The Dermal Up-and-Down Procedure: An Alternative Method for Acute Dermal Systemic Toxicity Testing

U.S. agencies that regulate chemicals and chemical products require acute dermal systemic toxicity testing to estimate the potential for life-threatening or fatal toxicity from dermal exposures. The proposed dermal up-and-down procedure (UDP) is a sequential sampling design that can potentially reduce the use of animals for acute dermal systemic toxicity testing of nontoxic compounds by 85%. Sequential testing is a powerful statistical sampling technique that allows fewer animals to be used than simultaneous testing of multiple groups of animals with multiple doses as specified in current regulatory test guidelines. In the proposed dermal UDP, individual animals are dosed sequentially, with 48 hours between doses. The response of each animal is used to determine the dose applied to the next animal. If an animal dies, the next animal is tested at a lower dose. If an animal lives, the next animal is tested at a higher dose (with the exception of testing at the default starting doses). The proposed dermal UDP merges the main and limit tests in the current test guidelines into a single test by starting at traditional limit test doses, 2000 mg/kg or 5000 mg/kg, based on regulatory needs. The dose-spacing factor for test substance doses is 4.2. The default doses based on a starting dose of 5000 mg/kg are 5000, 1200, 300, 70, 15, and 4 mg/kg. If test results are to be based on 2000 mg/kg as a starting dose, then the default doses are 2000, 500, 100, 25, and 5 mg/kg. If an investigator, prior to testing animals, expects that the dose expected to produce lethality in 50% of the animals tested (LD50) is less than the default starting dose, testing should start one step below the estimated LD50. The proposed dermal UDP can reduce animal use while providing regulatory agencies with a dermal LD50 estimate for dermal hazard classification. (ILS staff supported by NIEHS Contract N01-ES 35504: SRA staff supported by NIEHS Contract GS-23F-9806H.)