Mylepsinum (Primidone)

Primidone is employed in the management of seizure disorders by stabilizing neuronal excitability.

• Generalized tonic‑clonic seizures: reduces frequency and severity of convulsive episodes.
• Partial (focal) seizures: helps control focal seizure activity and prevents progression.
• Epilepsy (overall): contributes to overall seizure control as part of a therapeutic regimen.

• After oral administration, primidone is rapidly absorbed and extensively metabolized to phenobarbital and phenylethylmalonamide. The active metabolites enhance GABA‑mediated chloride influx, increasing inhibitory neurotransmission and lowering neuronal excitability, which suppresses the spread of epileptic discharges.

Primidone may cause a range of adverse reactions, from mild to severe.

Common Side Effects

• Drowsiness: feeling unusually sleepy or fatigued.
• Dizziness: light‑headed sensation, especially when standing.
• Nausea: upset stomach or urge to vomit.
• Ataxia: loss of coordination and balance.
• Blurred vision: temporary visual disturbances.
• Fatigue: reduced energy and endurance.

Serious or Rare Side Effects

• Severe skin reactions (e.g., Stevens‑Johnson syndrome).
• Blood dyscrasias such as agranulocytosis or leukopenia.
• Hepatic dysfunction, including elevated liver enzymes.
• Suicidal thoughts or mood changes.
• Respiratory depression, especially with other CNS depressants.
• Life‑threatening rash or hypersensitivity reactions.

When prescribing primidone, clinicians should consider several safety measures.

• Dose titration: start low and increase gradually under medical supervision.
• Renal/hepatic impairment: adjust dose if organ function is compromised.
• Concomitant CNS depressants: monitor for additive sedation and respiratory effects.
• Pregnancy: risk unknown; use only if benefit outweighs potential harm.
• Driving and operating machinery: may cause drowsiness; avoid until individual response is known.
• Store at ambient temperature: keep in the original container, protect from moisture and light.

Primidone can interact with several medicines, requiring careful management.

Major Interactions (Avoid)

• Phenobarbital: additive central nervous system depression.
• Alcohol: increased sedation and risk of respiratory depression.
• Other barbiturates: heightened risk of overdose and severe CNS effects.

Moderate Interactions (Monitor Closely)

• Carbamazepine (CYP450 inducer): may increase primidone metabolism, reducing efficacy.
• Erythromycin (CYP450 inhibitor): may raise primidone plasma levels, increasing toxicity risk.
• Oral contraceptives: primidone may reduce hormonal efficacy, requiring alternative contraception.