Phenobarbital Flashcards
What is the class of Phenobarbital?
Barbiturate
What is Phenobarb used for?
to treat insomnia and preop for sedative effects;
anticonvulsant for acute trtment of partial seizures and tonic-clonic seizures
What is the MOA of Phenobarb?
- potentiates GABA
- mimics GABA
- increases influx of Cl- hyperpolarizing the membrane
- depresses the sensory cortex, causes drowsiness/sedation, decreases motor activity
How is phenobarb metabolized?
CYP450 inducer and metabolized in liver by hydroxylation and glucuronide conjugation. also excreted unchanged in the urine as high as 60%-90%!!
What is the e 1/2 l for phenobarb?
53-140 hours
What is the onset for PO? IV? for phenobarb
20-60 min onset PO
5 min IV
What is the DOA of phenobarb? PO? IV?
po 6-10 hours
IV 4-10hours
IS phenobarb protein bound?
weakly to moderately PB 20-40%
What are side effects of Phenobarb?
- BM suppression
- Agranulocytosis
- Thrombocytopenia
- Liver toxicity
- Osteopenia
- Rash
- Stevens-johnson
- apnea
- respiratory depression
- sedation
- insomnia
- hallucinations
- confusion
- dizziness
- n/v
What are the contraindications to phenobarb?
- Hypersensitivity to barbs
- resp disease
- dyspnea
- a/w obstruction
- severe liver disease
- porphyria
- pregnancy
What are drug interactions with Phenobarb?
they are enzyme inducers! increased metabolism of:
- Phenytoin
- Antiarrhythmics
- anticonvulsants
- antipsychotics
- beta blockers
- CCBs
- Cimetidine
- loop diuretics
What are CYP2C19 inducers that would decrease the levels of effectiveness of Phenobarb?
- aminoglutethimide
- Carbamazepine
- phenytoin
- rifampin
What is the pre-op sedation dose of phenobarb?
IM 100-200mg 1-1.5hrs before the procedure
What is the anticonvulsant loading dose of phenobarb?
10-20mg/kg initially followed by 5 mg/kg q15-30 min until seizure controlled or max dose of 30mg/kg reached
