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Biomedical subjects

R Whelpton

Publications and source records attributed to R Whelpton.

At least 37 records · Page 2Linked to original sources
PubMed1993

Are intraligamentary injections intravascular?

A pressure type syringe was used to give intraligamentary injections (IL) to upper teeth of two formulations commonly used in general practice, lignocaine and prilocaine. Assay of plasma levels of drug was carried out by high performance liquid chromatography. Results of assays after intraligamentary injections were then compared with results of assays after intravenous injections of plain drug in the same subjects. Both formulations of local anaesthetic were found as peak levels in the circulation, presumably after intraosseous spread, by 2 minutes following the intraligamentary injections. For lignocaine the peak amount was nearly 7% of the intravenous dose and for prilocaine the peak amount was 25% of the intravenous dose, at 2 minutes after injection. It was concluded that IL injections for healthy adults were unlikely to cause systemic unwanted effects when given in small doses.

Adult↗
PubMed1990

Determination of plasma nefopam by liquid chromatography and electrochemical detection.

A liquid chromatographic method for the determination of plasma nefopam is presented. A combination of liquid- and solid-phase extraction and electrochemical detection gave clean extracts and, hence, a low limit of detection. Calibration curves were linear over at least two orders of magnitude (1-100 ng/ml) making the method suitable for pharmacokinetic studies.

Chromatography, Liquid↗
PubMed1990

The binding of physostigmine to human serum albumin.

The binding of [3H]physostigmine to crystallized human serum albumin (HSA) has been investigated using equilibrium dialysis. The percentage bound to 1% (w/v) HSA decreased from 18 to 4% as the total concentration of physostigmine increased from 3.3 nM to 2.7 microM (0.9 to 750 ng mL-1). A single class of specific binding sites with a large affinity constant, K = 8 x 10(7) L mol-1, was identified. The concentration of binding sites was approximately 3 nM. The Michaelis constants for human serum cholinesterase and albumin were the same; an explanation for these results is that the drug is binding to a trace cholinesterase, in the albumin.

Binding Sites↗
PubMed1989

Solid phase extraction for an improved assay of physostigmine in biological fluids.

A simple, selective and very sensitive assay is described for the quantification of physostigmine in blood, plasma and urine. The most appropriate solid phase column was selected after a systematic investigation of nine types of phase. The conditions for solid phase extraction were optimized using [3H]physostigmine so that the overall recoveries were greater than 90%. Physostigmine was retained on alkaline treated cyanopropyl columns and eluted into the minimum volume of methanol, obviating the need for an evaporation step. Extracted samples were quantified by HPLC with a three electrode coulometric detection system. The limit of detection was 50 pg/mL for a 0.5 mL plasma sample. The precision (CV) for 0.5 mL plasma samples containing 50 pg was 8.1%. Application of the method to plasma, blood and urine samples is presented.

Chromatography↗
PubMed1989

Ionization constants, octanol partition coefficients and cholinesterase inhibitor constants for chlorpromazine and its metabolites.

The relationship between the lipophilic character of chlorpromazine and seven of its metabolites and their ability to inhibit horse serum cholinesterase (Ki) has been investigated. Log(1/Ki) values were correlated with log P octanol partition coefficients (r = 0.88, P less than 0.01, n = 8). The inhibitor values ranged from 2.7 x 10(-6) M for chlorpromazine to 48.6 x 10(-6) M for monodesmethylchlorpromazine sulphoxide. Ionization constants were determined by limiting solubility, spectrophotometry and pH-partition characteristics. Demethylated metabolites were more basic than the tertiary amines and the sulphoxides were slightly less basic than the corresponding sulphides.

Chemical Phenomena↗
PubMed1987

Analysis of solutions containing glutathione and inorganic nitrite: application to nitroglycerin metabolism studies.

Nitroglycerin (GTN) is metabolized to 1,2-dinitroglycerin (1,2-GDN) and 1,3-dinitroglycerin (1,3-GDN) in vivo and in liver homogenates. 1,2-GDN and 1,3-GDN are converted to isomers of glyceryl mononitrate (GMN) in vivo. The denitration reactions yield inorganic nitrite (NO(-)(2)) which is oxidized to inorganic nitrate (NO(-)(3)). Denitration involves utilization of glutathione (GSH). In attempting to use the Bratton-Marshall assay for NO(-)(2) in studies of GTN metabolism in vitro, and in attempting to use Ellman's reagent for GSH in the same research, apparent concentrations of both NO(-)(2) and GSH were noticed lower than anticipated. Apparent mutual interference by NO(-)(2) and GSH in their respective assays was then found. Development of a specific liquid chromatographic method for measurement of NO(-)(2), NO(-)(3), GSH and oxidized glutathione (GSSG) permitted the study of the interaction of NO(-)(2) and GSH, which yielded NO(-)(3) and GSSG.

Journal Article↗
PubMed1986

Chromatographic separation of thioridazine sulphoxide and N-oxide diastereoisomers: identification as metabolites in the rat.

(+/-)-Thioridazine and (+/-)-desmethylthioridazine have been oxidized to produce a number of chiral sulphoxide and amine oxide compounds. Diastereoisomeric isomers were separated by thin-layer and high performance liquid chromatography. Thioridazine-5-sulphoxide, N-desmethylthioridazine-5-sulphoxide and thioridazine-N-oxide diastereoisomers were found to be thioridazine metabolites following dosing in rats or after in-vitro incubation with rat liver homogenate.

Animals↗
PubMed1985

Sensitive liquid chromatographic method for physostigmine in biological fluids using dual-electrode electrochemical detection.

A liquid chromatographic method using dual-electrode detection has been developed for determination of physostigmine in biological fluids. The limit of detection is in the order of 25-50 pg mol-1 of plasma. A high sample throughput is obtained by a single solvent extraction step and autoinjection into the chromatograph. Data following oral doses of physostigmine are presented.

Adult↗
PubMed1983

Effects of chlorpromazine and promazine on the visual aftereffects of tilt and movement.

The effects of chlorpromazine (CPZ) and promazine on the visual aftereffects of tilt and motion were measured. CPZ markedly reduced the strength of both aftereffects, while promazine produced a smaller and not always significant reduction. Control experiments suggested that the effects were produced in the central visual system rather than by several possible peripheral artefacts or by drowsiness. The effects are discussed with reference to the pharmacological activity of the drugs and their influence on the strength of inhibition in the visual cortex, both in normal subjects and in schizophrenic illness.

Adaptation, Ocular↗
PubMed1981

Bratton-Marshall and liquid-chromatographic methods compared for determination of sulfamethazine acetylator status.

Synthesis of acetylsulfamethazine has made possible an evaluation of the Bratton-Marshall assay for this compound. Hydrolysis is an essential step in the assay, which depends on color development with the sulfamethazine formed in the hydrolysis. Sulfamethazine decomposes under the conditions needed for hydrolysis of acetylsulfamethazine, and this leads to depressed values for acetylsulfamethazine and to low figures for clinical "percent acetylation." Because of this, a simple "high-pressure" liquid-chromatographic procedure was developed for the assay; it requires no hydrolysis, is rapid in application, and can be applied to as little as 10 microL of capillary blood obtained by finger-to-puncture. We found that the cutoff point between "slow" and "fast" acetylators, when this method was used on samples from 75 subjects collected about 6 h after dosage, was 40% "acetylation" in plasma.

Adult↗