Methanesulfonamide, N-[2-[(4,6-dimethoxy-1,3,5-triazin-2-yl)carbonyl]-6-fluorophenyl]-1,1-difluoro-N-methyl-

Endpoint summary

Additional information

Absorption, distribution, excretion and metabolism of Triafamone were investigated in the rat after single oral administration using two different labelling positions. The test substance was uniformly labelled with 14C either in the phenyl- or in the triazine ring.

In the study using the phenyl label (M-444151-03-1), a low dose of 2 mg/kg bw and a high dose of 200 mg/kg bw was administered to groups of 4 animals of both sexes. Another group of 6 male rats were orally treated with the low dose of 2 mg/kg. These animals were subjected to bile-duct cannulation so that besides urine and faeces also bile could be collected. Additionally, one male and female rat each were dosed with the low dose, in order to investigate the metabolites in plasma and to address the stability of collected plasma samples during storage in a freezer at ≤ -18°C.

In the study using the triazine label (M-441124-03-1), only the low dose of 2 mg/kg bw was administered to groups of 4 male and female animals. All animals except those of the bile-cannulation test and the plasma investigation group were sacrificed after 72 h.Urine and faeces were collected in intervals between dosing and sacrifice. The radioactivity concentrations in plasma were followed by collection of micro samples from each animal over the whole testing period. In the bile-cannulation experiment, bile, urine, and faeces were collected in intervals between dosing and sacrifice 24 h after dosing. The plasma samples from the animals of plasma investigation test were collected at sacrifice 1 h after dosing. The total radioactivity, representing the sum of the parent compound and metabolites, was determined in urine and faeces, bile, plasma, and in organs and tissues collected at sacrifice. The metabolism was investigated in urine, bile, plasma and extracts of faeces.

Recovery

The total recoveries in all test groups were almost complete since between approx. 94.7% and 105.5% of the administered dose was found in the excreta and the body of the rats at sacrifice.

Absorption

Based on the bile-cannulation test, the absorption rate accounted for about 96% of the given dose because the amount of radioactivity in the collected bile sample could be added to the amounts found in urine and the body excluding the gastrointestinal tract. The absorption commenced immediately after dosing as can be seen from the quick increase of radioactivity in plasma micro samples. This also indicated that the given dose was almost completely absorbed from the GI-tract and thus was quickly systemically bioavailable.

Distribution

The distribution of the radioactivity within the body was fast and the maximum plasma levels (Cmax) were already reached between 20 and 40 minutes after administration in the low dose tests. In the high dose tests, Cmax was reached at approx. 4 h after administration due to an obviously ongoing absorption of the test compound from the gastrointestinal tract. The plasma concentrations declined to approx. 50% of Cmax within 1.5 to 2 h in the low dose tests and within 8 to 12 h in the high dose tests for both sexes. A further decline to less than 1% of the maximum value was observed within 24 h in the low dose tests and within about 32 h in the high dose groups. Overall, male rats exhibited about twofold higher plasma concentrations compared to females during the entire experimental period. The mean values of the equivalent concentrations C in plasma of the four animals of each test were used for a toxicokinetic modelling. Except the mean residence times (MRT), all other toxicokinetic parameters , i.e. tmax, Cmax, t1/2 abs, t1/2 elim and Area Under the Curve (AUC), were significantly higher in male rats which is probably caused by a longer residence time of the radioactivity in the blood before being excreted mainly via urine but also via faeces. On the other hand the comparable MRT-values indicated that the absorption and elimination processes were comparable in both sexes.

Excretion

The excretion of the total radioactivity was fast and occurred mainly via urine. Female rats showed a slightly higher renal excretion rate of ca. 83 and 87% than males with ca. 77 and 80%. The excretory behaviour of rats treated with the low dose was comparable to those of high dose tests. The major part of the given dose was excreted within 24 h after treatment.

The toxicokinetic behaviour (absorption, distribution and excretion) of Triafamone was also investigated in male and female rats by Whole Body Autoradioluminography (WBAL). The rats received a single oral dose of 5 mg/kg bw of the test compound uniformly labelled with 14C either in the phenyl ring (M-443301-0 -1) or in the triazine ring (M-443241-01-1). The distribution of total radioactivity and elimination from blood, organs and tissues were analysed qualitatively and quantitatively. One rat each was taken for cryosectioning at 1, 4, 8, 24, 48, 72, 120, and 168 h after administration. The amounts of radioactivity in excreta (urine and faeces) and exhaled carbon dioxide were additionally determined for selected time periods.

Triafamone was readily absorbed from the gastrointestinal tract and distributed throughout the body immediately after administration. The excretion of radioactivity via urine and faeces was almost complete after 2 days with renal excretion as the predominant route. For male rats, up to ca. 85% of the administered dose was recovered in urine and up to ca. 24% in faeces. Urinary excretion was slightly higher in females and amounted up to ca. 89%. Only 0.01% of the administered dose was exhaled as 14CO2 or other volatiles during a sampling period of 48 hours after administration of phenyl-U-14C-labelled Triafamone. The corresponding figures found in the study using the triazine labelled test compound were 0.2–0.4% of the given dose. This demonstrated that the both rings of the molecule were stable with regard to the formation of carbon dioxide or other small volatile fragments.

Independent of the label employed, the maximum radioactivity concentrations (CEQmax: expressed as μg a.s. equiv./g) were reached in male rats for all organs and tissues at one hour after administration (tmax). At this time, the values for liver and kidney were significantly higher than in blood, suggesting a preferred clearance from blood and distribution mainly to those organs that are mainly responsible for metabolism (liver) and excretion (kidney). All other tissues and organs exhibited distinctly lower levels as in blood, and very low levels were found in the brain, vitreal body, spinal cord, renal fat, nasal mucosa and muscle. Also in female rats the maximum radioactivity concentrations were reached for all organs and tissues at one hour after administration. At this time, the values for liver and kidney were also significantly higher than in blood as found for males but the absolute amount was only about half or one-third as high as in males. The figures for the other organs and tissues were also similar to those found in male animals.

In both studies, the concentrations declined rapidly to approx. 1–2% of the respective maximum concentrations and further below the limit of quantification until sacrifice at seven days post administration. Only in liver and kidney of the male rats and in the nasal mucosa of the female rats trace amounts of radioactivity were still detected at that time.

Overall conclusion

The results of these studies clearly show that male and female rats exhibited a very similar absorption, distribution and excretion behaviour. Any accumulation or retention of radioactivity administered with either [phenyl-UL-14C]- or [triazine-UL-14C] Triafamone can be excluded for male and female rats.