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Toxicity Testing in the 21st Century: A Vision and a Strategy
The committee extensively considered the expanded use of tiered testing (Option II) to alleviate some of the concerns with present practice. The tiered approach to toxicity testing entails a stepwise process for screening and evaluating the toxicity of agents that still relies primarily on test results in whole animals. The goal of tiered testing is to generate pertinent data for more efficient assessment of potential health risks posed by an environmental agent, taking into consideration available knowledge on the chemical and its class, its modes or mechanisms
TABLE 2-1 Options for Future Toxicity-Testing Strategies
Option I In Vivo
Option II Tiered In Vivo
Option III In Vitro and In Vivo
Option IV In Vitro
Animal biology
Animal biology
Primarily human biology
Primarily human biology
High doses
High doses
Broad range of doses
Broad range of doses
Low throughput
Improved throughput
High and medium throughput
High throughput
Expensive
Less expensive
Less expensive
Less expensive
Time-consuming
Less time-consuming
Less time-consuming
Less time-consuming
Use of relatively large numbers of animals
Use of fewer animals
Use of substantially fewer animals
Use of virtually no animals
Based on apical end points
Based on apical end points
Based on perturbations of critical cellular responses
Based on perturbations of critical cellular responses
Some screening using computational and in vitro approaches; more flexibility than current methods
Screening using computational approaches possible; limited animal studies that focus on mechanism and metabolism
