Biomedical subjects

Amitava Dasgupta

Publications and source records attributed to Amitava Dasgupta.

At least 19 recordsLinked to original sources

PubMed2006

Usefulness of monitoring free (unbound) concentrations of therapeutic drugs in patient management.

Drugs are bound to various serum proteins in different degrees and only unbound or free drug is pharmacologically active. Although free drug concentration can be estimated from total concentration, for strongly bound drugs, prediction of free level is not always possible. Conditions like uremia, liver disease and hypoalbuminemia can lead to significant increases in free drug resulting in drug toxicity even if the concentration of total drug is within therapeutic range. Drug-drug interactions may also lead to a disproportionate increase in free drug concentrations. Elderly patients may have increased free drug concentrations due to hypoalbuminemia. Elevated free phenytoin concentrations have also been reported in patients with AIDS and pregnancy. Currently free drug concentrations of anticonvulsants such as phenytoin, carbamazepine and valproic acid are widely measured in clinical laboratories. Newer drugs such as mycophenolic acid mofetil and certain protease inhibitors are also considered as candidates for monitoring free drug concentration.

Convulsants↗

PubMed2006

Ginseng: Cardiotonic in adult rat cardiomyocytes, cardiotoxic in neonatal rat cardiomyocytes.

Ginsengs are widely used to improve cardiac health and circulation. Loosely termed as ginsengs, Asian (Panax), Siberian and Ashwagandha (Indian Ginseng) Indian ginsengs are prepared from different plants. We tested the popular belief of cardiotonic effects of ginsengs using both neonatal and adult rat cardiomyocytes, comparing extracts from the three ginsengs. Addition of 10% v/v of extract (100 microl of extract/ml of culture medium) of each of the ginsengs resulted in a rapid (<10 s) cessation of beating in neonatal cardiomyocytes due to calcium overload, while sequential dilutions revealed that treatment with a low dose (0.01% v/v, 0.1 microl/ml of the medium) resulted in constant, regular beats (transients), and a slight elevation of diastolic calcium without overload. Addition of extracts to sparking, calcium-tolerant adult cardiomyocytes resulted in initiation of calcium transients, and adult cells were able to tolerate exposure to high concentrations of extract. Cardiotonic effects in adult cells (cardiotoxicity in neonatal cells) were most profound with Asian ginseng (2.6 times that of Siberian ginseng, 1.6 times that of Indian ginseng) probably due to the active ingredients (ginsenosides in Asian, eleutherosides in Siberian and withanolides in Indian) being structurally different. We conclude that fully developed cardiomyocytes are able to accommodate higher doses of ginseng than neonatal cells, and that the effects of ginseng on newly formed, developing myocytes, could be extremely deleterious to the fetus. However, for adults, ginseng might well be a 'tonic' in its ability to increase beating and intramyocytic calcium levels.

Animals↗

PubMed2006

Curriculum content and evaluation of resident competency in clinical pathology (laboratory medicine): a proposal.

Ten years have passed since the Graylyn Conference Report on Laboratory Medicine Clinical Pathology training was issued. Over that period, the Accreditation Council for Graduate Medical Education substantially revised the requirements for training programs; the American Board of Pathology amended both the requirements and the periods needed for certification; and the discipline itself, along with the broader discipline of pathology, evolved significantly. Recently, a curriculum proposal in anatomical pathology was published as a potential template to be used by training programs to help meet these new and evolving needs. Toward the same end, the Academy of Clinical Laboratory Physicians and Scientists has now developed a template for a curriculum in clinical pathology (laboratory medicine), taking into account newly designated and revised areas of residency core competency, the alterations in training requirements promulgated by the Accreditation Council for Graduate Medical Education and American Board of Pathology, and the rapidly developing nature of the discipline itself. The proposed clinical pathology curriculum defines goals and objectives for training, provides guidelines for instructional methods, and gives examples of how outcomes can be assessed. This curriculum is presented as a potentially helpful outline for use by pathology residency training programs.

Clinical Competence↗

PubMed2006

Curriculum content and evaluation of resident competency in clinical pathology (laboratory medicine): a proposal.

Ten years have passed since the Graylyn Conference Report on Laboratory Medicine/Clinical Pathology training was issued. Over that time period, the Accreditation Council for Graduate Medical Education (ACGME) substantially revised the requirements for training programs, the American Board of Pathology (ABP) amended both the requirements and the time periods needed for certification, and the discipline itself, along with the broader discipline of pathology, evolved significantly. Recently, a curriculum proposal in anatomic pathology was published as a potential template to be used by training programs to help meet these new and evolving needs. Toward the same end, the Academy of Clinical Laboratory Physicians and Scientists has now developed a template for a curriculum in clinical pathology (laboratory medicine), taking into account newly designated and revised areas of residency core competency, the alterations in training requirements promulgated by the ACGME and ABP, and the rapidly developing nature of the discipline itself. The proposed clinical pathology curriculum defines goals and objectives for training, provides guidelines for instructional methods, and gives examples of how outcomes can be assessed. This curriculum is presented as a potentially helpful outline for use by pathology residency training programs.

Clinical Competence↗

PubMed2006

Effectiveness of activated charcoal and equilibrium dialysis in removing Asian, American, Siberian and Indian ginseng from human serum.

BACKGROUND: Ginsengs are used by the general population worldwide and toxicity of various ginsengs has been reported. We studied the effectiveness of activated charcoal and in vitro equilibrium dialysis for removal of Asian, American, Siberian and Indian ginseng from human serum by measuring digoxin-like immunoreactivity using the fluorescence polarization immunoassay. METHODS: 1xPBS (phosphate buffered saline) or drug free serum pool was supplemented with Asian, American, Siberian or Indian ginseng extract in amount expected in overdose. The aliquots of supplemented buffer or serum pool were treated with activated charcoal (15 or 50 mg of activated charcoal/ml of buffer/serum) for 5, 10, 20 and 30 min and digoxin-like immunoreactivities were compared with the original specimens. Other drug free serum pools were also supplemented with various ginsengs and then passed through a small column packed with activated charcoal or subjected to in vitro equilibrium dialysis against phosphate buffer at pH 7.4. RESULTS: Complete removal of digoxin-like immunoreactivity from buffer solution or serum pool supplemented with various ginsengs can be achieved by treatment with activated charcoal. Moreover, when serum pools supplemented with various ginsengs were passed through columns packed with activated charcoal, we observed complete removal of digoxin-like immunoreactivity. In addition, significant removal of digoxin-like immunoreactivity was observed when serum pools supplemented with ginsengs were subjected to equilibrium dialysis for 24 h. CONCLUSIONS: Removal of digoxin-like immunoreactivity from buffer solution or serum due to the presence of ginsengs can be achieved by treatment with activated charcoal in vitro but complete removal of digoxin-like activity from serum is not possible even after 24 h of equilibrium dialysis.

Americas↗

PubMed2006

St. John's wort does not interfere with therapeutic drug monitoring of 12 commonly monitored drugs using immunoassays.

St. John's wort, a popular herbal remedy for depression, is known to interact with many Western drugs because of the ability of its components to induce liver enzymes. Lower concentrations of various drugs due to increased clearance have been reported. Because immunoassays are commonly used in clinical laboratories for therapeutic drug monitoring, we studied the potential interference of St. John's wort with commonly monitored therapeutic drugs. Drug-free serum pools were supplemented with St. John's wort to achieve in vitro St. John's wort concentrations mimicking in vivo concentrations after both recommended use and overdose. Concentrations of digoxin, tricyclic antidepressants (TCAs), phenytoin, carbamazepine, theophylline, valproic acid, quinidine, phenobarbital, procainamide, and N-acetyl procainamide were measured in serum. Pooled serum specimens from patients who were taking a particular drug were also supplemented in vitro with concentrations of St. John's wort to investigate whether observed concentrations changed after supplementation with St. John's wort. The effect of St. John's wort on cyclosporine and tacrolimus (FK 506) was studied in whole blood. We found no significant interference from St. John's wort with any assay studied. Moreover, when drug-free serum was supplemented with very high concentrations of hypericin (2 microg/mL) and hyperforin (2 microg/mL) pure standard, we observed no apparent drug level with any immunoassay. The presence of both hypericin and hyperforin was also confirmed by thin layer chromatography (TLC) in both preparations of St. John's wort. We conclude that immunoassays may be used to measure levels of therapeutic drugs in patients who self-medicate with St. John's wort.

Antidepressive Agents, Tricyclic↗

PubMed2006

A new enzyme-linked chemiluminescent immunosorbent digoxin assay is virtually free from interference of spironolactone, potassium canrenoate, and their common metabolite canrenone.

Spironolactone and potassium canrenoate (aldosterone antagonist diuretics) are sometimes used in conjunction with digoxin for patient management. Spironolactone, potassium canrenoate, and their common metabolite canrenone interfere with serum digoxin measurement using various immunoassays. Recently a new enzyme-linked chemiluminescent immunosorbent digoxin assay (ECLIA-Digoxin) became commercially available for application on the ADVIA IMS 800i modular system (Bayer HealthCare, Tarrytown, NY). We investigated the potential interference of spironolactone and related compounds in this assay by comparing the results with the fluorescence polarization immunoassay (FPIA), which is known to have significant cross-reactivity with these compounds as well as a turbidimetric assay for digoxin with no known cross-reactivity with spironolactone and related compounds. Aliquots of drug free serum were supplemented with therapeutic and above therapeutic concentrations of spironolactone, canrenone, and potassium canrenoate, and apparent digoxin concentrations were measured. No apparent digoxin concentration was observed using the ECLIA-Digoxin or turbidimetric assay. When serum pools prepared from patients receiving digoxin were further supplemented with these compounds, we observed no significant change in digoxin concentrations in the presence of these compounds with the ECLIA-Digoxin. We conclude that this assay is virtually free from interferences from spironolactone, potassium canrenoate and their common metabolite canrenone.

Artifacts↗

PubMed2006

The new enzyme-linked immunosorbent digoxin assay on the ADVIA Integrated Modular System is virtually free from oleander interference.

Despite known toxicity of oleander, this product is used in herbal preparations. Oleander interferes with various digoxin immunoassays. It is possible that a person taking digoxin also may take oleander-containing herbal products, and digoxin immunoassays interfering with oleander cannot be used for therapeutic monitoring of digoxin. Recently, Bayer Diagnostics introduced a new enzyme-linked chemiluminescent immunosorbent digoxin assay for application on the ADVIA IMS System (ECLIA-digoxin). We studied potential interference of oleander with this new digoxin assay and found that this assay is virtually free from oleander interference. When aliquots of drug-free serum pools were supplemented with ethyl alcohol extract of oleander leaf or pure oleandrin standard, we observed significant apparent digoxin concentration when measured by the fluorescence polarization immunoassay (FPIA) but minimal digoxin-like immunoreactivity using the ECLIA digoxin assay. Because cross-reactivity should be studied in the presence of primary analyte, we prepared 2 serum pools using sera from patients receiving digoxin. Then aliquots of first digoxin pool were supplemented with oleandrin standard and aliquots of second digoxin pool with oleander extract. We observed significant increases in apparent digoxin concentration in the presence of both oleandrin and oleander extract using the FPIA. However, we observed no statistically significant change in digoxin concentration when ECLIA digoxin assay was used, indicating that this assay is virtually free from oleander interference.

Cardenolides↗

PubMed2006

False-positive serum tricyclic antidepressant concentrations using fluorescence polarization immunoassay due to the presence of hydroxyzine and cetirizine.

A recent report indicates that hydroxyzine and its active metabolite cetirizine interfere with the PENTINA carbamazepine assay. The potential interference of hydroxyzine and cetirizine with the fluorescence polarization immunoassay (FPIA) and CEDIA assay of carbamazepine as well as with the fluorescence polarization immunoassay of tricyclic antidepressants (TCA) was studied. Aliquots of drug-free serum pools were supplemented with various concentrations of hydroxyzine and cetirizine representing therapeutic, mild to moderate toxic as well as very toxic concentrations. Then apparent carbamazepine and TCA concentrations were measured by immunoassays. Although no interference of hydroxyzine and cetirizine was observed with carbamazepine assays (FPIA and CEDIA), significant apparent TCA concentrations were observed when aliquots of drug-free serum were supplemented with hydroxyzine or cetirizine. Mathematical formula was devised to predict hydroxyzine and/or cetirizine concentration in serum based on observed apparent TCA levels. Hydroxyzine and cetirizine also falsely increased total TCA values when aliquots of serum pool prepared from patients receiving TCA were further supplemented with these drugs. In conclusion, hydroxyzine and cetirizine do not interfere with the FPIA and CEDIA carbamazepine assays but interfere with the measurement of total TCA using the FPIA.

Antidepressive Agents, Tricyclic↗

PubMed2006

New enzyme-linked chemiluminescent immunosorbent digoxin assay is free from interference of Chinese medicine DanShen.

DanShen is a traditional Chinese medicine indicated for cardiovascular diseases. The potential interference of DanShen with serum digoxin measurement was investigated using a new enzyme-linked chemiluminescent immunosorbent (ECLIA) digoxin assay. Aliquots of drug-free serum were supplemented with ethyl acetate extract of DanShen (4 different brands studied), and apparent digoxin concentrations were measured by the ECLIA as well as fluorescence polarization immunoassay (FPIA) and a turbidimetric assay for comparison. Mice were also fed 4 DanShen preparations and apparent digoxin concentrations were subsequently measured. In another experiment, serum pools containing digoxin were further supplemented with DanShen extracts and digoxin concentrations were measured again by all 3 assays. No apparent digoxin concentration was observed when aliquots of drug-free serum pools were supplemented with DanShen and digoxin concentrations were measured by the ECLIA or the turbidimetric assay. In contrast, significant apparent digoxin concentrations were observed using FPIA, and the highest apparent digoxin concentration was observed with brand 4 of DanShen extract. Similarly, when mice were fed with this herb, significant apparent digoxin concentrations were also observed using FPIA, but neither ECLIA nor turbidimetric assay showed any apparent digoxin concentration. When aliquots of digoxin pool were further supplemented with various DanShen extract, the apparent digoxin concentrations were significantly increased when FPIA was used. In contrast, digoxin concentrations in the presence of DanShen extract compared well with the digoxin concentration of the original pool when ECLIA or turbidimetric assay was used. We conclude that DanShen does not interfere with serum digoxin measurement using a more recently released ECLIA digoxin assay.

Animals↗

PubMed2006

Effect of plantain on therapeutic drug monitoring of digoxin and thirteen other common drugs.

INTRODUCTION: Plantain, a herbal remedy, has been reported to interfere with therapeutic drug monitoring of digoxin. We evaluated three commercially available plantain products for potential interference with therapeutic drug monitoring of digoxin and 13 other common drugs. METHOD: Dry content of plantain capsule or plantain leaf was extracted with either methanol or ethanol:water (60:40 by volume), added to drug-free serum and apparent digoxin was measured by both fluorescence polarization immunoassay and microparticle enzyme immunoassay. Using immunoassays, we also measured apparent concentrations of 13 other drugs (tobramycin, procainamide, tricyclic antidepressants, quinidine, carbamazepine, phenytoin, theophylline, valproic acid, amikacin, gentamycin, phenobarbital, salicylate and acetaminophen [paracetamol]) due to the presence of plantain. In separate experiments, a serum pool prepared from patients receiving digoxin was further supplemented with plantain and observed digoxin values were compared with original digoxin concentration. The presence of any cardiac glycoside in plantain was also investigated using thin layer chromatography (TLC). RESULTS: We observed no apparent digoxin in the presence of plantain in serum. Moreover, when aliquots of digoxin serum pool were supplemented with various amounts of plantain, the observed digoxin concentrations in the presence of plantain compared well with original digoxin concentration. TLC analysis did not show the presence of either digoxin or digitoxin in plantain products studied. Moreover, plantain did not affect immunoassay results of the 13 other drugs studied. CONCLUSIONS: The plantain products studied did not interfere with therapeutic drug monitoring of digoxin as well as 13 other commonly monitored drugs.

Cardiac Glycosides↗

PubMed2006

Curriculum content and evaluation of resident competency in clinical pathology (laboratory medicine): a proposal.

Ten years have passed since the Graylyn Conference Report on Laboratory Medicine/Clinical Pathology training was issued. During that period, the Accreditation Council for Graduate Medical Education (ACGME) substantially revised the requirements for training programs, the American Board of Pathology (ABP) amended the requirements and the time needed for certification, and the discipline itself along with the broader discipline of pathology, evolved significantly. Recently, a curriculum proposal in anatomic pathology was published as a potential template to be used by training programs to help meet these new and evolving needs. Toward the same end, the Academy of Clinical Laboratory Physicians and Scientists has developed a template for a curriculum in clinical pathology (laboratory medicine), taking into account newly designated and revised areas of residency core competency, the alterations in training requirements promulgated by the ACGME and ABP, and the rapidly developing nature of the discipline itself The proposed clinical pathology curriculum defines goals and objectives for training, provides guidelines for instructional methods, and gives examples of how outcomes can be assessed. This curriculum is presented as a potentially helpful outline for use by pathology residency training programs.

Clinical Competence↗

PubMed2006

Herbal remedies: effects on clinical laboratory tests.

CONTEXT: Complementary and alternative medicine (herbal medicines) can affect laboratory test results by several mechanisms. OBJECTIVE: In this review, published reports on effects of herbal remedies on abnormal laboratory test results are summarized and commented on. DATA SOURCES: All published reports between 1980 and 2005 with the key words herbal remedies or alternative medicine and clinical laboratory test, clinical chemistry test, or drug-herb interaction were searched through Medline. The authors' own publications were also included. Important results were then synthesized. DATA SYNTHESIS: Falsely elevated or falsely lowered digoxin levels may be encountered in a patient taking digoxin and the Chinese medicine Chan Su or Dan Shen, owing to direct interference of a component of Chinese medicine with the antibody used in an immunoassay. St John's wort, a popular herbal antidepressant, increases clearance of many drugs, and abnormally low cyclosporine, digoxin, theophylline, or protease inhibitor concentrations may be observed in a patient taking any of these drugs in combination with St John's wort. Abnormal laboratory results may also be encountered owing to altered pathophysiology. Kava-kava, chaparral, and germander cause liver toxicity, and elevated alanine aminotransferase, aspartate aminotransferase, and bilirubin concentrations may be observed in a healthy individual taking such herbal products. An herbal product may be contaminated with a Western drug, and an unexpected drug level (such as phenytoin in a patient who never took phenytoin but took a Chinese herb) may confuse the laboratory staff and the clinician. CONCLUSIONS: Use of alternative medicines may significantly alter laboratory results, and communication among pathologists, clinical laboratory scientists, and physicians providing care to the patient is important in interpreting these results.

Clinical Laboratory Techniques↗

PubMed2005

Analytical performance evaluation of a new turbidimetric immunoassay for valproic acid on the ADVIA 1650 analyzer: effect of gross hemolysis and high bilirubin.

Valproic acid is an anticonvulsant that requires careful therapeutic drug monitoring. Valproic acid is also used in psychiatric patients. Bayer Diagnostics (Tarrytown, NY) recently marketed a turbidimetric immunoassay for monitoring valproic acid concentrations in serum or plasma using the ADVIA 1650 analyzer. We evaluated the performance of this new assay by comparing it with a widely used fluorescence polarization immunoassay (FPIA) on the AxSYM analyzer (Abbott Laboratories, Abbott Park, IL). The total coefficient of variation (CV) for the low control of this new assay was 6.8% (mean = 30.7, SD = 2.1 microg/mL, n = 44) while the corresponding CVs for the medium and high controls were 3.3% (mean = 81.0, SD = 2.7 microg/mL, n = 44) and 5.9% (mean = 142.9, SD = 8.4 microg/mL, n = 44), respectively. The assay is linear up to a serum valproic acid concentration of 170 microg/mL, and the detection limit is 4.4 microg/mL. We observed an excellent correlation between the FPIA of valproic acid and the turbidimetric assay using specimens from 52 different patients who were receiving valproic acid. Using the valproic acid concentrations obtained by the FPIA as the x-axis, and the corresponding valproic acid concentrations obtained by the turbidimetric assay as the y-axis, we developed the following regression equation: y = 1.03 x+1.55 (r = 0.98). With this new assay, high concentrations of bilirubin (unconjugated 30 mg/dL and conjugated 30 mg/dL) and gross hemolysis (4+, hemoglobin: 1,500 mg/dL) have no effect on measurements of valproic acid concentration. We conclude that the new turbidimetric assay for valproic acid can be used for routine therapeutic drug monitoring of valproic acid in clinical laboratories.

Anticonvulsants↗

PubMed2005

Analytic performance evaluation of a new turbidimetric immunoassay for carbamazepine on the ADVIA 1650 analyzer: effect of carbamazepine 10,11-epoxide.

Carbamazepine, an anticonvulsant, requires therapeutic drug monitoring. Recently Bayer HealthCare, Diagnostics Division released a turbidimetric immunoassay of carbamazepine on the ADVIA 1650 analyzer. We evaluated the analytic performance of this assay by comparing values obtained with this new assay in sera of 54 patients receiving carbamazepine with the values obtained by using a widely used fluorescence polarization immunoassay (FPIA) and a chemiluminescent immunoassay (CLIA). The new turbidimetric immunoassay for carbamazepine showed excellent precision. The low control showed a total CV of 4.9% (mean 2.86, SD 0.14 microg/mL), the medium control demonstrated a total CV of 3.5% (mean 7.79, SD 0.27 microg/mL), and the high control showed a total CV of 4.8% (mean 16.15, SD 0.78 microg/mL). The assay was linear up to a carbamazepine concentration of 20 microg/mL. The assay showed excellent dilution recovery and recovery of samples supplemented with carbamazepine (mean recovery 102.2%). We observed an excellent correlation between the values obtained by the FPIA (x-axis) assay and the new turbidimetric (y-axis) assay (y = 0.96 x - 0.46, r = 0.99, n = 54). We also observed excellent correlation between the values obtained by the CLIA (x-axis) and the turbidimetric (y-axis) assay (y = 1.10 x -0.32, r = 0.99, n = 54). However, the slope of 1.10 was higher than the slope of 0.96 observed with the regression equation obtained by using values obtained by the FPIA and the turbidimetric assay. The positive bias obtained with the new turbidimetric assay compared with the CLIA assay resulted from lower cross reactivity of carbamazepine 10,11-epoxide, the active metabolite of carbamazepine, with CLIA. On the other hand, the cross reactivity of the metabolite is similar between the new turbidimetric assay and the FPIA assay. We conclude that the new turbidimetric assay can be used for routine monitoring of carbamazepine in clinical laboratories.

Carbamazepine↗

PubMed2005

New enzyme-linked immunosorbent digoxin assay on the ADVIA IMS 800i system is virtually free from interference of endogenous digoxin-like immunoreactive factors.

Endogenous digoxin-like immunoreactive factors (DLIF) may crossreact with antidigoxin antibody and falsely elevate immunoassay results. Recently, a new enzyme-linked immunosorbent chemiluminescent assay for digoxin has been available for use on the ADVIA IMS (Integrated Modular System) 800i analyzer (Bayer Diagnostics). We studied potential interference of DLIF with this new digoxin assay. We analyzed 30 serum specimens from patients who have pathologic conditions that may increase serum DLIF concentrations. These patients were never exposed to digoxin or other agents that may lead to a measurable digoxin concentration. We also analyzed 10 specimens from neonates, 10 cord blood specimens, and 10 amniotic fluid specimens. Apparent digoxin concentrations were measured using the new enzyme-linked immunosorbent digoxin assay (IMS-Digoxin), a fluorescence polarization immunoassay (FPIA), and also a chemiluminescent immunoassay (CLIA, run on ACS:180(R) system from Bayer Diagnostics). We observed measurable apparent digoxin levels with the FPIA in 4 uremic patients (range 0.21-0.36 ng/mL, digoxin equivalent), 7 patients with liver disease (range 0.21-0.72 ng/mL), and 3 patients in the third trimester of pregnancy (0.22-0.66 ng/mL). We also observed measurable DLIF concentrations with the FPIA in 2 neonates (0.22 and 0.36 ng/mL), 5 cord blood specimens (range 0.21-1.18 ng/mL), and 5 amniotic fluid specimens (0.21-0.50 ng/mL). None of these DLIF-positive specimens showed any measurable digoxin concentration using the IMS-Digoxin or the CLIA assay. When serum specimens containing elevated concentrations of DLIF but no digoxin (as measured by FPIA) were supplemented with known concentrations of digoxin, we observed falsely elevated digoxin concentrations, as expected, only by the FPIA. In contrast, we observed a good agreement between the target and observed concentrations when the new IMS-Digoxin or the CLIA assay was used. We conclude that the IMS-Digoxin assay is free from interference of DLIF.

Adult↗

PubMed2005

Analytic performance evaluation of a new turbidimetric immunoassay for phenytoin on the ADVIA 1650 analyzer: effect of phenytoin metabolite and analogue.

Phenytoin is an anticonvulsant that requires therapeutic drug monitoring. Recently, Bayer HealthCare, Diagnostics Division released a turbidimetric immunoassay of phenytoin on the ADVIA 1650 analyzer. We evaluated the analytic performance of this assay by comparing values obtained in 52 patients receiving Phenytoin using this new assay with the values obtained by using a widely used fluorescence polarization immunoassay (FPIA). The new turbidimetric immunoassay for phenytoin showed the following imprecision with the low, medium, and high controls: total CV of 5.2% (mean 4.81 microg/mL), 3.7% (mean 16.24 microg/mL), and 4.1% (mean 22.65 microg/mL), respectively. The detection limit of the assay was 0.79 microg/mL, and the assay was linear up to a phenytoin concentration of 46.1 microg/mL. The assay showed excellent dilution recovery and recovery of spiked samples (mean recovery 101.4% and 94.4%, respectively). We observed an excellent correlation between the values obtained by the FPIA (x-axis) assay and the new turbidimetric (y-axis) assay (y=1.06 x-0.61, r=0.98, n=52). We also determined the cross-reactivity of 5-(p-hydroxyphenyl)-5-phenylhydantoin (HPPH), a major metabolite of phenytoin, and of oxaprozine, an analogue with a similar chemical structure to phenytoin, in both phenytoin assays. Both assays showed almost no cross-reactivity to oxaprozine and only small (5%-8%) cross-reactivity to HPPH. We also found that the turbidimetric assay was free from interference at least up to 1200 mg/dL of hemolysis, 30 mg/dL of free bilirubin, 34.5 mg/dL of conjugated bilirubin, and 750 mg/dL of triglyceride (Intralipid). When a drug-free serum was followed by a serum sample containing 38.5 microg/mL of phenytoin, no sample probe carryover effect was observed. We conclude that the new turbidimetric assay can be used for routine monitoring of phenytoin in clinical laboratories.

Bilirubin↗

PubMed2005

Effect of ultrafiltrate volume on determination of free phenytoin concentration.

Monitoring free phenytoin concentration is clinically useful for patients with uremia, hepatic disease, hypoalbuminemia, and related conditions. Free phenytoin is commonly measured by immunoassay in the protein-free ultrafiltrate prepared by centrifuging serum for 20-30 minutes, using an appropriate ultrafiltration device. We studied the effect of centrifugation time (15-40 minutes) and protein concentrations on ultrafiltration volume, and the related effects on measured free phenytoin concentrations. Temperature was ambient for all studies. The ultrafiltration volumes were directly proportional to centrifugation time and were inversely proportional to the protein concentrations. Although ultrafiltration volume significantly increased with longer centrifugation time, the measured free phenytoin concentrations did not increase proportionately. The concentration of phenytoin in the residual serum retained in the ultrafiltration device did not change proportionally either. Therefore, equilibrium of phenytoin concentrations between the ultrafiltrate and retentate was maintained, regardless of centrifugation time or protein concentration.

Blood Proteins↗