Phenobarbital partition coefficient

Phenobarbital is utilized as a daytime sedative and anticonvulsant. It also induces several cytochrome P450 isozymes. Compared to other barbiturates, phenobarbital has a low oil/water partition coefficient, which results in slow distribution into the brain. It is available for oral, intravenous, or intramuscular administration. Doses for epileptic patients range from 60 to 200 mg per day. After a single oral dose of 30 mg, peak serum concentrations averaged 0.7 mg/L (n = 3). Repeated doses over a period of 7 days resulted in an average peak concentration of 8.1 mg/L.6 Chronic administration of 200 mg per day as anticonvulsant medication resulted in an average blood concentration of 29 mg/L (range = 16 to 48 mg/L).8... 

Bush and Helman (I6) determined primidone in urine and blood as phenobarbital, after oxidation of the former vdth dichromate. Primidone auid any phenobarbital in the samples were extracted with ether. The ether extracts were extracted with 0,1 M ethanolamine to remove phenobarbital, and then evaporated to dryness. The residue was treated with 0,0l 2 M potassium dichromate in 9.5 M sulfuric acid to oxidize primidone to phenobarbital. The phenobarbital formed was extracted into ether, and the ether washed with pH 6,2 buffer, 0,1 N hydrochloric acid, and water. Finally, the phenobarbital formed was extracted into 0.1 M ethanolamine and determined from its ultraviolet absorption at pH 9,3, 7,3, and 5 3. Partition coefficients for primidone in several solvent systems were also determined,... 

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