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Goodchild CS, Serrao JM, Sear JW, Anderson BJ. Pharmacokinetic and Pharmacodynamic Analysis of Alfaxalone Administered as a Bolus Intravenous Injection of Phaxan in a Phase 1 Randomized Trial. Anesth Analg 2020; 130:704-714. [DOI: 10.1213/ane.0000000000004204] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Luca GC, Barter LS, Pypendop BH. Pharmacokinetics of ketamine following a short intravenous infusion to isoflurane-anesthetized New Zealand White rabbits (Oryctolagus cuniculus). Vet Anaesth Analg 2020; 47:334-340. [PMID: 32222343 DOI: 10.1016/j.vaa.2020.02.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2019] [Revised: 02/11/2020] [Accepted: 02/12/2020] [Indexed: 11/25/2022]
Abstract
OBJECTIVE To describe the pharmacokinetics of ketamine following a short intravenous (IV) infusion to isoflurane-anesthetized rabbits. STUDY DESIGN Prospective experimental study. ANIMALS A total of six adult healthy female New Zealand White rabbits. METHODS Anesthesia was induced with isoflurane in oxygen. Following determination of isoflurane minimum alveolar concentration (MAC), the isoflurane concentration was reduced to 0.75 MAC and ketamine hydrochloride (5 mg kg-1) was administered IV over 5 minutes. Blood samples were collected before and at 2, 5, 6, 7, 8, 9, 13, 17, 21, 35, 65, 125, 215 and 305 minutes after initiating the ketamine infusion. Samples were processed immediately and the plasma separated and stored at -80 °C until analyzed for ketamine and norketamine concentrations using liquid chromatography-mass spectrometry. Compartment models were fitted to the concentration-time data for ketamine and for ketamine plus norketamine using nonlinear mixed-effects (population) modeling. RESULTS A three- and five-compartment model best fitted the plasma concentration-time data for ketamine and for ketamine plus norketamine, respectively. For the ketamine only model, the volume of distribution at steady state (Vss) was 3217 mL kg-1, metabolic clearance was 88 mL minute-1 kg-1 and the terminal half-life was 59 minutes. For the model including both ketamine and norketamine, Vss were 3224 and 2073 mL kg-1, total metabolic clearance was 107 and 52 mL minute-1 kg-1 and terminal half-lives were 52 and 55 minutes for the parent drug and its metabolite, respectively. CONCLUSIONS AND CLINICAL RELEVANCE This study characterized the pharmacokinetics of ketamine and norketamine in isoflurane-anesthetized New Zealand White rabbits following short IV infusion. The results obtained herein will be useful to determine ketamine infusion regimens in isoflurane-anesthetized rabbits.
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Affiliation(s)
- Genevieve C Luca
- Veterinary Medical Teaching Hospital, University of California, Davis, CA, USA
| | - Linda S Barter
- Veterinary Surgical and Radiological Sciences, University of California, Davis, CA, USA.
| | - Bruno H Pypendop
- Veterinary Surgical and Radiological Sciences, University of California, Davis, CA, USA
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Pypendop BH, Ahokoivu H, Honkavaara J. Pharmacokinetics of vatinoxan in male neutered cats anesthetized with isoflurane. Vet Anaesth Analg 2019; 47:70-75. [PMID: 31806431 DOI: 10.1016/j.vaa.2019.10.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2019] [Revised: 08/04/2019] [Accepted: 10/05/2019] [Indexed: 11/18/2022]
Abstract
OBJECTIVE To characterize the pharmacokinetics of vatinoxan in isoflurane-anesthetized cats. STUDY DESIGN Prospective experimental study. ANIMALS A group of six adult healthy male neutered cats. METHODS Cats were anesthetized using isoflurane in oxygen. Venous catheters were placed to administer the drug and sample blood. Vatinoxan, 1 mg kg-1, was administered intravenously over 5 minutes. Blood was sampled before and at various times during and up to 8 hours after vatinoxan administration. Plasma vatinoxan concentration was measured using liquid chromatography/tandem mass spectrometry. Compartment models were fitted to the time-concentration data using population methods and nonlinear mixed effect modeling. RESULTS A three-compartment model best fitted the data. Typical value (% interindividual variability) for the three volumes (mL kg-1), the metabolic clearance and two distribution clearances (mL minute-1 kg-1) were 34 (55), 151 (35), 306 (18), 2.3 (34), 42.6 (25) and 5.6 (0), respectively. Hypotension increased the second distribution clearance to 10.6. CONCLUSION AND CLINICAL RELEVANCE The pharmacokinetics of vatinoxan in anesthetized cats were characterized by a small volume of distribution and a low clearance. An intravenous bolus of 100 μg kg-1 of vatinoxan followed by constant rate infusions of 55 μg kg-1 minute-1 for 20 minutes, then 22 μg kg-1 minute-1 for 60 minutes and finally 10 μg kg-1 minute-1 for the remainder of the infusion time is expected to maintain the plasma concentration within 90%-110% of the plasma vatinoxan concentration previously shown to attenuate the cardiovascular effects of dexmedetomidine (25 μg kg-1) in conscious cats.
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Affiliation(s)
- Bruno H Pypendop
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA, USA.
| | - Hanna Ahokoivu
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA, USA
| | - Juhana Honkavaara
- Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California, Davis, CA, USA
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Huang W, Isoherranen N. Sampling Site Has a Critical Impact on Physiologically Based Pharmacokinetic Modeling. J Pharmacol Exp Ther 2019; 372:30-45. [PMID: 31604807 DOI: 10.1124/jpet.119.262154] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2019] [Accepted: 10/09/2019] [Indexed: 12/11/2022] Open
Abstract
It has been shown that arterial (central) and venous (peripheral) plasma drug concentrations can be very different. While pharmacokinetic studies typically measure drug concentrations from the peripheral vein such as the arm vein, physiologically based pharmacokinetic (PBPK) models generally output simulated concentrations from the central venous compartment that physiologically represents the right atrium, a merge of the superior and inferior vena cava. In this study, a physiologically based peripheral forearm sampling site model was developed and verified using nicotine, ketamine, lidocaine, and fentanyl as model drugs. This verified model allows output of simulated peripheral venous concentrations that can be meaningfully compared with observed pharmacokinetic data from the arm vein. The generalized effect of PBPK model sampling site on simulation output was investigated. Drugs and metabolites with large volumes of distribution showed considerable concentration discrepancy between the simulated central venous compartment and the peripheral arm vein after intravenous or oral administration, resulting in significant differences in values for C max and time taken to reach C max (t max ) In addition, the simulated central venous metabolite profile showed an unexpected profile that was not observed in the peripheral arm vein. Using fentanyl as a model compound, we show that using the wrong sampling site in PBPK models can lead to biased model evaluation and subsequent erroneous model parameter optimization. Such an error in model parameters along with the discrepant sampling site could dramatically mislead the pharmacokinetic prediction in unstudied clinical scenarios, affecting the assessment of drug safety and efficacy. Overall, this study shows that PBPK model publications should specify the model sampling sites and match them with those employed in clinical studies. SIGNIFICANCE STATEMENT: Our study shows that sampling from the central venous compartment (right atrium) during physiologically based pharmacokinetic model development gives rise to biased model evaluation and erroneous model parameterization when observed data are collected from the peripheral arm vein. This can lead to a clinically significant error in predictions of plasma concentration-time profiles in unstudied scenarios. To address this error, we developed and verified a novel peripheral sampling site model to simulate arm vein drug concentrations that can be applied to different drug dosing scenarios.
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Affiliation(s)
- Weize Huang
- Department of Pharmaceutics, School of Pharmacy, University of Washington, Seattle, Washington
| | - Nina Isoherranen
- Department of Pharmaceutics, School of Pharmacy, University of Washington, Seattle, Washington
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Talke P, Anderson BJ. Pharmacokinetics and pharmacodynamics of dexmedetomidine-induced vasoconstriction in healthy volunteers. Br J Clin Pharmacol 2018; 84:1364-1372. [PMID: 29495085 PMCID: PMC5980451 DOI: 10.1111/bcp.13571] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2017] [Revised: 01/20/2018] [Accepted: 02/20/2018] [Indexed: 12/31/2022] Open
Abstract
AIMS Alpha-2 agonists are direct peripheral vasoconstrictors, which achieve these effects by activating vascular smooth muscle alpha-2 adrenoceptors. The impact of this response during dexmedetomidine infusion remains poorly quantified. Our goal was to investigate the pharmacokinetic (PK) and pharmacodynamic (PD, vasoconstriction) effects of a computer-controlled dexmedetomidine infusion in healthy volunteers. METHODS After local ethics committee approval, we studied 10 healthy volunteers. To study the peripheral vasoconstrictive effect of dexmedetomidine without concurrent sympatholytic effects, sympathetic fibres were blocked with a brachial plexus block. Volunteers received a dexmedetomidine target-controlled infusion for 15 min, to a target concentration of 0.3 ng ml-1 . Arterial blood samples were collected during and for 60 min after dexmedetomidine infusion for PK analysis. Peripheral vasoconstriction (PD) was assessed using finger photoelectric plethysmography. PK/PD analysis was carried out using nonlinear mixed-effect models. RESULTS We found that the computer-controlled infusion pump delivered mean concentrations greater than 0.3 ng ml-1 over the 15-min infusion duration. The peripheral vasoconstrictive effect correlated with dexmedetomidine plasma concentrations during and after the infusion. A three-compartment model provided a better fit to the data than a two-compartment model. CONCLUSIONS We found that dexmedetomidine-induced vasoconstriction is concentration dependent over time. Dexmedetomidine PK were best estimated by a three-compartment model with allometric scaling. Our results may contribute to future modelling of dexmedetomidine-induced haemodynamic effects.
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Affiliation(s)
- Pekka Talke
- University of California San Francisco500 Parnassus Avenue, MUE455San FranciscoCA94143USA
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Pharmacokinetics of dexmedetomidine in isoflurane-anesthetized New Zealand White rabbits. Vet Anaesth Analg 2017; 44:876-882. [PMID: 28655497 DOI: 10.1016/j.vaa.2017.01.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2016] [Revised: 01/18/2017] [Accepted: 01/18/2017] [Indexed: 11/20/2022]
Abstract
OBJECTIVE To characterize the pharmacokinetics of dexmedetomidine when administered as a short intravenous (IV) infusion to isoflurane-anesthetized rabbits. STUDY DESIGN Experimental study. ANIMALS A total of six healthy adult female New Zealand White rabbits. METHODS Rabbits were anesthetized with isoflurane in oxygen. Following determination of isoflurane minimum alveolar concentration (MAC), the anesthetic dose was reduced to 0.7 × MAC, and dexmedetomidine hydrochloride (20 μg kg-1) was infused IV over 5 minutes. Arterial blood samples were obtained immediately before and at 1, 2, 5, 6, 7, 10, 15, 30, 60, 90, 120, 240 and 360 minutes following termination of the infusion. Samples were transferred into tubes containing ethylenediaminetetraacetic acid and centrifuged immediately. The plasma was harvested and stored at -80 °C until analyzed. Concentrations of dexmedetomidine in plasma were determined by liquid chromatography mass spectrometry. Compartment models were fitted to the time and concentration data using nonlinear regression. RESULTS A three-compartment model best fit the data set. Median volume of distribution at steady state and terminal half-life were 3169 mL kg-1 (range, 2182-3859 mL kg-1) and 80 minutes (range, 72-88 minutes), respectively. CONCLUSIONS AND CLINICAL RELEVANCE The pharmacokinetics of dexmedetomidine in isoflurane-anesthetized, healthy, New Zealand White rabbits were characterized in this study. Data from this study can be used to determine dosing regimens for dexmedetomidine in isoflurane-anesthetized rabbits.
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Carroll GL, Boothe DM, Hartsfield SM, Waller MK, Geller SC. Pharmacokinetics and selected behavioral responses to butorphanol and its metabolites in goats following intravenous and intramuscular administration. Vet Anaesth Analg 2016; 28:188-195. [PMID: 28404243 DOI: 10.1046/j.1467-2987.2001.00071.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2000] [Accepted: 02/05/2001] [Indexed: 11/20/2022]
Abstract
OBJECTIVE To evaluate disposition of a single dose of butorphanol in goats after intravenous (IV) and intramuscular (IM) administration and to relate behavioral changes after butorphanol administration with plasma concentrations. DESIGN Randomized experimental study. ANIMALS Six healthy 3-year-old neutered goats (one male and five female) weighing 46.5 ± 10.5 kg (mean ± D). METHODS Goats were given IV and IM butorphanol (0.1 mg kg-1) using a randomized cross-over design with a 1-week interval between treatments. Heparinized blood samples were collected at fixed intervals for subsequent determination of plasma butorphanol concentrations using an enzyme linked immunosorbent assay (ELISA). Pharmacokinetic values (volume of distribution at steady state [VdSS], systemic clearance [ClTB], extrapolated peak plasma concentration [C0] or estimated peak plasma concentration [CMAX], time to estimated peak plasma concentration [TMAX], distribution and elimination half-lives [t1/2], and bioavailability) were calculated. Behavior was subjectively scored. A two-tailed paired t-test was used to compare the elimination half-lives after IV and IM administration. Behavioral scores are reported as median (range). A Friedman Rank Sums test adjusted for ties was used to analyze the behavioral scores. A logit model was used to determine the effect of time and concentration on behavior. A value of p < 0.05 was considered significant. RESULTS Volume of distribution at steady state after IV administration of butorphanol was 1.27 ± 0.73 L kg-1, and ClTB was 0.0096 ± 0.0024 L kg-1 minute-1. Extrapolated C0 of butorphanol after IV administration was 146.5 ± 49.8 ng mL-1. Estimated CMAX after IM administration of butorphanol was 54.98 ± 14.60 ng mL-1, and TMAX was 16.2 ± 5.2 minutes; bioavailability was 82 ± 41%. Elimination half-life of butorphanol was 1.87 ± 1.49 and 2.75 ± 1.93 hours for IV and IM administration, respectively. Goats became hyperactive after butorphanol administration within the first 5 minutes after administration. Behavioral scores for goats were significantly different from baseline at 15 minutes after IV administration and at 15 and 30 minutes after IM administration. Both time and plasma butorphanol concentration were predictors of behavior. Behavioral scores of all goats had returned to baseline by 120 minutes after IV administration and by 240 minutes after IM administration. Conclusions and Clinical Relevance The dose of butorphanol (0.1 mg kg-1, IV or IM) being used clinically to treat postoperative pain in goats has an elimination half-life of 1.87 and 2.75 hours, respectively. Nonpainful goats become transiently excited after IV and IM administration of butorphanol. Clinical trials to validate the efficacy of butorphanol as an analgesic in goats are needed.
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Affiliation(s)
- Gwendolyn L Carroll
- Department of Veterinary Small Animal Medicine and Surgery, Texas A & M University, College Station, TX, USA
| | - Dawn M Boothe
- Department of Veterinary Physiology and Pharmacology, Texas A & M University, College Station, TX, USA
| | - Sandee M Hartsfield
- Department of Veterinary Small Animal Medicine and Surgery, Texas A & M University, College Station, TX, USA
| | - Mandy K Waller
- Department of Veterinary Small Animal Medicine and Surgery, Texas A & M University, College Station, TX, USA
| | - Sue C Geller
- Department of Veterinary Anatomy and Public Health, Texas A & M University, College Station, TX, USA
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Hedges AR, Pypendop BH, Shilo Y, Stanley SD, Ilkiw JE. Impact of the blood sampling site on time-concentration drug profiles following intravenous or buccal drug administration. J Vet Pharmacol Ther 2014; 37:145-50. [PMID: 24745064 DOI: 10.1111/jvp.12075] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The aim of this study was to examine the effect of the sampling site on the drug concentration-time profile, following intravenous or buccal (often called 'oral transmucosal') drug administration. Buprenorphine (20 μg/kg) was administered IV or buccally to six cats. Blood samples were collected from the carotid artery and the jugular and medial saphenous veins for 24 h following buprenorphine administration. Buprenorphine concentration-time data were examined using noncompartmental analysis. Pharmacokinetic parameters were compared using the Wilcoxon signed rank test, applying the Bonferroni correction. Significance was set at P < 0.05. Following IV administration, no difference among the sampling sites was found. Following buccal administration, maximum concentration [jugular: 6.3 (2.9-9.8), carotid: 3.4 (1.9-4.9), medial saphenous: 2.5 (1.7-4.1) ng/mL], area under the curve [jugular: 395 (335-747), carotid: 278 (214-693), medial saphenous: 255 (188-608) ng·min/mL], and bioavailability [jugular: 47 (34-67), carotid: 32 (20-52), medial saphenous: 23 (16-55)%] were higher in the jugular vein than in the carotid artery and medial saphenous vein. Jugular venous blood sampling is not an acceptable substitute for arterial blood sampling following buccal drug administration.
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Pypendop BH, Ilkiw JE. Pharmacokinetics of dexmedetomidine after intravenous administration of a bolus to cats. Am J Vet Res 2014; 75:441-5. [PMID: 24762015 DOI: 10.2460/ajvr.75.5.441] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVE To characterize the pharmacokinetics of dexmedetomidine after IV administration of a bolus to conscious healthy cats. ANIMALS 5 healthy adult spayed female cats. PROCEDURES Dexmedetomidine was administered IV as a bolus at 3 doses (5, 20, or 50 μg/kg) on separate days in a random order. Blood samples were collected immediately before and at various times for 8 hours after drug administration. Plasma dexmedetomidine concentrations were determined with liquid chromatography-mass spectrometry. Compartment models were fitted to the concentration-time data by means of nonlinear regression. RESULTS A 2-compartment model best fit the concentration-time data after administration of 5 μg/kg, whereas a 3-compartment model best fit the data after administration of 20 and 50 μg/kg. The median volume of distribution at steady-state and terminal half-life were 371 mL/kg (range, 266 to 435 mL/kg) and 31.8 minutes (range, 30.3 to 39.7 minutes), respectively, after administration of 5 μg/kg; 545 mL/kg (range, 445 to 998 mL/kg) and 56.3 minutes (range, 39.3 to 68.9 minutes), respectively, after administration of 20 μg/kg; and 750 mL/kg (range, 514 to 938 mL/kg) and 75.3 minutes (range, 52.2 to 223.3 minutes), respectively, after administration of 50 μg/kg. CONCLUSIONS AND CLINICAL RELEVANCE The pharmacokinetics of dexmedetomidine was characterized by a small volume of distribution and moderate clearance and had minimal dose dependence within the range of doses evaluated. These data will help clinicians design dosing regimens once effective plasma concentrations are established.
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Affiliation(s)
- Bruno H Pypendop
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616
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Hedges AR, Pypendop BH, Shilo-Benjamini Y, Stanley SD, Ilkiw JE. Pharmacokinetics of buprenorphine following intravenous and buccal administration in cats, and effects on thermal threshold. J Vet Pharmacol Ther 2013; 37:252-9. [DOI: 10.1111/jvp.12084] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Accepted: 09/19/2013] [Indexed: 11/28/2022]
Affiliation(s)
- A. R. Hedges
- Department of Surgical and Radiological Sciences; School of Veterinary Medicine; University of California; Davis CA USA
| | - B. H. Pypendop
- Department of Surgical and Radiological Sciences; School of Veterinary Medicine; University of California; Davis CA USA
| | - Y. Shilo-Benjamini
- Department of Surgical and Radiological Sciences; School of Veterinary Medicine; University of California; Davis CA USA
| | - S. D. Stanley
- California Animal Health and Food Safety Laboratory System; School of Veterinary Medicine; University of California; Davis CA USA
| | - J. E. Ilkiw
- Department of Surgical and Radiological Sciences; School of Veterinary Medicine; University of California; Davis CA USA
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Upton RN, Foster DJR, Christrup LL, Dale O, Moksnes K, Popper L. A physiologically-based recirculatory meta-model for nasal fentanyl in man. J Pharmacokinet Pharmacodyn 2012; 39:561-76. [PMID: 22903816 DOI: 10.1007/s10928-012-9268-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2011] [Accepted: 08/03/2012] [Indexed: 12/31/2022]
Abstract
Pharmacokinetic (PK) and pharmacodynamic (PD) data were available from a study of a nasal delivery system for the opioid analgesic fentanyl, together with data on the kinetics of fentanyl in arterial blood in man, and in the lung and brain of sheep. Our aim was to reconcile these data using a physiologically-based population recirculatory PK-PD model, with emphasis on achieving a meta-model that could simultaneously account for the arterial and venous (arm) concentrations of fentanyl, could relate PD effects (pain scores) to the CNS concentrations of fentanyl, and could account for the effect of body size and age on fentanyl kinetics. Data on the concentration gradients of fentanyl across brain, lung and muscle were used to develop sub-models of fentanyl kinetics in these organs. The sub-models were incorporated into a "whole body" recirculatory model by adding additional sub-models for a venous mixing compartment, the liver and gut, the kidney and the "rest of the body" with blood flows and organ volumes based on values for a Standard Man. Inter-individual variability was achieved by allometric scaling of organ size and blood flows, evidence-based assumptions about the effect of weight and age on cardiac output, and inter-individual variability in the free fraction in plasma and hepatic extraction of fentanyl. Post-operative pain scores were found to be temporally related to the predicted brain concentrations of fentanyl. We conclude that a physiologically-based meta-modelling approach was able to describe clinical PK-PD studies of fentanyl whilst providing a mechanistic interpretation of key aspects of its disposition.
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Affiliation(s)
- Richard N Upton
- Australian Centre for Pharmacometrics, University of South Australia, North Terrace, Adelaide, Australia.
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Oertel BG, Vermehren J, Zimmermann M, Huynh TT, Doehring A, Ferreiros N, Senzel S, Schmitz-Rixen T, Erbe M, Geisslinger G, Harder S, Angst MS, Lötsch J. Necessity and Risks of Arterial Blood Sampling in Healthy Volunteer Studies. Clin Pharmacokinet 2012; 51:629-38. [DOI: 10.1007/s40262-012-0001-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Tuk B, Danhof M, Mandema JW. The impact of arteriovenous concentration differences on pharmacodynamic parameter estimates. JOURNAL OF PHARMACOKINETICS AND BIOPHARMACEUTICS 1997; 25:39-62. [PMID: 9353693 DOI: 10.1023/a:1025767710234] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
In many pharmacodynamic investigations venous drug concentrations are measured and linked to effect-site concentrations by means of a traditional first-order effect-compartment model to estimate pharmacodynamic (PD) parameters. This analysis ignores the underlying physiology that arterial blood supplies both the venous sampling site and effect site. Recently, an extended effect-compartment model has been proposed that reflects physiology by postulating a first-order rate constant of equilibrium between arterial and effect-site concentrations (ke0) as well as first-order rate constant between arterial and venous concentrations (kv0). In the current paper, we evaluate the bias in PD parameter estimates if venous drug concentrations are measured and linked to effect-site concentrations by a traditional effect compartment as a function ke0, kv0, and the drug's elimination half-life (T1/2); we present an analytical solution to the differential equations characterizing the extended effect-compartment model; and we evaluate the performance of the extended effect-compartment model to estimate pharmacodynamic parameters on the basis of venous drug concentrations. Time profiles of venous drug concentrations and drug effect were simulated for a wide range of different values of the half-life of ke0 (T1/2,e0), the half-life of kv0 (T1/2,v0), and T1/2. The simulations showed that a significant bias (up to 90%) in PD parameter estimates occurred for certain values of T1/2,e0, T1/2,v0, and T1/2 if venous drug concentrations are linked to effect-site concentrations by a traditional effect-compartment model. This model misspecification is not apparent from the results of the fitting procedure. The extended effect-compartment model provided unbiased but imprecise PD parameter estimates. The extended effect-compartment model was also able to analyze instances in which the venous concentrations equilibrate slower with the arterial concentrations than the effect-site concentrations, and proteresis is observed in the concentration--effect relationship. It is concluded that if the apparent T1/2 of the drug in the time period in which the decline in pharmacological effect is most pronounced is greater than 5 times T1/2,e0 and T1/2,e0 is greater than T1/2,v0 there is no need to model the underlying arteriovenous equilibrium delay. Under these conditions a traditional first-order link between venous and effect-site concentrations will yield accurate and reliable (less than 10% bias) estimates of the PD parameters such as Emax, EC50 and N. If T1/2 is less than 5 times T1/2,e0 or if T1/2,v0 is greater than T1/2,e0, the underlying arteriovenous equilibration delay needs to be taken into account in the model to obtain unbiased estimates of the PD parameters. This applies for almost all values of T1/2.v0. Arteriovenous equilibration delay can be best taken into account by measuring arterial blood concentrations. If this is not possible, the extended effect-compartment link model can be used. However, a large number of effect measurements needs to be obtained to estimate the model parameters accurately.
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Affiliation(s)
- B Tuk
- Leiden/Amsterdam Center for Drug Research, Division of Pharmacology, The Netherlands
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