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Faragher RJ, Motto JM, Kaminski MA, Schwan AL. A convenient synthesis of13C4-Leflunomide and its primary metabolite13C4-A77 1726. J Labelled Comp Radiopharm 2003. [DOI: 10.1002/jlcr.701] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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2
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Rose MJ, Agrawal N, Woolf EJ, Matuszewski BK. Simultaneous determination of unlabeled and carbon-13-labeled etoricoxib, a new cyclooxygenase-2 inhibitor, in human plasma using HPLC-MS/MS. J Pharm Sci 2002; 91:405-16. [PMID: 11835200 DOI: 10.1002/jps.10038] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
A method for the simultaneous determination of etoricoxib and its carbon-13 analog ((13)C(6)-etoricoxib) from human plasma has been developed and used to support bioavailability studies. Plasma samples (0.5 mL) were extracted by using a 3M Empore 96-well plate (C(8)) and the resulting extracts were analyzed by using a PE-Sciex API-3000 HPLC-MS/MS with a heated nebulizer interface (500 degrees C). The method was validated with two different calibration curve ranges, one for etoricoxib (5 to 2500 ng/mL) determined in the presence of lower concentrations of (13)C(6)-etoricoxib (0.5 to 250 ng/mL), and a second curve for the quantitation of similar concentrations of both etoricoxib and (13)C(6)-etoricoxib (0.5 to 250 ng/mL). Extraction recoveries of etoricoxib, (13)C(6)-etoricoxib, and a methylated internal standard were >70% over the range of concentrations included in both calibration curves. Intraday precision and accuracy for the quantitation of etoricoxib were 7.8% relative standard deviation (RSD) or less and within 3.4% respectively over the range of 5 to 2500 ng/mL, and 10.8% RSD or less and within 4 % respectively over the range of 0.5 to 250 ng/mL. Within-batch precision and accuracy for the quantitation of (13)C(6)-etoricoxib over the range of 0.5 to 250 ng/mL were 8.3% RSD or less and within 2.3%, respectively. The validated assay was used in support of human clinical trials.
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Affiliation(s)
- M J Rose
- Merck Research Laboratories, Department of Drug Metabolism, West Point, Pennsylvania 19486, USA.
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3
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Pierce CH, Lewandowski TA, Dills RL, Morgan MS, Wessels MA, Shen DD, Kalman DA. A comparison of 1H8- and 2H8-toluene toxicokinetics in men. Xenobiotica 1999; 29:93-108. [PMID: 10078842 DOI: 10.1080/004982599238830] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
1. To examine the bioequivalence of an isotope-labelled tracer to study toxicant disposition, we conducted 33 controlled human exposures to a mixture of 50 ppm 1H8-toluene and 50 ppm 2H8-toluene for 2 h, and measured concentrations in blood and breath, and metabolite levels in urine for 100 h post-exposure. 2. A physiologically based kinetic (PBK) model found that compared with 1H8-toluene, 2H8-toluene had a 6.4+/-13% (mean+/-SD) lower AUC, a 6.5+/-13% higher systemic clearance (1.46+/-0.27 versus 1.38+/-0.25 l/h-kg), a 17+/-22% larger terminal volume of distribution (66.4+/-14 versus 57.2+/-10 l/kg) and a 9.7+/-26% longer terminal half-life (38+/-12 versus 34+/-10 h) (p < 0.05 for all comparisons). 3. The higher 2H8-toluene clearance may have been due to an increased rate of ring oxidation, consistent with the 17% higher observed fraction of 2H5- versus 1H5-cresol metabolites in urine. 4. The larger terminal volume and half-lives for 2H8-toluene suggested a higher adipose tissue/blood partition coefficient. 5. Observed isotope differences were small compared with interindividual differences in 1H8-toluene kinetics from previous studies. 6. The PBK model allowed us to ascribe observed isotope differences in solvent toxicokinetics to underlying physiologic mechanisms.
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Affiliation(s)
- C H Pierce
- Department of Environmental Health, University of Washington, Seattle 98195, USA
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4
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Chapter 18 Drug interactions. ACTA ACUST UNITED AC 1997. [DOI: 10.1016/s0165-7208(97)80165-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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5
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Browne TR. Chapter 2 Isotope effect: Implications for pharmaceutical investigations. PHARMACOCHEMISTRY LIBRARY 1997. [DOI: 10.1016/s0165-7208(97)80149-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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6
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Chapter 16 Biotransformation and excretion: Pharmacokinetic studies. ACTA ACUST UNITED AC 1997. [DOI: 10.1016/s0165-7208(97)80163-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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7
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Browne TR, Szabo GK, McEntegart C, Evans JE, Evans BA, Miceli JJ, Quon C, Dougherty CL, Kres J, Davoudi H. Bioavailability studies of drugs with nonlinear pharmacokinetics: II. Absolute bioavailability of intravenous phenytoin prodrug at therapeutic phenytoin serum concentrations determined by double-stable isotope technique. J Clin Pharmacol 1993; 33:89-94. [PMID: 8429121 DOI: 10.1002/j.1552-4604.1993.tb03910.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Measurement of the absolute bioavailability of phenytoin (PHT) derived from test doses of phenytoin prodrug (PPD) at therapeutic PHT serum concentrations is complicated by two problems: 1) the area under the serum concentration versus time curve (AUC) produced by a given size of test dose will vary directly with background PHT serum concentration due to the nonlinear pharmacokinetic properties of PHT; 2) PPD is more water soluble than PHT, making renal excretion of PPD more likely. The authors describe a double-stable isotope method that obviates these two problems. Using only six subjects, the authors were able to demonstrate bioequivalence of PHT derived from intravenous PPD with intravenous PHT by current FDA standards for AUC ratio of test/reference formulation (90% confidence intervals between 0.80 and 1.20; ratio > or = 0.80 in > or = 80% of subjects; statistical power to detect a difference of 0.20 with a probability of 0.80).
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Affiliation(s)
- T R Browne
- Department of Neurology and Pharmacology and Experimental Therapeutics, Boston University School of Medicine, MA
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9
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Browne TR, Greenblatt DJ, Schumacher GE, Szabo GK, Evans JE, Evans BA. New pharmacokinetic methods. III. Two simple test for "deep pool effect". J Clin Pharmacol 1990; 30:680-5. [PMID: 2401747 DOI: 10.1002/j.1552-4604.1990.tb03626.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
If a portion of administered drug is distributed into a "deep" peripheral compartment, the drug's actual elimination half-life during the terminal exponential phase of elimination may be longer than determined by a single dose study or a tracer dose study ("deep pool effect"). Two simple methods of testing for "deep pool effect" applicable to drugs with either linear or nonlinear pharmacokinetic properties are described. The methods are illustrated with stable isotope labeled (13C15N2) tracer dose studies of phenytoin. No significant (P less than .05) "deep pool" effect was detected.
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Affiliation(s)
- T R Browne
- Department of Neurology, Boston University School of Medicine, MA
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10
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Browne TR, Greenblatt DJ, Szabo GK, Evans JE, Evans BA. New pharmacokinetic methods: I. Estimation of mean serum concentration from trough serum concentration. J Clin Pharmacol 1990; 30:482-8. [PMID: 2355100 DOI: 10.1002/j.1552-4604.1990.tb03612.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
An equation is derived to estimate mean steady state serum concentration (Css) from trough steady state serum concentration (Cmin) which can be used for drugs with either linear or nonlinear pharmacokinetic properties. In 15 subjects receiving phenytoin monotherapy, estimated Css did not differ significantly from measured Css, while Cmin differed significantly (P less than .0001) from measured Css and estimated Css. Clearance (CL) and elimination half-life (t1/2) values determined by stable isotope tracer methods or by standard equations and measured Css or estimated Css did not differ significantly, while CL and t1/2 values calculated with standard equations and Cmin differed significantly (P less than .02) from values obtained by any of the other three methods. We conclude: 1) Cmin values and CL and t1/2 values calculated with Cmin values may differ significantly from Css values and CL and t1/2 values calculated with Css; 2) accurate estimates of Css and of CL and t1/2 can be obtained using our procedure to correct a Cmin value to an estimated Css value.
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Affiliation(s)
- T R Browne
- Department of Neurology, Boston University School of Medicine, MA
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11
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Browne TR. Stable isotopes in clinical pharmacokinetic investigations. Advantages and disadvantages. Clin Pharmacokinet 1990; 18:423-33. [PMID: 2191819 DOI: 10.2165/00003088-199018060-00001] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- T R Browne
- Department of Neurology, Boston University School of Medicine, Massachusetts
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12
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Genty E, Brazier JL, Lesca P, Riviere JL. Absence of an isotope effect in induction of cytochrome P-450 and xenobiotic metabolizing enzyme activities by stable isotope-labelled phenobarbital isotopomers. Biochem Pharmacol 1989; 38:3885-7. [PMID: 2597175 DOI: 10.1016/0006-2952(89)90600-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- E Genty
- Laboratorie d'Etudes Analytiques et Cinétiques du Médicament Faculté de Pharmacie, Lyon, France
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13
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Benchekroun Y, Ribon B, Falconnet JB, Cherrah Y, Brazier JL. Pharmacokinetic equivalence of 5(ethyl(2H)5)- and unlabelled phenobarbitone. J Clin Pharmacol 1989; 29:168-73. [PMID: 2715374 DOI: 10.1002/j.1552-4604.1989.tb03308.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The present study shows the absence of in vivo pharmacokinetic isotope effect on phenobarbitone (PB) C5-ethyl deuteration (PBd5) following oral administration to man of equimolar PB/PBd5 mixtures (0.40 mmol each). Plasma PB and PBd5 (17 days) and urine PB, PBd5 and parahydroxy-metabolites (PBOH, PBHOd5) levels were determined by GC-MS. Isotope effect research includes comparison of pharmacokinetic parameters, study of time-dependence of isotope ratios (IRs) in plasma and urine (linearity test), comparison of IRs between samples and administered mixtures (Mann Whitney's test) and comparison of PBOH/PBOHd5 ratios before and after urine enzymatic hydrolysis (Student's two tailed t-test). No significant isotope effect was observed on pharmacokinetic parameters, PB hydroxylation or PBOH conjugation (x less than or equal to 5%); which the absence of pentadeuteration-induced alteration in PB's HSA binding parameters (binding mode, Ka, N) corroborates (x less than or equal to 5%). These results establish bioequivalence of PB and PBd5; the latter can be used with benefit in stable-isotope clinical pharmacology (steady state pharmacokinetics, drug interactions...) investigations as well as bioavailability studies of PB preparations.
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Affiliation(s)
- Y Benchekroun
- Laboratoire D'Etudes Analytiques Et Cinetiques Du Medicament, Faculte De Pharmacie, Lyon, France
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Cherrah Y, Falconnet JB, Desage M, Brazier JL, Zini R, Tillement JP. Study of isotope effects on protein binding by gas chromatography/mass spectrometry of theophylline-phenobarbitone and 2H, 13C, 15N isotopomers. BIOMEDICAL & ENVIRONMENTAL MASS SPECTROMETRY 1988; 17:245-50. [PMID: 3191256 DOI: 10.1002/bms.1200170403] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
We describe a comparative study of human serum albumin (HSA) binding by equilibrium dialysis (pH 7.4, 37 degrees C, 3 h) for two groups of isotopic analogues: theophylline and 1-C(2H3)theophylline; unlabelled, 5(ethyl(2H5],-5(phenyl(2H5] and 1,3-15N;2-13C-phenobarbitone. Bound and free drug fractions are quantified by combined gas chromatography/mass spectrometry. In three instances, protein binding parameters are greatly affected by isotopic substitution, namely for: theophylline and 1-C(2H3)theophylline with isotope effects on total binding site concentration (N), affinity constant (Ka) and extent of HSA binding (%) respectively, equal to: NL/NH = 0.51; KaL/KaH = 1.78; %L/%H = 0.96 (L (light) and H (heavy) represent the unlabelled and labelled analogue respectively); phenobarbitone/-5-(phenyl(2H5]phenobarbitone, NL/NH = 1.72; KaL/KaH = 0.56; %L/%H = 1.26; phenobarbitone/1,3-15N;2-13C phenobarbitone, NL/NH = 2.95; KaL/KaH = 0.44; %L/%H = 1.32, together with a change from one (saturable) to two (saturable + non-saturable) families of albumin binding sites in the latter case. Contrasting with these data, no HSA binding isotope effect was observed on phenobarbitone C5 ethyl deuteration.
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Affiliation(s)
- Y Cherrah
- LEACM Faculty of Pharmacy, Lyon, France
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Cherrah Y, Falconnet JB, Desage M, Brazier JL, Zini R, Tillement JP. Study of deuterium isotope effects on protein binding by gas chromatography/mass spectrometry. Caffeine and deuterated isotopomers. BIOMEDICAL & ENVIRONMENTAL MASS SPECTROMETRY 1987; 14:653-7. [PMID: 2962673 DOI: 10.1002/bms.1200141115] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
A study of the binding to human serum albumin (HSA) of caffeine and its deuterated isotopomers, 1-C2H3-,3-C2H3-, 1,7-(C2H3)2-, 3,7-(C2H3)2- and 1,3,7-(C2H3)3-caffeine, was performed by equilibrium dialysis. Free and bound fractions were measured by gas chromatography/mass spectrometry. Important and significant (Fischer and Student tests) isotope effects were observed on binding parameters: sites total concentration (N = 1732 microM for 1,3,7-(C2H3)3-caffeine versus 822 microM for caffeine; number of sites (n = 3 for 1,3,7-(C2H3)3-caffeine v. 1 for caffeine); and extent of binding (46% for 1,3,7-(C2H3)3-caffeine v. 27% for caffeine). A study of competition for HSA binding between caffeine and its 1,3,7-(C2H3)3- and 3,7-(C2H3)2-isotopomers confirmed the results obtained in direct binding studies. These isotope effects are discussed in terms of (a) tools for molecular pharmacology, (b) precautions to be taken when such labelled drugs are used in clinical pharmacology.
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Affiliation(s)
- Y Cherrah
- LEACM Faculty of Pharmacy, Lyon, France
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Fischer C, Heuer B, Heuck K, Eichelbaum M. Quantification of nitrendipine by stable isotope dilution and electron-capture negative ion chemical ionization. BIOMEDICAL & ENVIRONMENTAL MASS SPECTROMETRY 1986; 13:645-50. [PMID: 2952187 DOI: 10.1002/bms.1200131202] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The electron-capture properties of nitrendipine, a 1,4-dihydro-pyridine derivative with antihypertensive activity, have been applied to develop a sensitive and specific assay in biological fluids using capillary column gas chromatography and measurement in negative ion chemical ionization mode. The synthesis of a 13C4-labelled analogue suitable as a biological internal standard for bioavailability studies and of a 2H8-labelled analogue, which serves as internal standard, is described. The electron-capture positive ion chemical ionization and electron-capture negative ion chemical ionization mass spectra of nitrendipine and its isotope-labelled analogues are compared. The assay has a detection limit of 100 pg ml-1 plasma with a coefficient of variation of 10.2% using the selected ion monitoring mode and electron-capture negative ion chemical ionization. The method is specific, sensitive and accurate to determine terminal half-life times after intravenous and oral administration of nitrendipine and its 13C-analogue. From the nearly identical plasma concentration-time profile of nitrendipine and its 13C-labelled analogue, an isotopic effect can be excluded. Thus, the synthesized 13C4-analogue should be well suited as a biological standard for bioavailability studies.
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Abstract
The use of stable isotope-labeled compounds for pharmacologic studies requires careful consideration of the nature of the stable isotope label (2H, 13C, 15N, 18O) and its position of incorporation in the molecule. When deuterium is used, improper positioning can lead to significant primary isotope effects. Primary isotope effects occur when the breaking of the bond to the heavy isotope is the rate-limiting step in a reaction (or metabolic transformation). A reaction will proceed slower for the molecule with the heavy isotope label because of the mass difference between the light and the heavy isotope. In addition to these primary isotope effects, smaller but nevertheless important secondary isotope effects, physicochemical isotope effects, active hydrogen/deuterium exchange, or isotope effects associated with either the enzyme-catalyzed biotransformation or the mass spectrometric ionization and fragmentation can be operative. In mechanistic studies, isotope effects are used to their advantage; however, in pharmacokinetic studies, the occurrence of isotope effects can lead to grossly misleading biologic and analytic results: the metabolism of the drug will differ when 'in vivo' isotope effects are operative, and isotope effects occurring during the analysis procedure will obscure the true metabolic profile of the drug.
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Abstract
Stable-isotope techniques offer advantages over older methods in safety, sensitivity, specificity, and reduction in numbers of subjects required and analytic determinations for some types of pharmacology studies. In addition to their use as internal standards in gas chromatography-mass spectrometry analytic methods, stable isotopes have been successfully employed in studies of absorption, bioavailability, distribution, biotransformation, excretion, metabolite identification, time-dependent and dose-dependent pharmacokinetic changes, drug interactions, pharmacologic changes during pregnancy, mutagenicity, and teratogenicity.
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Browne TR, Evans JE, Szabo GK, Evans BA, Greenblatt DJ. Studies with stable isotopes II: Phenobarbital pharmacokinetics during monotherapy. J Clin Pharmacol 1985; 25:51-8. [PMID: 3973064 DOI: 10.1002/j.1552-4604.1985.tb02800.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Six healthy adults receiving no other medications were given tracer doses of 90 mg of stable isotope-labeled phenobarbital (PB) intravenously before, and four weeks after, and 12 weeks after beginning therapy. Serum samples were collected for 96 hours after each injection, and the concentration of stable isotope-labeled PB in each sample was determined by gas chromatographic mass spectrometry. The volume of distribution, elimination half-life, and total clearance of PB did not differ significantly on any of the three occasions measured. Phenobarbital clearance did not correlate significantly with total PB serum concentration. Clearances determined from single-dose studies before beginning PB therapy accurately predicted steady-state PB serum concentrations. Therefore, it is not necessary to adjust PB dosage for time-dependent or dose-dependent changes in clearance during monotherapy. In addition, clearance or serum concentration determined at one dosing rate directly predicts serum concentration at another dosing rate.
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