| OBSERVATION'S |
Phenobarbital is a barbiturate that has been used extensively as an anticonvulsant since 1912.1,2 it is generally administered to epileptic patients in oral doses, often in conjunction with other anticonvulsant drugs. Oral absorption of Phenobarbital is complete but slow, with peak plasma concentrations reached several hours after intake.1 Approximately 50% of the drug is bound to plasma proteins, with binding to a similar extent in tissue. After dosing, 25-50% is excreted unchanged in the urine.3 The remainder is metabolized almost exclusively in the liver to inactive metabolites, mainly the parahydroxyphenyl and the N-glucoside derivatives.1,4,5 Monitoring serum concentrations of Phenobarbital has been recommended for effective patient therapy because of phenobarbital’s narrow therapeutic index and wide interindividual variability in the rate of metabolism and clearance.6,7 Immunoassays using a fluorescence polarization technique for phenobarbital have been published.8,9 Rall TW, Schleifer LS. Drugs effective in the therapy of the epilepsies. In: The pharmacological basis of therapeutics, Goodman Gilman A. ed. Pergamon Press Inc., New York 1990: 436-461. Buchthal F, Lennox-Buchthal MA. Phenobarbital: relation of serum concentration to control of seizures. In: Woodbury DM, Penry JK, Schmidt RP, eds. Antiepileptic Drugs, New York: Raven Press 1972: 335-341. Barnhart ER. Pub. Physician’s Desk Reference. Oradell, NJ: Medical Economics Co., Inc., 1991: 1261-1263. Glazko AJ. Antiepileptic Drugs: biotransformation, metabolism and serum half-life. Epilepsia 1975; 16: 367-391. Eadie MJ. Formation of active metabolites of anticonvulsant drugs. A review of their pharmacokinetic and therapeutic significance. Clin Pharmacokinet 1991; 21(1): 27-41. Kutt H, Penry K. Usefullness of blood levels of antiepileptic drugs. Arch Neurol 1974; 31-283-288. Waddell WJ, Butler TC. The distribution and excretion of Phenobarbital. J Clin Invest 1957; 36: 1217-1226. Lu-Steffes M, Jolley ME, Pittluck G, et al. Fluorescence polarization immunoassays of phenytoin and phenobarbital. ClinChem 1981; 27: 1093. Sidki AM, Poufarzaneh, Rowell FD, Smith DS. Direct determination of Phenobarbital in serum of plasma by polarization fluoroimmunoassay. Therapeutic Drug Monitoring 1982; 4:397. |
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