First draft prepared by
Dr G. Roberts
Toxicology Evaluation Section
Commonwealth Department of Human Services and Health
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
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. 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
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 &
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
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
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,
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.