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

Screening using computational approaches



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