Bis(tributyltin) oxide

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Nov 1977 to Feb 1978

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

absorption

distribution

excretion

Qualifier:

no guideline followed

Principles of method if other than guideline:

113Sn-labelled tributyltinoxide was given to rats (190 to 210 g) as an aqueous suspension in doses of 5 mg/kg by the intragastric and the intraduodenal route. Following preliminary studies to determine the rate of absorption and the rate of elimination (female/male animals), the distribution and the elimination of the 113Sn-labelled substance was examined in four experimental groups (male animals).
Organ and tissue specimens were removed from animals 24 hours after termination of treatment (after the last dose). In group IV, the urine was measured in daily fractions and the faeces in weekly fractions.

GLP compliance:

yes

Remarks:

40 CFR Part 792

Radiolabelling:

yes

Remarks:

(113 Sn)

Species:

rat

Strain:

other: Wistar-han

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Weight at study initiation: male rats were reported to weigh between 190 to 210 grams
- Individual metabolism cages: yes
- Diet: ad libitum (Altromin rat pellets/standard diet tpf 1324)
- Water: ad libitum (tap water)

Rats were barrier sustained.

Route of administration:

other: intragastric and intraduodenal route

Vehicle:

other: Tween and ethanol

Details on exposure:

Aqueous suspension of 750 mg % Tween 60 and 1 % ethanol containing 1 mg/ml tributyltin oxide. Doses of 5 mg/kg were given

Duration and frequency of treatment / exposure:

Group 1: single dose
Group 2: once-daily dose for 3 days
Group 3: once-daily dose for 7 days
Group 4: once-daily dose for 14 days

Dose / conc.:

5 mg/kg bw/day

No. of animals per sex per dose / concentration:

5 males/4 females
For the most part the animal experiments were carried out in male rats. Studies on absorption of the substance were conducted in female animals.

Control animals:

no

Details on study design:

The substance was administered to the animals intragastrically as a suspension. In addition to the preliminary measurements to determine the rate of absorption and the elimination half-life following a single administration, another four experimental gropus were studied for the distribution and elimination of the 113 Sn-labelled substance following a single dose and repeated daily dose of 5 mg/kg.

Details on dosing and sampling:

After administration of the substance, the animals were kept in metabolic cages to measure the percentage of administered dose eliminated in the urine and in the feces. They were allowed food and water ad libitum. In Group 4, the elimination of the 113Sn-labelled dose equivalents administered was determined in the sample of urine collected over the week. In each of the groups 1-3, excreta were pooled, leaving one urine and one fecal sample for each animal. 24 hours after the last dose of the substance the animals were bled to death under ether narcosis, and the organs and tissues were removed.
For the 113Sn measurement a maximum of 15 g of biological material was used in each case. Specimens of a total weight of > 15 g were first homogenised with distilled water. All specimens were measured individually. Counting was done in a gamma-scintillation spectrometer (Packard Model 5285) set at the 125J energy spectrum.

Statistics:

Calculated means ± standard deviation in % of a single dose per total organ or in micrograms per gram of fresh tissue. Percentage in the blood was calculated on the basis of a total volume of 68 ml/kg. Of fatty tissue, the skin, the bone marrow, the lymph nodes, the spinal cord, and the skeletal muscle, only aliquots were used, so that the carcass contained most of the radioactivity of these tissues. The results of the measurments in % of a single dose per total organ were calculated for these specimens on one gram of fresh tissue.
The 113Sn measurements relate to the total radioactivity. The radioactivity in the study was not differentiated into unchanged substance and possible metabolites. To determine the half-life, the slope of the line was calculated using the following:

bxy = ((Σx*y) -((Σx*y)/n))/(Σx² - ((Σx/n)²)

Preliminary studies:

No information

Type:

absorption

Results:

Only about 20% of i.g. tributyltinoxide administered in dosed of 5 mg/kg is absorbed

Type:

excretion

Results:

Biphasic elimination at an average half-life of 12 ± 1 h and 3 ± 0.7 days

Details on absorption:

When given intraduodenal doses of 5 mg/kg to rats with acute biliary and urethral catheters, TBTO was absorbed to only about 20%. After 24 hours, the amount of absorbed substance eliminated by the kidneys corresponded to 1.3 ± 0.6% of the administered dose (% adm. dose) and the amount excreted with the bile, to 6.4 ± 1.9 % adm. dose. The percentage of dose found in the body was 7.8 ± 1.5%.
Compared to intragastric single dosing in intact animals, there was no marked difference in neither the amount measured in the urine 24 hours post dosing nor in the amount recovered after the same time in the faeces and in the bile plus intestinal tract, respectively.

Details on distribution in tissues:

24 hours after administration of a single dose, an average of 11.9 ± 1.9% of the dose was measured in the animal body (excluding GIT). This corresponds to a concentration of the 0.66 ± 0.07 ug of 113 Sn dose equivalents/g fresh tissue. The determinations carried out in the tissues revealed that about 50% of the radioactivity recovered in the animal was present in the liver and 10% in the kidney. Compared to the levels measured in the blood, the concentration of radioactive substance detected in the liever and in the kidneys was on average 70 and 80 times higher, respectively.

After repeated daily dosing, a steady state between absorption and elimination of the labelled compound could not be demonstrated until the end of the 14-day treatment.

A comparison of the 113Sn concentrations in the tissue specimens of groups II-IV with the corresponding data of treatment group I (single dose) showed a marked accumulation in all speciments as well as in the whole animal. After 14-days of treatment (group IV) the average accumulation factors were calculated to range between 2.1 and 7.4. The degree of accumulation (KNF) was as follows:
heart, bone marrow, liver 2-3
blood, lungs, nodes, kidneys, pancreas 3-4
spleen adrenal glands, thyroid gland 4-5
fatty tissue, brain, skin, spinal cord, skeletal muscle, thymus 5-6
testis, carcass >7 (7.4)

The autoradiograph of the 24 hour dose presented as illustration 1 in the attached illustration figure 3 demonstrates that there is an above average concentration of radioactivity in the colon and stomach (high density areas). In the liver and small intestine the concentration of radioacitive substance is noticeably less than that of the stomach or the colon. In other areas no differentiation of tissue structures is detectable; however the section of the kidney is missing. The sutoradiogram of the distribution of radioactivity taken on day 3 and 7 after adminsitration is similar to that taken 24 hours post dosing. In the gastric region the distribution is easily differentiated between the stomach wall and the contents. In the kidney (Illustration 3 of figure 3 renal cortex), radioactivity can clearly be detected.

Details on excretion:

Following a single i.g. (5 mg/kg) adminsitration the ratio of dose equivalents eliminated in the urine and the faeces was about 1:14. Up to day 7 post administration, an average of 6.5 ± 1.6% of the dose was recovered in the urine and 88.1 ± 7.7% of the dose in the faeces. At that time 3.5 ± 0.4% of the administered dose could still be detected in the body, excluding the gastro-intestinal tract. It could be demonstrated with the experimental results obtained in rats with acute biliary and urethral fistulas, that on an average about 80% of the dose administered by the intestinal route was not absorbed. Thus the amount eliminated through the hepatic system via faeces could be about 10 to 15% of the administered dose. In conclusion, the ratio of absorbed substance eliminated with the urine and with the faeces is around 1:3.
Daily measurements of the renal elimination (intact animals) showed a biphasic course and a half life of 12 ± 1 hour (period of day 1 to day 3 post administration) and 3.0 ± 0.7 days (day 4 to day 7 post dosing) (phase 1 excluded animal no. 2; phase II excluded animal no.1; no unequivocally first order kinetics of excretion). Within the seven-day experimental period, and average of 93% of the radioactivity recovered in the urine was eliminated during phase I and 7% during phase II.
In the experimental animals with acute biliary and urethal fistulas, biliary elimination of the administered dose during the period from 2-24 hours post administration was found to be monophasic, with a half-life of 4.4 ± 1.9 hours.

With repeated daily doses for up to 14 days, 96.0 ± 2.4% of the total dose administered was recovered in the urine and the faeces between the begining of the experiment and 24 hours after the last dose. Up to day 3 of the treatment there was a marked increase in the daily amount of the dose eliminated by the kidneys, from an average of 6 to 15% of the single dose administered. In the course of the study (day 3 to day 14 of the treatment) it was measured that on average about 13 ± 2% of a single dose was recovered daily in the renal excretion.

Metabolites identified:

not specified

Group Treatment (Days) % Radioactivity Recovered in Animal Accumulation Factor Liver Kidneys Carcass Other organs Liver Kidneys Carcass Other Organs I 1 54 10 34 5 II 3 44 9 43 4 1.5 1.5 2.3 1.3-4.9 III 7 36 8 52 4 2.3 2.1 4.8 1.4-5.2 IV 14 29 8 59 4 2.8 3.5 7.4 2.1-7.4

Conclusions:

Only about 20% of i.g. tributyltinoxide administered of 5 mg/kg is absorbed. The concentration of radioactive substance measured in the body after a two-week treatment is about four times higher than after a single dose; the accumulation factor in organs and tissues is 2-7. A steady state between absorption and elimination of the substance was not reached during the 14-day period. There is sustained gastric secretion of radioacitivity, which could be of importance with regard to the percentages of administered dose that are excreted.

Executive summary:

The purpose of this study to characterize the pharmacokinetic properties of the substance (absorption, distribution, accumulation, elimination) in rats. Rats were administered 113 Sn-labelled tributyltin oxide as an aqueous suspension in doses of 5 mg/kg by the intragastric and the intraduodenal route. The distribution and elimination of the radio-labelled substance was studied in four experimental groups:

Group 1: single dose

Group 2: once-daily dose for 3 days

Group 3: once-daily dose for 7 days

Group 4: once-daily dose for 14 days

Organ and tissue specimens were removed in each case 24 hours after termination of treatment. Only about 20% of i.g. tributyltinoxide administered of 5 mg/kg is absorbed. The concentration of radioactive substance measured in the body after a two-week treatment is about four times higher than after a single dose; the accumulation factor in organs and tissues is 2-7. A steady state between absorption and elimination of the substance was not reached during the 14-day period. There is sustained gastric secretion of radioactivity, which could be of importance with regard to the percentages of administered dose that are excreted.

Reference 2

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

18th June 1985 to 29th July 1985

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

absorption

excretion

Qualifier:

no guideline followed

Principles of method if other than guideline:

To clarify the extent that tributyltin oxide passes through the blood-placenta and/or the blood/brain barrier. To determine whether treatment with TBTO leads to a specific enrichment of active substance or metabolites in selected organs. The intention of the study was to reinvestigate absorption and elimination of TBTO after intragastric administration.

GLP compliance:

yes

Radiolabelling:

yes

Remarks:

(113 Sn)

Species:

rat

Strain:

other: Wistar =0Han

Sex:

female

Details on test animals or test system and environmental conditions:

Bred at Schering
Body weight : 260-300 g
Kept in separate metabolism cages
Food and water ad libitum

Route of administration:

other: intragastic route

Vehicle:

peanut oil

Details on exposure:

Nine animals were treated on day 18 p.c. The concentration of total radioactivity and metabolically unchanged substance was ascertained

Duration and frequency of treatment / exposure:

One exposure

Dose / conc.:

25 mg/kg bw (total dose)

No. of animals per sex per dose / concentration:

9 pregant females for the single dose

Control animals:

not specified

Details on study design:

Animals were placed in metabolism cages after recieving intragastric administrations of 113 Sn Labeled tributyltin oxide on the 18th day post conception. Three animals were sacrificed on days 1, 2, and 3, and organs and tissues were removed. Proportions of total radioactivity and of metabolically unchanged substances were ascertained.

Details on dosing and sampling:

Females were dosed on 18th day post conception.
Sacrificing 3 animals at each instance, organs and tissues were removed on days 1,2, and 3 post administration

Statistics:

The data were calculated manually using a desk-top calculator (type Triumph 1214 and Hewlett-Packard 97), The graphic presentation of the distribution pattern was generated by the program BARC (EDP System CHB). The half-life derived from the time course (In C vs. t) was obtained by regression computation of the linear zones visible within the semilogarithmic plot.
There are two figures for the residue determination in the animal. Data referring to carcasses were measured after excision of gastrointestinal tract and all organs listed in Tables I and II. Data referring to "remainder of body" were calculated as the sum of radiolabel found in carcass and Organs but exclusive the GIT. For calculation wet weights were taken into consideration.

Preliminary studies:

No information

Details on absorption:

TBTO is incompletely absorbed after intragastric administration of 25 mg/kg dissolved in peanut oil. Comparing the kinetic paratmers after i.v. administration of the stubstance with the present findings, it can be presumed that about 30% of the dose is absorbed from the GI tract.

Details on distribution in tissues:

In lipophilic tissue, the substance is a mainly metabolically unchanged substanced that is found. In the liver, high levels of systemically available dose in the form of metabolites are found. Substance and metabolites are distributed therefore specifically according to tissue. Both the substance and the 113 Sn metabolites pass the blood brain barrier as well as the blood-placenta barrier. Nevertheless, the concentration reached in the fetus is much lower than in the mother animal.

Details on excretion:

After intragastric administration the ratio of renal and fecal exretion was about 1:20. Up to day 3 p. administration, a mean of 4 ± 1 % of the dose was excreted with the urine, and 85 ± % with the feces. The renal exretion recorded on the three occasions did not point to any clearly exponential course of elimination

Metabolites identified:

yes

Details on metabolites:

The concentrations of 113 Sn metabolites and unchanged substance were much lower in the fetus than in the mother animal. It is presumed that repeated administration will lead to an accumulation of substance and metabolites

Table I: ZK 21 955; Tributyltin oxide (TBTO); Toxicokinetics; Rat Distribution of total radiolabel among tissues following intragastric administration of Sn labelled TBTO to pregnant rats. Figures are mean findings + Standard deviation (n =3) in % per dose per total organ and in ppm wet tissue (µg/g)

 

 

Time p. adm. (d)	day 1		day 2		day 3
Specimen	% of dose	ppm (µg/g)	% of dose	ppm (µg/g)	% of dose	ppm (µg/g)
Blood (58 ml/kg)	0.073 ± 0.043	0.31 ± 0.18	0.03 (N)	0.13 (N)	**	**
Plasma		0.19 ± 0.03 (n = 2)		0.063 (N)		**
Fat (abdominal)*	0.035 ± 0.004	2.4 ± 0.3	0.032 ± 0.036	2.2 ± 2.5	0.017 ± 0.003	1.2 ± 0.2
Brain	0.44 ± 0.01	1.9 ± 0.4	0.029 ± 0.010	1.3 ± 0.6	0.026 ± 0.003	1.1 ± 0.2
Liver	4.7 ± 0.6	29.5 ± 1.3	3.5 ± 2.0	19.9 ± 12.5	3.2 ± 0.4	17.9 ± 1.2
Kidneys	0.32 ± 0.06	16.6 ± 2.4	0.26 ± 0.12	14.0 ± 7.7	0.28 ± 0.02	14.0 ± 1.9
Skeletal muscles*	0.016 ± 0.002	1.1 ± 0.2	0.013 ± 0.008	0.93 ± 0.53	0.012 ± 0.002	0.84 ± 0.15
Carcass	5.2 ± 1.6	2.1 ± 0.7	2.7± 0.9	1.1 ± 0.4	2.0 ± 0.3	0.79 ± 0.11
Gastrointestinal tract	40.0 ± 24.4	99.7 ± 59.9	4.8 ± 4.0	13.7 ± 11.3	0.87 ± 0.15	2.9 ± 0.7
Foetuses	0.26 ± 0.04	0.72 ± 0.11	0.24 ± 0.17	0.36 ± 0.24	0.12 ± 0.01	0.17 ± 0.01
Placenta	0.12 ± 0.01	1.2 ± 0.2	0.080 ± 0.060	0.58 ± 0.40	0.41 ± 0.002	0.37 ± 0.04
Amniotic fluid	**	**	**	**	**	**
Total^1)	10.7 ± 1.4	3.4 ± 0.4	6.8 ± 3.1	1.9 ± 0.9	5.8 ± 0.8	1.6 ± 0.2
In animal^1)	10.7 ± 1.4		6.8 ± 3.1		5.8 ± 0.8
In urine	1.8 ± 0.5		3.0 ± 1.5		4.2 ± 0.8
In faeces^2)	33.6 ± 29.1		81.2 ± 4.9		85.2 ± 4.8
Balance	86.1 ± 4.8		95.7 ± 4.1		96.0 ± 4.7
+^113Sn TBTO equivalent calculated on the basis of Sn radioactivity * Figures refer to 1 g wet weight (values not included in the balance as an aliquot of the remainder of the body) ** detection limit of method used 20 ng/mL (N) limit of detection, n = 2 1) excluding gastrointestinal tract 2) including gastrointestinal tract

 

Table II: ZK 21 955; Distribution of metabolically unchanged substance in body tissues Figures are mean findings ± Standard deviation (n =3) in % per dose per total organ and in ppm wet tissue (µg/g)

 

Time p. adm. (d)	day 1		day 2		day 3
Specimen	% of dose	ppm (µg/g)	% of dose	ppm (µg/g)	% of dose	ppm (µg/g)
Blood (58 ml/kg)	0.013 (N)	0.057 (N)	**	**	**	**
Plasma		0.050 (N)		**		**
Fat (abdominal)*	0.024 ± 0.001	1.7 ± 0.1	0.019 ± 0.017	1.3 ± 1.2	0.014 ± 0.004	0.95 ± 0.29
Brain	0.012 ± 0.008	0.49 ± 0.27	0.009 ± 0.011	0.42 ± 0.50	0.005 ± 0.005	0.22 ± 0.24
Liver	0.11 2) 0.12	0.74 ± 0.76	0.041 ± 0.033	0.24 ± 0.21	0.031 ± 0.017	0.18 ± 0.11
Kidneys	0.060 ± 0.015	3.1 ± 0.8	0.048 ± 0.043	2.5 ± 2.1	0.015 ± 0.006	0.72 ± 0.28
Skeletal muscles*	0.004 ± 0.003	0.27 ± 0.23	0.007 ± 0.002	0.46 ± 0.14	0.003 ± 0.001	0.17 ± 0.07
Carcass	4.9 ± 2.5	2.0 ± 1.0	2.0 ± 0.7	0.81 ± 0.29	1.7 ± 0.3	0.67 ± 0.11
Gastrointestinal tract	34.9 ± 20.2	86.9 ± 49.7	1.8 ± 1.4	5.3 ± 4.0	0.46 ± 0.11	1.5 ± 0.3
Foetuses	0.13 ± 0.01	0.37 ± 0.04	0.058 ± 0.041	0.086 ± 0.058	0.066 ± 0.002	0.091 ± 0.007
Placenta	0.053 ± 0.039	0.55 ± 0.42	0.028 ± 0.026	0.20 ± 0.18	0.013 ± 0.006	0.12 ± 0.05
Amniotic fluid	**	**	**	**	**	**
Total^1)	5.3 ± 2.6	1.7 ± 0.8	2.2 ± 0.8	0.62 ± 0.22	1.8 ± 0.3	0.50 ± 0.06
In animal^1)	5.3 ± 2.6		2.2 ± 0.8		1.8 ± 0.3
In urine	0.030 ± 0.015		0.051 ± 0.026		0.056 ± 0.031 (n = 2)
In faeces^2)	29.4 ± 25.4		64.3 ± 8.5		53.9 ± 8.0
Balance	69.5 ± 4.3		68.4 ± 6.3		56.2 ± 7.9
+^113Sn TBTO equivalent calculated on the basis of Sn radioactivity * Figures refer to 1 g wet weight (values not included in the balance as an aliquot of the remainder of the body) ** detection limit of method used 20 ng/mL (N) limit of detection, n = 2 1) excluding gastrointestinal tract 2) including gastrointestinal tract

 

Conclusions:

Approximately 30% of the dose is absorbed from the GI tract. The available portion of dose is excreted very slowly. Substance and metabolites are distributed according to tissue. Both the substance and the labelled metabolites pass the blood brain barrier as well as the blood-placenta barrier. The concentration reach in the foetus is much lower than in the mother.

Executive summary:

Nine rats were placed in metabolism cages after receiving intragastric administrations of 113 Sn labelled tributyltin oxide on the 18th day post conception. Three animals were sacrificed on days 1, 2, and 3, and organs and tissues were removed. Proportions of total radioactivity and of metabolically unchanged substances were ascertained. Approximately 30% of the dose is absorbed from the GI tract. The available portion of dose is excreted very slowly. Substance and metabolites are distributed according to tissue. Both the substance and the labelled metabolites pass the blood brain barrier as well as the blood-placenta barrier. The concentration reach in the foetus is much lower than in the mother. It is presumed that repeated administration will lead to an accumulation of substance and metabolites.

Reference 3

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

7 May 1984 to 17 January 1985

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

excretion

metabolism

Principles of method if other than guideline:

Animal experiments were conducted in female rats having body weights of about 200 g. 113 Sn-labelled active ingredient was available for the studies. The labelled substance was administered to the animals intravenously in the form of an alcoholic/aqueous solution (ethanol/water 1:1) at a dose of 1 mg/kg, and intragastrically in the form of an oily solution (peanut oil) at a dose of 25 mg/kg.

GLP compliance:

yes

Remarks:

40 CFR Part 792

Radiolabelling:

yes

Remarks:

(113 Sn) specific activity 92.5 kBq/mg

Species:

rat

Strain:

Wistar

Sex:

female

Details on test animals or test system and environmental conditions:

Body weight 190-210 grams, bred at Schering.

Route of administration:

other: intravenous and intragastric

Vehicle:

other: intravenous = ethanol/water, intragastric = peanut oil

Details on exposure:

The labelled substance was administered intravenously at a dose of 1 mg/kg and intragastrically at a dose of 25 mg/kg (specific activity 92.5 or 2312.5 kBq/kg respectively).

Duration and frequency of treatment / exposure:

Single exposure

Dose / conc.:

1 mg/kg bw (total dose)

Remarks:

(intravenous)

Dose / conc.:

25 mg/kg bw (total dose)

Remarks:

(intragastric)

No. of animals per sex per dose / concentration:

3 female rats per dose group

Control animals:

not specified

Details on study design:

The courses of radioactivity concentration and metabolically unchanged substance, as well as the moiety of 113 Sn compounds in blood were measured. At each measurement time point, three animals were sacrificed under ether anaesthesia by exsanguination

Details on dosing and sampling:

Sample collection: Plasma was obtained from the blood and kept in a deep-freezer until analysed. Radioactivity determination was carried out in the individual samples. The unchanged substance was separated from the individual (intravenous) or mixed samples (intragastric) by extraction with toluene. For total radioactivity balancing, the moiety of administered 113Sn dose equivalents eliminated with urine and faeces was measured up to 72 h p. adm. (i.v./i.g.). In contrast to the other animal groups which were kept in Macrolone cages, this group were kept in metabolic cages. In addition the dose moeity of 113Sn substances in the gastrointestinal tract and remaining body of the animals was determined in the animal group sacrificed after 48 hours.
113Sn measurement: A maximum sample aliquot of 3 g or 3 mL was used for radioactivity measurement. Counting was done in a gamma scintillation spectrmeter (Messrs. LKB/model 1282).
Only 1.8% of 113Sn decays into the 648 keV state and 98.2% 393 keV state of 113Sn, due to the relatively weak gamma-ray emission (~20 % total CPM) the X-ray radiations of 113Sn emitted as secondary radiation at 24 keV (~60% total CPM) was measured.
Standardisation: An accurately measured portion of the formulation administered was diluted with a defined volume of methanol. Then 6 samples of this were measured using a known moiety of this standard solution (analogue standard).
Active ingredient measurement: After checking the pH value (7-8), 1 mL of plasma was pipetted into a disposable glass tube and extracted with 3 mL of toluene for 30 minutes on a Heidolph rotor. After separation of the phases (centrifugation, freezing-out of aqueous phase), the organic phase was decanted and the radioactivity in the extract measured against a correspondingly treated standard (blank plasma sample to which TBTO had been added).
HPLC spectra of 113Sn substances:
Plasma - for the analysis, equal plasma aliquots from 3 experimental animals were combined to form one mixed sample per time point. The time points were selected so that, as far as possible the spectra represent the initial and terminal parts of plasma levels.
A 15-mL portion of methanol was added dropwise to every 3-mL of the mixed sample, shaken of the Whirlmix, and the resultant protein precipitate removed by centrifugation. The aqueous-methanolic supernatant was freeze-dried and, immediately before chromatographic separation, the lyophilizate was taken up in 350 µL of methanol + µL of perchloric acid. For analysis 400 µL of this solution was used.
Urine - after i.g. administration of 25 mg/kg, the native urine from 3 animals (0-48 hours p.adm.) was pooled to form a mixed sample. Immediately before analysis, 25% pechloric acid was added and 200 µL of the sample chromatographed.
HPLC system: 2 high-pressure pumps. type FR30 (Messrs. Knauer) sample injection system, type RH 7120 (Messrs. Rheodyne) fraction collector, type 328 (Messrs. Isco).
HPLC conditions:
column: LiChrosorb RP18 10 µm
250 x 4.6 mm (Messrs. Bischoff)
eluent/pump A: water/methanol 1:1 + 0.01 mol sodium dodecyl sulphate + 0.1 % pechloric acid
eluent/pump B: methanol + 0.01 mol sodium dodecyl sulphate + 0.1 % pechloric acid
gradient (A after B): 20 minute Linear, 10 minute pump B
Flow rate: 2 mL/min
temperature 20-25 °C
analysis time: 30 minutes
fractionation: 5 fractions/minute

Statistics:

Calculation and storage of data took place on the CHB Computer (Honeywell Bull). The programmes /TB/P, /TB/U and SZGR were used. For rats, a blood volume of 58 mL/kg and a plasma volume of 31 ml/kg were taken as a basis. The data on blood and plasma volumes were taken from: Blood and Other Body Fluids, ed. D.S. Dittmer, Fed. of Am. Soc. for Exp, Biology, Washington 1961.
Evaluation of the time curves (ln C vs. t) was done by means of a regression calculation of the linear parts visible in the semilogarithmic grid.
The disposition phases (excluding total radioactivity) were calculated by the "peeling-off method" (reference: Schnelle U. and Garrett E.R., J. Pharm.. Sci. 62, 3: 362 (1973)).
The volumes of distribution (AVD«c and ß) were calculated by the formula:

AVDα = D/(boα + boβ)

AVDß = D/boβ

where boα and boß are the ordinate intercepts after extrapolation of the α and ß-phases (peeling-off method) to
t = 0 and D the dose.
Total clearance was calculated by the formula:

Cl tot = D/AUC

where D is the dose and AUC the area under the plasma level curve after i.v. injection.
The bioavailability after intragastric administration was estimated by means of a comparison of the AUC after intragastric and intravenous administration (100 %).

BA (%) = (AUC i.g./AUV i.v.) x (dose i.v./dose i.g.) x 100

Preliminary studies:

No information.

Details on absorption:

After i.g. administration (25 mg/kg), the substance dissolved in peanut oil is absorbed by rats with considerable delay and incompletely. A gastrointestinal TBTO absorption of at least 55% can be derived from a comparison of the AUC value and the moieties of radioactive substances in the animal. Bioavailability of TBTO asborbed from the GI tract is 100%.

Details on distribution in tissues:

After i.v. and i.g. administration, TBTO and/or 113 Sn metabolites enter cellular constituents of blood

Details on excretion:

The main portion of systematically available substance is eliminated via the bile with the feces.

Toxicokinetic parameters:

AUC: 0 - 72 h p.adm.

Metabolites identified:

yes

Details on metabolites:

The metabolic fate of TBTO is to a large extent identical after i.v. and i.g. administration. Within a short time, the substance hydrolyzes and forms the tributyltin cation which is present in the organism. This cation is assigned to unchanged substance or TBTO. In plasma, in addition to the unchanged substance a principal metabolite, only slightly more polar in the HPLC system, was found whose relative proportion in the metabolite spectrum increases over the time course. The metabolic pattern of the urine sample consists mainly of polar metabolite groups which were not detectable in plasma. Data on biotransformation of TBTO available points to the possibility of mainly tri- and ditin alkyls being present in plasma. In urine, on the other hand, in addition to inorganic tin mainly monotin alkyls might be present.

At 5 min p. inj. (1st measurement time point), on an average 2.6 ± 0.4 % of the ¹¹³Sn dose or 853 ± 138 ng/mL (¹¹³Sn-TBTO dose equivalents) was measured in total plasma. The moiety of unchanged substance in total radioactivity (5-min value) amounted to about 92 %.Subsequently, the active ingredient concentration decreased in two phases with half-lives of t l/2α =6 minutes and t 1/2 ß = 3.6 hours. By extrapolation of the phases to t = 0, an apparent volume of distribution (AVD) of 0.9 1/kg (α-phase) and 14.6 1/kg (ß-phase) can be calculated. The total clearance was calculated as 40 ml/min/kg, The area under the plasma level curve (AUC) amounted to 416 ng x h/ml The concentration of total radiolabel in plasma decreased in three phases for which half-lives of 10 minutes, 4.9 hours, and 19.7 hours were estimated. The AUC amounted to 1239 ng x h/ml.

 

Absorption of intragastrically administered substance took place with a half-life of about 10 h. The maximum active ingredient concentration (of total radioactivity) was measured as 156 ng/mL 8 h p.adm. (535 ± 71 ng/mL 24 h p.adm.). In the post-maximum range of disposition, a monophasic course with a half-life of about 14 h was determined both for the active ingredient and total radioactivity. The area under the plasma level curve amounted to 5656 ng x h/mL (18925 ng x h/mL). On an average, a comparison of the areas under the active ingredient level curves after i.v. and i.g. administration yielded a bioavailability of 54

 

It was shown that the radioactive substances in blood exhibit distinctly higher Sn concentrations than those in plasma. Throughout the period of the study (i.v., i.g.), the ratio of concentrations of Sn substances in plasma and blood was about 1:2 to 1:3.

After i.v, (i.g.) administration, the ratio of the dose moieties eliminated with urine and faeces was about 1:4 (1:6). On an average, up to 24 h 9 ± 3 % of the dose (4 ± 1 % of the dose) had been eliminated with urine and 31 ± 4 % of the dose (1 ± 2 % of the dose) with faeces. During the study, which lasted up to 3 days, on an average 14 ± 3 % of the dose (11 ± 1 % of the dose) was recovered in urine and 52 ± 3 % of the dose (62 ± 5 % of the dose) in faeces.

 

The balance of the ¹¹³Sn moieties eliminated by both routes of excretion amounted to 66 + 3 % of the dose (72 ± 4 % of the dose). After the i.v. dose, when renal elimination was measured at 3 time points, a half-life of about 8 h was estimated. After i.g, administration, figures did not fit into a first order kinetics of elimination, probably because of slow absorption process.

 

48 hours after i.v. (i.g.) administration, on an average 27 ± 2 % (14 ± 4 %) of dose equivalents administered had been localized in the animals’ bodies excluding the gastrointestinal tract. Accordingly, 3 ± 1 % (57 ± 25 %) of the ¹¹³Sn dose administered was recovered in the gastrointestinal tract.

 

After direct injection of 20 ng onto the HPLC column the substance dissolved in methanol (2 mg/ml) was recovered completely. A homogeneous substance peak with a retention time of 16.2 min was detectable in the radiochromatogram. In the case of spiked blank plasma after sample preparation {protein precipitation with methanol, freeze-drying, taking up the residue in methanol/perchloric acid) it was only possible to assign 92 % of radioactivity to the unchanged substance chromatographically, although the HPLC analysis was carried out immediately. It was shown that a moiety of about 8 % of radioactivity was not absorbed by the column material. Hence, in the available HPLC spectra of plasma samples it is not possible to State to what extent the respective early eluted peak represents an artificial decomposition product or a metabolite. Once we knew the abovementioned findings, radiochromatographs of the renally eliminated ¹¹³Sn substances were recorded without prior purification of the urine.

 

In the present study, the metabolite spectra in the area of initial and terminal Sn plasma levels after i.v. (1 mg/kg) and i.g. administration (25 mg/kg) of the labelled substance were compared.

 

After i.V. injection, in addition to the metabolically unchanged substance (RRT = 1.0) and excluding the unabsorbed Sn Zone it was mainly possible only to detect one metabolite (RRT = 0,92). On the other hand, after the i.g. dose the principal components demonstrated after the i.v, dose and three other metabolites were found. However, the latter's share in total radioactivity was of minor importance.

 

The urine collected 0 - 48 h after i.g. administration of 25 mg/kg was analysed. In the urine sample the moiety of metabolite fractions found in plasma (i,v./i.g,) was relatively small. It was only possible to assign about 2 % of totally eluted radioactivity to the metabolically unchanged active ingredient. On the basis of RRT of > 0.89 about 9 % of the renally eliminated Sn substances were identical to the metabolite groups found in plasma. About 90 % of the Sn substances (4 principal metabolites) have a relative retention time of <0.89. About 10 % of the radioactivity measured in urine was eluted from the coluran without absorption.Extraction of Sn substances from biological material.

 

It was possible to determine the concentration of metabolically unchanged substance in plasma and urine by means of extraction with toluene, keeping the pH value constant (7 - 8). As the HPLC analysis of sample extracts shows, the moiety of extractable metabolites was practically insignificant compared with that of the active ingredient. In the case of plasma to which Sn-TBTO had been added and in the case of urine samples (pH 8), about 90 % of the radioactivity employed was extracted with toluene, On the basis of the Spectrum of Sn substances eliminated renally up to 48 h p.adm, (i.g.) it was possible to demonstrate that with a pH gradient (pH 8, pH 3.5, pH<l) metabolite groups can be separated, to a large extent selectively, by extraction with toluene, Assignment of the 113 Sn metabolite groups separated from urine was done by HPLC analysis of the sample extracts.

 

An attempt to identify 4 of the principal metabolites isolated from urine by means of mass spectrography failed, this was attributed to problems due to oxidative influences during purification and analysis.

Conclusions:

1. After i.g. administration (25 mg/kg), the substance dissolved in peanut oil is absorbed by rats with considerable delay and incompletely, A gastrointestinal TBTO absorption of at least 55 % can be derived from a comparison of the AUC values and the moieties of radioactive substances in the animal (i.v./i.g,).
2. On the basis of previous investigations (Res.Rep. No. IC-KI 1), there are suggestions that the type of formulation might have an effect on gastrointestinal absorption of the active ingredient. As follows from the data reported in Res.Rep. IC-KI 1, after i.g. administration of an aqueous/ethanolic Suspension (5 mg/kg) only about 20 % of 113Sn-TBTO was absorbed by rats.
3. Bioavailability of TBTO absorbed from gastrointestinal tract seems to be 100 %.
4. After i.v. and i.g. administration, TBTO and/or Sn metabolites enter cellular constituents of blood.
5. The main portion of systemically available substance (i.v./i.g.) is eliminated via the bile with faeces. Elimination of some of the dose is rather slow.
6. The metabolic fate of TBTO is to a large extent identical after i.v. and i.g. administration. Within a Short time, the substance hydrolyses and forms the tributyltin cation which is present in the organism. This cation is assigned to unchanged substance or TBTO throughout this report.
In plasma, in addition to the unchanged substance a principal metabolite, only slightly more polar in the HPLC System, was found whose relative proportion in the metabolite spectrum increases over the time course.
The 113Sn substance (including TBTO) detected in plasma are only found to a slight extent in urine pattern.
The metabolic pattern of the urine sample consists mainly of polar metabolite groups which were not detectable in plasma.
It was not possible to identify the chemical structure of the chromatographically separated tin compounds.
However, the data on biotransformation of TBTO available so far point to the possibility of mainly tri- and ditin alkyls being present in plasma. In urine, on the other hand, in addition to inorganic tin mainly monotin alkyls might be present.

Executive summary:

Animal experiments were conducted in female rats having body weights of about 200 g. 113 Sn-labelled active ingredient was available for the studies. The labelled substance was administered to the animals intravenously in the form of an alcoholic/aqueous solution (ethanol/water 1:1) at a dose of 1 mg/kg, and intragastrically in the form of an oily solution (peanut oil) at a dose of 25 mg/kg. The courses of radioactivity concentration and metabolically unchanged substance, as well as the moiety of 113 Sn compounds in blood were measured. At each measurement time point, three animals were sacrificed under ether anaesthesia by exsanguination. After i.g. administration (25 mg/kg), the substance dissolved in peanut oil is absorbed by rats with considerable delay and incompletely. A gastrointestinal TBTO absorption of at least 55% can be derived from a comparison of the AUC value and the moieties of radioactive substances in the animal. Bioavailability of TBTO asborbed from the GI tract is 100%.The main portion of systemically available substance is eliminated via the bile with faeces. The metabolic fate of TBTO is to a large extent identical after i.v. and i.g. administration. Within a short time, the substance hydrolyzes and forms the tributyltin cation which is present in the organism. This cation is assigned to unchanged substance or TBTO. In plasma, in addition to the unchanged substance a principal metabolite, only slightly more polar in the HPLC system, was found whose relative proportion in the metabolite spectrum increases over the time course. The metabolic pattern of the urine sample consists mainly of polar metabolite groups which were not detectable in plasma. Data on biotransformation of TBTO available points to the possibility of mainly tri- and ditin alkyls being present in plasma. In urine, on the other hand, in addition to inorganic tin mainly monotin alkyls might be present.

Reference 4

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1984

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

documentation insufficient for assessment

Reason / purpose for cross-reference:

reference to other study

Objective of study:

other: pharamacokinetcs

Qualifier:

no guideline followed

Principles of method if other than guideline:

The tin content of different organs of the maternal animals and of the whole foetus was determined after TBTO treatment. After a single-oral treatment with 117 mg TBTO/kg bw, the total tin content in 11.5 day old embryos was determined.

GLP compliance:

yes

Remarks:

40 CFR Part 792

Radiolabelling:

no

Species:

mouse

Strain:

NMRI

Sex:

female

Details on test animals or test system and environmental conditions:

Species, strain: NMRI mice
Source: Zentralinstitut fur Versuchstiere, Hanover FRG
Conditions: spf
Diet: food (Altromin1324) and tap water provided ad libitum
Mating: 2 h
Pregnancy determined 24 h after mating by observation of plug

Route of administration:

oral: gavage

Vehicle:

olive oil

Details on exposure:

Pregnant mice were given a single administration test material in olive oil by gavage on day 10 of gestation

Duration and frequency of treatment / exposure:

Sacrificed 2-48 h after single treatment

Dose / conc.:

117 mg/kg bw (total dose)

Control animals:

yes

Details on study design:

Removed maternal serum, liver, brain, spleen, kidney, skeletal muscle and heart
Organs were removed and frozen in liquid nitrogen
Approximately 20 mg of freeze dried tissues and sera were ashed overnight in a low temperature asher
Residue was dissoved in 200 µl 0.1 HCl
Tin was measured in an atomic absorbption spectrophotomer with graphite furance
Calibration was performed with SnCl2.H2O

Details on dosing and sampling:

Mice treated by gavage with 117 mg/kg in test material in olive oil on GD10.
Pregnant mice were sacrificed 2-48 h after oral treatment with TBTO

Statistics:

No data

Type:

distribution

Results:

Total tin content in whole embryos increased

Type:

distribution

Results:

Total tin content in maternal serum and organs increased

Details on distribution in tissues:

12.5 h after a single oral treatment with 117 mg/kg test material, the total tin content of embryos was found to be 9.5 nmol/g wet weights (70% greater than the normal value) in 11.5-day-old embryos. The total concentration of tin in maternal liver was increased to a similar extent (by approximately 60%) over the normal level between 6-24 h after treatment. No other organ studied showed similarly high increases in total tin content. These increased levels were maintained over a period of more than 48 h, the maximum reached 6 h after oral administration. Increasing tin levels were measured in the embryos over a period of 12 h, after which time the concentration dropped continuously, due perhaps to growth of the embryos during the period studied and also to elimination processes, since the effect is also seen in maternal liver. Since only tin and not TBTO was measured, the authors could not establish whether the original compound or some metabolite(s) was responsible for the increased tin levels in the embryos. Studies by Aldridge et al. (1977) have shown that tritbutyltin derivatives are metabolized by a cytochrome P-450-dependent system derived from liver microsomes, resulting in various (alpha to delta)-hydroxybutyl-dibutyl tin metabolites.

Transfer type:

blood/placenta barrier

Observation:

distinct transfer

Remarks:

distinct transfer (increase in embyo tin levels

Transfer type:

blood/brain barrier

Observation:

no transfer detectable

Remarks:

tin levels were constant

Metabolites identified:

not specified

Details on metabolites:

Tin content was measured

Figure 5 represented a time course of nmol Sn/g weight weight in maternal liver and embyro up to 48 h after oral dosing

Figure 6 represented nmol Sn/g wet weight over intrinsic concentrations in serum, brain, kidney, liver, emmbryo, spellen, muscle and heart.

Tin content of all tissues increased but to different degrees. Maximal increases were found in the fetuses and in maternal liver (70 and 60% respectively. The highest peaks were seen in maternal liver 6 h after treatment, whereas the tin livel in embryos increased over a period of 12 h. The hihg level was matinaed in maternal liver for at least 26 h, whereas in the embryos the level dropped 12 h after treatment. The concnetration in serum was only slightly raised after treatment. The concentration in serum was only slightly raised over a period of 48 h after treament (~20%) and the tin concentrtation in brain was found to be constatn (8.5 to 9 µmol/kg wet weight).

Conclusions:

Tin levels increased in maternal liver and embryos after a single administration of TBTO. Levels decreased over time and were measured up to 48 h

Executive summary:

Distribution of tin was determined in maternal serum and organs as well as embyros after a single oral gavage treatment of TBTO to pregnant mice. Maximal increases were found in the fetuses and in maternal liver (70% and 60% at 6h and 12 h respectively. Tin levels were maintained in the maternal liver for atlesst 26 h. Slight increases in kidney tin levels were observed by not notable. Tin concentration in serum was only slight raised over a period of 48 h after treatment (~20%) and brain tin levels remained constant.

Description of key information

Rats were administered 113 Sn-labelled tributyltin oxide as an aqueous suspension in doses of 5 mg/kg by the intragastric and the intraduodenal route. The distribution and elimination of the radio-labelled substance was studied in four experimental groups:

Group 1: single dose

Group 2: once-daily dose for 3 days

Group 3: once-daily dose for 7 days

Group 4: once-daily dose for 14 days

Organ and tissue specimens were removed in each case 24 hours after termination of treatment. Only about 20% of i.g. tributyltinoxide administered of 5 mg/kg is absorbed. The concentration of radioactive substance measured in the body after a two-week treatment was about four times higher than after a single dose; the accumulation factor in organs and tissues is 2-7. A steady state between absorption and elimination of the substance was not reached during the 14-day period. There was sustained gastric secretion of radioactivity, which could be of importance with regard to the percentages of administered dose that are excreted.

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Additional information

Kuhne, G. (1984) was selected as the key study for this endpoint. The study is performed in compliance with GLP and to good scientific standards. The study was considered adequate for assessment and given a reliability score of 2.

 

Kuhne G (1986), Kuhne (1985) and Davis A (1986) were provided as supporting studies. All the results were in agreement. The two studies by Kuhne G were assigned reliability scores of 2, the third supporting study, Davis A (1986) was assigned a reliability score of 4 as it was a review of previously reported studies, and as such it was not possible to determine the reliability of the data from the limited data reported.