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Biomedical subjects

G A Ellard

Publications and source records attributed to G A Ellard.

At least 37 records · Page 2Linked to original sources
PubMed1989

Isoniazid-related hepatotoxicity: a study of the effect of rifampicin administration on the metabolism of acetylisoniazid in man.

It has been proposed that isoniazid-induced hepatotoxicity may be increased by concomitant rifampicin treatment and that this could be mediated by inducing the metabolism of the isoniazid metabolite monoacetylhydrazine to potent acylating agents capable of causing liver necrosis. To investigate this postulated mechanism we studied the kinetics of the metabolism of acetylisoniazid in a slow and a rapid acetylator prior to and after rifampicin administration. Pretreatment with rifampicin did not modify the metabolism of acetylisoniazid to any noteworthy extent nor did it increase the metabolism by non-acetylation routes of the monoacetylhydrazine liberated in vivo from acetylisoniazid.

Acetylation↗
PubMed1986

The bioavailability of isoniazid, rifampin, and pyrazinamide in two commercially available combined formulations designed for use in the short-course treatment of tuberculosis.

The bioavailability of isoniazid, rifampin, and pyrazinamide in 2 combined formulations of the 3 drugs (Rifater) for use primarily in the short-course chemotherapy of tuberculosis has been studied in Chinese patients in Singapore and Hong Kong. One formulation, containing 50 mg isoniazid, 120 mg rifampin, and 300 mg pyrazinamide per tablet is suitable for daily use, whereas the other, containing higher proportions of isoniazid and pyrazinamide, is designed for intermittent treatment, each tablet containing 125 mg isoniazid, 100 mg rifampin, and 375 mg pyrazinamide. Appropriate dosages for the Chinese patients, whose average weight was approximately 50 kg, were 5 and 6 tablets, respectively. Plasma concentrations of the 3 drugs after giving such dosages of the 2 combined formulations were compared in 16 patients, 8 in Singapore and 8 in Hong Kong, by means of a crossover study, with the concentrations obtained when identical doses of the 3 drugs were given using standard separate drug formulations. The concomitant urinary excretions of the drugs and their major metabolites were also estimated. Very similar results were obtained whether the drugs were given as the combined preparations or in their standard separate formulations, demonstrating the excellent bioavailability of all 3 drugs in each of the 2 combined formulations.

Acetylation↗
PubMed1986

A double-blind randomized controlled trial of the effect of a low- versus a middle-tar cigarette on respiratory symptoms--a feasibility study.

A feasibility study of a double-blind, randomized controlled trial of the effect of a low-versus a middle-tar cigarette on respiratory symptoms is described. A smoking questionnaire was sent to 19,366 households. Returned questionnaires (64%) yielded 604 middle-tar cigarette smokers aged 20-44 years; 342 replied to a health warning stating that they did not want to or had failed to stop smoking and of these 183 volunteered for the trial. Thus about every 100 households originally mailed yielded one volunteer. Of the volunteers, 95 men were randomly allocated to be sold a middle-tar cigarette and 88 to be sold a low-tar cigarette of identical appearance. The cigarettes were sold at three different reduced prices and the men were asked to smoke them for five weeks. There was a 22% drop-out and this was unrelated to type of cigarette smoked. A reduction in price of 20% was sufficient incentive for volunteers to participate. Cigarette butts were collected weekly or fortnightly and urine samples were collected initially and after three and five weeks. Compliance with the trial cigarettes was good. The excretion of nicotine metabolites, number of cigarettes smoked and average butt weight for men allocated the low-tar cigarette was not significantly different from that of those allocated the middle-tar cigarette. This suggested that the former compensated for the 37% reduction in the nicotine yield of their cigarette by taking more frequent or deeper puffs from their cigarette. The implications of these results for a large-scale, randomized controlled trial are discussed.

Adult↗
PubMed1986

A simple, inexpensive urine test of smoking.

Three novel colorimetric methods of detecting urinary nicotine metabolites called the barbituric acid, diethylthiobarbituric acid (DETB) and DETB-extraction methods were evaluated for use as a simple cheap objective test of smoking. Urine samples were collected from 103 male smokers and 78 male nonsmokers working at two London factories. The smokers recorded the number of cigarettes smoked over the previous 36 hours. All three methods correctly classified the smokers. The DETB-extraction method had a lower false-positive rate (averaging 3% on morning and afternoon urine samples) than either the DETB or barbituric acid methods (12% and 6% respectively) and was the best procedure for classifying subjects as 'smokers' or 'non-smokers'. Using a quantitative variant of the barbituric acid method, there was a significant correlation (r = 0.85, p less than 0.001) between the urinary nicotine metabolites/creatinine ratios and number of cigarettes smoked. However, the ratios for smokers of 6-15, 16-25, and 26 or more cigarettes overlapped considerably. The methods can be performed very rapidly and reagent costs are equivalent to less than one penny per test.

Barbiturates↗
PubMed1985

A simple, inexpensive urine test of smoking.

Three novel colorimetric methods of detecting urinary nicotine metabolites called the barbituric acid, diethylthiobarbituric acid (DETB), and DETB extraction methods were evaluated for use as a simple, cheap, objective test of smoking. Urine samples were collected from 103 male smokers and 78 male non-smokers working at two London factories. The smokers recorded the number of cigarettes smoked over the previous 36 hours. All three methods correctly classified the smokers. The DETB extraction method had a lower false positive rate (averaging 3% on morning and afternoon urine samples) than either the DETB or the barbituric acid method (12% and 6% respectively) and was the best procedure for classifying subjects as "smokers" or "non-smokers." When a quantitative variant of the barbituric acid method was used there was a significant correlation (r = 0.85, p less than 0.001) between the ratios of urinary nicotine metabolites to creatinine and the number of cigarettes smoked. The ratios for smokers of 6-15, 16-25, and 26 or more cigarettes, however, overlapped considerably. The methods can be performed very rapidly and the reagent cost is equivalent to less than 1p per test.

Barbiturates↗
PubMed1985

An experimental study of the antileprosy activity of a series of thioamides in the mouse.

A series of substituted thioamides have been studied to establish whether their structure-activity pattern against Mycobacterium leprae is similar to that displayed against M. tuberculosis. Antileprosy activity was evaluated in the mouse foot pad using both the kinetic and continuous methods. Ethionamide and prothionamide were found to be the most active compounds and to be of approximately equal potency. Thioisonicotinamide was about five times less active. 2-t-Butyl-thioisonicotinamide, 2-dimethylamino-thioisonicotinamide, and pyrazine carbonic thioamide were inactive at the dosages tested. High-pressure liquid chromatographic methods were devised to study the potential influence of pharmacological factors on their in vivo activity. Fecal measurements suggested that all of the thioamides were well absorbed when fed in the diet. After intravenous administration, all of the thioamides were rapidly eliminated from the mouse. The differences in their elimination rates probably played only a minor role in affecting their relative antileprosy activities. It was concluded that the structural requirements for antileprosy and antituberculosis activity of the thioamides are probably similar.

Amides↗
PubMed1984

A comparison of the blood levels and urinary excretion of ethionamide and prothionamide in man.

The blood levels and urinary excretion of the anti-mycobacterial drugs ethionamide and prothionamide have been compared after oral dosage in man. High pressure liquid chromatographic methods were used to determine the two closely related thioamides and their microbiologically active sulphoxide metabolites after the ingestion of both single and combined doses of the two drugs. Both drugs were rapidly eliminated from the body, the half-life for the urinary excretion and removal from the plasma of prothionamide being slightly less than that of ethionamide. Less than 0.1% of the orally administered doses were excreted unchanged in the faeces. Plasma concentrations of ethionamide and its sulphoxide metabolite were substantially higher than those of prothionamide and prothionamide sulphoxide. The implications of these findings for the use of ethionamide or prothionamide in the treatment of lepromatous leprosy are discussed.

Biotransformation↗