Stahl's Essential Psychopharmacology Online
In Collaboration With
Primidone
Therapeutics
Brands
• Mysoline
Generic?
Yes
Class
• Antiepileptic drug (AED)
Commonly Prescribed for
(FDA approved in bold)
• Generalized tonic-clonic, psychomotor, and partial seizures (monotherapy and adjunctive, children and adults)
• Essential tremor
• Long QT syndrome
• Psychosis
How the Drug Works
• Primidone and its 2 metabolites (phenobarbital and phenylethylmalonamide) raise seizure thresholds or alter seizure patterns
• The exact mechanism of action is unknown but likely enhances GABA-A receptor activity
• Depresses glutamate excitability, alters sodium, calcium and potassium channel conductance
How Long Until It Works
• Seizures - should decrease by 2 weeks
• Essential tremor - should improve tremors in 1-2 weeks
If It Works
• Seizures - goal is the remission of seizures. Continue as long as effective and well-tolerated. Consider tapering and slowly
stopping after 2 years without seizures, depending on the type of epilepsy
• Essential tremors - tremors improve but usually do not remit. Use lowest effective dose
If It Doesn't Work
• Increase to highest tolerated dose
• Epilepsy: consider changing to another agent, adding a second agent or referral for epilepsy surgery evaluation. When adding
a second agent, keep in mind drug interactions
Best Augmenting Combos for Partial Response or Treatment-Resistance
• Epilepsy: drug interactions complicate multi-drug therapy. Primidone itself is a second-line agent in developed countries
due to AE profile
Tests
• CBC, hepatic and kidney function panels at baseline and every 6 months