AZAPERONE First draft prepared by Dr G. Roberts Toxicology Evaluation Section Commonwealth Department of Human Services and Health Canberra, Australia 1. EXPLANATION Azaperone is a butyrophenone neuroleptic tranquillizer which had been previously evaluated at the thirty-eighth meeting of the Committee (Annex 1, reference 97). At that time, an ADI was not established and the Committee requested the following information before reviewing the compound again: 1. Additional data from genotoxicity studies, which should include: (a) A study with Salmonella typhimurium strains that were reported by one laboratory to be sensitive to azaperone and some of its metabolites, and (b) studies with cultured mammalian cells in which a variety of effects are investigated, including chromosomal aberrations and the induction of mutations. The results of these studies would determine whether further data are required. 2. Studies from which a NOEL for pharmacological effects in humans could be derived. 3. A justification for the protocol utilized in the reproduction study in rats that was submitted, and in particular for the very limited dosing regimen used in the females and the failure to dose the males. 4. Studies on the concentrations of residues of azaperone and azaperol in both muscle and fat of pigs treated with azaperone over a 3-day period. This monograph addendum summarizes the data that have become available since the previous evaluation (Annex 1, reference 98). 2. BIOLOGICAL DATA 2.1 Toxicological studies 2.1.1 Special studies on genotoxicity The results of an in vitro study of azaperone is summarized in Table 1. Table 1. Result of a genotoxicity study on azaperone Test system Test object Concentration Results Reference Forward Mouse 33-237 µg/ml1 Negative van de Waar & mutation lymphoma 18-100 µg/ml2 Enninga, 1993 (L5178Y TK +/-) 1 Without exogenous metabolic activation. 2 With exogenous metabolic activation (aroclor 1254-induced rat liver microsomes). In two independent experiments, azaperone did not induce forward mutations; appropriate positive control substances gave the expected responses, demonstrating the sensitivity of the assay (van de Waart & Enninga, 1993). 3. COMMENTS The information provided included data from a recent genotoxicity assay and an evaluation report that discussed all toxicological and pharmacodynamic data considered to be relevant to the establishment of an ADI for azaperone. The Evaluation Report (Van Cauteren et al. , 1994) states that azaperone should not be considered carcinogenic because it is not genotoxic, it is not structurally similar to known carcinogens, and no unexpected adverse effects were demonstrated in the toxicity studies. Evidence in support of a negative structure-activity relationship between azaperone and known carcinogens was not available. The Committee considered that such information should be provided. The Committee reconsidered the results from the previously reviewed genotoxicity assays. Conflicting results were reported in two studies of azaperone in the Salmonella typhimurium mutation assay. In one study, positive results were obtained with azaperone and some of its synthesized metabolites in the presence of an exogenous metabolic activation system. In the second and more thorough study of azaperone, no mutagenic effect was observed. The metabolites were not tested in this second study. The mutagenicity of azaperone and its metabolites in the Salmonella assay remains unresolved. A new study on cultured mouse lymphoma cells showed no mutagenic effects and micronucleus and dominant lethal tests have shown no evidence for genotoxic activity. The Committee concluded that the weight of evidence suggests that azaperone has low potential for genetic damage. In relation to reproductive toxicity studies, the evaluation report stated that no adverse effects were found in the male genital tract in rats dosed up to 18 months. For this reason a male fertility study was not performed. Although histological changes were not observed in the male reproductive tract, this is only one aspect in the assessment of reproductive performance. Therefore, the Committee concluded that male fertility had not been adequately assessed and a study to assess reproduction and fertility in males was necessary. Details were provided that confirmed the NOEL for sedation in humans of 30 µg/kg bw. However, the Committee was unwilling to use this study in establishing an ADI because the observations were of a subjective nature and the experiment was poorly controlled. Reconsidering the pharmacological data, the NOEL of 630 µg/kg bw in a sensitive assay in the dog was considered to represent a more objective and appropriate measure of the pharmacological activity of azaperone. 4. EVALUATION The Committee considered that the pharmacological effects of azaperone were the most relevant for the determination of the ADI. Using the NOEL of 630 µg/kg bw for pharmacological activity in dogs and a safety factor of 200, a temporary ADI of 0-3 µg/kg bw was established. 5. REFERENCES VAN CAUTEREN, H., LAMPO, A., VANPARYS, Ph., MAES, L., ENGELEN, M. & VAN LEEMPUT, L. (1994). Review report on the toxicological, pharmacokinetic and pharmacodynamic documentation related to azaperone. Unpublished Report No. V8672 from Janssen Research Foundation. Submitted to WHO by Janssen Pharmaceutica, Beerse, Belgium. VAN DE WAART, E.J. & ENNINGA, I.C. (1993). Evaluation of the mutagenic activity of azaperone in an in vitro mammalian cell gene mutation test with L5178Y mouse lymphoma cells (with independent repeat). Unpublished Report No. 94635 by RCC Notox. Submitted to WHO by Janssen Pharmaceutica, Beerse, Belgium.
See Also: Toxicological Abbreviations Azaperone (WHO Food Additives Series 29) Azaperone (WHO Food Additives Series 41) AZAPERONE (JECFA Evaluation)