201
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Abstract
An overview of the pharmacokinetics of dirlotapide in beagle dogs is presented. The following mean parameters were observed after a 0.3-mg/kg i.v. dose of dirlotapide: plasma clearance of 7.8 mL/min/kg and volume of distribution of 1.3 L/kg. Following single oral doses of 0.05, 0.3, and 1.0 mg/kg to fed dogs and 0.3 mg/kg to fasted dogs using the commercial formulation, mean C(max) of 7.5, 46, 97, and 31 ng/mL, respectively, were observed at mean t(max) of 0.8-2.0 h. AUC and C(max) increased with increasing dose, but not proportionally. Oral bioavailability was 22-41%. Exposure, as reflected by AUC, was 54% higher in the fed than fasted state. In a 14-day repeated-dose study (0.3 mg/kg dose), the mean accumulation ratio was 3.7. In a 3-month study at doses of 0.4-2.5 mg/kg, accumulation ratios ranged from 2.0 to 6.7 at day 29 and from 1.3 to 4.1 at day 87. In summary, dirlotapide exhibited low clearance, low first-pass metabolism, moderate volume of distribution, low-to-moderate oral bioavailability, a modest food effect, and variable accumulation. Large interanimal variability in systemic exposure was noted for all routes and doses, but there were no consistent sex differences.
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Affiliation(s)
- D A Merritt
- Pfizer Animal Health, Veterinary Medicine Research & Development, Kalamazoo, MI 49001, USA.
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202
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Hubenov H, Bakalov D, Krastev S, Yanev S, Haritova A, Lashev L. Pharmacokinetic studies on tobramycin in horses. J Vet Pharmacol Ther 2007; 30:353-7. [PMID: 17610409 DOI: 10.1111/j.1365-2885.2007.00860.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The objective of the study was to evaluate the pharmacokinetics of tobramycin in plasma and urine in the horse (n = 7) after intravenous administration of a dose of 4 mg/kg b.w. Plasma tobramycin concentrations were assayed microbiologically and by means of HPLC analyses. Pharmacokinetic parameters, calculated on the basis of concentrations determined with the microbiological assay were not statistically different from those obtained when data from HPLC analysis were used, but the microbiological assay was more sensitive in the detection of low plasma and urine values. The values of the total body clearance (Cl(B)) were 101.4 +/- 30.1 and 130.0 +/- 49.9 mL/kg/h, respectively. The overall extraction ratio was 2.9%. The determined capacity of elimination of tobramycin in horses was similar to those for other aminoglycosides. Within 24 h after treatment, 57.6 +/- 12.2% of injected antibiotic was excreted in the urine.
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Affiliation(s)
- H Hubenov
- Department of Surgery, Faculty of Veterinary Medicine, Trakia University, Stara Zagora, Bulgaria
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203
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Fernández-Varón E, Cárceles CM, Marín P, Martos N, Escudero E, Ayala I. Pharmacokinetics of difloxacin after intravenous, intramuscular, and intragastric administration to horses. Am J Vet Res 2007; 67:1076-81. [PMID: 16740105 DOI: 10.2460/ajvr.67.6.1076] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVE To study the pharmacokinetics of difloxacin (5 mg/kg) following IV, IM, and intragastric (IG) administration to healthy horses. ANIMALS 6 healthy mature horses. PROCEDURES A crossover study design with 3 phases was used (15-day washout periods between treatments). An injectable formulation of difloxacin (5%) was administered IV and IM in single doses (5 mg/kg); for IG administration, an oral solution was prepared and administered via nasogastric tube. Blood samples were collected before and at intervals after each administration. A high-performance liquid chromatography assay with fluorescence detection was used to determine plasma difloxacin concentrations. Pharmacokinetic parameters of difloxacin were analyzed. Plasma creatine kinase activity was monitored to assess tissue damage. RESULTS Difloxacin plasma concentration versus time data after IV administration were best described by a 2-compartment open model. The disposition of difloxacin following IM or IG administration was best described by a 1-compartment model. Mean half-life for difloxacin administered IV, IM, and IG was 2.66, 5.72, and 10.75 hours, respectively. Clearance after IV administration was 0.28 L/kg.h. After IM administration, the absolute mean +/- SD bioavailability was 95.81 +/- 3.11% and maximum plasma concentration (Cmax) was 1.48 +/- 0.12 mg/L. After IG administration, the absolute bioavailability was 68.62 +/- 10.60% and Cmax was 0.732 +/- 0.05 mg/L. At 12 hours after IM administration, plasma creatine kinase activity had increased 7-fold, compared with the preinjection value. CONCLUSIONS AND CLINICAL RELEVANCE Data suggest that difloxacin is likely to be effective for treating susceptible bacterial infections in horses.
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Affiliation(s)
- Emilio Fernández-Varón
- Department of Pharmacology, Faculty of Veterinary Medicine, University of Murcia, Campus de Espinardo, 30.071-Murcia, Spain
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204
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Switała M, Hrynyk R, Smutkiewicz A, Jaworski K, Pawlowski P, Okoniewski P, Grabowski T, Debowy J. Pharmacokinetics of florfenicol, thiamphenicol, and chloramphenicol in turkeys. J Vet Pharmacol Ther 2007; 30:145-50. [PMID: 17348900 DOI: 10.1111/j.1365-2885.2007.00827.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
The pharmacokinetics of florfenicol (FF), thiamphenicol (TP) and chloramphenicol (CP) after single intravenous (i.v.) or oral (p.o.) administration was studied in an independent cross-over study in broiler turkeys. All the fenicol antibiotics were administered at a dose of 30 mg/kg b.w. and their concentrations in plasma samples were assayed using the same validated high-performance liquid chromatography method. Pharmacokinetic parameters were calculated by a noncompartmental method. The kinetic profiles of the compounds were compared with the results of the structure-activity relationship. According to the proposed mathematical description, no differences in plasma clearance values for the studied antibiotics were observed. The mean residence time values of FF, TF, and CP after i.v. injection were 3.37+/-0.63, 2.43+/-0.29, and 2.12+/-0.21 h, respectively. The mean values of Varea for FF (1.39+/-0.31 L/kg) and TP (1.31+/-0.19 L/kg) were similar, but significantly different from that of CP (1.04+/-0.12 L/kg). The bioavailabilities of FF, TP, and CP after oral administration were 82%, 69%, and 45%, respectively. Differences in the bioavailability values of the compared fenicol antibiotics correspond to the ratio of the apolar/polar surface areas of their particles.
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Affiliation(s)
- M Switała
- Department of Biochemistry, Pharmacology and Toxicology, Agricultural University of Wroclaw, Wroclaw, Poland.
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205
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Uhrig SR, Papich MG, KuKanich B, Mama KR, Wagner AE, Chapman PL, Hellyer PW. Pharmacokinetics and pharmacodynamics of morphine in llamas. Am J Vet Res 2007; 68:25-34. [PMID: 17199415 DOI: 10.2460/ajvr.68.1.25] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVE To assess the pharmacokinetics and pharmacodynamics of morphine in llamas. ANIMALS 6 healthy adult llamas. PROCEDURES Llamas received morphine sulfate in a randomized crossover design. In phase 1, they received IV or IM administration of morphine at 0.05 or 0.5 mg/kg, respectively; in phase 2, they received IV administration of morphine at 0.05, 0.25, or 0.5 mg/kg. Plasma morphine and morphine-6-glucuronide concentrations were determined by validated methods. Body temperature, heart rate, respiratory rate, sedation, and analgesia were assessed and compared with plasma concentrations by regression analysis. RESULTS Total body clearance was similar between IV administration of morphine sulfate at 0.25 and 0.5 mg/kg (mean +/- SD, 25.3 +/- 6.9 mL/min/kg and 27.3 +/- 5.9 mL/min/kg, respectively), and linearity was demonstrated between these doses. Bioavailability of morphine following IM administration at 0.5 mg/kg was 120 +/- 30%. Body temperature and sedation increased as the dose of morphine administered increased. Heart rate was unaffected by varying doses. Respiratory rate decreased as dose increased. Analgesia was difficult to assess as a result of high individual variability. Intravenous administration of morphine at 0.25 mg/kg provided the most consistent increase in tolerance to electric stimulation. Pharmacodynamic modeling revealed a sigmoidal relationship between plasma concentration and sedation score. CONCLUSIONS AND CLINICAL RELEVANCE Morphine was characterized by a large apparent volume of distribution and high systemic clearance in llamas. A prolonged half-life was observed with IM injection. Intravenous administration of morphine sulfate at 0.25 mg/kg every 4 hours is suggested for further study.
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Affiliation(s)
- Samantha R Uhrig
- Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA
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206
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Fernández-Varón E, Ayala I, Marín P, Carrión A, Martos N, Escudero E, Cárceles CM. Pharmacokinetics of danofloxacin in horses after intravenous, intramuscular and intragastric administration. Equine Vet J 2006; 38:342-6. [PMID: 16866202 DOI: 10.2746/042516406777749245] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
REASONS FOR PERFORMING STUDY Danofloxacin is a fluoroquinolone developed for veterinary medicine showing an excellent activity. However, danofloxacin pharmacokinetics profile have not been studied in horses previously. OBJECTIVE To study the pharmacokinetics following i.v., i.m. and intragastric (i.g.) administration of 1.25 mg/kg bwt danofloxacin to 6 healthy horses. METHODS A cross-over design was used in 3 phases (2 x 2 x 2), with 2 washout periods of 15 days (n = 6). Danofloxacin (18%) was administered by i.v. and i.m. routes at single doses of 1.25 mg/kg bwt. For i.g. administration an oral solution was prepared and administered via nasogastric tube. Danofloxacin concentrations were determined by HPLC assay with fluorescence detection. Tolerability at the the site of i.m. injection was monitored by creatine kinase (CK) activity. RESULTS Danofloxacin plasma concentration vs. time data after i.v. and i.g. administration could best be described by a 2-compartment open model. The disposition of i.m. administered danofloxacin was best described by a one-compartment model. The terminal half-lives for i.v., i.m. and i.g. routes were 6.31, 5.36 and 4.74 h, respectively. Clearance value after i.v. dosing was 0.34 l/kg bwt/h. After i.m. administration, absolute bioavailability was mean +/- s.d. 88.48 +/- 11.10% and Cmax was 0.35 +/- 0.05 mg/l. After i.g. administration, absolute bioavailability was 22.36 +/- 6.84% and Cmax 0.21 +/- 0.07 mg/l. CK activity following i.m. dosing increased 3-fold over pre-injection levels 12 h after dosing and subsequently approached (but did not reach) normal values at 72 h post dose. CONCLUSIONS Systemic danofloxacin exposure achieved in horses following i.m. administration was consistent with the predicted blood levels needed for a positive therapeutic outcome for many equine infections. Conversely, danofloxacin utility by the i.g. route was limited by low bioavailability. Tolerability associated with i.m. administration was high. POTENTIAL RELEVANCE Pharmacokinetics, blood levels and good tolerability of i.v. and i.m. administration of danofloxacin in horses indicates that it is likely to be effective for treating sensitive bacterial infections.
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Affiliation(s)
- E Fernández-Varón
- Department of Pharmacology, Faculty of Veterinary Medicine, University of Murcia, Spain
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207
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Lainesse C, Frank D, Meucci V, Intorre L, Soldani G, Doucet M. Pharmacokinetics of clomipramine and desmethylclomipramine after single-dose intravenous and oral administrations in cats. J Vet Pharmacol Ther 2006; 29:271-8. [PMID: 16846464 DOI: 10.1111/j.1365-2885.2006.00742.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A cross-over study was performed in six adult spayed cats to determine the pharmacokinetics of clomipramine and its metabolite, desmethylclomipramine (DCMP) after intravenous (0.25 mg/kg) and oral (0.5 mg/kg) single-dose administrations. Plasma clomipramine and DCMP were measured by high-performance liquid chromatography at regular intervals for up to 30 h. Intravenous clomipramine best fit a two-compartmental model yielding an elimination rate constant of 0.037-0.09 h(-1) from which a mean half-life of 12.3 h was calculated. Mean clomipramine AUC(0--infinity) (ngxh/mL), clearance (L/hxkg), V(ss) (L/kg) and MRT (h) values were 652.5, 0.393, 5.0, and 13.5, respectively. Compartmental modeling for clomipramine, after oral administration, and DCMP after both administrations, produced wide parameter estimates and plots of residuals indicated poor goodness of fit. Noncompartmental analysis yielded mean AUC(0--30 h) (ngxh/mL), C(max) (ng/mL) and T(max) (h) of 948.3, 87.5 and 6.2 for clomipramine, and 613.8, 34.8, and 12.8 for DCMP respectively after oral administration. Clomipramine bioavailability was 90%. The present study showed marked pharmacokinetic variability for clomipramine and DCMP through biphasic absorption and potential genetic variability in clomipramine metabolism. It was concluded that population pharmacokinetics would allow better characterization of clomipramine variability that may explain the variability in clinical response noted in cats.
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Affiliation(s)
- C Lainesse
- Département de biomédecine vétérinaire, Faculté de Médecine Vétérinaire, Université de Montréal, St Hyacinthe, QC, Canada.
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208
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Schwarzwald CC, Sams RA, Bonagura JD. Pharmacokinetics of the calcium-channel blocker diltiazem after a single intravenous dose in horses. J Vet Pharmacol Ther 2006; 29:165-71. [PMID: 16669860 DOI: 10.1111/j.1365-2885.2006.00733.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The pharmacokinetics of diltiazem were determined in eight healthy horses. Diltiazem HCl, 1 mg/kg i.v., was administered over 5 min. Venous blood samples were collected at regular intervals after administration. Plasma concentrations of diltiazem and desacetyldiltiazem were determined by high-performance liquid chromatography. A second, putative metabolite was detected, but could not be identified due to the lack of an authentic standard. Data were analyzed by nonlinear least-squares regression analysis. The median (minimum-maximum) peak plasma concentration of diltiazem was 727 (539-976) ng/mL. Plasma diltiazem concentration vs. time data were best described by a two-compartment model with first-order drug elimination. The distribution half-life was 12 (6-23) min, the terminal half-life was 93 (73-161) min, the mean residence time was 125 (99-206) min, total plasma clearance was 14.4 (10.4-18.6) mL/kg/min, and the volume of distribution at steady-state was 1.84 (1.46-2.51) L/kg. The normalized ratio of the area under the curve (AUC) of desacetyldiltiazem to the AUC of diltiazem was 0.088 (0.062-0.179). The disposition of diltiazem in horses was characterized by rapid distribution and elimination and a terminal half-life shorter than reported in humans and dogs. Because of the reported low pharmacologic activity, plasma diltiazem metabolite concentrations were not considered clinically important.
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Affiliation(s)
- C C Schwarzwald
- Department of Veterinary Clinical Science, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210, USA.
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209
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Kästner SBR, Pakarinen SM, Ramela MP, Kutter APN, Boller J, Huhtinen MK. Comparative pharmacokinetics of medetomidine enantiomers in goats and sheep during sevoflurane anaesthesia. J Vet Pharmacol Ther 2006; 29:63-6. [PMID: 16420304 DOI: 10.1111/j.1365-2885.2006.00701.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- S B R Kästner
- Equine Clinic, Anaesthesia Section, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.
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210
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Yap CW, Li ZR, Chen YZ. Quantitative structure-pharmacokinetic relationships for drug clearance by using statistical learning methods. J Mol Graph Model 2005; 24:383-95. [PMID: 16290201 DOI: 10.1016/j.jmgm.2005.10.004] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2005] [Revised: 10/04/2005] [Accepted: 10/04/2005] [Indexed: 10/25/2022]
Abstract
Quantitative structure-pharmacokinetic relationships (QSPkR) have increasingly been used for the prediction of the pharmacokinetic properties of drug leads. Several QSPkR models have been developed to predict the total clearance (CL(tot)) of a compound. These models give good prediction accuracy but they are primarily based on a limited number of related compounds which are significantly lesser in number and diversity than the 503 compounds with known CL(tot) described in the literature. It is desirable to examine whether these and other statistical learning methods can be used for predicting the CL(tot) of a more diverse set of compounds. In this work, three statistical learning methods, general regression neural network (GRNN), support vector regression (SVR) and k-nearest neighbour (KNN) were explored for modeling the CL(tot) of all of the 503 known compounds. Six different sets of molecular descriptors, DS-MIXED, DS-3DMoRSE, DS-ATS, DS-GETAWAY, DS-RDF and DS-WHIM, were evaluated for their usefulness in the prediction of CL(tot). GRNN-, SVR- and KNN-developed models have average-fold errors in the range of 1.63 to 1.96, 1.66-1.95 and 1.90-2.23, respectively. For the best GRNN-, SVR- and KNN-developed models, the percentage of compounds with predicted CL(tot) within two-fold error of actual values are in the range of 61.9-74.3% and are comparable or slightly better than those of earlier studies. QSPkR models developed by using DS-MIXED, which is a collection of constitutional, geometrical, topological and electrotopological descriptors, generally give better prediction accuracies than those developed by using other descriptor sets. These results suggest that GRNN, SVR, and their consensus model are potentially useful for predicting QSPkR properties of drug leads.
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Affiliation(s)
- C W Yap
- Department of Computational Science, National University of Singapore, Blk SOC1, Level 7, 3 Science Drive 2, Singapore 117543, Singapore
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211
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Toutain PL, Lees P. Integration and modelling of pharmacokinetic and pharmacodynamic data to optimize dosage regimens in veterinary medicine. J Vet Pharmacol Ther 2005; 27:467-77. [PMID: 15601441 DOI: 10.1111/j.1365-2885.2004.00613.x] [Citation(s) in RCA: 159] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In veterinary drug development procedures, pharmacokinetic (PK) and pharmacodynamic (PD) data have generally been established in separate, parallel studies to assist in the design of dosage schedules for subsequent evaluation in clinical trials. This review introduces the concept of PK/PD modelling, an approach in which PK and PD data are generated in the same study, and used to derive numerical values for PD parameters based on drug plasma concentrations. The PD parameters define the efficacy, potency and slope (sensitivity) of the concentration-effect relationship. It is proposed that the parameters derived from PK/PD modelling may be used as an alternative and preferred approach to dose titration studies for selecting rational dosage regimens (both dose and dosing interval) for further evaluation in clinical trials. In PK/PD modelling, the explicative variable for effect is the plasma concentration profile. The PK/PD approach provides several advantages over dose-titration studies, including determination of a projected dosage regimen by investigation of a single dose, in contrast to dose-ranging studies which by definition require testing of multiple dosage. Implementation of PK/PD modelling in the veterinary drug development process is currently constrained by the limited number of veterinary studies performed to date, and the consequently limited understanding of PK/PD concepts and their absence from regulatory authority guidelines. Nevertheless, PK/PD modelling has major potential for rational dosage regimen determination, as it considers and quantifies the two main sources of interspecies variability (PK and PD). It is therefore applicable to interspecies extrapolation and to multiple species drug development. As well as the currently limited appreciation of PK/PD principles in the veterinary scientific community, a further constraint in implementing PK/PD modelling is the need to validate PK/PD approaches and thereby gain confidence in its value by pharmaceutical companies and regulatory authorities.
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Affiliation(s)
- P L Toutain
- UMR 181 Physiopathologie et Toxicologie Expérimentales INRA/ENVT, Ecole Nationale Vétérinaire de Toulouse, Toulouse cedex 03, France.
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212
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Abstract
Terminal plasma half-life is the time required to divide the plasma concentration by two after reaching pseudo-equilibrium, and not the time required to eliminate half the administered dose. When the process of absorption is not a limiting factor, half-life is a hybrid parameter controlled by plasma clearance and extent of distribution. In contrast, when the process of absorption is a limiting factor, the terminal half-life reflects rate and extent of absorption and not the elimination process (flip-flop pharmacokinetics). The terminal half-life is especially relevant to multiple dosing regimens, because it controls the degree of drug accumulation, concentration fluctuations and the time taken to reach equilibrium.
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Affiliation(s)
- P L Toutain
- UMR 181 Physiopathologie et Toxicologie Expérimentales INRA/ENVT, Ecole Nationale Vétérinaire de Toulouse, Toulouse cedex 03, France.
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213
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Abstract
Bioavailability is a key pharmacokinetic parameter which expresses the proportion of a drug administered by any nonvascular route that gains access to the systemic circulation. Presented in this review are the different approaches to measurement of bioavailability (absolute and relative), including the case in which intravenous administration is impossible. The rate of drug absorption is also discussed with special emphasis on the possible difficulties encountered using C(max) and T(max) or curve fitting to evaluate the rate of drug absorption.
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Affiliation(s)
- P L Toutain
- UMR 181 Physiopathologie et Toxicologie Expérimentales INRA/ENVT, Ecole Nationale Vétérinaire de Toulouse, Toulouse cedex 03, France.
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