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Biomedical subjects

B C Choi

Publications and source records attributed to B C Choi.

67 records · Page 4Linked to original sources
PubMed1985

N-Nitroso compounds and human cancer. A molecular epidemiologic approach.

N-Nitroso compounds are known to be potent animal carcinogens. However, evidence of their effect on human cancers is inconclusive, and further investigations are needed. A mathematical model to create indices of nitrate, nitrite, and N-nitrosamine exposures, both exogenous and endogenous, is described in this paper. Estimation of the endogenous formation is based on the current knowledge of biochemistry and chemical kinetics of these compounds. The model can be applied to analyze data regarding the dietary history and use of tobacco products and alcoholic beverages obtained from epidemiologic questionnaires. Exposure levels of study and control subjects to these compounds can then be compared by conventional epidemiologic methods. This is an approach toward the combination of conventional epidemiologic methods and laboratory findings to study disease etiology.

Adult↗
PubMed1985

Erythema multiforme (Stevens-Johnson syndrome)--chart review of 123 hospitalized patients.

The charts of 123 patients hospitalized with erythema multiforme were reviewed. Antecedent infections and the administration of drugs were associated with 15 and 32% of the cases, respectively. Pyrexia arthralgia, photosensitivity, abnormal liver function tests and abnormal urine sediment were common findings. The length of stay in hospital was 12.6 +/- 0.7 days (mean +/- SE), time to initial improvement after onset was 10.3 +/- 0.6 days and time to complete resolution was 23.0 +/- 2.4 days. The presence of bullous skin lesions and greater overall severity were associated with longer hospitalization. Antecedent respiratory tract symptoms were related to shorter hospitalization. Steroid therapy was not associated with a shorter time for initial improvement to occur, while the average length of stay in hospital was 4.2 days longer than that for the patients not treated with corticosteroid.

Age Factors↗
PubMed1984

Methodological issues in case-control studies: II. Test statistics as measures of efficiency.

The ratio of test statistics has been used to compare the efficiency of matched and unmatched designs, and stratified and pooled analyses for case-control studies. The index has been computed for a wide range of population conditions and it is concluded that (a) pooled analysis is always more efficient than stratified analysis when such pooling leads to a valid estimate of the relative risk, (b) the loss of efficiency by matching in the classic overmatching situation can be substantial, (c) in the confounding situation either design may be more efficient but generally the difference is small. These results add support to the contention that matching is rarely justified in case-control studies.

Analysis of Variance↗
PubMed1984

Methodological issues in case-control studies IV: Validity and efficiency of various analysis strategies for continuous variables using the unconditional logistic regression model.

Computer simulation has been used to evaluate the performance of the unconditional logistic regression model when used to analyse continuous data from case-control studies. The size of the bias in the odds ratio estimate introduced by small sample sizes and by the use of the incorrect analysis model has been estimated for various underlying population conditions, together with the power as a measure of efficiency. It is concluded that the model is robust over a wide range of exposures to the risk factor, in the sense that both small sample sizes and use of the incorrect model introduced relatively small biases. The power of the test is again little altered by use of the incorrect analysis model.

Aged↗
PubMed1984

Epidemiological assessment of risk to humans from exposure to nitrosamines.

In order for epidemiologists to evaluate the 'nitrosamine hypothesis' it is necessary to develop measures of human exposure to N-nitrosamines - both exogenous and when formed internally through consumption precursors. Dissatisfied with indefinite findings using indirect indices of N-nitrosamine exposure, we have attempted to derive an index based on the known kinetics of N-nitrosamine formation. This has been applied in a case-control study of cerebral tumours and resulted in a suggestive finding of increased risk for exogenous but not total N-nitrosamine exposure. A potential difficulty with our index is doubt as to whether vegetable sources of nitrates and consequent endogenous formation of nitrites indeed result in N-nitrosamine exposure, in view of the possible presence of blocking agents or of vitamin C consumed at the same time as vegetables. Further work is necessary, but we hope to apply the index in a case-control study of gastric cancer currently under analysis.

Dimethylnitrosamine↗
PubMed1983

Methodological issues in case-control studies: validity and power of various design/analysis strategies.

Computer stimulations have been used to estimate the efficiency, as measured by the statistical power, of various combinations of design and analysis strategies for case-control studies. Conditions under which the various forms of analysis yield consistent relative risk estimators are derived for the general model. The results indicate that the loss of efficiency resulting from the use of a less than optimum design or analysis strategy in many real life situations is small. Practical considerations are of more importance than theoretical statistical ones in deciding upon appropriate strategies. It is concluded that matching is rarely, if ever, justified in most case-control studies of chronic diseases.

Adult↗
PubMed1981

Some biochemical and pharmacological properties of an epoxide metabolite of alclofenac.

The properties of an epoxide metabolite of alclofenac have been investigated in a number of in vitro and in vivo tests. Alclofenac epoxide was shown to inhibit the activity of yeast alcohol dehydrogenase and form a conjugate with cysteine. The epoxide, but not alclofenac itself, showed mutagenic effects on strains of Salmonella typhimurium sensitive to alkylating agents, but had no effect on strains sensitive to intercalating agents. In addition the epoxide was active in a cell transformation assay using as a target Syrian hamster cells. No acute toxic reactions were observed in mice treated with alclofenac epoxide and the compound was devoid of analgesic and acute antiinflammatory activity. Alclofenac epoxide was found to be a sensitising agent in the guinea-pig when administered either by injection with complete Freud's adjuvant or topically as an ethanolic solution. It is postulated that the formation of the epoxide may explain some of the therapeutic and toxicological properties of alclofenac in man.

Alcohol Oxidoreductases↗
PubMedDate not supplied

The economic impact of smoking in Canada.

A cost-benefit analysis of smoking, using an attributable risk approach, has been carried out for Canada and for three regions within Canada. The total cost of the consequences of tobacco use--in terms of extra deaths, disability, hospitalization, physician services, and fire losses due to tobacco use--in all cases exceeded the total consumer expenditure for tobacco products. The excess was estimated to have a range from $14 to $127 (1983 Canadian dollars) per person per year. This represents the amount that an individual in society would gain, on average, if tobacco use was eliminated from the society for one year. Tobacco use was also found to be responsible for 12 to 17 per cent of all adult deaths, 4 to 5 per cent of all adult disability days, 12 to 14 per cent of all days of hospitalization, and 2 to 3 per cent of all physician visits.

Canada↗
PubMedDate not supplied

The 1996 and 1997 National survey of physician asthma management practices: background and study methodology.

OBJECTIVES: To collect national baseline information on asthma management practices by physicians, and to compare these practices with the recommendations of the Canadian Asthma Consensus Conference ('the guidelines'). DESIGN: Cross-sectional survey of representative samples of physicians in Canada in late 1996 and early 1997. POPULATION STUDIED: Five specialty types of physicians who manage asthma patients: respirology, pediatrics, internal medicine, allergy and clinical immunology, and general practice and family medicine. Stratified sampling by province and specialty was used to select physicians for the study. Weighting was used in the analysis to generalize the results to the national level for the five specialty groups of physicians. METHOD: Mailed questionnaire, self-administered by the respondent; three mailings of the questionnaires were used to increase the response rate. MAIN RESULTS: The frequency with which each of the five specialty types chose specific asthma management choices was determined, using weighted percentages representative of the specialty groups on a national basis. ANOVA determined the statistically significant differences among the five specialties in choosing particular asthma management actions. Then, logistic regression was used to calculate the odds ratios showing an association between the characteristics of the physician respondents and specific asthma management choices that they made in the survey. CONCLUSIONS: The data analysis demonstrated significant variations among physicians in asthma management practices, according to specialty type and other characteristics. The initial report was released in April 1998, and manuscripts for journal submissions are being prepared.

Adolescent↗
PubMedDate not supplied

Physician asthma management practices in Canada.

OBJECTIVES: To establish national baseline information on asthma management practices of physicians, to compare the reported practices with the Canadian Consensus recommendations and to identify results potentially useful for interventions that improve physician asthma management practices. DESIGN: National, stratified cross-sectional survey. SETTINGS: The 10 provinces and two territories of Canada, from 1996 to 1997. PARTICIPANTS: Questionnaires were sent to 4489 physicians stratified by province/territory and specialty group (family/general practice, respirology, internal medicine, pediatrics and allergy/immunology); 2605 responses were received. OUTCOME MEASURES: Methods for the diagnosis, treatment, education and follow-up of patients with asthma ('asthma management practices'). RESULTS: Significant variations existed among the five specialty groups in asthma management practices. A low use of objective measures of airflow limitation to assist with diagnosis was found among some respondents (mostly family physicians). Up to 40% of physicians regarded the daily fixed dosing (three or four times a day) of inhaled, short acting beta2-agonist as 'first-line therapy' for moderate to severe asthma. A minority of physicians reported using written action plans for patients or referring them to other health professionals for asthma education. Insufficient time during appointments and a perceived lack of appropriate educational materials were frequently cited as reasons for not providing asthma education. The perceived knowledge of the Canadian Consensus recommendations varied among physicians but was lowest among nonspecialists. CONCLUSIONS: The survey showed variations in certain aspects of the management of asthma by physicians. The findings will help to target specific areas for future physician education programs and other behavioural change strategies.

Asthma↗
PubMedDate not supplied

Pharmacokinetic changes of oral sulfamethoxazole in rabbits with diabetes mellitus induced by alloxan.

Because physiological changes occurring in diabetes mellitus patients could alter the pharmacokinetics of the drugs used to treat infectious diseases resulting from diabetic complications, the pharmacokinetics of sulfamethoxazole (sulfamethoxazole is usually used to treat secondary infectious diseases resulting from diabetic mellitus) were investigated after oral administration of the drug (50 mg/kg) to control rabbits and rabbits with acute (experiment was performed at fifth day after two consecutive days intravenous administration of alloxan) and chronic (experiment was performed at thirteenth day after first, second, sixth, and tenth days intravenous administration of alloxan) diabetes mellitus induced by alloxan. Impaired kidney and liver functions were observed in acute and chronic diabetes mellitus groups based on plasma chemistry data, and liver and kidney microscopy. After oral administration of sulfamethoxazole to acute and chronic groups, the plasma concentrations tended to be higher and this resulted in a significantly greater area under the plasma concentration-time curve from time zero to time infinity, AUC (6001 and 3867 compared with 1569 microg h/ml). This could be due to significantly slower (2-3 times) renal clearance because of impaired kidney function. The effects of diabetes on the pharmacokinetics of oral sulfamethoxazole were more considerable in acute group; the AUC and the maximum plasma concentration were significantly greater and higher, respectively, than those in control and chronic groups. After oral administration, some pharmacokinetic parameters of sulfamethoxazole were significantly different in diabetes mellitus.

Administration, Oral↗
PubMedDate not supplied

A comprehensive evaluation of the 1993 city of Toronto smoking by-laws.

Effective January 1, 1993, the City of Toronto's two smoking by-laws--one regarding workplaces and another regarding public places--were replaced and amended respectively. Smoking is now prohibited in all workplaces (unless in a designated smoking area), and in at least 50% of eating areas in restaurants. Through a workplace telephone survey and restaurant inspection records, the implementation and enforcement of the by-laws were evaluated. Eighty-three per cent of the workplaces were completely smoke-free and 7% had restricted smoking to a designated area. A majority (76%) of the managers and owners were in favour of regulatory controls on smoking in workplaces. Eighty-six per cent of restaurants complied with requirements for a minimum 50% smoke-free area and signage, and nearly 4% of the sampled restaurants banned smoking throughout the entire premises even though this is not currently required.

Constitution and Bylaws↗