prescribing considerations

• Introduce and adjust cautiously to limit dizziness, ataxia, nausea and sedation.
• Avoid abrupt withdrawal because seizures or status epilepticus may occur.
• Review renal, hepatic and respiratory impairment, frailty and older age.
• Undertake a comprehensive interaction review.
• For epilepsy, maintain continuity of a specific manufacturer’s product.
• Discuss pregnancy risks, effective contraception and pre-conception review where relevant.

Contraindications and cautions

• Hypersensitivity to primidone, phenobarbital or product excipients
• Acute intermittent porphyria
• Contraindicated interacting medicines specified in current product information
• Previous primidone- or phenobarbital-associated SJS, TEN or DRESS

Monitoring

• Clinical response, adherence, seizure pattern or tremor control
• Sedation, ataxia, visual effects and falls risk
• Rash or systemic hypersensitivity, particularly early in treatment
• Mood, suicidal thoughts and behavioural change
• Renal and hepatic status where impairment affects handling
• Blood counts if symptoms suggest cytopenia or megaloblastic anaemia
• Bone health and vitamin D risk during long-term treatment
• Interactions and loss of efficacy when co-medication changes

Clinical pharmacology

Primidone is rapidly absorbed and partly metabolised in the liver to phenobarbital and PEMA, both with antiseizure activity. Primidone and phenobarbital induce hepatic enzymes; phenobarbital has substantially more prolonged elimination than primidone.

Formulation and product differences

• The selected Enodama product is a white to off-white, uncoated, unscored tablet intended to be swallowed whole with water.

Tablet

Route: Oral

Strengths: 50 mg, 125 mg, 250 mg