Risk assessment and biological mechanisms: lessons learned, future opportunities

Spontaneous and Drug-Induced Hepatic Pathology of the Laboratory Beagle Dog, the Cynomolgus Macaque and the Marmoset

This review focuses on the background hepatic pathology present in three of the most commonly used species in the safety assessment of drugs, namely the beagle dog, the marmoset and the cynomolgus macaque. Both the nonneoplastic and neoplastic pathology are reviewed with a discussion on the potential impact that significant background pathology might have on the interpretation of any drug-induced pathology during subsequent testing. Although specific instances, such as parasitological infection in wild-caught primates can pose problems of interpretation, in general the background pathology in both the dog and the nonhuman primates, is not significantly different from that seen in the liver of laboratory rodents and with experience should not pose significant problems for the experienced pathologist. The relative merits of the primate versus the dog as a choice of second species are also considered in some detail. Although there is an inbuilt prejudice that the primate will more closely mimic subsequent effects that might occur in man in the clinic, insofar as the liver is concerned, there are many instances where the dog has been more representative of human exposure and metabolism and there is little evidence to show that the nonhuman primate is consistently better than dog in predicting human liver toxicity. As with most areas of science, comparative toxicology would dictate that the more information gained, from as wide a range of species as is practical, will give the best assessment for any subsequent problems in the clinic. This pragmatic approach should prove to be more successful than one based entirely upon an assumption, and in many cases the assumption is incorrect, that the primate always predicts human toxicity better than the nonprimate, including the dog.

Is a quantitative risk assessment of air quality in underground parking garages possible?

Little information is available about the health risks associated with time spent in underground parking garages. The objective of this study was to determine whether it is possible to quantify the health risks associated with these garages without epidemiologic data on the subject. We followed the standard procedure for health risk assessment. We searched the literature for pollutant concentrations in the air samples of underground parking garages, the hazards associated with their inhalation, and their toxicological reference values. Conditions of occupational and user exposure were estimated by scenarios and taken into account to discuss toxicological reference values by modifying (with Haber's law) the adjustment factors for exposure frequency and duration. Risk quantification was possible for 39 pollutants. Acute exposures to CO and NO2 exceed toxicological reference values, as does chronic exposure to benzene for threshold effects. The risk of a carcinogenic effect associated with benzene may be greater than 10(-5). Excess exposure to air pollution indicators (PM and NO2) is also elevated, judging by the WHO Air Quality Guidelines, and also when comparing to levels with reported effects in epidemiologic studies. The risk associated with underground parking garages can be evaluated only in part. The information available is nonetheless sufficient to justify actions to reduce exposure.

PRACTICAL IMPLICATIONS

The risks associated with exposure in underground parking garages cannot be thoroughly evaluated because of inadequate knowledge of exposures and of the toxicity of pollutants. The available knowledge is nonetheless sufficient to advise that risk management measures should be taken to reduce both acute and chronic exposures.

Risk assessment in regulatory policy making for human and veterinary public health

Risk assessment is the method of systematically identifying and assessing factors that influence the probability and consequences of a negative event occurring. One responsibility of veterinary medicine is to protect animal and human health. Food animal production uses antibiotics to enhance production. Regulators evaluate new production technology to ensure animal safety and safe, edible products and to make public policy decisions by assessing risks/benefits. The U.S. Food and Drug Administration, Center for Veterinary Medicine's (CVM's) first risk assessment addressed the potential human health impact of campylobacter effects associated with the use of fluoroquinolines in food-producing animals. CVM used the Monte Carlo method to estimate risk byprobability distributions that reflect the uncertainty and variability in the data used for the assessment. Enterococci faecium is a species more likely to be resistant to antibiotics of last resort. Effective control of multidrug-resistant enterococci will requirea better understanding of the transfer of E. faeciumfrom animals to humans and the interaction between E. faecium, the hospital environment, and humans; prudent antibiotic use; better contact isolation in hospitals; and better surveillance. CVM will model these factors in a second, more complex risk assessment designed to examine the indirect transfer of resistance from animals to humans. Use of risk assessments allows researchers, the industry, regulatory authorities, and educators to make better policy decisions regarding antimicrobial use in food animals and humans and the development of resistance. Today the question of whether the use of antimicrobials for growth enhancement infood animals should or should not be terminated for the benefit of human health remains unresolved.

Educational issues in clinical pharmacology: who are our audiences and what are their specialized needs? One specialized need: "understanding the role of veterinary medicine in public health"

When considering educational issues and the need to update the curriculum for clinical pharmacologists for the new millennium, a number of questions must be raised. Who are our audiences? What are the specialized needs? This educational article identifies the audience, which includes those with diverse degrees such as MDs, PhDs, PharmDs, RNs, DVMs, and other non-MD prescribers working in academia, industry, clinical research organizations, and government in multifaceted disciplines requiring a knowledge base of physiology, pharmacology, biochemistry, anatomy, microbiology, pathology, medicine, and the drug development process of preclinical and clinical studies complete with protocols, pharmacokinetics, and statistics. One specialized current educational issue for clinical pharmacologists to understand is the impact of animal therapeutic and subtherapeutic use of antimicrobials on antibiotic use in human medicine.

Unexpected tumour findings in lifetime rodent bioassay studies--what to do?

Currently, the majority of substances tested in lifetime bioassays in rodents are not mutagenic and, therefore, at the most weakly carcinogenic, generally by epigenetic mechanisms. It thus appears obvious that only marginal increases of tumour incidences can be expected in lifetime bioassays and that, therefore, every aspect of a potential carcinogenic effect must be thoroughly evaluated. This paper describes a series of key factors, which should be looked at in order to exclude that the lifetime bioassay in question is flawed for design, technical or qualification reasons. It also provides some hints whether there is indeed a real effect and not just a variation of the spontaneous tumour incidences. Tumour findings must be seen in the context of the animal model, the pharmcokinetics and pharmcodynamics of the test substance, as well as any other observation in the present or other studies with the test substance, including non-tumour findings and--in particular--potential precursor lesions and effects on feed intake and survival. The possibility that the observed carcinogenic effects may be species-specific and not relevant for man is discussed. It is also important to check what findings are reported with similar substances or substances with the same pharmacological effect. Data from additional investigations on material of the same study and/or mechanistic studies are often needed to support the final risk assessment.

Using molecular epidemiology in assessing exposure for risk assessment

Quantitative estimation of health risks depends on exposure characterization, the nature of the dose response relationships, and the toxicity of the agents involved. The greatest uncertainties in risk assessment almost always arise from sparse or inadequate exposure data, inadequate understanding of exposure mechanisms, and insufficient understanding of the exposure-dose-response pathway. Additional sources of uncertainty arise when mixed or multiple exposures are implicated in the disease pathway, and as a result of variability in both exposures and responses within and between individuals. Here we consider the role of exposure assessment in the risk assessment process, the use of biological markers or molecular epidemiology to contribute to improvements in exposure assessment for risk assessment, and uncertainties associated with the use of biological markers.