Acute toxicity.

1. Inventory of methods currently available From the regulatory point of view, the main objective of acute toxicity testing is basically to classify chemicals according to their intrinsic toxicity as required by the EEC directive on classification, packaging, and labelling of dangerous substances (Council Directive 67/548/EEC and subsequent amendments). This requirement aims to protect public health by regulating exposure to potentially dangerous materials. Classification of chemicals is done on the basis of the medium lethal dose (LD50) value, defined as “the statistically derived single dose of a substance that can be expected to cause death in 50% of the animals in an experimental group”. The LD50 concept was first introduced in 1927 for establishing the toxic potency of biologically active compounds such as digoxin (1). Since the end of the 1970 ́s the LD50 test has been widely criticised for both scientific and animal welfare reasons (2, 3), and the test procedure has been modified in various ways to reduce the number of animals required, and to reduce the suffering caused to any animal used (4). This modification to the classical LD50 test includes the fixed-dose procedure, OECD TG 420 (5), the acute-toxic-class method, OECD TG 423 (6), and the up-and-down procedure, OECD TG 425 (7). In 2002 the original LD50 test, OECD 401 (8), has been deleted from the OECD guidelines.