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Toxicological information

Basic toxicokinetics

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Administrative data

basic toxicokinetics in vivo
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
4 (not assignable)
Rationale for reliability incl. deficiencies:
other: Study well conducted but no guideline followed and only few tissues examined for a distribution and metabolism study.
Cross-referenceopen allclose all
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to other study

Data source

Reference Type:

Materials and methods

Objective of study:
Test guideline
no guideline followed
Principles of method if other than guideline:
Radiolabelled halothane was administered to pregnant mice by inhalation route and to newborn mice by intraperitoneal injection. Then animals were killed and an autoradiography was performed in order to study the distribution and the metabolism of halothane in maternal tissues and in newborn mice.
GLP compliance:
not specified

Test material

Constituent 1
Chemical structure
Reference substance name:
EC Number:
EC Name:
Cas Number:
Molecular formula:
Details on test material:
- Name of test material (as cited in study report): Halothane
- Physical state: no data
- Lot/batch No.: no data
- Expiration date of the lot/batch: no data
- Stability under test conditions: assumed to be stable during the test (sponsor responsibility)
- Storage condition of test material: no data
- Other: source: Radiochemical centre, Amersham, England
14 C-labelled halothane (specific activity3.59 mCi/mM)

Test animals

Details on test animals or test system and environmental conditions:
- Source: no data
- Age at study initiation: about 3 months old and newborn (5 days old)
- Weight at study initiation: male rats: no data
- Housing: no data
- Diet (e.g. ad libitum): pellet diet (R3) (Ewos, Södertälje, Sweden), ad libitum
- Water (e.g. ad libitum): tap water, ad libitum
- Acclimation period: no data
- Temperature (°C): 23°C
- Humidity (%): no data
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): no data
IN-LIFE DATES: From: To: no data

Administration / exposure

Route of administration:
other: inhalation for pregnant mice and intraperitoneal for newborns
olive oil
Details on exposure:

- Exposure apparatus: the exposure was performed in an all-glass chamber which allows 4 mice to be exposed simultaneously. The chamber used was a modification of an earlier apparatus, described by Bergman (1979). The halothane was diluted with olive oil and liberated from the oil solutions by gentle heating.
- Method of holding animals in test chamber: no data
- Source and rate of air: no data
- Method of conditioning air: no data
- System of generating particulates/aerosols: not applicable
- Composition of vehicle (if applicable): no data
- Concentration of test material in vehicle (if applicable): no data
- Method of particle size determination: not applicable
- Treatment of exhaust air: no data

TEST ATMOSPHERE (if not tabulated): not applicable
- Particle size distribution:
- MMAD (Mass median aerodynamic diameter) / GSD (Geometric st. dev.):
Duration and frequency of treatment / exposure:
10 min
Doses / concentrations
Doses / Concentrations:
Pregnant mice: 100 µCi of 14C-labelled halothane
Newborn: 5 µCi of 14C-halothane
No. of animals per sex per dose / concentration:
36 pregnant mice
4 newborns
Control animals:
Positive control reference chemical:
no positve control
Details on study design:
no details
Details on dosing and sampling:
PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: see table 7.1.1/1
- Time and frequency of sampling: 0, 1, 4 or 24 hrs after the treatment with halothane
- Other:

- Tissues and body fluids sampled: see Table 7.1.1/1
- Time and frequency of sampling: 0, 1, 4 or 24 hrs after the treatment with halothane
- From how many animals: (samples pooled or not): 4
- Method type(s) for identification: Liquid scintillation counting
- Limits of detection and quantification: no data
- Other:

No data

Results and discussion

Preliminary studies:
not applicable

Toxicokinetic / pharmacokinetic studies

Details on absorption:
not applicable
Details on distribution in tissues:
Autoradiograms of pregnant mice showed a very high uptake of radioactivity in the maternal brain, body fat, nasal mucosa, blood, liver, kidney and lung, immediately after inhalation of 14C-halothane. Non-volatile radioactivity was present in a small but significant amount in the same organs, except body fat and brain, immediately after inhalation. The high levels of volatile radioactivity registered in the brain and body fat only by low-temperature autoradiography indicate an uptake of 14C-halothane itself. Low temperature autoradiography, as compared to autoradiography of freeze-dried and evaporated sections, showed that non-metabolized 14C-halothane was present in the tissues, particulary in body fat, up to 1 hr after the inhalation. In contrast to the volatile radioactivity, 14C-halothane metabolites were retained in relatively large amounts in certain maternal tissues, such as liver, kidney, eye and lungs, with peak values at 4 hrs after inhalation while the levels had decreased considerably at 24 hrs, except in the eyes and bronchi. Non-extractable radioactivity derived from 14C-halothane was seen in nasal mucosa, bronchi and liver at all survival times. The liver radioactivity had a mottled appearance, showing a centrilobular distribution.

Low-temperature autoradiography showed that 14C-halothane itself passed over the embryo and foetus at all studied stages of gestation. In early gestation (day 11), the radioactivity was rather evenly distributed between the different embryonic structures. In mid- (day 14) and late (day 17) gestation, there were more differentiated foetal distribution patterns with a higher concentration of radioactivity in blood and liver, as compared with other foetal organs.
At 1 hr after inhalation of 14C-halothane, autoradiograms obtained by low temperature and conventional autoradiography showed the same distribution patterns in foetal tissues, indicating that the major part of the volatile 14C-halothane had left the foetus. An interesting observation was the high concentration (among the highest in the body) in amniotic fluid, which was seen at 1 hr through 24 hrs after inhalation. Autoradiograms revealed low levels of radioactivity in embryonic and foetal tissues immediately after inhalation. The level was increasing with time, with a peak value at 4 hrs after inhalation. In early gestation, especially the neuroepithelium but also other structures revealed high concentrations. In late gestation, on the contrary, the foetal brain had a low concentration as compared to foetal tissues. All radioactivity in foetal tissues and in amniotic fluid was extractable in early as well as in late gestation.

Autoradiograms of the 5 day old mice injected intraperitoneally with 14C-halothane showed that volatile as well as non-volatile radioactivity was distributed in the same organs as was the case in adult mice exposed by inhalation. This pertains to extracted tissues as well, where a retention was observed in liver and respiratory epithelium (nasal mucosa and bronchi).

See details in Table 7.1.1/1
Transfer into organs
Test no.:
Transfer type:
blood/placenta barrier
distinct transfer
Halothane accumulated in the amniotic fluid. Accumulation is relatively slow (peak at 4 hrs). As halothane is a lipid-soluble compound, it easily passed membranes including those of the placenta. An accumulation in the fluids of the maternal eyes occurred
Details on excretion:
Not applicable

Metabolite characterisation studies

Metabolites identified:

Any other information on results incl. tables

Table 7.1.1/1: Concentrations in maternal organs, in amniotic fluid, in foetuses and placentas of non-volatile radioactivity at 0, 4, and 24 hrs after a 10 min. inhalation period of 14C-halothane. Concentrations are expressed in dpm per µL or mg +/- SEM (n=4)


0 hr

4 hrs

24 hrs


6.6 ± 2.4

67 ± 22

2.0 ± 0.2


89 ± 33

223 ± 48

5.1 ± 2.4


106 ± 46

414 ± 99

13 ± 2.6


17 ± 8.6

174 ± 47

4.4 ± 0.7


28 ± 19

285 ± 75

7.4 ± 1.3


15 ± 9

131 ± 25

4.1 ± 0.7


15 ± 5.7

181 ± 85

5.6 ± 0.9


35 ± 27

195 ± 22

1.9 ± 0.5


19 ± 9.5

179 ± 37

8.6 ± 2.9


2.4 ± 0.9

175 ± 25

5.1 ± 0.5


4.2 ± 1.9

190 ± 37

5.5 ± 0.8

Amniotic fluid

0.2 ± 0.1

86 ± 19

6.8 ± 1.4

 Dpm : desintegration per minute

Applicant's summary and conclusion

Interpretation of results (migrated information): high bioaccumulation potential based on study results
Under the test conditions, halothane accumulated in the amniotic fluid. The accumulation is relatively slow (peak at 4 hrs). As halothane is a lipid-soluble compound, it easily passed membranes including those of the placenta. In addition to the amniotic fluid, an accumulation in the fluids of the maternal eyes occurred, which was more apparent at low temperature autoradiography.
Executive summary:

In a distribution and metabolism study, halothane (99%) was administered to C57BL pregnant mice by inhalation or to 5 days old newborn mice by intraperitoneal injection. The pregnant mice were exposed to vapors of carbon 14 labelled halothane diluted in olive oil at the dose of 100 µCi for 10 min at different stages of gestation (11, 14 or 17 days of gestation). Newborn mice were exposed to 5 µCi 14C-halothane in a single injection by intraperitoneal route.

At different time point after the exposure (0, 1, 4 or 24 hrs), the mice were killed and the animals were examined by conventional whole-body autoradiography or by low temperature autoradiography which allowed the registration of volatile radioactivity. Radioactivity was quantified by liquid scintillation counting.

Under the test conditions, halothane accumulated in the amniotic fluid. The accumulation is relatively slow (peak at 4 hrs). As halothane is a lipid-soluble compound, it easily passed membranes including those of the placenta. In addition to the amniotic fluid, an accumulation in the fluids of the maternal eyes occurred, which was more apparent at low temperature autoradiography.