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Biomedical subjects

M A Brooks

Publications and source records attributed to M A Brooks.

At least 55 records · Page 3Linked to original sources
PubMed1981

Differential pulse amperometric detection of drugs in plasma using a dropping mercury electrode as a high-performance liquid chromatographic detector.

High-performance liquid chromatographic separation prior to reductive electrochemical determination at its dropping mercury electrode imparts specificity and sensitivity not attainable by conventional polarographic analysis of drugs and their metabolites. The utility of this novel approach is demonstrated by the analysis of chlordiazepoxide and its N-desmethyl metabolite in plasma which previously required thin-layer chromatographic separation prior to polarographic measurement. A mobile phase of methanol-isopropanol--0.0075 M acetate buffer, pH 3.5 (53:5:42), is used with the detector operated in the differential pulse mode at Ep = -0.820 V vs. Ag/AgCl. The response was linear (r = 0.998) in the concentration range of 0.05--2.0 micrograms/ml plasma for each component. The minimum detectability for each component under these conditions is 5.0 ng injected at a current range of 0.5 microamperemeter full scale. Techniques for oxygen removal and hydrodynamic consideration for the pumping system are presented.

Chlordiazepoxide↗
PubMed1981

Pharmacokinetics of ceftriaxone in humans.

Pharmacokinetics of the investigational cephalosporin ceftriaxone were studied after 30-min intravenous infusions of three ascending single doses of 0.5, 1, and 2 g crossed over in 12 normal subjects. Serially collected plasma and urine samples were analyzed for ceftriaxone by high-performance liquid chromatography. Plasma concentration-time profiles were characterized by a linear two-compartment open model with the following respective mean (+/- standard deviation) parameters at 0.5-, 1-, and 2-g dose levels: elimination half-life, 6.5 +/- 0.7, 6.2 +/- 0.8, and 5.9 +/- 0.7 h; apparent volume of distribution, 8.5 +/- 1.1, 9.0 +/- 1.1, and 10.1 +/- 1.0 liters; and plasma clearance, 929 +/- 150, 1,007 +/- 130, and 1,190 +/- 150 ml/h. The respective renal excretion parameters were as follows: renal clearance, 373 +/- 60, 399 +/- 50, and 533 +/- 128 ml/h; and percentage of dose excreted unchanged in the 48-h urine samples, 41 +/- 8, 39 +/- 5, and 43 +/- 10. The 6-h elimination half-life of ceftriaxone was 2- to 10-fold longer than those reported for marketed and other known investigational cephalosporins. The small dose-related increases in the apparent volume of distribution and clearance parameters can be explainhe 48-h urine samples, 41 +/- 8, 39 +/- 5, and 43 +/- 10. The 6-h elimination half-life of ceftriaxone was 2- to 10-fold longer than those reported for marketed and other known investigational cephalosporins. The small dose-related increases in the apparent volume of distribution and clearance parameters can be explainhe 48-h urine samples, 41 +/- 8, 39 +/- 5, and 43 +/- 10. The 6-h elimination half-life of ceftriaxone was 2- to 10-fold longer than those reported for marketed and other known investigational cephalosporins. The small dose-related increases in the apparent volume of distribution and clearance parameters can be explained by the concentration-dependent plasma protein binding of ceftriaxone in humans. The impact of the small dose-dependent changes in the pharmacokinetics of ceftriaxone is anticipated to be of negligible clinical significance.

Adult↗
PubMed1980

Determination of estramustine and its 17-keto metabolite in plasma by high-performance liquid chromatography.

A rapid, sensitive and specific high-performance liquid chromatographic (HPLC) assay was developed for the determination of estramustine and its 17-keto metabolite in plasma. The assay involves extraction of the compounds into hexane from plasma buffered to pH 9.0, the residue obtained by evaporation of the hexane extract is dissolved in the mobile phase hexane-ethanol (92.5:7.5) with HPLC analysis performed on a 5-micrograms silica gel column using a fluorescence detector with excitation at 195 nm and emission at wavelengths greater than 250 nm. The overall recoveries and limits of sensitivity for estramustine and the 17-keto metabolite are 74.7% and 40 ng/ml of plasma and 85.1% and 50 ng/ml of plasma, respectively. The method was used to obtain plasma concentration-time profiles in three subjects with prostatic cancer following oral administration of a single 7 mg/kg dose of estramustine phosphate.

Chromatography, High Pressure Liquid↗
PubMed1979

High-pressure liquid chromatographic determination of amoxicillin in urine.

A rapid and specific high-pressure liquid chromatographic (HPLC) assay was developed for the simultaneous determination of amoxicillin and its pencilloic acid metabolite in urine. The two compounds, assayed directly in urine or after dilution with water-methanol (85:15), are separated by reversed-phase chromatography and quantitated spectrofluorometrically following postcolumn derivatization with fluorescamine. Linear calibration curves were measured in the ranges of 25-250 and 50-400 ng injected for amoxicillin and the penicilloic acid metabolite, respectively. The sensitivity limit of the assay is 2.5-5.0 microgram/ml of urine for amoxicillin and the penicilloic acid metabolite. Urine samples (0-8 hr) taken from six subjects following single 250-mg po doses and assayed by HPLC showed ranges of cumulative percent of the dose excreted as amoxicillin and the penicilloic acid metabolite (reported as amoxicillin equivalents) of 50.2-68.0, and 21.6-30.0%, respectively. An excellent correlation (r = 0.985) was demonstrated for the measurement of amoxicillin concentrations by the HPLC and microbiological assays.

Amoxicillin↗
PubMed1978

Noninvasive polarographic measurement of drug dissolution.

Polarographic analysis was applied successfully to dissolution studies and content uniformity assessment of both capsules and tablets, using a dropping mercury electrode with the modified Levy beaker method. The described noninvasive technique places the polarographic sensor probe directly into the dissolution flask and thus simplifies dissolution measurement by eliminating transfer lines and pumps typically required with the invasive (sampling) mode of analysis. A continuous sampling flowcell with polarographic detection was also evaluated for invasive measurements. Continuous dissolution profiles and content uniformity were determined for chlordiazepoxide, trimethoprim, ornidazole, and isoniazid, using the invasive and noninvasive sampling modes. Results obtained for these drugs showed excellent precision with both sampling techniques. In addition, excellent correlation to UV spectrophotometric data was obtained.

Electrodes↗
PubMed1977

Determination of chlordiazepoxide, diazepam, and their major metabolites in blood or plasma by spectrophotodensitometry.

An analytical procedure was developed for the determination of chlordiazepoxide, diazepam and their major metabolites in blood or plasma. Demoxepam, a metabolite of chlordiazepoxide, is determined by spectrofluorometry after extraction. The remaining compounds are determined by spectrophotodensitometry after thin-layer chromatographic separation. The sensitivity limit of the spectrofluorometric determination of demoxepam is 0.1 to 0.2 microgram while that of the spectrophotodensitometric determination of chlordiazepoxide, diazepam and their N-desmethyl metabolites is 0.05 to 0.2 microgram. The sensitivity and specificity of the assay renders it suitable for monitoring plasma levels of chlordiazepoxide and its major metabolites following single or chronic oral administration of chlordiazepoxide hydrochloride. The sensitivity limit for diazepam and nordiazepam, its major metabolite, renders the assay useful only for the determination of plasma concentrations resulting from high dosage of diazepam. The assay was used to determine chlordiazepoxide and its metabolites following oral administration of Librium. The data showed a significant correlation to those obtained on the same specimens by differential pulse polarography and by radioimmunoassay.

Chlordiazepoxide↗
PubMed1977

Determination of clorazepate and its major metabolites in blood and urine by electron capture gas-liquid chromatography.

A sensitive and specific blood level method employing differential extraction was developed for the determination of clorazepate and its N-desmethyldiazepam metabolite by electron capture gas-liquid chromatography (GLC-ECD). The assay requires the initial extraction of N-desmethyldiazepam, the major metabolite, into benzene-methylene chloride (90:10) from the biological sample made alkaline with 0.1 N NaOH. The samples is then acidified with 2 N HCl to decarboxylate clorazepate to N-desmethyldiazepam, which is then extracted into benzene-methylene chloride (90:10) after adjusting the pH to 12.8 with NaOH. The two extracts are evaporated and the residues are dissolved in benzene which contains griseofulvin as the reference standard. These solutions are assayed by GLC-ECD. The overall recovery and sensitivity limit of the assay for clorazepate is 60+/-5% (S.D.) and 4.0 ng/ml blood, respectively, while that for N-desmethyldiazepam is 95+/-5% (S.D.) and 4.0 ng/ml blood, respectively. The urinary excretion of clorazepate was determined by the measurement of the levels of N-desmethyldiazepam and oxazepam, the major urinary metabolites of clorazepate, both prior to and after enzymatic deconjugation. These methods were applied to the measurement of clorazepate and its metabolites in blood and urine following a single 15-mg dose of clorazepate dipotassium.

Anti-Anxiety Agents↗
PubMed1977

Isolation of cell lines from embryos of the cockroach, Blattella germanica.

Cell lines were isolated from three stages of embryos of Blattella germanica dissociated with trypsin. The lines have been subcultured 50 to 134 times in 3 years. Line UM-BGE-1 was isolated from germ band embryos at stages of segmentation and limb-bud formation (5 days old). Line UM-BGE-2 was derived from embryos at dorsal closure (7 days old). Line UM-BGE-4 arose from embryos in the germ band and dorsal closure stages (5 and 7 days old): these cells colonize as hollow spheres or vesicles. Line UM-BGE-5, isolated during organogenesis (10 days old), developed into two distinct sublines. Subline alpha is composed of round cells that do not attach to the flask. Subline beta grows as an attached monolayer; the cells can be removed with a saline solution containing 20 mM disodium dihydrogen Versenate. Most of the cells of these lines have the diploid chromosome number (23 or 24) excepting line UM-BGE-1 in which the tetraploid number predominates

Cell Adhesion↗
PubMed1976

N-desmethyldiazepam: a new metabolite of chlordiazepoxide in man.

Following administration of chlordiazepoxide HCl to man, N-desmethyldiazepam, a known metabolite of diazepam (Valium), was identified in plasma. The metabolite was identified on the basis of its thin-layer chromatographic (TLC) mobility, electron-capture gas-chromatographic (EC-GC) retention time, and mass spectrum relative to authentic N-desmethyldiazepam. Plasma levels of N-desmethyldiazepam in subjects receiving both single and chronic doses of chlordiazepoxide were determined by an EC-GC method with a limit of sensitivity of 10 ng/ml using 2-ml samples and by a radioimmunoassay procedure which had a limit of sensitivity of 20 ng/ml using a 0.1-ml sample. Both assay methods gave good agreement for the levels of N-desmethyldiazepam. In subjects receiving a single 30-mg oral or intravenous dose of chlordiazepoxide, measurable levels of N-desmethyldiazepam in plasma (10 to 60 ng/ml) were obtained 24 to 72 hr after administration. In 5 subjects receiving 10 mg of chlordiazepoxide three times a day, steady-state levels of N-desmethyldiazepam in plasma were reached after about 1 wk of administration. The mean maximum and minimum steady-state levels of N-desmethyldiazepam were 260 and 220 ng/ml of plasma, respectively. Similar steady-state levels were observed on treatment with 30 mg of chlordiazepoxide over 24 hr.

Animals↗
PubMed1976

Determination of nitroimidazoles in biological fluids by differential pulse polarography.

A sensitive differential pulse polarographic assay was developed for the determination of metronidazole, ornidazole, and 2-nitro-1H-imidazole-1-(3-methoxy-2-propanol) in plasma. The compounds are selectively extracted into ethyl acetate from a protein-free filtrate of plasma, buffered to pH 7.0 +/- 0.2. The residue of the ethyl acetate extract is dissolved in 0.1 N NaOH and analyzed by differential pulse polarography for the reduction of the nitro group at approximately -0.600 v versus the saturated calomel electrode. The overall recovery from plasma was about 55 +/- 3.0% (SD) for the three compounds investigated. A TLC step after the ethyl acetate extraction may also be included to ensure specificity. This step reduced the overall recovery to approximately 45%. The sensitivity limit of detection from plasma using a 2-ml sample is 0.1 mug/ml. The assay may also be employed for the analysis of urine. The urine is adjusted to pH 7.0 +/- 0.2 and extracted with ethyl acetate, and the residue is analyzed as described for plasma. The assay was applied to the determination of ornidazole in blood and urine in the dog following 10 mg/kg po.

Animals↗
PubMed1976

The dissociation of insect embryos for cell culture.

Procedures and solutions were developed for dissociating embryos of Blattella germanica in preparation for primary cell culture. Trypsin solutions were maximally effective at 0.01% for germ bands but higher concentrations, 0.05 to 0.1% were needed for embryos in later stages.

Animals↗
PubMed1975

Spectrofluorometric determination of the antibiotic lasalocid in blood.

A spectrofluorometric assay was developed for the determination of the antibiotic lasalocid in dog blood, based on the intrinsic fluorescence of the compound in ethyl acetate. The assay can measure "total" levels of drug and any metabolites present. The specificity of the assay was verified by TLC separation of the dog blood extract, which indicated the presence of only intact drug. The overall recovery (+/- SD) of lasalocid was 62.0 +/- 3.6% in the concentration range of 1.0-10 mug of compound/ml of dog blood. The sensitivity of the assay is 0.5 mug/ml. The assay was applied to the determination of blood levels of lasalocid in the dog following the intravenous administration of a 5-mg/kg dose.

Animals↗