TOX2000 Notes.docx - TOX2000 Notes Regulatory Toxicology Lec 1 Can potentially toxic substances be used \u201csafely\u201d Risk Assessment Paradigm Hazard

TOX2000 Notes.docx - TOX2000 Notes Regulatory Toxicology...

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TOX2000 NotesRegulatory ToxicologyLec 1-Can potentially toxic substances be used “safely”?Risk Assessment Paradigm -Hazard assessment oToxicological description of what substance is capable of doing-Dose response evaluationoEffects you would see at various levels of exposure, adverse effects-Exposure assessmentoModify exposureo35% of cancer due to tobaccooreduce exposure-Risk characterizationoWhat you’ve done, how you’ve done it, limitationsDetermination of Safety:-Risk = Hazard (toxicity) x exposure-To minimize risk, must minimize exposure-When exposure increases, risk increases as well-Hazard is a natural property of toxicological agent-Exposure: any route it is taken up – occupational, food, air, waterPotential exposure pathways in assessing exposure of the general public:1.Researcha.Lab and field observationsb.Information on extrapolation methodsc.Field measurements, characterization of populationsd.Research needs identified from risk assessment processes2.Risk assessmenta.Taking data and putting into a risk characterizationb.Toxicity assessment hazard identification and dose response assessmentc.Exposure assessment emissions characterization3.Risk managementa.Minister of health needs to determine if its an acceptable riskb.Development of regulatory options
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c.Evaluation of public health, economic, social, political consequences of regulatory optionsHazard assessment and dose response evaluation:-Hazard assessment: involves identification and description of the toxicological features of the substance being considered; it is not an expression of riskoDoes not tell you assessment of riskToxicological studies-Acute-Eye and skin irritancy-Sub-chronic-Chronic-Carcinogenicity-Reproductive-Teratology (developmental)Acute-Primarily labelling information carried out in rats and mice-Can be traditional median lethal dose or more contemporary “limit” studyEye and skin irritants-Carried out in rabbits-Eye studies don’t have to be done if chemical physical properties predict irritancy-Considerable debate on rabbit as an appropriate model for eye irritancySub-chronic-Conducted in rats-Periods of up to 90 days-Typically oral route-Most useful for planning of long term feeding studiesChronic-Must include at least 90% of anticipated life span-Often include mice and rats-Study parameters include body weight, hematology (blood), biochemistry and gross pathologySept 24 Lec 2Chronic dog-Studied from 6 months to a year-Used since 1975/1980
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-Little practical value because group sizes are small (2 dogs)-Not statistically useful-Used to identify whether results with rat or mice are consistent -To make studies more relevant is to increase dose (exposure) level, however this is not realistic as we are not exposed to such high levels in real life-MTD (maximum tolerated dose) – highest practical dose to inject without affecting an animalCarcinogenicity -Doses selected in part on the basis of 90 day studies-Often approach a maximum tolerated dose for a high dose-
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