Pesticide residues in food - 2003 - Joint FAO/WHO Meeting on Pesticide Residues

First draft prepared by
D. Andrew, R. Shillaker & I. Dewhurst
Pesticides Safety Directorate, Department for Environment,
Food and Rural Affairs, York, England

Methoxyfenozide (N-tert-butyl-N’-(3-methoxy-o-toluoy)-3,5-xylohydrazide) is a dia-cylhydrazine insecticide that acts as an ecdysone agonist. Methoxyfenozide has not been evaluated previously by the JMPR. The Meeting noted that the purity of the material tested (>98%) was higher than that of the material proposed for commercialization (97%), but concluded that the findings were applicable to the proposed technical specification and production material.

The studies of toxicity with methoxyfenozide were performed between 1994 and 1998. The purity of the methoxyfenozide used in the majority of studies (98-99.2%) was higher than that of the proposed technical specification (purity, 97%). Data supplied confirmed that the specifications of the main toxicity batch were consistent with those of the production material. Overall, the Meeting concluded that the material tested was adequately representative of the production material.

1.1 Absorption, distribution and excretion

The toxicokinetics and metabolism of methoxyfenozide in rats were investigated using the following ¹⁴C-labelled test materials: (i) [methoxyphenyl ring uniform label-¹⁴C]methoxyfenozide ("A-ring label"), radiochemical purity, 98.2%; (ii) S[dimethylphenyl ring uniform label-¹⁴C]methoxyfenozide ("B-ring label"), radiochemical purity, 99.0%; (iii) t-butyl [¹⁴C]methoxyfenozide ("t label"), radiochemical purity, 96.4%.

Rats

In a study of absorption, distribution, metabolism, and excretion that was designed to comply with the pesticide assessment guidelines of the United States Environmental Protection Agency (EPA) and Japan and that complied with good laboratory practice (GLP), forty-two groups of Sprague-Dawley rats (up to five animals of each sex per group) were given either A-ring, B-ring or t-butyl-labelled [¹⁴C]methoxyfenozide at a nominal dose of 10 or 1000 mg of active substance/kg bw, by oral gavage. The test materials were prepared as suspensions in 0.5% aqueous methylcellulose. The [¹⁴C]methoxyfenozide was combined with appropriate amounts of unlabelled (¹²C) methoxyfenozide for dilution of radioactivity at the highest dose and with ¹³C-labelled (A-ring carbonyl; B-ring methyl; t-butyl carbon) methoxyfenozide for identification of metabolites.

Three basic experimental designs were used: one to determine the excretion, distribution, and mass balance of radioactivity (120 h after dosing), one to evaluate the pharmacokinetics of radioactivity in the blood (to determine the time to C_max and ½ C_max), and one to determine the tissue distribution of radioactivity at C_max, ½ C_max and 5 days after dosing. Biliary excretion was investigated in bile-duct cannulated rats given a dose of 10 mg/kg bw by gavage. In addition to the single dose experiments, one group of animals received diets containing unlabelled methoxyfenozide at a concentration of 200 mg/kg (equivalent to 20 mg/kg bw per day) for 2 weeks before receiving a single oral dose of [¹⁴C-A-ring]methoxyfenozide at 10 mg/kg. Another group received five daily oral doses of [¹⁴C-A-ring]methoxyfenozide at 10 mg/kg by gavage. The amount of radiolabel contained in exhaled air was determined using activated charcoal and sodium hydroxide traps and liquid scintillation counting (LSC) after appropriate sample preparation.

Figure 1. Structure of methoxyfenozide

The excretion of radiolabel after a single oral dose of A-ring, B-ring or t-butyl-labelled methoxyfenozide followed a similar pattern, regardless of dose (representative data for A-ring-labelled material are presented in Tables 1-3). For each dose, the results for the excretion, pharmacokinetics and tissue distribution of radioactivity were generally comparable for males and females. The overall recovery of ¹⁴C ranged from 97% to 104% of the administered dose for all experiments, including the biliary excretion experiment. Most of the radiolabel was excreted during the first 24 h after administration of a single oral dose, primarily in the faeces, which contained 58-77% of the administered dose at day 1 (86-97% after 5-7 days). Females consistently excreted a greater proportion of the administered dose in the urine. Minimal amounts of radiolabel (0.10-0.23%) remained in the tissues and carcass at 5 days after a single dose. Less than 0.2% of the administered dose was exhaled as ¹⁴CO₂. These data indicate that the A-ring and B-ring remain associated during the metabolism of methoxyfenozide. Pre-treatment of animals with diets containing methoxyfenozide for 2 weeks, or with five daily doses of ¹⁴C-labelled methoxyfenozide did not appreciably alter absorption or distribution (Table 1).

Table 1. Recovery of A-ring-labelled [¹⁴C]methoxyfenozide (%) in rats

From Watts & Longacre, 1998
^a 14 days at 200 mg/kg [¹²C]methoxyfenozide plus a single dose of [¹⁴C-A-ring]methoxyfenozide at 10 mg/kg bw administered by gavage
^b Six daily doses administered by gavage

Table 2. Toxicokinetic half-lives (T_1/2) for elimination and peak concentration of radiolabel in plasma in rats given a single oral dose of A-ring-labelled [¹⁴ C]methoxyfenozide by gavage

From Watts & Longacre (1998)

Table 3. Mean concentration (pg equivalents/g) of radioactivity in blood, carcass, and tissues in rats given a single oral dose of A-ring-labelled [¹⁴ C]methoxyfenozide

From Watts & Longacre (1998)

The biliary excretion of radiolabel after a single oral dose of [¹⁴C-A-ring]methoxyfenozide at 10 mg/kg was investigated in bile-duct cannulated rats (Table 1). Biliary excretion was rapid, with 22% (females) and 50% (males) of the administered dose being excreted within 12 h. Overall, 38% (females) and 64% (males) of the radiolabel was excreted in bile within 72 h. Considerable variability between individual animals was seen in cannulated female rats (bile, 13-55%; and urine, 5-43% within 72 h), but the overall amount absorbed (in bile, urine, carcass and tissues) was similar for all four females (56-67%). Taking the biliary component into account, the overall extent of oral absorption of methoxyfenozide at a dose of 10 mg/kg bw was 60-70% in both sexes.

Toxicokinetic parameters for plasma and blood were investigated after a single dose of [¹⁴C]methoxyfenozide (at a lower and higher dose for each labelling position) by gavage. Findings were similar, irrespective of labelling position. [¹⁴C]Methoxyfenozide was rapidly absorbed, with maximum concentrations of radioactivity in blood and plasma being observed 15-30min after dosing (Table 2). The maximum concentrations were similar for each radiolabel and sex at each dose, but tended to be slightly higher in males, especially at the lower dose. Peak blood concentrations were not proportional to the dose administered, i.e. peak concentrations in blood and plasma at the highest dose were only 24-68-fold higher than at the lowest dose, which is indicative of saturation of absorption. Values for the area under the curve (AUC) were not calculated. Elimination of radiolabel from the plasma followed a biphasic pattern (Table 2), with secondary peaks indicative of enterohepatic circulation (especially in females). In rats given the test compound at the higher dose, the overall elimination half-life of radiolabel from the plasma was longer than in rats given the lower dose. These results are consistent with saturation of the elimination pathway for parent compound and/or its metabolites in rats at the higher dose in both sexes, with these effects being more prominent in females.

The tissue distribution of radioactivity was investigated after a single dose of A-ring-labelled or t-labelled methoxyfenozide administered by gavage (at C_max, ½ C_max and at 5 days after dosing at 10 or 1000 mg/kg bw), and after a single dose of B-ring-labelled methoxyfenozide (5 days after dosing at 10 mg/kg bw). Tissue distribution was also investigated after dosing with A-ring-labelled methoxyfenozide at 10 mg/kg bw as a pulse dose (5 days after dosing) and as a repeated dose (at 0.25 h after the last dose, at about C_max).

Similar results were seen in all experiments. The absorbed radioactivity was widely distributed, with the highest concentration of absorbed radioactivity found in the liver at 0.5-2 h after dosing (the higher concentrations found in the stomach and intestinal tract were attributed to largely unabsorbed material). Tissue distributions for the A-ring radiolabel are given in Table 3. Clearance from the body was extensive; 5 days after a single dose of 10 mg/kg bw, the highest percentage of radioactivity, representing <0.1% of the administered dose, was found in the liver (Watts & Longacre, 1998).

1.2 Biotransformation

A proposed metabolic pathway for methoxyfenozide in rats is shown in Figure 2.

Figure 2. Proposed metabolic pathway for methoxyfenozide in rats

From Watts & Longacre (1998)
M14 and M24 = main faecal metabolites
M16 and M26 (glucuronides of M14 and M24) = main biliary metabolites

Metabolites in the urine, faecal, and bile samples from the study described above were identified and quantified. Most data were obtained for methoxyfenozide labelled with ¹⁴C in the A ring and t-butyl group. Urine samples (mostly collected up to 24 h after dosing) were analysed directly by reverse-phase high-performance liquid chromatography (HPLC) and normal-phase thin-layer chromatography (TLC). Faeces (collected up to 24-48 h after dosing) were homogenized, extracted with acetonitrile and then partitioned to yield methylene chloride and aqueous fractions (which were analysed by reverse-phase HPLC and TLC) and post-extraction solids. Bile samples were analysed directly by reverse-phase HPLC and liquid chromatography-mass spectrometry (LC-MS). Metabolites were characterized and identified by TLC, gas chromatography-mass spectrometry (GC-MS) and/or LC-MS and compared with available reference standards. Selected metabolites were also derivatized for structural confirmation.

[¹⁴C]Methoxyfenozide was metabolized extensively. A total of 31 metabolites, of which 25 were identified, were isolated from the rat urine and faeces. In addition, 24 metabolites were found in the bile and characterized; of these, 12 were identified (four were unique to bile). Table 4 summarizes the distribution of metabolites in the urine and faeces for methoxyfenozide labelled on the A-ring. Similar patterns were seen with B-ring, and t-butyl-labelled methoxyfenozide.

Table 4. Major metabolites of A-ring-labelled methoxyfenozide in rats (% of administered dose)

From Watts & Longacre (1998)
NA, Not applicable; PES, Post-extraction solids

Parent compound was found only in the faeces (not in the urine or bile) and comprised 14-26% and 30-39% of the administered dose for animals at the lower and higher doses, respectively, indicating that animals at the lower dose metabolized a greater fraction of the administered dose compared with animals at the higher dose. Seven metabolites (M10, M14, M16, M22, M24, M28, M30) were found to be present in faeces plus urine each at >2% of the administered dose. The predominant metabolites were M14 (desmethylated parent) and M24 (hydroxy methyl derivative). Parent compund plus these seven metabolites accounted for 74-90% of the administered dose (in faeces plus urine) in all groups. For each of these groups, the total of parent plus identified metabolites accounted for >83% of the administered dose, i.e. the metabolic profile of methoxyfenozide in faeces and urine was well defined. Less than 5% of the administered dose was present as metabolites formed from the cleavage of the amide bridge.

Two metabolites, M1 6 (A-ring glucuronide of M14) and M26 (A-ring glucuronide of M24), were the main metabolites in bile. M16 was present at 13% and 18% in males and females respectively, M26 was present at 5% in males and 11% in females, all other metabolites represented <3% of the administered dose. The presence of M16 and M26 at higher concentrations in bile than in faeces indicates that these two metabolites were subject to subsequent hydrolysis.

The primary pathway probably involves demethylation of the A-ring methoxy moiety to form the corresponding phenol (M14), which is conjugated with glucuronic acid to form M16. Hydroxylation on the B-ring methyl moieties is also a significant metabolic pathway. Cleavage of methoxyfenozide to release either of the rings or the t-butyl group is only a minor pathway; none of the cleaved metabolites (M06, M07, M13, M32-36) were present at >2% of the dose. In males, however, cleaved metabolites represented up to about 50% of the metabolites found in urine. There was an indication that males cleaved more of the absorbed dose than did females, on the basis of urinary metabolite patterns.

Results for the animals receiving diets containing methoxyfenozide for 14 days plus a single dose of [¹⁴C]methoxyfenozide at 10 mg/kg bw by gavage showed evidence of induction of metabolism. Concentrations of M22, M28 and M30 increased, while concentrations of M14 and M24 were reduced relative to concentrations in animals that received only a single dose of [¹⁴C]methoxyfenozide at 10 mg/kg bw (Table 4) (Watts & Longacre, 1998).

1.3 Dermal absorption

The dermal absorption in vivo of methoxyfenozide formulated as an aqueous flow-able liquid (RH-112,485 2F) or as a wettable powder (RH-112,485 280WP) was tested in rats in a study that was designed to comply with US EPA guidelines and GLP. The methoxyfenozide administered was uniformly labelled with ¹⁴C on the methoxyphenyl ring; this is acceptable given the limited cleavage seen in studies of oral metabolism. To provide data on exposure to the concentrated product and in-use-dilutions, groups of four male Crl : CD BR rats received radiolabelled methoxyfenozide at three aqueous dilutions (0.025, 0.25, or 2.5% w/v), applied in a volume of 100 µl to a shaved area of about 10 cm² for 1, 10, or 24 h. Systemically absorbed methoxyfenozide was defined as the radiolabel found in the carcass, urine (plus urine funnel and cage washes), faeces, and whole blood.

For RH-112,485 2F, the total mean recovery of radiolabel in all groups ranged from 98% to 114%. After an exposure of 1, 10, or 24 h to ¹⁴C-labelled RH-112,485 2F formulation diluted in water to a concentration of 2.5, 0.25, or 0.025% w/v, a small amount of radiolabel (<1-4%) was systemically absorbed.

For RH-112,485 280 WP, three animals with poor recoveries were excluded from further analysis. The total mean recovery of radiolabel in all groups ranged from 85% to 110%. After an exposure of 1, 10, or 24 h to ¹⁴C-labelled RH-112,485 280 WP at a concentration of 2.5, 0.25, or 0.025% w/v, <1-2% of radiolabel was systemically absorbed.

Findings were similar for both formulations. The amount of radiolabel that was systemically absorbed did not increase linearly between the 10-h and 24-h exposure periods, indicating that most of the radiolabel that remained in or on the skin after washing was tightly bound and was not available for systemic absorption. This study shows that methoxyfenozide is poorly absorbed (<4%) after dermal exposure to either of the formulated products or in-use dilutions. The low rate of dermal absorption may be attributed to very low solubility in water (3.3 mg/l at 20°C) (Watts & Frederick, 1998).

2.1 Acute toxicity

(a) General toxicity

The acute toxicity of methoxyfenozide is summarized in Table 5. All studies used methoxyfenozide of 98% purity, and complied with the applicable OECD guideline and GLP. Methoxyfenozide is of low acute toxicity when administered by the oral, dermal and inhalation routes. No specific signs of toxicity were reported.

Table 5. Acute toxicity of methoxyfenozide

MMAD, mass median aerodynamic diameter

(b) Ocular and dermal irritation and dermal sensitization

2.2 Short-term studies of toxicity

(a) Oral administration

(b) Dermal exposure

Rats

This study of toxicity exceeded the basic requirements of OECD guideline 410 (1981), notably in terms of the number of animals used and the extent of the histopathological examination. The study complied with GLP. Methoxyfenozide (purity, 98%), a powder, was moistened with tap water (1:1, w/v) and applied to the shaved intact skin (about 10% of the total body surface area) of Crl:CD®BR rats (10 of each sex per group) at a dose of 0, 75, 300 or 1000 mg/kg bw per day for 5 days per week over a 4-week period (20 exposures). The exposure site was covered with an occlusive dressing, which was removed after 6 h and the exposure site was washed with soap solution and then wiped. Animals were observed routinely for mortality, signs of ill health, reaction to treatment, body weight and food consumption. Application sites were evaluated for skin irritation before each daily treatment and at terminal sacrifice. Haematology (including methaemoglobin measurement, but not reticulocyte count) and clinical chemistry were performed at terminal sacrifice. An indirect ophthalmoscopic examination was performed before initiation of dosing and at the end of the dosing period. An extensive histopathological examination (including treated and non-treated skin) was conducted for all control animals and animals at the highest dose. In addition, kidneys, liver, lungs and all gross lesions from all animals were examined histopathologically.

All rats survived to termination. There was no evidence of substance-related effects on clinical signs, skin irritation, ocular effects, haematology, clinical chemistry, organ weight or histopathology. A reduction in food consumption (13%) in week 4 and reduced body-weight gain (16% between days 0-28) in males at 1000 mg/kg bw per day was not considered to be an effect of clear toxicological importance; there was no statistically significant decrease in body weight and no effect on food consumption or body-weight gain was seen in females. The NOAEL was 1000 mg/kg bw per day, the highest dose tested (Parno et al., 1998a).

2.3 Long-term studies of toxicity and carcinogenicity

Mice

Groups of 60 male and 60 female Crl:CD-1®(ICR)BR (VAF Plus) mice were given diets containing methoxyfenozide (purity, 98%) at a concentration of 0, 70, 2800, or 7000 mg/kg for 18 months. These concentrations resulted in mean intakes of 0, 10.0, 405 or 1020 mg/kg bw per day in males, and 0, 12.8, 529 or 1354 mg/kg bw per day in females. Mice had access to food ad libitum and were housed individually. Satisfactory stability, homogeneity and content of the test material were demonstrated. Mice were observed routinely for mortality, ill health, reaction to treatment, body weight and feed consumption. After 12 and 18 months of treatment, white blood cell differential counts were conducted for all control mice and mice at the highest dose. An extensive histopathological examination was performed for these mice, as well as on mice that died in groups receiving the other doses. Microscopic examination for survivors at the lowest and intermediate doses was limited to liver, kidneys, lungs and gross lesions. The study report included an independent peer review that confirmed the conclusions of the original pathologist. The study complied with OECD guideline 451 (1981) and GLP.

No effects on survival were observed in mice at any dose. A total of 43-48 males per group and 47-52 females per group survived to termination. There were no compound-related clinical signs indicative of systemic toxicity in any of the treatment groups. There were no substance-related effects on body weight, cumulative body-weight gain, food consumption, white blood cell counts or non-neoplastic pathology findings. A slight (8-10%) but statistically significant reduction in kidney weight in males at 2800 and 7000 mg/kg was not considered to be substance-related, in the absence of a dose-response relationship, the lack of an effect on relative kidney weight and no associated histopathological findings. A slight dose-related increase in absolute liver weight (9-13%) and relative liver weight (12-18%) in males at 2800 and 7000 mg/kg was considered to be of no toxicological importance because the increases were not statistically significant, were not seen in females and there were no related histopathological findings. A slight increase in the incidence of extramedullary haematopoiesis in the spleen was noted at the highest dose (males, 55%; females, 72%, versus 43% and 57% in controls respectively). This finding was consistent with effects on erythrocytes seen in shorter studies, but was not statistically significant and was only slightly above the high background rate in controls.

The incidence of bronchiolo-alveolar adenoma or carcinoma was slightly increased in females at 2800 and 7000 mg/kg (10% for each group) compared with controls, and 70 mg/kg (3.3% for each group) (Table 16). There was no clear evidence of an increased incidence in males. The trend in females was statistically significant, but no pair-wise comparison was statistically significant. The incidence of these adenomas (3-8%) and carcinomas (3-7%) in females at 2800 and 7000 mg/kg was within the range for historical controls for adenomas (up to 15%) and carcinomas (up to 10%) reported for female Charles River mice of this strain (Lang, 1995; no data were available from the test facility). Overall, it was considered that the lung tumours were not treatment-related.

Table 16. Incidence of lung tumours in mice given diets containing methoxyfenozide for 18 months

From Robinson et al. (1998)

The NOAEL for carcinogenicity and non-neoplastic effects was 7000 mg/kg (equal to 1020 mg/kg per day), the highest dose tested (Robinson et al., 1998).

Rats

Groups of 70 male and 70 female Sprague-Dawley rats were given diets containing methoxyfenozide (purity, 98%) at a concentration of 0 (control), 200, 8000, or 20 000 mg/kg. These concentrations resulted in mean intakes of 0, 10.2, 411 and 1045 mg/kg per day in males, and 0, 11.9, 491 and 1248 mg/kg per day in females. The study complied with GLP and OECD guideline 453. Rats had access to food ad libitum and were housed individually. Satisfactory stability homogeneity and content of the test material were demonstrated. All rats were observed daily for signs of ill health or reaction to treatment. Physical examinations were performed weekly. Body weight and food consumption were monitored weekly for the first 13 weeks of dosing and once every fourth week thereafter. Ophthalmoscopic examinations were performed on all rats during the period before the start of dosing, and on all surviving rats before the termination of treatment. Urine analysis parameters were evaluated for at least 10 rats of each sex per group at 3, 6, 12 and 18 months of treatment, and again before the termination of treatment. Haematology (including methaemoglobin from 6 months) and clinical chemistry parameters were measured from 20 rats of each sex per group at 3, 6, 12 and 18 months (there was no information on fasting status). At the time of the terminal necropsies, blood samples were collected and analysed from 20 rats of each sex per group, or from all surviving animals when less than 20 animals remained in a group. The same animals were bled on each occasion when possible. White blood cell differential count was conducted for controls and animals at the highest dose only. At 12 months, 10 rats of each sex per group were necropsied and organ weights were recorded. All rats surviving to termination were necropsied and organ weights recorded. An extensive histopathological examination was performed for all controls and animals at the highest dose at sacrifice at 12 months and at termination, and on all animals not surviving to termination. At scheduled necropsy of animals at the lowest and intermediate doses, histopathological examination was limited to kidneys, liver, lungs, gross lesions and any tissues with potentially treatment-related lesions in animals at the highest dose. Mammary glands and pituitary glands of all females were examined histopathologically. An independent peer review by a second pathologist confirmed the histopathological findings.

Survival was poor in all groups, but overall this was considered not to have a significant impact on the interpretation of the results. There was an indication that time to 50% mortality was reduced at 20 000 mg/kg (Table 17). Less than 50% survival at 2 years (as recommended in the OECD guideline 453) is a recognized problem with the strain of rat used in this study (Charles River Sprague-Dawley rats, Crl:CD®BR).

Table 17. Survival data for rats given diets containing methoxyfenozide in a study of chronic toxicity and carcinogenicity

From Anderson & Gillette (1998)

No substance-related clinical signs of toxicity were noted at any concentration. Body weight was decreased in females at 20 000 mg/kg from week 45 onwards, which was statistically significant (p < 0.05) from week 73. Cumulative body-weight gain in males at the highest dose was reduced by 2.5% at week 53 and by 6% at termination and was not considered to be an adverse effect. There were no effects on food consumption.

Statistically significant, minimal to slight haematological changes were observed at 8000 mg/kg and 20 000 mg/kg in both sexes (Table 18). At 8000 mg/kg, erythrocyte count was decreased in both sexes, and haemoglobin concentration and erythrocyte volume fraction were decreased in males at week 14. At 20 000 mg/kg, erythrocyte counts, haemoglobin, and erythrocyte volume fraction were decreased during the first year of treatment. A slight increase in platelets and a minimal increase in methaemoglobin formation was seen at 20 000 mg/kg during the second year of treatment. The only clinical chemistry finding of note was an increase in plasma gamma-glutamyl transferase at >8000 mg/kg, consistent with the observed hepatotoxicity. Statistically significant decreases in bilirubin and alkaline phosphatase were seen at >8000 mg/kg, but were not considered to be of toxicological importance. There were no consistent effects on any urine analysis parameters. Ophthalmoscopic examination at termination of treatment indicated there were no ocular lesions associated with treatment.

Table 18. Haematology findings in rats given diets containing methoxyfenozide for up to 99 weeks

From Anderson & Gillette (1998)
^a Means of 20 animals per dose per time-point, except at termination, when there were 15-20 animals per dose
* Significant difference from control (p < 0.05); ANOVA, Dunnett t-test
ND, Not determined

Increases in relative and absolute liver weights were seen at >8000 mg/kg in both sexes, with an increase in female adrenal weights at 20 000 mg/kg (Table 19). No treatment-related gross changes were seen. Primary target organs were kidney (glomerular nephropathy), liver (hepatocellular hypertrophy) and thyroid (follicular hyperplasia) (Tables 20 and 21). Effects were seen consistently at >8000 mg/kg. An increase in the severity of glomerular nephropathy at 200 mg/kg did not fit the dose-response relationship and was considered to be incidental. There were also several substance-related pathological changes in females at the highest dose, which the study investigators considered were secondary to uraemia that occurred as a result of severe chronic progressive glomerulonephropathy. These included increases in mineralization of the heart, aorta and structures in the kidney; fibrous osteodystrophy of the bone. Acute to subacute inflammation and erosion/ulceration of the forestomach and mineralization and associated giant cell inflammation of the glandular stomach were also increased at 8000 mg/kg (Table 20).

Table 19. Mean liver and adrenal weights in rats given diets containing methoxyfenozide for up to 99 weeks

From Anderson & Gillette (1998)
* Significant difference from control (p < 0.05); ANOVA, Dunnett t-test

Table 20. Histopathology findings in rats given diets containing methoxyfenozide for up to 99 weeks