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Kiang TKL, Ranamukhaarachchi SA, Ensom MHH. Revolutionizing Therapeutic Drug Monitoring with the Use of Interstitial Fluid and Microneedles Technology. Pharmaceutics 2017; 9:E43. [PMID: 29019915 PMCID: PMC5750649 DOI: 10.3390/pharmaceutics9040043] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2017] [Revised: 10/04/2017] [Accepted: 10/07/2017] [Indexed: 12/29/2022] Open
Abstract
While therapeutic drug monitoring (TDM) that uses blood as the biological matrix is the traditional gold standard, this practice may be impossible, impractical, or unethical for some patient populations (e.g., elderly, pediatric, anemic) and those with fragile veins. In the context of finding an alternative biological matrix for TDM, this manuscript will provide a qualitative review on: (1) the principles of TDM; (2) alternative matrices for TDM; (3) current evidence supporting the use of interstitial fluid (ISF) for TDM in clinical models; (4) the use of microneedle technologies, which is potentially minimally invasive and pain-free, for the collection of ISF; and (5) future directions. The current state of knowledge on the use of ISF for TDM in humans is still limited. A thorough literature review indicates that only a few drug classes have been investigated (i.e., anti-infectives, anticonvulsants, and miscellaneous other agents). Studies have successfully demonstrated techniques for ISF extraction from the skin but have failed to demonstrate commercial feasibility of ISF extraction followed by analysis of its content outside the ISF-collecting microneedle device. In contrast, microneedle-integrated biosensors built to extract ISF and perform the biomolecule analysis on-device, with a key feature of not needing to transfer ISF to a separate instrument, have yielded promising results that need to be validated in pre-clinical and clinical studies. The most promising applications for microneedle-integrated biosensors is continuous monitoring of biomolecules from the skin's ISF. Conducting TDM using ISF is at the stage where its clinical utility should be investigated. Based on the advancements described in the current review, the immediate future direction for this area of research is to establish the suitability of using ISF for TDM in human models for drugs that have been found suitable in pre-clinical experiments.
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Affiliation(s)
- Tony K L Kiang
- Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB T6G 2E1, Canada.
| | - Sahan A Ranamukhaarachchi
- Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
| | - Mary H H Ensom
- Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, BC V6T 1Z3, Canada.
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Simmel F, Kirbs C, Erdogan Z, Lackner E, Zeitlinger M, Kloft C. Pilot investigation on long-term subcutaneous microdialysis: proof of principle in humans. AAPS JOURNAL 2012; 15:95-103. [PMID: 23065438 DOI: 10.1208/s12248-012-9412-z] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2012] [Accepted: 09/11/2012] [Indexed: 11/30/2022]
Abstract
Reliable drug concentration measurements at the target site are increasingly demanded and can be achieved by microdialysis. The aim of this pilot study was to demonstrate the proof of principle of long-term subcutaneous microdialysis in humans. For long-term microdialysis, a special setting implementing both concentric and linear catheters has been developed ensuring good clinical practice compliance, tolerability, and convenience for participants and personnel. As a model compound, moderately lipophilic voriconazole was selected as a well-characterized drug in in vitro microdialysis experiments. Multiple in vivo relative recovery (RR) determinations for microdialysis were performed by retrodialysis during the entire study (n = 48 samples). Continuous microdialysis was successfully applied and well tolerated over 87 h in three adults for the first time. RR revealed low intra-individual (coefficient of variation (CV) = 4.4-12.5%) and inter-individual variability (CV = 4.3-12.5%) across all samples and catheters. Lower RR values were consistently determined for linear catheters. One catheter leakage was managed without an impact on the reliability of the RR values. Overall, RR values were calculated to be 73.3% (linear: CV = 18.5%, n = 23) and 84.9% (concentric: CV = 5.6%, n = 23). Long-term microdialysis application over almost 4 days was feasible by reliable multiple RR (proof of principle), well tolerated, and reduced the burden in humans avoiding several catheter insertions, thereby allowing to monitor concentration-time courses continuously. Moreover, a moderately lipophilic drug has been proven suitable for in vivo microdialysis, as previously suggested by in vitro microdialysis.
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Affiliation(s)
- Franziska Simmel
- Institute of Pharmacy, Department of Clinical Pharmacy, Martin-Luther-Universitaet Halle-Wittenberg, 06120, Halle, Germany
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Jayachandra Babu R, Dayal PP, Pawar K, Singh M. Nose-to-brain transport of melatonin from polymer gel suspensions: a microdialysis study in rats. J Drug Target 2011; 19:731-40. [PMID: 21428693 DOI: 10.3109/1061186x.2011.558090] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
PURPOSE Exogenous melatonin (MT) has significant neuroprotective roles in Alzheimer's and Parkinson's diseases. This study investigates the delivery MT to brain via nasal route as a polymeric gel suspension using central brain microdialysis in anesthetized rats. METHODS Micronized MT suspensions using polymers [carbopol, carboxymethyl cellulose (CMC)] and polyethylene glycol 400 (PEG400) were prepared and characterized for nasal administration. In vitro permeation of the formulations was measured across a three-dimensional tissue culture model EpiAirway(™). The central brain delivery into olfactory bulb of nasally administered MT gel suspensions was studied using brain microdialysis in male Wistar rats. The MT content of microdialysis samples was analyzed by high performance liquid chromatography (HPLC) using electrochemical detection. The nose-to-brain delivery of MT formulations was compared with intravenously administered MT solution. RESULTS MT suspensions in carbopol and CMC vehicles have shown significantly higher permeability across Epiairway(™) as compared to control, PEG400 (P < 0.05). The brain (olfactory bulb) levels of MT after intranasal administration were 9.22, 6.77 and 4.04-fold higher for carbopol, CMC and PEG400, respectively, than that of intravenous MT in rats. In conclusion, microdialysis studies demonstrated increased brain levels of MT via nasal administration in rats.
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Affiliation(s)
- R Jayachandra Babu
- Department of Pharmacal Sciences, Harrison School of Pharmacy, Auburn University, Auburn, AL, USA.
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Clinckers R, Smolders I, Vermoesen K, Michotte Y, Danhof M, Voskuyl R, Della Pasqua O. Prediction of antiepileptic drug efficacy: the use of intracerebral microdialysis to monitor biophase concentrations. Expert Opin Drug Metab Toxicol 2009; 5:1267-77. [PMID: 19611404 DOI: 10.1517/17425250903146903] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Biophase concentrations of antiepileptic drugs can differ significantly from pharmacokinetics in plasma. A crucial determinant in the disposition of antiepileptic drugs to the brain is represented by the blood-brain barrier. There is growing evidence that this barrier can alter the availability of antiepileptic drugs at the target site. The permeability of the blood-brain barrier becomes particularly relevant in epileptic conditions and in drug refractory situations. In vivo, intracerebral microdialysis is a valuable technique to determine biophase drug concentrations as it enables investigation of antiepileptic drug transport and distribution in the brain as a function of time. The present review illustrates that intracerebral microdialysis is an indispensable tool for the assessment of the pharmacokinetics of antiepileptic drugs. In addition, we demonstrate how microdialysis data can be used in conjunction with mechanism-based pharmacokinetic/pharmacodynamic modeling for dose selection and optimization of the therapeutic regimen for novel compounds.
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Affiliation(s)
- Ralph Clinckers
- Vrije Universiteit Brussel (VUB), Pharmaceutical Institute, Research Group Experimental Pharmacology, Department of Pharmaceutical Chemistry and Drug Analysis (labo FASC), Laarbeeklaan 103, Building G, 1090 Brussels, Belgium.
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Lindberger M, Tomson T, Ståhle L. Unbound valproate fraction in plasma and subcutaneous microdialysate in steady state and after a single dose in humans. Ther Drug Monit 2003; 25:378-83. [PMID: 12766568 DOI: 10.1097/00007691-200306000-00020] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The aim of the current study was to characterize the observed discrepancy between unbound plasma valproate (VPA) in single dose and steady state in humans. Unbound and total plasma VPA and subcutaneous microdialysate VPA concentrations were estimated in single dose (6 subjects, n = 33) and steady state (11 subjects, n = 110). Trough plasma samples from 14 patients with total VPA concentrations of 300 micromol/L and 14 patients with VPA concentrations ranging from 600 to 700 micromol/L were analyzed for the unbound VPA fraction and compared with the unbound VPA fraction in spiked plasma samples from healthy subjects containing similar total VPA concentrations. The unbound plasma VPA fraction was significantly higher (P < 0.001) in the steady-state group compared with the single-dose group. The unbound VPA fraction was significantly higher in steady state compared with spiked plasma samples at high and low total VPA concentrations (P < 0.001). The difference between microdialysate and unbound plasma VPA concentrations was significant in the steady-state group (P < 0.001), while no difference was observed in the single-dose group. The mean (+/- SD) subcutaneous microdialysate-to-unbound plasma ratio in the single-dose and steady-state groups was 1.08 (+/- 0.401) and 0.74 (+/- 0.123), respectively. The ratio difference between the groups was significant (P < 0.001). The results of the current study show that unbound plasma fractions of VPA are consistently higher in steady state compared with single dose. Together with the finding of higher unbound VPA fraction in steady state compared with spiked plasma samples, these results provide indirect evidence of displacement of VPA from plasma proteins by product(s) of VPA biotransformation. In addition, subcutaneous microdialysate VPA levels were consistently lower than unbound plasma levels in steady state but not after single dose. The mechanisms underlying this observation need to be studied further.
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Affiliation(s)
- Martin Lindberger
- Departments of Neurology, Karolinska Institute, Huddinge University Hospital, Stockholm, Sweden.
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Lindberger M, Tomson T, Wallstedt L, Ståhle L. Distribution of Valproate to Subdural Cerebrospinal Fluid, Subcutaneous Extracellular Fluid, and Plasma in Humans: A Microdialysis Study. Epilepsia 2003. [DOI: 10.1046/j.1528-1157.2001.4220256.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Mathy FX, Denet AR, Vroman B, Clarys P, Barel A, Verbeeck RK, Préat V. In vivo tolerance assessment of skin after insertion of subcutaneous and cutaneous microdialysis probes in the rat. Skin Pharmacol Physiol 2003; 16:18-27. [PMID: 12566825 DOI: 10.1159/000068290] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2002] [Accepted: 05/27/2002] [Indexed: 11/19/2022]
Abstract
The purpose of the study was to evaluate the trauma induced by insertion of the linear microdialysis probe in the subcutaneous and dermal tissue in the rat and to check if the microdialysis probe insertion affects transdermal drug delivery. Non-invasive bioengineering methods (TEWL, Laser Doppler Velocimeter, Chromameter) as well as histology were combined to characterize these effects. The results showed that the dermal and subcutaneous insertion of microdialysis probes did not change skin permeability, blood flow and color, confirming the safety of this technique. The probe depth did not influence the trauma. No significant physical damage after probe insertion was noticed. Thus, the present work validates the use of microdialysis in dermatopharmacokinetics studies after topical or systemic drug delivery.
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Affiliation(s)
- F-X Mathy
- Unité de Pharmacie Galénique, Métabolisme, Nutrition et Toxicologie, Université Catholique de Louvain, Belgium
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Abstract
During the last decade microdialysis has been successfully applied to assess cutaneous drug delivery of numerous substances, indicating the large potential for bioequivalence/bioavailability evaluation of topical formulations. The technique has been shown to be minimally invasive and supply pharmacokinetic information directly in the target organ for cutaneous drug delivery with high temporal resolution without further intervention with the tissue after implantation. However, there are a few challenges that need to be addressed before microdialysis can be regarded as a generally applicable routine technique for cutaneous drug delivery assessments. Firstly, the technique is currently not suitable for sampling of highly lipophilic compounds and, secondly, more studies are desirable for elucidation of the variables associated with the technique to increase reproducibility. The present literature indicates that the condition of the skin at the individual assessment sites is the main variable, but also variables associated with relative recovery, differentiation between the pharmacokinetic parameters (i.e., lag time, distribution, absorption and elimination rate) can influences the reproducibility of the technique. Furthermore, it has been indicated that cutaneous microdialysis in rats may be useful for prediction of dermal pharmacokinetic properties of novel drugs/topical formulations in man.
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Affiliation(s)
- Mads Kreilgaard
- Department of Neurochemistry and Discovery ADME, H Lundbeck A/S, Ottiliavej 9, DK-2500, Valby, Denmark.
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Garrison KE, Pasas SA, Cooper JD, Davies MI. A review of membrane sampling from biological tissues with applications in pharmacokinetics, metabolism and pharmacodynamics. Eur J Pharm Sci 2002; 17:1-12. [PMID: 12356415 DOI: 10.1016/s0928-0987(02)00149-5] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
This review provides an overview of membrane sampling techniques, microdialysis and ultrafiltration, and cites illustrations of their applications in pharmacokinetics, metabolism and/or pharmacodynamics. The review organizes applications by target tissue and general type of information gleaned. It focuses on recently published microdialysis studies (1999 to this writing) and offers the first review of ultrafiltration sampling studies. The advantages and limitations of using microdialysis and ultrafiltration sampling as tools for obtaining pharmacokinetic and metabolism data are discussed. Numerous examples are described including studies in which several types of data are collected simultaneously. Reports that study local metabolism of drug delivered through the probe are also presented.
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Affiliation(s)
- Kenneth E Garrison
- Department of Chemistry, College of the Ozarks, Point Lookout, MO 65726, USA
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Lindberger M, Tomson T, Lars S. Microdialysis sampling of carbamazepine, phenytoin and phenobarbital in subcutaneous extracellular fluid and subdural cerebrospinal fluid in humans: an in vitro and in vivo study of adsorption to the sampling device. PHARMACOLOGY & TOXICOLOGY 2002; 91:158-65. [PMID: 12530465 DOI: 10.1034/j.1600-0773.2002.910402.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The purpose of the study was to determine if binding of the drugs to the sampling equipment during microdialysis would influence the results for carbamazepine, phenytoin and phenobarbital. In vitro experiments with microdialysis catheters and separate parts of catheters were performed to estimate the degree of drug binding to the dialysis equipment. A mathematical model to calculate drug binding and recovery is proposed. In vivo protein unbound carbamazepine concentrations in subcutaneous extracellular fluid at different flow rates (6 patients), unbound carbamazepine (1 patient) and unbound phenobarbital (I patient) in subdural cerebrospinal fluid and subcutaneous extracellular fluid were estimated and the in vivo data were compared to the in vitro results and data generated by the mathematical model. Binding to the soft outlet polyurethane tubing was extensive and variable for phenytoin, which precluded in vivo testing, but limited and more predictable for carbamazepine and phenobarbital. None of the three compounds bound to the hard internaltubing. Phenytoin and phenobarbital did not bind to the dialysis membrane, while a small degree of binding may be present for carbamazepine. In vivo estimates of carbamazepine protein unbound subcutaneous extracellular concentrations by microdialysis, adjusted for binding to the plastic tubing, were 81% of protein unbound plasma concentrations. In single case studies, subdural cerebrospinal fluid and subcutaneous extracellular levels of carbamazepine and phenobarbital were similar and when corrected for binding to the plastic tubings they were also close to protein unbound plasma concentrations. Microdialysis can be used for reliable estimations of protein unbound carbamazepine and possibly phenobarbital concentrations when drug binding to the plastic tubing is considered. Reliable estimation of unbound phenytoin is not possible at present.
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Affiliation(s)
- Martin Lindberger
- Department of Neurology, Karolinska Institute, Huddinge University Hospital, S-14186 Huddinge, Sweden.
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Lindén K, Zhou XX, Ståble L. Validation of microdialysis sampling for oral availability studies by means of a new ganciclovir prodrug. PHARMACOLOGY & TOXICOLOGY 2002; 90:297-302. [PMID: 12403050 DOI: 10.1034/j.1600-0773.2002.900602.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Microdialysis sampling was validated for oral availability studies using ganciclovir (9-(1, 3-dihydroxy-2-propoxymethyl) guanine) and a ganciclovir prodrug (9-(1-L-valyloxy-3-octadecanoyloxy-prop-2-oxymethyl) guanine). Three different techniques were used in the study; microdialysis, blood and urinesampling. The oral uptake (11+/-2%) and the urinary recovery (106+/-5%) were determined. Animals given ganciclovir subcutaneously were subject either to microdialysis and blood sampling or to microdialysis alone. There was no significant difference between microdialysis and blood sampling in terms of blood concentration data, CL, Vd, half-life or AUC by means of Student's t-test. The oral bioavailability of the prodrug was 40+/-7% estimated from microdialysis sampling data and 48+/-4% estimated from urine sampling data. It is concluded that microdialysis is a valid method to use in pharmacokinetic studies of oral availability as well as for basic pharmacokinetic parameter estimation.
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Affiliation(s)
- Karin Lindén
- Department of Clinical Pharmacology, Karolinska Institute, Huddinge Hospital, Sweden.
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Mathy FX, Preat V, Verbeeck RK. Validation of subcutaneous microdialysis sampling for pharmacokinetic studies of flurbiprofen in the rat. J Pharm Sci 2001; 90:1897-906. [PMID: 11745747 DOI: 10.1002/jps.1139] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The objective of this study was to validate subcutaneous (sc) microdialysis sampling to study flurbiprofen pharmacokinetics and plasma protein binding in the awake freely moving rat. A linear microdialysis probe was manufactured using a Hemophane hollow fiber which was tested in vitro and in vivo for the recovery of flurbiprofen and naproxen used as retrodialysis marker. Flurbiprofen was administered intraperitoneally and intravenously at a dose of 20 mg/kg in rats. In both cases, conventional blood sampling and sc microdialysis sampling were simultaneously performed. The microdialysates were analyzed on-line by high-pressure liquid chromatography. Naproxen, which was shown to have a similar in vivo loss by retrodialysis as flurbiprofen (71.5 +/- 0.9% and 71.0 +/- 0.8% respectively, n = 3), was used to continuously monitor probe recovery. Concentration-dependent protein binding of flurbiprofen was demonstrated in vivo based on experiments with a simultaneous sc microdialysis and blood sampling. Values of unbound fraction were similar to those reported previously by intravenous microdialysis sampling, demonstrating that the sc unbound concentrations are very similar to those in the central compartment. There was no significant difference among pharmacokinetic parameters (AUC, CL, t(1/2z), Vd) for total or unbound flurbiprofen determined after intraperitoneal and intravenous administration. Subcutaneous microdialysis is a simple yet powerful tool to study the pharmacokinetics and the in vivo plasma protein binding of flurbiprofen in the awake unrestrained rat.
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Affiliation(s)
- F X Mathy
- Université Catholique de Louvain, Unité de Pharmacie Galénique, Industrielle et Officinale, 7320, 1200 Brussels, Belgium
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Lindberger M, Tomson T, Wallstedt L, Ståhle L. Distribution of valproate to subdural cerebrospinal fluid, subcutaneous extracellular fluid, and plasma in humans: a microdialysis study. Epilepsia 2001; 42:256-61. [PMID: 11240599 DOI: 10.1046/j.1528-1157.2001.26600.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We sought to study the time course of the distribution of valproate (VPA) to subdural cerebrospinal fluid (CSF) in relation to subcutaneous extracellular fluid (ECF) and plasma after a single oral dose and to study the distribution to these three compartments under steady-state conditions. Microdialysis was used to estimate unbound VPA concentrations in subdural CSF and subcutaneous ECF, and blood samples were drawn for estimation of total and unbound VPA plasma concentrations in four patients with drug-resistant partial epilepsy undergoing presurgical evaluation with subdural EEG monitoring. Three patients were given a single oral dose of VPA, and one patient was receiving regular VPA treatment. VPA was analyzed by gas chromatography with flame ionization detection. The distribution of VPA to subdural CSF was rapid (Tmax, 3.5 h in two patients and 5.5 h in one patient) and subject to a minor delay in all three patients compared with that in the subcutaneous tissue ECF (Tmax, 2.5 h in all three patients), which in turn exhibited no evidence of a distribution delay compared with plasma. Subdural CSF levels of VPA were slightly lower than subcutaneous ECF levels (mean ratio, 0.78) and unbound plasma levels (mean ratio, 0.91). VPA rapidly enters the subdural CSF in unbound concentrations marginally lower than those obtained in subcutaneous ECF and plasma. These findings provide a pharmacokinetic rationale for acute administration of VPA. The good correlation between VPA concentrations in subcutaneous ECF and subdural CSF indicates that estimation of unbound VPA concentrations in subcutaneous tissue using microdialysis sampling has the potential to be useful for monitoring purposes.
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Affiliation(s)
- M Lindberger
- Department of Neurology, Karolinska Institute, Huddinge University Hospital, S-14186 Huddinge, Sweden.
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Abstract
The introduction of in vivo microdialysis (MD) to clinical pharmacological studies has opened the opportunity to obtain previously inaccessible information about the drug distribution process to the clinically relevant target site. The aim of this review is to provide a comprehensive overview of the current literature about MD in drug delivery studies from a clinical perspective. In particular the application of MD in clinical--antimicrobial, oncological and transdermal--and neurological research will be described and the scope of MD in pharmacokinetic-pharmacodynamic (PK-PD) studies will be discussed. It is concluded that MD has a great potential for both academic and industrial research, and may become the method of choice for drug distribution studies in humans.
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Affiliation(s)
- M Müller
- Department of Clinical Pharmacology, Division of Clinical Pharmacokinetics, Vienna University School of Medicine, Vienna General Hospital - AKH Wien, Währinger Gürtel 18-20, A-1090, Vienna, Austria.
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Ståhle L. On mathematical models of microdialysis: geometry, steady-state models, recovery and probe radius. Adv Drug Deliv Rev 2000; 45:149-67. [PMID: 11108972 DOI: 10.1016/s0169-409x(00)00108-3] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Commonly used methods for microdialysis recovery measurement are reviewed and the zero flow and no net flux methods are suggested as the most robust in practice. Six different mathematical models of microdialysis assumptions are investigated and compared for varying dialysis probe radius. One transmitter (dopamine), three metabolites (DOPAC, HVA and 5HIAA) and two drugs (caffeine and theophylline) were studied. Histology and functional response to a drug were measured. Deficiencies were demonstrated for several of the models, the one best explaining experimental data includes both passive diffusion and active tissue regulation in a cylindrical symmetric geometry. The recovery decreased with decreasing probe radius but smaller probes caused less tissue injury. It is concluded that a mathematical model of microdialysis must include diffusional and physiological processes in order to accurately account for experimentally observed phenomena. The experiments also demonstrated that, for small brain nuclei, the size of the nucleus may influence the recovery.
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Affiliation(s)
- L Ståhle
- Department of Clinical Pharmacology, Karolinska Institute, Huddinge Hospital, SE-14186, Huddinge, Sweden.
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Lindberger M, Tomson T, Ohman I, Wallstedt L, Ståhle L. Estimation of topiramate in subdural cerebrospinal fluid, subcutaneous extracellular fluid, and plasma: a single case microdialysis study. Epilepsia 1999; 40:800-2. [PMID: 10368083 DOI: 10.1111/j.1528-1157.1999.tb00783.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
PURPOSE To estimate topiramate (TPM) concentrations in subdural cerebrospinal fluid (CSF), subcutaneous extracellular fluid (ECF), and plasma and to study the correlation of TPM concentrations in these three different compartments. METHODS In this single case study of a patient with drug-resistant partial epilepsy undergoing presurgical evaluation with subdural EEG monitoring, we used microdialysis to estimate concentrations of unbound TPM in CSF of the subdural space and ECF of abdominal subcutaneous tissue. Blood samples were drawn for estimation of TPM concentrations in plasma. RESULTS The correlation between unbound TPM concentrations in subdural CSF and abdominal subcutaneous ECF was good. The mean ratio of ECF/CSF TPM concentration was 0.93 (SD+/-0.03) and the correlation coefficient was 0.98. The mean ratio of ECF/total plasma TPM was 0.75 (SD+/-0.06), and the correlation coefficient was 0.99. The mean ratio of CSF/total plasma TPM was 0.81 (SD+/-0.06), and the correlation coefficient was 0.97. CONCLUSIONS Assuming a protein binding of TPM of approximately 13%. it is concluded that, based on nine microdialysis samples from a single subject, TPM levels in the CSF at the cortical surface are approximately the same as the unbound plasma levels. Additional patients should be studied to confirm the results.
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Affiliation(s)
- M Lindberger
- Department of Neurology, Karolinska Institute, Huddinge Hospital, Sweden
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