Primidone: Difference between revisions
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{{MedTemplate | {{MedTemplate | ||
| generic | | generic = Primidone | ||
| brand | | brand = Mysoline | ||
| structure | | structure = | ||
| classes | | classes = [[:Category:Anticonvulsants|Anticonvulsant]], [[:Category:Barbiturates|Barbiturate (parent compound)]], [[:Category:Tremor medicines|Tremor medicine]] | ||
| | | uses = <vote slug="partial-seizures-monotherapy-use">Partial-onset and generalized tonic-clonic seizures (FDA)</vote>, <vote slug="essential-tremor-use">Essential tremor (widely used and AAN-guideline-supported as first-line alongside propranolol)</vote> | ||
| uses | | starting_dose = Seizures: 100-125 mg PO at bedtime x 3 days, then BID, then TID, escalating to 750-1500 mg/day. Essential tremor: 25-50 mg PO at bedtime, titrate slowly to 250-750 mg/day | ||
| starting_dose | | preparations = Tablets 50, 250 mg | ||
| preparations | | fda_max = 2 g/day (seizures); typically much lower for essential tremor | ||
| | | pill_id = | ||
| routes = Oral | |||
| | | onset = Anticonvulsant effect emerges with slow titration over weeks; tremor effect over weeks | ||
| | | duration = BID-TID dosing | ||
| | | halflife = Primidone 5-15 hours; '''phenobarbital active metabolite 50-150 hours'''; PEMA (phenylethylmalonamide) active metabolite 16 hours<ref name="mysoline-label">FDA Prescribing Information, Mysoline (primidone), Bausch/various, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2010/009170s032lbl.pdf</ref> | ||
| | | bioavailability = ~90% (oral)<ref name="mysoline-label" /> | ||
| | | pregnancy = Substantial teratogenic signal (barbiturate class effects including neonatal withdrawal and hemorrhagic disease of newborn).{{citation needed}} | ||
| legal = [[USLegal:Prescription only|Rx-only]] in US. '''Federally non-controlled despite being a barbiturate''', a paradoxical situation given that its primary active metabolite phenobarbital is Schedule IV<ref name="mysoline-label" /> | |||
| | | mechanism = <vote slug="primidone-mech-claim">Barbiturate that metabolizes to two active species: '''phenobarbital''' (the major contributor to seizure control, mediating GABA-A receptor potentiation) and '''PEMA (phenylethylmalonamide)''', which contributes to seizure control and is the leading candidate to explain the essential-tremor efficacy. Phenobarbital alone does not reliably suppress tremor at non-sedating doses, so PEMA's independent action is the proposed mechanism for the tremor indication.</vote> Strong CYP3A4 induction via the phenobarbital metabolite produces many interactions (reduces oral contraceptives, warfarin, many psychotropics). Essential-tremor efficacy is the unique pharmacological selling point<ref name="mysoline-label" />. | ||
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}} | }} | ||
== References == | |||
<references /> | |||
[[Category:Anticonvulsants]] | |||
[[Category:Barbiturates]] | |||
[[Category:Tremor medicines]] | |||
Latest revision as of 07:30, 23 May 2026
Primidone
Mysoline
Experience
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Summary
Common uses
Partial-onset and generalized tonic-clonic seizures (FDA)0, Essential tremor (widely used and AAN-guideline-supported as first-line alongside propranolol)0
Pharmacy
Starting dose
Seizures: 100-125 mg PO at bedtime x 3 days, then BID, then TID, escalating to 750-1500 mg/day. Essential tremor: 25-50 mg PO at bedtime, titrate slowly to 250-750 mg/day
Preparations
Tablets 50, 250 mg
US FDA Max
2 g/day (seizures); typically much lower for essential tremor
Pharmacology
Routes
Oral
Onset
Anticonvulsant effect emerges with slow titration over weeks; tremor effect over weeks
Duration
BID-TID dosing
Half-life
Primidone 5-15 hours; phenobarbital active metabolite 50-150 hours; PEMA (phenylethylmalonamide) active metabolite 16 hours[1]
Bioavailability
~90% (oral)[1]
Pregnancy
Substantial teratogenic signal (barbiturate class effects including neonatal withdrawal and hemorrhagic disease of newborn).[citation needed]
Legal status
Purported mechanism
Barbiturate that metabolizes to two active species: phenobarbital (the major contributor to seizure control, mediating GABA-A receptor potentiation) and PEMA (phenylethylmalonamide), which contributes to seizure control and is the leading candidate to explain the essential-tremor efficacy. Phenobarbital alone does not reliably suppress tremor at non-sedating doses, so PEMA's independent action is the proposed mechanism for the tremor indication.0 Strong CYP3A4 induction via the phenobarbital metabolite produces many interactions (reduces oral contraceptives, warfarin, many psychotropics). Essential-tremor efficacy is the unique pharmacological selling point[1].
References
- ↑ 1.0 1.1 1.2 1.3 FDA Prescribing Information, Mysoline (primidone), Bausch/various, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2010/009170s032lbl.pdf