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Reference
Endpoint:
basic toxicokinetics in vivo
Type of information:
migrated information: read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Study period:
1978-10-30 to 1980-11-04
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Objective of study:
toxicokinetics
Principles of method if other than guideline:
The study was conducted to dermine the possible cumulative effects of ¹⁴C HEDP administered in drinking water over 2 years.
GLP compliance:
not specified
Radiolabelling:
yes
Species:
rat
Strain:
Wistar
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Winkelmann GmbH, BOrchen

- Age at study initiation: ca. 8 weeks

- Weight at study initiation: ca 200 g

- Fasting period before study: no

- Housing: Makrolon cages
- Individual metabolism cages: no 93 animals per cage)

- Diet: Altromin Haltungsdiät, ad libitum

- Water (e.g. ad libitum): test substance was administered in water, which was available ad libitum. Water consumption was measured in the first and second weeks, and then every two weeks, to obtain an average daily dose and a cumulative dose.

- Acclimation period: no information

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20°C (test animals) 21°C (control animals)

- Humidity (%): 50% (isotope lab, test animals) 60% (control animals)

- Air changes (per hr): no information

- Photoperiod (hrs dark / hrs light): natural daylight, therefoer variable.

IN-LIFE DATES: From: approx October 4th 1978 To: November 11th 1980
Route of administration:
oral: drinking water
Vehicle:
water
Duration and frequency of treatment / exposure:
Continuous via ad libitum drinking water over 2 years.
Dose / conc.:
0.184 mg/kg bw/day
Remarks:
equivalent to a total intake of 134 mg/kg bw.
No. of animals per sex per dose:
150 male test animals, 75 controls
Control animals:
yes, concurrent no treatment
Details on study design:
- Dose selection rationale: The dose used was chosen on the assumption that a certain amount (10%) can be swallowed by using a tooth-paste containing 0.5 -1% HEDP.

- Rationale for animal assignment (if not random): no information
Details on dosing and sampling:
PHARMACOKINETIC STUDY ( distribution)

- Tissues and body fluids sampled: blood, tibia

- Time and frequency of sampling: every four weeks in four test animals and two control animals.

- Radioactivity of organs was determined after drying.

- X-rays were taken to determine distribution of radiation, and morphology of bones.

- Other: Test animals remaining after 106 weeks treatment were observed for another 33 weeks, and then killed. Necroscopies were carried out.

Statistics:
t-test for water and food consumption, U-test for organ weight.
Type:
distribution
Results:
small amount of test substance found in bones 0.033% in total skeleton; 0.0065% after test period
Details on absorption:
After 4 weeks 0.069 mg HEDP/kg bone (1.1 µg absolute) was found in the skeleton. This is equivalent to 0.033% of the substance administered. After 104 weeks the amount in the skeleton was 0.0065% of the overall intake. As the radioactive levels of all organs and tissue samples with the exception of bone and intestine were only slightly above the limit of detection, the amount of HEPD absorbed from drinking water was apparently low.
Details on distribution in tissues:
Very little radioactivity was detected anywhere except in the bones. About 95% of the absorbed HEDP was found in the skeleton and 3% in the liver.
Details on excretion:
not specified
Metabolites identified:
not specified
Details on metabolites:
not specified

X ray studies showed that there was no influence of HEDP on morphology and length of bones.

Food consumption and body weight increased slightly in comparison with the control group.

No treatment related effects were observed in the following evaluations:

macroscopical and microscopical examinations

blood chemistry (including determination of magnesium, iron and zinc in serum)

urinalysis

bone marrow smears

organ weight determination

determination of calcium and phosphor in trachaea and tibia

Table 1 Distribution of ¹⁴C after 2 year exposure to 3.3 ppm ¹⁴C-HEDP in drinking water

Organ

¹⁴C-activity in % overall intake

¹⁴C-activity, relative distribution (%)

Intestine

5.7 ± 5.4 x 10ˉ³

40.70

Bones

7.6 ± 1.2 x 10ˉ³

54.30

Thyroid gland

1.3 ± 0.2 x 10ˉ⁵

0.09

Stomach

1.0 ± 0.7 x 10ˉ⁴

0.71

Bladder

4.2 ± 1.2 x 10ˉ⁵

0.30

Liver

2.6 ± 1.1 x 10ˉ⁴

1.86

Lungs

2.1 ± 0.5 x 10ˉ⁵

0.15

Tongue

4.7 ± 4.7 x 10ˉ⁶

0.03

Kidneys

3.1 ± 0.1 x 10ˉ⁵

0.22

Testicles

4.0 ± 1.7 x 10ˉ⁵

0.28

Eyes

2.8 ± 1.9 x 10ˉ⁶

0.02

Muscles

2.2 ± 0.5 x 10ˉ⁵*

-

Spleen

6.6 ± 0.9 x 10ˉ⁶

0.05

Pancreas

2.3 ± 0.8 x 10ˉ⁵

0.16

Brain

1.0 ± 0.6 x 10ˉ⁵

0.07

Heart

5.6 ± 1.9 x 10ˉ⁶

0.04

Skin

1.7 ± 1.3 x 10ˉ⁵*

-

Sum without stomach and intestine

8.0 ± 1.1 x 10ˉ³

-

Total sum

1.4 ± 0.7 x 10ˉ²

98.9

* Tissue weight not known

Conclusions:
Interpretation of results: absortion in bones was approximately 0.0065% of the amount of substance consumed.
Continuous oral intake of radio-labelled HEDP 2-Na led to a small amount of HEDP in the bones. During the test period the amount of HEDP was 0.033% in the total skeleton.; by the end of the test period the proportion was to 0.0065%. It is concluded that a small proportion of HEDP administered in drinking water is absorbed in the intestinal tract and reaches the bones. The amount in the skeleton decreases after administration ceases.

Description of key information

Key value for chemical safety assessment

Additional information

Based on the available data, no major differences appear to exist between animals and humans with regard to the absorption, distribution and elimination of phosphonic acid compounds in vivo. Uptake and elimination of disodium HEDP (CAS No 7414-83-7) by humans is generally consistent with that seen in animals. The toxicokinetics of the sodium and potassium salts of HEDP are not expected to be different to those of the parent acid, as the salts are well water soluble and the dissosiation is mainly dependent on the ambient pH in the gastrointestinal tract. Therefore the following information and predictions are applicable to tetrasodium HEDP.

Absorption

Oral

The physicochemical properties of phosphonic acid compounds, notably their high polarity, charge and complexing power, suggests that they will not be readily absorbed from the gastrointestinal tract. This is supported by experimental data which confirm that absorption after oral exposure is low, averaging 2-7% in animals and 2-10% in humans.

Gastrointestinal pH is a major determinant influencing uptake, and is relatively acidic in the stomach (range: pH 1 - 4) and slightly more alkaline in the intestine (pH 4 - 7). The number of ionisations of the phosphonic acid moiety increases with increasing pH, rising from 1 - 2 at low pH (i.e. stomach) to 4 - 6 at more neutral pH (reflective of conditions in the intestine). The negative charge on each molecule also increases with each ionisation, further reducing the already low potential for uptake. Stability constants for the interaction of phosphonic acids with divalent metal ions are high, and indicate strong binding, especially at lower pHs. Complexation of a metal with a phosphonic acid would produce an ion pair of charge close to neutral which might favour absorption; however the overall polarity of the complex would remain high thereby counteracting this potential. Overall, these considerations indicate that ingested phosphonic acid compounds will be retained within the gut lumen.

In a long-term investigation, 10% of a daily dose of disodium HEDP (20 mg/kg bwt/d for 6 - 12 mo) was absorbed from the gastrointestinal tract of osteoporotic female patients with around 2% of the dose eliminated in urine (Heaney and Saville, 1976). Limited information from Gural (1984; quoted in IUCLID data sheet for CAS No. 2809-21-4) noted that the oral bioavailability of 1000 mg 14C-disodium etidronate in human volunteers was 2%.

For the derivation of the DNEL, an oral absorption of 5% matches best animal and human data.

 

Dermal

HEDP is too hydrophilic to be well absorbed through the skin. This is supported by a dermal absorption study in rats which resulted in a dermal absorption of 0.46 % of the adminstered dose of sodium HEDP (Henkel 1982). For the calculation of the dermal DNEL, a dermal absorption of 0.5% can be assumed.

Inhalation

The vapour pressure of HEDP is extremely low (<10E-08 Pa). Consequently, inhalation of HEDP vapour is not possible. It is possible that a dust (from solid) or aerosol (from aqueous solution) of HEDP could be inhaled. In case of aerosol formation (spraying applications), droplets of water are typically in the range of 50-100 µm, which is higher than the respirable fraction (5-7 µm) or the inhalable fraction (10-15 µm). Conservatively, an inhalative uptake of 5% is taken into account and used for the derivation of an inhalation DNEL

Distribution

Bone distribution studies (Mőnkkőnen et al., 1989) demonstrate that the concentration of HEDP in mouse tibia and femur is maximal 2 hr following a single i.v. injection of 25 mg/kg bwt (approx. 13% of dose present in long bones; bone:plasma ratio equals 93), with detectable amounts of14C still present 12 months post-dose (5% of dose). Whole body autoradiography (Larsson and Rohlin, 1980) confirms deposition of14C on peripheral bone surfaces and in epiphyseal cartilage from long bones of rats within 30 min of HEDP treatment (single or 4 consecutive i.p. doses, 50 mg/kg bwt; 21.4 μCi/kg bwt). The overall pattern of distribution was similar irrespective of the age of the animals (1 d, 4 d, 25 d) or pre-conditioning with HEDP for up to 16 d. Studies in rats (Micheal et al., 1972) given 0.5 - 1000 mg/kg bwt14C disodium HEDP (CAS No 7414-83-7; supporting substance) revealed a dose-dependent increase in the amount of radiolabel present in tibia (0.02 - 580 μequiv./g tissue) and mandible (0.01 - 350 μequiv./g tissue) (time post-exposure not stated).

Metabolism

There are no data on the metabolism of HEDP.Metabolism of ATMP in vivo appears limited. Of the proportion of an oral dose excreted in urine, 25% is present as parent substance, approx. 50% as N-methyl derivative and the remainder as an unidentified product (Hotz et al., 1995). Conversion of orally administered PACs to carbon dioxide by the rat has been variously reported as 0% (Hotz et al., 1995), 0.2% (Michael et al., 1972) or 10% (Henkel KgaA, 1983a), with 0.4% conversion described in humans (Procter and Gamble, 1978).

Excretion

Mean urinary recovery was 1.8% for 4 volunteers given 5 mg/kg bwt 14C-labelled disodium HEDP (specific activity unknown) after 2-3 wk pre-conditioning with unlabelled material (30 mg/kg bwt/d) (Recker and Saville, 1973). Faecal recovery of label over 5 d was 90%, with 3% of the dose excreted in urine over 24 hr, in another 5 human subjects given 30 mg/kg disodium HEDP (pre-treated as above) (Recker and Saville, 1973). Mean intestinal uptake of disodium HEDP was estimated as 3% in the first group (dose = 5 mg/kg bwt) and 7% in the second group (dose = 30 mg/kg bwt). Broadly similar faecal recoveries of 70 - 90% over 6 d were reported by Caniggia and Gennari (1977) in volunteers given an oral dose of 100 mg disodium HEDP containing 20 μCi32P, although only limited experimental details are available for this study.

In a distribution and elimination study, male mice were given HEDP (25 mg/kg bwt; 49.5 μCi/kg bwt) by i.v. injection, and selected tissues analysed for14C for up to 360 d post-treatment (Mőnkkőnen et al., 1989).14C-HEDP disappeared rapidly from plasma, with 91% of the dose removed within 5 min and 99.8% by 2 hr (none present at 12 hr time-point). Levels in kidney were maximal 5 min post-treatment (approx. 32% of dose) and decreased thereafter (1-2% at 2 hr; trace at 12 hr; undetectable at 48 hr), consistent with rapid urinary elimination of the administered material.

Faecal excretion over 72 hr accounted for 80-95% of the dose eliminated by rat, monkey or rabbit, with <4% present in urine, small amounts present in carcass (up to 7% of dose) and trace amounts detected in soft tissues (up to 0.5% of dose). Less than 0.2% of the dose was exhaled as14C-carbon dioxide by the rat. Intestinal absorption appeared greater in the dog, with 9-10% of the dose eliminated in urine over 72 hr and 60-80% present in faeces. Soft tissues from the dog accounted for up to 1.5% of the dose, however carcass values were highly variable (<1% or 12%). Preconditioning of rats (0.5% unlabelled disodium HEDP in diet for 30 d prior to gavage administration of label) did not have any obvious influence on elimination (Michael et al., 1972).

Faecal elimination of labelled disodium HEDP (50 mg/kg bwt; 225 μCi/kg bwt) by the rat was greater following gavage administration (47% of dose) than after i.p. injection (4%) (Michael et al., 1972). Urinary excretion (33% versus 6%) and retention in carcass (51% versus 11%) were greater after parenteral administration. Trace amounts of label were present in rat bile irrespective of the route of exposure (0.1% after i.p. treatment, <0.01% after gavage) indicating negligible enterohepatic recirculation.

References

Caniggia, A and Gennari, C (1977) Kinetics and intestinal absorption of 32P-HEDP in man. Calc Tissue Res 22, 428 - 429.

Gural, PG (1984) Pharmacokinetics and gastrointestinal absorption behaviour of etidronate. Dissertation, University of Kentucky, Lexington. Cited in European Chemicals Bureau IUCLID Data Sheet for CAS No 2809-21-4.

Heaney, RP and Saville, MD (1976) Etridonate disodium in postmenopausal osteoporosis. Clin Pharmacol Therap, 20, 593 - 604.

Henkel KGaA (1982) Unpublished data, Archive No. TBD820064.

Henkel KGaA (1983a) Unpublished data, Archive No 830091. Cited in European Chemicals Bureau IUCLID Data Sheet for CAS No 6419-19-8.

Hotz, KJ, Warren, JA, Kinnett, ML and Wilson, AGE (1995) Study of the pharmacokinetics of absorption, tissue distribution and excretion of ATMP in Sprague-Dawley rats. Unpublished report, Ceregen (a unit of Monsanto Company Environmental Health Laboratory) St Louis, MO, Report Number MSL 14475, 6 December 1995

Larsson, SE and Ahlgren, O. (1992) Effects of disodium ethane-1-hydroxy-1,1-diphosphonate (HEDP) in adult normal and selectively parathyroidectomized rats. 1. Effects on plasma calcium, bone tissue and adrenal glands at low or normal calcium intake. Metab Bone Dis and Rel Res 4, 121 - 127.

Michael, WR, King, WR and Wakim, JM (1972) Metabolism of disodium ethane-1-hydroxy-1,1-diphosphonate (disodium etidronate) in the rat, rabbit, dog and monkey. Toxicol Appl Pharmacol, 21, 503 - 515.

Mőnkkőnen, J, Koponen, H-M and Ylitalo, P (1989) Comparison of the distribution of three bisphosphonates in mice. Pharmacol. Toxicol. 65, 294 - 298.

Procter and Gamble (1978) Unpublished data, Report ECM BTS 476, E-8218, MVL-YE 205, European Chemicals Bureau IUCLID Data Sheet for CAS No 15827-60-8.

Recker, RR and Saville, PD (1973) Intestinal absorption of disodium ethane-1-hydroxy-1,1-diphosphonate (disodium etidronate) using a deconvolution technique. Toxicol Appl Pharmacol, 24, 580 - 589.