Biomedical subjects

D W Fretthold

Publications and source records attributed to D W Fretthold.

3 recordsLinked to original sources

PubMed1979

High pressure liquid chromatography for simultaneous analysis of anticonvulsants: comparison with EMIT system.

We present a new high pressure liquid chromatography (HPLC) method for the simultaneous analysis of primidone, phenobarbital, phenytoin, and carbamazepine in serum. The chromatographic separation is carried out using an Altex model 110-A pump, a 250 times 4.6 mm column containing 5 mum Spherisorb ODS particles and a variable wavelength ultraviolet detector set at 197 nm. The mobile phase is a mixture of acetonitrile, distilled water, and 1.75 M phosphoric acid (27:72.8:0.2). The flow rate is 1.5 ml/min, and the analysis time is 17 min. A 200 mul aliquot of serum is buffered at pH 5 and extracted with dichloromethane. The extract is evaporated to dryness and dissolved in methanol for chromatographic analysis. Cyclopal is used as the internal standard and quantification is achieved using peak height ratios. This HPLC method is evaluated for precision and accuracy with reference to the EMIT system. The least-squares regression analysis of comparison data for the drugs shows a favorable correlation. Also, a paired t-test indicates no significant difference for the HPLC and EMIT values for primidone, phenobarbital, phenytoin, and carbamazepine. From this study we conclude that this HPLC method could be successfully used for the simultaneous therapeutic monitoring of the four anticonvulsants.

Anticonvulsants↗

PubMed1978

The effect of acid--base changes on skeletal muscle twitch tension.

The effects of acid--base alterations produced by changing bicarbonate (metabolic type), carbon dioxide tension (respiratory type), or both bicarbonate and carbon dioxide tension (compensated type) on skeletal muscle twitch tension, intracellular pH, and intracellular potassium were studied in vitro. Hemidiaphragm muscles from normal rats and rats fed a potassium-deficient diet were used. Decreasing the extracellular pH by decreasing bicarbonate or increasing CO2 in the bathing fluid produced a decrease in intracellular pH, intracellular K+, and muscle twitch tension. However, at a constant extracellular pH, an increase in CO2 (compensated by an increase in bicarbonate) produced an increase in intracellular K+ and twitch tension in spite of a decrease in intracellular pH. The effect on twitch tension of the hemidiaphragms showed a rapid onset, was reversible, persisted until the buffer composition was changed, and was independent of synaptic transmission. It is concluded that the twitch tension of the skeletal muscle decrease with a decrease in intracellular K+. The muscle tension also decreases with an increase in the ratio of intracellular and extracellular H+ concentration. However, there is no consistent relationship between muscle tension and extracellular or intracellular pH. The muscle tension of the diaphragms taken from K+-deficient rats is more sensitive to variations in CO2, PH, and bicarbonate concentration of the medium than that of the control rat diaphragms.

Acid-Base Equilibrium↗

PubMedDate not supplied

Drug-testing methods and reliability.

The methods used by laboratories to analyze urine collected from employees are described. Federally designed procedures designed for analyzing government employee samples have become the highest standard for performing such tests, although at present there are no guidelines that specifically address drug testing in the private sector. Samples and analysis should be handled in a manner that ensures that test results are legally defensible. Enzyme immunoassay is the technique used to perform the initial test on these samples. Positive test samples identified by this method are tested again by gas chromatography-mass spectrometry. Potential problems with these analytical methods, additional safeguards, and data demonstrating the reliability of this approach are presented.

Environment↗