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Biomedical subjects

P M Kabra

Publications and source records attributed to P M Kabra.

At least 19 recordsLinked to original sources
PubMed1990

Extended life for blood serum analysis columns using dual zone chromatographic materials.

Column lifetimes of novel dual zone material (DZM) adsorbents were evaluated by direct serum injection analysis for drugs by high-performance liquid chromatography. Porous silica was converted to DZMs in which the outer zone was enriched in an immobilized lipophobic moiety, the perfluorobutylethylenesilyl group, and the internal zone was enriched in a lipophilic octadecylsilyl group. Performance during repetitive serum analyses for phenobarbital and carbamezepine by reverse phase HPLC was compared to that of control adsorbents of the same composition but without the dual zone distribution. The DZM columns had lifetimes up to 4 times longer than the controls. Furthermore, under these conditions, even the control columns had considerably longer lifetimes than conventional but more retentive reverse phase columns. The DZM column lifetimes also appeared to be comparable to or better than those of the recently introduced Pinkerton packings and have much better adsorbent design flexibility and pH operating latitute.

Blood Chemical Analysis↗
PubMed1990

Laboratory monitoring of cyclosporine levels: guidelines for the dermatologist.

The following guidelines are recommended for laboratory monitoring of circulating levels of cyclosporine in dermatology patients. Measurements should be determined as trough levels in whole blood, not plasma or serum. The measurements should be performed with an assay that is specific for the parent cyclosporine compound (e.g., a high-performance liquid chromatography method or a specific monoclonal immunoassay). The results of nonspecific immunoassays that detect cyclosporine as well as its metabolites are difficult to interpret and cannot readily be compared among different studies or laboratories. In psoriasis patients, the circulating concentration of cyclosporine does not correlate reliably with the therapeutic response. Some patients may achieve an excellent response with blood levels in the range of 50 ng/ml; others may show little or no response despite blood levels as high as 200 ng/ml. In patients with a poor clinical response, monitoring of cyclosporine levels may be useful to confirm that the drug has been taken and may provide an estimate of the degree of absorption and metabolism of the parent compound. Because an upper limit of safety for the circulating concentration of cyclosporine has not been clearly defined, one should attempt to achieve a therapeutic response with the lowest possible dose. Clinicians must carefully monitor patients for signs of cyclosporine toxicity, regardless of the circulating concentration of the drug. Whole blood levels exceeding 250 ng/ml should be avoided.

Blood Specimen Collection↗
PubMed1990

Cosegregation of the renin allele of the spontaneously hypertensive rat with an increase in blood pressure.

The spontaneously hypertensive rat (SHR) exhibits alterations in the renin-angiotensin-aldosterone system which are similar to those that characterize patients with "nonmodulating" hypertension, a common and highly heritable form of essential hypertension. Accordingly, we determined whether the inheritance of a DNA restriction fragment length polymorphism (RFLP) marking the renin gene of the SHR was associated with greater blood pressure than inheritance of a RFLP marking the renin gene of a normotensive control rat. In an F2 population derived from inbred SHR and inbred normotensive Lewis rats, we found the blood pressure in rats that inherited a single SHR renin allele to be significantly greater than that in rats that inherited only the Lewis renin allele. To the extent that the SHR provides a suitable model of "nonmodulating" hypertension, these findings raise the possibility that a structural alteration in the renin gene, or a closely linked gene, may be a pathogenetic determinant of increased blood pressure in one of the most common forms of essential hypertension in humans.

Alleles↗
PubMed1988

Clinical analysis of individual steroids by column liquid chromatography.

At present, there are various LC methods available for the determination of estriol, aldosterone, and cortisol in urine, and for cortisol, cortisone, 11-deoxycortisol, corticosterone, 17-hydroxyprogesterone, estriol, vitamin D isomers, and various exogenous glucocorticoids in serum. The LC methods are more specific than the currently available RIAs or homogenous immunoassays. However, whether the data obtained by more specific LC methods are better clinically than the commonly used immunoassays for these steroids must still be proven. In this review, I have critically evaluated various LC methods currently available for the routine determination of clinically important steroids in the clinical laboratories. A complete evaluation and advantages and disadvantages of alternative techniques are beyond the scope of this review. However, the readers are urged to refer to the review articles and chapters listed in the reference section.

Chromatography, Liquid↗
PubMed1987

Liquid chromatographic determination of cyclosporine in whole blood with the advanced automated sample processing unit.

We describe a rapid, precise, cost-effective, and accurate isocratic liquid chromatographic (LC) procedure for determining cyclosporine in whole blood. The cyclosporine is extracted from 0.5 ml of whole blood together with 200 micrograms of cyclosporin D, added per liter as internal standard, by using an Advanced Automated Sample Processing (AASP) unit. The on-line solid-phase extraction is performed on an octasilane sorbent cartridge which is interfaced with a Perkin-Elmer 83 X 4.6 mm I.D. cartridge column, packed with 3-micron octadecyl packing. The column is eluted with a mobile phase containing acetonitrile-water (13:7) at a flow-rate of 1.0 ml/min at a column temperature of 70 degrees C. The column effluent is monitored at 210 nm. The absolute recovery of cyclosporine exceeded 87% and the linearity extended up to 2000 micrograms/l. Within-run and day-to-day coefficients of variation were less than 8%. The correlation between AASP-LC and manual Bond-Elut extraction-LC method was excellent (r = 0.97).

Autoanalysis↗
PubMed1987

Automated solid-phase extraction and liquid chromatography for assay of cyclosporine in whole blood.

In this rapid, precise, accurate, cost-effective, automated liquid-chromatographic procedure for determining cyclosporine in whole blood, the cyclosporine is extracted from 0.5 mL of whole blood together with 300 micrograms of cyclosporin D per liter, added as internal standard, by using an Advanced Automated Sample Processing unit. The on-line solid-phase extraction is performed on an octasilane sorbent cartridge, which is interfaced with a RP-8 guard column and an octyl analytical column, packed with 5-microns packing material. Both columns are eluted with a mobile phase containing acetonitrile/methanol/water (53/20/27 by vol) at a flow rate of 1.5 mL/min and column temperature of 70 degrees C. Absolute recovery of cyclosporine exceeded 85% and the standard curve was linear to 5000 micrograms/L. Within-run and day-to-day CVs were less than 8%. Correlation between automated and manual Bond-Elut extraction methods was excellent (r = 0.987). None of 18 drugs and four steroids tested interfered.

Chromatography, High Pressure Liquid↗
PubMed1986

Solid-phase extraction and determination of dansyl derivatives of unconjugated and acetylated polyamines by reversed-phase liquid chromatography: improved separation systems for polyamines in cerebrospinal fluid, urine and tissue.

A sensitive and simple liquid chromatographic assay with fluorometric detection for unconjugated and acetylated polyamines in biological fluids is described. After precolumn derivatization with dansyl chloride, unconjugated polyamines and acetylated polyamines were extracted by elution from a Bond-Elut C18 column and then separated on a reversed-phase column with gradient elution. The complete analysis of unconjugated putrescine, spermidine, and spermine in either hydrolyzed urine, cerebrospinal fluid or tissue could be accomplished within 20-26 min, while the simultaneous analysis of unconjugated polyamines and monoacetylpolyamines could be completed within 40 min. Unhydrolyzed urine and cerebrospinal fluid required a Bond-Elut cation-exchange clean-up before dansylation. Standard curves for the assay were linear up to 20 nmol/ml, and the within-day and day-to-day coefficients of variation were between 1.1 and 4.6% and between 1.6 and 11.8%, respectively. Results obtained with the method were compared with results obtained with a well established modified amino acid analyzer method for urine, tissue and cerebrospinal fluid samples. The correlation coefficients between these two methods were in the range 0.933-0.996. Detection limits between 50 and 150 fmol were achieved for unconjugated and acetylated polyamines. Of more than twenty drugs and amines tested for possible interference with the assay, only normetanephrine was found to have the same retention time as the internal standard 1,6-diaminohexane.

Acetylation↗
PubMed1986

Formation of bilirubin conjugates in human newborns.

Bilirubin conjugates in the serum of newborn human infants were investigated using the alkaline methanolysis-high-performance liquid chromatography method, a specific and sensitive method for measurement of unconjugated bilirubin and bilirubin mono- and diester conjugates. Serum samples were analyzed from 13 premature infants, 11 full term newborns, 22 healthy adults, seven pregnant women at term and their corresponding infants cord blood at delivery, 46 cord blood specimens obtained at unselected deliveries, three cord bloods from infants with maternal-fetal blood group incompatibility, and two cord bloods from infants with intrauterine hypoxia. Bilirubin conjugates were not detectable in the healthy adults, maternal blood, or in the cord blood specimens except from infants with blood group incompatibility or intrauterine hypoxia. The two isomeric monoconjugates of bilirubin appeared in serum during the first 24 to 48 postnatal h in both premature and full term infants, followed by the diconjugate on the 3rd day. Conjugated esters accounted for 2 to 5% of the total bilirubin, with the diconjugate constituting 21% of total conjugated pigment (day 3). In all instances, the unconjugated serum bilirubin concentration had increased to at least 2 mg/dl in the course of physiologic neonatal hyperbilirubinemia before bilirubin conjugates became detectable. Both premature and full term human infants displayed the identical pattern of bilirubin conjugation in serum.

Adult↗
PubMed1986

Liquid-chromatographic measurements of inosine, hypoxanthine, and xanthine in studies of fructose-induced degradation of adenine nucleotides in humans and rats.

We applied a sensitive, precise liquid-chromatographic method of analysis for inosine, hypoxanthine, and xanthine to the study of fructose metabolism in humans and in rats. In the rat, intravenous loading with fructose induced, within minutes, substantial increases in the concentrations of inosine, hypoxanthine, and xanthine in plasma and urine. In plasma, these concentrations peaked after 5 min, then practically disappeared within 10 min. As expected, the fructose-induced increase in hypoxanthine was greatly amplified by pretreating the rats with allopurinol, an inhibitor of xanthine oxidase. In a healthy human subject, intravenous administration of fructose also induced prompt, substantial, and rapidly reversing increases in the concentrations of these metabolites of adenine nucleotides in plasma. The finding that fructose induced almost-immediate increases in the plasma concentrations of inosine, hypoxanthine, and xanthine is consistent with previous studies in rats, in which parenteral administration of fructose induced almost-immediate decreases of total adenine nucleotides (ATP + ADP + AMP) in the liver, and increased concentrations of uric acid and allantoin in the plasma.

Adenine Nucleotides↗
PubMed1985

Liquid chromatographic analysis of clonazepam in human serum with solid-phase (Bond-Elut) extraction.

A simple, sensitive, selective and precise liquid-column chromatographic assay for clonazepam is described, in which 1 ml of serum containing 50 micrograms/l methylclonazepam as an internal standard is extracted by elution from a Bond-Elut column with 400 microliter of methanol. An aliquot of the eluate is injected on to a reversed-phase column and eluted with a mobile phase of acetonitrile--phosphate buffer (30:70) at a flow-rate of 2 ml/min at a column temperature of 50 degrees C. Detection is at 254 nm. Chromatography is complete in 12 min. A sensitivity of 2 ng/ml is attained when 1 ml of serum is extracted. Analytical recovery of the clonazepam added to serum ranged from 91% to 99% with a coefficient of variation of 6.0%. This assay for clonazepam has good precision, with coefficients of variation of 11% at 15 ng/ml and 2.6% at 50 ng/ml. There was no interference from any of the commonly used antiepileptics.

Benzodiazepinones↗
PubMed1985

Urinary catecholamines in iron-deficient rats at rest and following surgical stress.

The purpose of this study was to determine catecholamine concentrations both at rest and in response to a surgical stress in iron-deficient and control rats. Twenty-one-day-old rats were randomized to one of two groups which received a diet containing either 6 or 50 mg iron/kg. Three to five days later, when anemia was first detectable, urinary norepinephrine (NE) concentrations were already significantly elevated in the iron-deficient compared to control rats. In contrast, urinary dopamine (DA) became depressed after 10 days of the iron-deficient regimen. At 38 days of age, both groups were subjected to a surgical stress. NE and DA became elevated over baseline values in both diet groups during the 24-h period following surgery; NE remained significantly higher and DA significantly lower in the iron-deficient than in the control group. We conclude that changes in urine catecholamine concentration occur early in the development of iron deficiency and that they are characteristic of both baseline and stress conditions.

Animals↗
PubMed1985

Solid-phase extraction and liquid chromatography for improved assay of cyclosporine in whole blood or plasma.

In this simple, precise, accurate, and specific isocratic liquid chromatographic procedure for determining cyclosporine, the cyclosporine is extracted from 1 mL of whole blood or from plasma, with 500 micrograms of cyclosporin D added per liter as internal standard, by elution from a Bond-ElutTM C18 extraction column with 300 microL of a mixture of ethanol and tetrahydrofuran. A 100-microL aliquot of the eluate, injected onto a cyano-phase analytical column, is eluted with a mixture of acetonitrile and pH 7.0 phosphate buffer at a flow rate of 1.0 mL/min and at 50 degrees C. Detection is at 210 nm. The chromatography is complete in less than 14.0 min. The method can measure less than 10.0 micrograms/L. Analytical recovery of cyclosporine added to whole blood ranged from 99 to 109% for concentrations up to 2000 micrograms/L. Between-run CVs ranged from 6.4 to 6.6%. None of numerous drugs and steroids tested interfered. Results by radioimmunoassay exceeded by 20 to 350% those measured by the present method.

Chromatography, Liquid↗
PubMed1983

Liquid chromatography with fluorometric detection of unconjugated estriol in serum of pregnant women.

We describe a fluorometric liquid chromatographic assay for the measurement of unconjugated estriol in the serum of pregnant women. Estriol is extracted into methylene chloride/propanol-2 from serum by use of a Clin-Elut extraction column, the extract evaporated, and the residue redissolved in mobile phase. An aliquot is injected onto the liquid chromatograph and the estriol is separated on a reversed-phase octyl column with a mobile phase consisting of acetonitrile/phosphate buffer (23:77, v/v). The effluent is monitored by fluorescence detection. The proposed method offers good reproducibility (CV less than 7%), sensitivity (less than 0.5 micrograms/l), and accuracy. Of many drugs and steroids tested, only 16,17-epiestriol interferes with the estriol analysis.

Chromatography, Liquid↗
PubMed1983

Simultaneous very fast liquid-chromatographic analysis of ethosuximide, primidone, phenobarbital, phenytoin, and carbamazepine in serum.

We describe a sensitive, specific, and very fast liquid-chromatographic assay for simultaneously determining five anticonvulsants (ethosuximide, primidone, phenobarbital, phenytoin, and carbamazepine) by using commercially available 5- or 3-microns particle size reversed-phase columns and a microflow-cell-equipped ultraviolet detector. The anticonvulsant drugs are extracted from 200 microL of serum containing 50 mg of cyclopal per liter as an internal standard, by elution from a Bond-Elut (Analytichem International, Harbor City, CA 90710) column with 300 microL of methanol. A 5-microL aliquot of the eluate is applied to an analytical column and eluted with a mobile phase of acetonitrile/methanol/phosphate buffer, 20 mmol/L, pH 3.7 (13.5/35/51.5 by vol), at a flow rate of 3.0 mL/min and at 50 degrees C. Detection is at 210 or 195 nm. The chromatography is complete in less than 2.5 min with the 5-microns-particle column, and in less than 1.4 min with the 3-microns-particle column. The sensitivity of the method for all drugs is less than 1 mg/L. Analytical recovery of drugs added to serum ranged from 92 to 109% for concentrations up to 200 mg/L. Between-run precision (CV) ranged from 1.3 to 4.1%.

Carbamazepine↗
PubMed1983

Liquid-chromatographic determination of tobramycin in serum with spectrophotometric detection.

We describe a simple, precise, accurate, and specific liquid-chromatographic procedure for determination of tobramycin in 50 microL of serum. Tobramycin and the internal standard (sisomicin) are quantitatively converted into their trinitrophenyl derivatives by reaction with a water-soluble derivatizing agent (2,4,6-trinitrobenzenesulfonic acid) at 70 degrees C for 30 min. The derivatives are extracted from the crude reaction mixture by using a reversed-phase Bond-Elut C18 column, and separated on a reversed-phase octyl column with a mobile phase consisting of an acetonitrile/phosphate buffer (70/30 by vol) at a flow rate of 3.0 mL/min. The eluted compounds are detected at 340 nm, and quantified from their peak areas. Chromatography is complete in less than 4.5 min at the optimum column temperature of 50 degrees C. The lower limit of detection for tobramycin is less than 0.2 mg/L. Analytical recoveries for tobramycin varied from 94 to 99%, linearity extended to 25 mg/L, and day-to-day precision (CV) was between 4.6 and 5.1%. Numerous drugs and antibiotics tested do not interfere. Results correlate well (r greater than 0.95) with those by radioimmunoassay and EMIT.

Anti-Bacterial Agents↗