LD50 test

Rats that died after dermal exposure to unspecified doses of hexachloroethane during an LD50 test protocol displayed ataxia, tremors, and convulsions before death (Weeks et al. 1979). 

Rowan, A. (1981). The LD50 Test A critique and suggestions for alternatives. Pharmaceutical... 

Zbinden, G. and Flury-Roversi, M. (1981). Significance of the LD50 Test for the toxicological evaluation of chemical substances. Arch. Toxicol. 47 77-99. 

A commercially interesting low calorie fat has been produced from sucrose. Proctor Gamble has patented a mixture of penta- to octafatty acid ester derivatives of sucrose under the brand name Olestra. It was approved by the FDA in January 1996 for use as up to 100% replacement for the oil used in preparing savory snacks and biscuits. Olestra, a viscous, bland-tasting liquid insoluble in water, has an appearance and color similar to refined edible vegetable oils. It is basically inert from a toxicity point of view as it is not metabolized or absorbed. It absorbs cholesterol (low density lipoprotein) and removes certain fat-soluble vitamins (A, D, E, and K). Hence, Olestra has to be supplemented with these vitamins. No standard LD50 tests have been performed on Olestra however, several chronic and subchronic studies were performed at levels of 15% in the diet, and no evidence of toxicity was found. No threshold limit value (TLV), expressed as a maximum exposure per m3 of air, has been established, but it is estimated to be similar to that of an inert lipid material at 5 mg/m3. 

The value of the LD50 test and the problems associated with it have been reviewed (11). 

As a result of much recent controversy, the LD50 test has been the subject of considerable regulatory attention and as a result changes in requirements have been promulgated. These changes are intended to obtain more information but, at the same time, use fewer animals. 

Criticism of the LD50 Test. The criticisms of the test include ... 

It requires large numbers of experimental animals to obtain statistically acceptable values. Moreover the results of LD50 tests are known to vary with species, strain, sex, age, and so on (Table 21.4) thus the values are seldom closely similar from one laboratory to another despite the numbers used. 

Because, for regulatory purposes, the most important information needed concerns chronic toxicity, little useful information is derived from the LD50 test. The small amount of information that is acquired could be obtained as well from an approximation requiring only a small number of animals. 

Support of the LD50 Test. Continued use of the test has been advocated, however, on the grounds that it is of use in the following ways ... 

LC50 (median lethal concentration) The concentration of a test chemical that, when a population of test organisms is exposed to it, is estimated to be fatal to 50% of the organisms under the stated conditions of the test. Normally used in lieu of the LD50 test in aquatic toxicology and inhalation toxicology. 

Survey of the QSAR and in Vitro Approaches for Developing Non-animal Methods to Supersede the in Vivo LD50 Test. 

All attainable information should be used, including human experience. But this information should be restricted to that which pre-exists (e.g. the results of a skin LD50 test or historical information on skin corrosion). 

Spielmann H, Genschow E, Liebsch M, and Halle W (1999) Determination of the starting dose for acute oral toxicity (LD50) testing in the up-and-down procedure (UDP) from cytotoxicity data. ATLA 27 957-966. 

Schlede E, Genschow E, Spielmann H, Stropp G, Kayser D (2005) Oral acute toxic class method a successful alternative to the oral LD50 test. Regul Toxicol Pharmacol 42(1) 15-23. doi 10.1016/j.yrtph.2004.12.006... 

LD50 = 50% lethal dose. It should be emphasized (even in a book for organic chemists) that the LD50 test is now outdated because of the large number of mammals necessary to carry out such tests (see Zbinden, 1981). The European Community issued a statement (Anonymous, 1990) of its intention to replace the LD50 test by the so-called Fixed Dose Procedure. 

EkwaU, B, Bondesson, 1, CateU, J.V., Gomez-Lechon, M. J., Heiberg, S., Hogberg, J. Jover, R., Ponsoda, X., Rommert, L., Stenberg, KL., Walum, E. (1989) Cytoxocity evaluation of the first ten MEIC chemicals Acute lethal toxicity in man predicted by cytotoxicity in five ceUular assays and by oral LD50 tests in rodents. ATLA 17 83-100. 

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