primidone; desoxyphenobarbital (Primaclone, Mysoline)
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Introduction
Tradename: Primaclone, Mysoline.
Indications
- prophylactic management of tonic-clonic seizures & complex partial seizures
- not useful for absence seizures
- used alone or in combination with other anticonvulsants
- treatment of essential tremor
Dosage
- start 100-125 mg PO QHS
- increase over 10 days to 250 mg TID/QID
- max dose 2 g/day
- children:
- > 8 years: 125-200 mg PO TID
- < 8 years: 250 mg PO TID
- avoid abrubt discontinuation; may precipitate seizures
Tabs: 50 & 250 mg
Liquid: 250 mg/5 mL .
Pharmacokinetics
- 60-80% absorbed from the GI tract
- protein binding 0-20%
- metabolized to:
- approximately 40% of drug excreted unchanged into urine
- elimination 1/2life
elimination via liver
elimination via kidney
1/2life = 4-12 hours
protein binding = 0-20 %
elimination by hemodialysis = +
Monitor
Adverse effects
(same as phenobarbital)
- common (> 10%)
- less common (1-10%)
- uncommon (< 1%)
- megaloblastic anemia, maculopapular skin rash, behavioral change, leukopenia, malignant lymphoma-like syndrome, systemic lupus-like syndrome, diplopia, nystagmus
- neurologic:
- sedation, ataxia, confusion, dizziness & vertigo, impotence, depression, drowsiness, lethargy, may occasionally cause hyperexcitability in children
Drug interactions
- level increased by valproic acid & phenytoin
- carbamazepine in combination increases carbamazepine levels & diminishes primidone levels
- succinimides decrease primidone levels
- barbiturates induce cyt P450 1A2, 2C9 & 3A4
- may diminish levels of drugs metabolized by cyt P450 1A2, 2C9 & 3A4
- codaministration of isoniazid may increase primodone t1/2
- codaministration of acetazolamide may decrease absorption
- drug interaction(s) anticonvulsants with anti-bacterial agents
- drug interaction(s) anticonvulsants with statins
- drug interaction(s) of beta-adrenergic receptor antagonists with barbiturates
Laboratory
Mechanism of action
- related to barbiturates
- activation of inhibitory effect of GABA receptors by enhancing permeability of neurons to chloride
More general terms
Additional terms
- cytochrome p450 1A2 (cytochrome P3-450, phenacetin deethylase, cytochrome p450-4, CYP1A2)
- cytochrome P450 2C9; cytochrome P450 BP-1; cytochrome P450 MP-4; S-mephenytoin-4-hydroxylase; limonene 6-monooxygenase; limonene 7-monooxygenase (CYP2C9, CYP2C10)
- cytochrome P450 3A4 (cytochrome P450 C3, nifedipine oxidase, P450-PCN1, NF-25, CYP3A4)
- phenobarbital; PB; PHB (Luminal, Barbita, Solfoton)
- primidone in serum/plasma
Component of
References
- ↑ The Pharmacological Basis of Therapeutics, 9th ed. Gilman et al, eds. Permagon Press/McGraw Hill, 1996
- ↑ Harrison's Principles of Internal Medicine, 13th ed. Companion Handbook. Isselbacher et al (eds), McGraw-Hill Inc. NY, 1995, pg 700.
- ↑ The Pharmacological Basis of Therapeutics, 8th ed. Gilman et al, eds. Permagon Press/McGraw Hill pg 446
- ↑ 4.0 4.1 Drug Information & Medication Formulary, Veterans Affairs, Central California Health Care System, 1st ed., Ravnan et al eds, 1998
- ↑ Kaiser Permanente Northern California Regional Drug Formulary, 1998
- ↑ Clinical Guide to Laboratory Tests, NW Tietz (ed) 3rd ed, WB Saunders, Philadelpha 1995
- ↑ Prescriber's Letter 13(3): 2006 Cytochrome P450 drug interactions Detail-Document#: http://prescribersletter.com/(5bhgn1a4ni4cyp2tvybwfh55)/pl/ArticleDD.aspx?li=1&st=1&cs=&s=PRL&pt=3&fpt=25&dd=220233&pb=PRL (subscription needed) http://www.prescribersletter.com
- ↑ 8.0 8.1 deprecated reference