fixed-dose procedure fixed-dose procedure the fixed-dose procedure (fdp), proposed in 1992 by the british toxicology society, is a method to assess a substance's acute oral toxicity. in comparison to the older ld50 test developed in 1927, this procedure produces similar results while using fewer animals and causing less pain and suffering. as a result, in 1992 this test was proposed as an alternative to the ld50 test by the organisation for economic co-operation and development under oecd test guideline 420. however, the u.s. food and drug administration has begun to approve non-animal alternatives in response to research cruelty concerns and the lack of validity/sensitivity of animal tests as they relate to humans.