PROPAMOCARB
EXPLANATION
Propamocarb was evaluated for acceptable daily intake by the
Joint Meeting in 1984 (Annex 1, FAO/WHO, 1985b), after which a
toxicological monograph was published (Annex 1, FAO/WHO, 1985c). A
temporary ADI of 0 - 0.02 mg/kg b.w. was established at that time. The
further work or information required, and some of the information that
was identified, at the 1984 Joint Meeting, as being desirable were
considered at the present Meeting. These data are summarized in this
monograph addendum.
NOTE: Unless otherwise indicated, the studies summarized in this
monograph were conducted with Previcur N, an aqueous
formulation of technical propamocarb hydrochloride
containing approximately 65 - 70% of the active ingredient.
Unless otherwise specified, the dosages used in these
studies are expressed in terms of the formulation.
EVALUATION FOR ACCEPTABLE INTAKE
BIOLOGICAL DATA
Biochemical aspects
Metabolism and pharmacokinetics
The 1984 Joint Meeting, following its review of data submitted on
propamocarb, asked for further information on metabolism and
pharmacokinetic studies in mice and rats at multiple dosage levels.
Pharmacokinetic and metabolism studies have been conducted with
14C-propamocarb.HCl in female rats following single or multiple (14
and 21 days) oral treatments. These data were submitted to the
1984 Joint Meeting. The results show that the test substance is
quantitatively absorbed and very rapidly excreted, predominantly via
the urine. About 90% of the administered radiolabel was excreted in
the urine within 24 hours following single oral doses; a further 3 -
4% was recovered in the faeces. Repeated oral administration over 14
or 21 days did not significantly alter this pattern. Very Low levels
of radiolabelled equivalents remained in body tissues following single
oral administration (1.7% of the administered dose after 24 hours,
excluding the gastrointestinal tract), and even lower levels as a
percent of the total dose following multiple (14 or 21 day) treatments
(0.33%, equivalent to 4.6 - 7.0% of the last single dose), indicating
that accumulation of propamocarb equivalents was very low (Kopp
et al., 1979).
Seven urinary metabolites have been identified, which account for
66% of the excreted urinary radioactivity, the remainder being
distributed among at least 20 other substances. The main route of
metabolism appears to be an oxidation pathway with hydrolytic cleavage
occurring as a secondary route (Brühl & Celorio, 1982; 1984).
The results of toxicological studies are relevant in terms of
predicting interspecies differences in the pharmacokinetics and
metabolism of propamocarb. In long-term studies, mice received
propamocarb hydrochloride in the diet at levels up to 52 - 54 mg/kg
b.w./day (500 ppm) for 104 weeks, and rats received doses up to
36 - 45 mg/kg b.w./day (1000 ppm) for 106 - 110 weeks. There were no
signs related to treatment except for a possible marginal decrease in
food intake among female rats receiving 1000 ppm subsequent to week 78
(Hunter et al., 1983a; 1983b).
In addition, in a 90-day dietary study in rats, animals were fed
doses up to 5000 ppm (362 - 396 mg/kg b.w./day), resulting in slight
reductions in body weights in females and also in reduced food
efficiency of males and females (Kojima & Enomoto, 1982).
Acute oral toxicity studies in rats and mice administered single
doses up to 4800 mg/kg b.w. have shown very similar LD50 values
(2650 - 2800 mg/kg b.w. in mice and 2000 - 2900 mg/kg b.w. in rats),
with very similar signs of toxicity in both species, namely apathy,
hypokinesia, clonic convulsions, and staggering gait (Annex 1,
FAO/WHO, 1985c).
The lack of significant species-specific toxicological findings
in the long-term studies conducted at high dietary levels in rats and
mice, and the similarities of the toxicological signs on acute oral
administration in these species, indicate that propamocarb hydro-
chloride has a similar and very low order of toxicity in rats and
mice and therefore strongly suggests a lack of relevant inter-species
differences in the pharmacokinetics and metabolism of propamocarb
hydrochloride in these animals.
Toxicological studies
Short-term study
The 1984 Joint Meeting requested complete data on a 5-week
feeding study in rats known to have been performed. The results of
this study were submitted for consideration by the present Meeting.
Groups of 10 male and 10 female Wistar SPF rats were administered
Previcur N in their diets at concentrations of 0, 50, 500, or 5000 ppm
for 5 weeks. Variables examined included mortality, clinical signs,
food and water consumption, and body-weight changes. Ophthalmoscopy,
haematology, bone marrow examination, urinalysis, and blood chemistry
and coagulation studies were performed. Necropsies were performed,
liver, kidney and heart weights were determined at termination, and
histopathological examinations of the liver, stomach, urinary bladder,
kidneys, and heart were performed.
Statistically-significant decreases in bone marrow lymphocytes in
male rats at 50 ppm and above and in female rats at 500 ppm and above
were noted, together with a decrease in total serum cholesterol in
male animals at 50 ppm and above and an increase in serum sodium
levels in males at 50 ppm and above and in females at 500 ppm and
above (Staben & Schöbel, 1986).
Although statistically significant, these findings remained
within the normal range found for this strain of rat and therefore a
treatment-related effect is unlikely. In addition, significant effects
on cholesterol levels were not noted in the 2-year chronic and
oncogenicity dietary study in rats at dose levels up to 1000 ppm
(Hunter et al., 1983b) or in a 90-day dietary study in rats at dose
levels up to 5000 ppm. This latter study also showed no significant
effects on serum sodium concentrations (Kojima & Enomoto, 1982). The
findings in the 5-week dietary study in rats are therefore believed
not to have any biological significance.
Long-term studies
Rats
An analysis of the long-term study in rats that was reviewed by
the 1984 Joint Meeting (Hunter et al., 1983b), with particular
reference to statistical methods, was reviewed by the present Meeting.
A 2-stage process was used. The first step (a 1-tailed Fischer exact
test) was a screening stage, intended to identify rumour sites where a
statistically-significant effect was present, with no adjustment for
differential mortality. The number of animals at risk was taken as the
number present at the beginning of the study (60 animals/sex/group,
excluding the interim-kill and withdrawal groups). The second stage
was a more detailed analysis using the statistical method recommended
by the International Agency for Research on Cancer (IARC), which takes
into account both differential mortality and the context of the
observations, i.e. whether a tumour is "fatal" or "incidental". This
statistical method was applied to sites identified in the first stage
of analysis and also to some biologically-related tumour types
(Chanter & Offer, 1986).
The results of the statistical evaluation were as follows:
1. Subcutaneous fibroma (males, females, and sexes combined);
No statistically-significant effects were found.
2. Subcutaneous fibrosarcoma (males, females, and sexes
combined):
A statistically-significant increase in the incidence of this
lesion was noted only in males and only in the high-dose group (1000
ppm) when compared with controls (P = 0.013). The test for trend was
also statistically significant. No statistically-significant effects
were found in females or in males and females combined from any dose
group.
3. Subcutaneous fibroma and fibrosarcoma (males, females, and sexes
combined):
The results of the IARC analyses indicate that the incidence of
subcutaneous fibrosarcoma alone was statistically significant in male
rats at 1000 ppm, compared with controls, and that the test for trend
for subcutaneous fibrosarcoma alone was statistically significant.
However, no subcutaneous fibrosarcomas were observed in the male
control rats in this study, which is an unusually low incidence
when compared with the historical control range for the CD strain
of rat. The overall incidence of male and female rats bearing
subcutaneous fibrosarcoma in any of the dose groups in this study was
within the upper limit of the historical control range for this strain
of rat. In addition, in the absence of (a) a clear dose relationship,
(b) a statistically-significant increase in subcutaneous fibroma and
fibrosarcoma combined in male rats, or (c) an increase in subcutaneous
fibrosarcoma alone in female rats, it was concluded that the
distribution of subcutaneous fibrosarcoma in male rats in this study
is fortuitous and unlikely to be related to the dietary administration
of Previcur N.
4. Mammary fibroadenoma (females only):
The overall test for heterogeneity between groups was significant
(P = 0.03) and the number of tumour-bearing animals in the 200 ppm
group was significantly higher than in the controls (P = 0.009). The
test for non-linearity was also significant (P = 0.013), thus
invalidating the test for trend.
5. Any mammary tumour (females only):
No statistically-significant effects were found. The overall
incidences of mammary fibroadenoma in female rats in the 200 and
1000 ppm groups were within the upper limit of the historical control
range. In the absence of (a) a significant test for trend, (b) a dose
relationship, or (c) effects on the overall distribution of any
mammary tumours, the result was considered to be of no biological
significance.
Dogs
Four groups of 6 male and 0 female beagle dogs received Previcur
N in the diet at dose levels equivalent to 0, 1000, 3000, or
10,000 ppm for 2 years. One male and 1 female dog at 10,000 ppm were
kept for an additional 29-week recovery period. There were no deaths.
There were no signs or symptoms considered to be evidence of toxicity
related to treatment, although 1 female in the high-dose group showed
occasional ataxia. Food consumption, body-weight gain, hearing tests,
and ophthalmoscopic examinations during the first 6 months of the
study showed no remarkable differences between controls and treated
animals.
A loss of colour and reflectability of the tapetum lucium of the
ocular fundus was noted in both eyes of all animals at 10,000 ppm from
9 months onward. The severity of this lesion remained stationary or
increased very slowly for the remainder of the treatment period and
was not reversible up to 29 weeks after termination of treatment.
Subretinal haemorrhage occurred in 1 animal at week 88. In the other
11 dogs at this dose level the retina and remaining ocular tissues
were clinically unremarkable.
Clinical laboratory investigations comprising haematology,
clinical chemistry, and urinalysis showed no changes that could be
related to treatment. Bone marrow examinations, organ weights, and
organ-weight ratios showed no differences between test and control
group animals at termination of the study.
Pathological examination confirmed the ocular changes in all
animals at 10,000 ppm, which were confined entirely to the tapetum
lucidum. Electron microscopic examination showed that the lesions
consisted of degeneration of the cell-specific paraplasmatic
inclusions (rodlets), together with degenerative cytoplasmic changes
in numerous tapetal cells. The cell organelles, however, were largely
intact. No necrotic cells, macrophages, or other cell infiltrates were
demonstrated in the sections examined. The ocular tissues adjacent to
the tapetum (retina and choroid) were ultrastructurally normal.
Pathological examination also revealed chronic erosive gastritis
and/or acute gastric mucosal erosions in dogs in all groups, with a
higher incidence in the treated groups. Glomerulosclerosis, confined
to the juxtamedullary areas, was noted in dogs at 0, 3000, and
10,000 ppm. In the lower-dose groups, the degree of glomerulosclerosis
was minimal, while at 10,000 ppm it was minimal to moderate in 4
animals. Thus, it cannot be excluded that this lesion is
treatment-related. There were no other morphological findings which
were considered to be related to treatment.
The NOEL in this study was considered to be 1000 ppm Previcur N
in the diet when fed to male and female dogs for 2 years, equivalent
to approximately 24 mg propamocarb.HCl/kg b.w./day.
The oculotoxic changes noted in the dogs at 10,000 ppm have not
been seen in non-tapetal animals and this lesion is therefore
considered to be a species-specific effect. The absence of this ocular
structure (tapetum lucidum) in humans excludes the possibility of this
oculotoxic lesion occurring in man due to exposure to Previcur N
(Bathe et al., 1985).
COMMENTS
To satisfy the requirement that further evaluation of historical
data on the incidence of subcutaneous fibrosarcoma in the CD strain of
rats used in the long-term study be performed, a 2-stage statistical
process was used. The first step was a 1-tailed Fischer exact test
used as a screening stage and the second was a method recommended by
the International Agency for Research on Cancer (IARC), which takes
into account both differential mortality and the context in which the
observations were made (fatal or incidental rumours).
The results of the evaluation showed no significant excess of any
of the tumour combinations examined (fibroma, fibrosarcoma, male,
female, combined sexes, and mammary rumours). Controls showed no
subcutaneous fibrosarcomas, an atypical value in view of historical
control data. No dose relationships for the induction of tumours were
seen.
From the complete data on the 24-month oral (feeding) study in
beagle dogs, significant findings were a degenerative change in the
tapetum lucidum, a species-specific effect, and therefore irrelevant
to humans. Erosive gastritis was seen in control and test animals, but
at a higher incidence in the treated group.
The data provided on metabolism and pharmacokinetic studies in
mice and rats were considered by the Joint Meeting to have dealt with
the relevant uncertainties in this area.
LEVEL CAUSING NO TOXICOLOGICAL EFFECT
Rat: 200 ppm in the diet, equivalent to 10 mg/kg b.w./day
Dog: 1000 ppm in the diet, equivalent to 25 mg/kg b.w./day
ESTIMATE OF ACCEPTABLE DAILY INTAKE FOR MAN
0 - 0.1 mg/kg b.w.
STUDIES WHICH WILL PROVIDE INFORMATION VALUABLE FOR THE CONTINUED
EVALUATION OF THE COMPOUND
Observations in humans.
REFERENCES
Bathe, R., Frei, T. Luetkemeir, H., Ellghausen, H., Schlotke, B,
1985 Weisse, I, & Terrier, C. 24-Month oral (feeding) study with
Previcur N in beagle dogs. Unpublished report No. PF-81.812
from Huntingdon Research Centre and Schering AG. Submitted
to WHO by Schering Aktiengessellschaft, Berlin (West).
Brühl, R. & Celorio, J. Propamocarb hydrochloride; Metabolism in rats.
1982 Unpublished report submitted to WHO by Schering
Aktiengessellschaft, Berlin (West).
Brühl, R. & Celorio, J. Metabolic pathway of propamocarb hydrochloride
1984 in the rat. Unpublished report submitted to WHO by Schering
Aktiengessellschaft, Berlin (West).
Chanter, D. & Offer, J. Supplement 1. Previcur N (SN 66,752): The
1986 statistical analysis of selected rumour types from a
long-term dietary administration study in rats (SHG.165-G
/801056). Unpublished report No. SHG 219/86203/2 from
Huntingdon Research Centre and Schering AG. Submitted
to WHO by Schering Aktiengessellschaft, Berlin (West).
Hunter, B., Watson, M., Read, R.M., Prentice, D.E., Woodhouse, R.N.,
1983a Cherry, C.P., & Gibson, W.A. Previcur N (SN 66,752):
Potential tumorigenicity to mice in dietary administration
for 104 weeks. Unpublished report from Huntingdon Research
Centre, UK. Submitted to WHO by Schering
Aktiengessellschaft, Berlin (West).
Hunter, B., Jones, D.R., Heywood, R., Street, A.E., Jolly, D.W.,
1983b Offer, J.M., & Gibson, W.A. Previcur N (SN 66,752): Toxicity
and potential tumorigenicity in dietary administration to
rats for 104 weeks. Unpublished report No. SHG 165/801056/2
from Huntingdon Research Centre and Schering AG. Submitted
to WHO by Schering Aktiengessellschaft, Berlin (West).
Kojima, K. & Enomoto, M. Previcur N: Three-month subchronic oral
1982 toxicity study in rats. Unpublished report from Biosafety
Research Centre, Foods, Drugs, & Pesticides, Japan.
Submitted to WHO by Schering Aktiengessellschaft, Berlin
(West).
Kopp, R., Hümpel, M., Kühne, G., Aner, B., Klawa, D., & Rzadkiewicz,
1979 M. Pharmacokinetics of propamocarb hydrochloride on single
and repeated oral administration of 0.5 mg/kg in rats.
Unpublished report from Schering AG. Submitted to WHO by
Schering Aktiengessellschaft, Berlin (West).
Staben, P. & Schöbel, C. Previcur N: Subacute systemic tolerance study
1986 in rats with dietary administration over a period of 5
weeks. Unpublished report No. PF 5/86 from Schering AG.
Submitted to WHO by Schering Aktiengessellschaft, Berlin
(West).
See Also:
Toxicological Abbreviations
Propamocarb (Pesticide residues in food: 1984 evaluations)
Propamocarb (Pesticide residues in food: 1984 evaluations)
Propamocarb (JMPR Evaluations 2005 Part II Toxicological)