Norflurane

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics

Type of information:

experimental study

Adequacy of study:

key study

Study period:

29 May 1991 to 18 October 1991

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1991

Reference 2

Reference Type:

publication

Title:

Metabolic fate and disposition of 1,1,1,2-tetrafluoroethane (HFC 134a) in the rat following a single exposure by inhalation.

Author:

Ellis MK, Gowans LA, Green T, Tanner RJN

Year:

1993

Bibliographic source:

Xenobiotica 93:719-729

Materials and methods

Objective of study:

other: pharmacokinetics and metabolism

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

Norflurane

EC Number:

212-377-0

EC Name:

Norflurane

Cas Number:

811-97-2

Molecular formula:

C2H2F4

IUPAC Name:

1,1,1,2-tetrafluoroethane

Details on test material:

- Name of test material (as cited in study report): 1,1,1,2-Tetrafluoroethane (HFC 134a)
- Substance type: pure active substance
- Physical state: gas at room temperature (supplied as liquefied gas)
- Analytical purity: >99.34%
- Impurities (identity and concentrations):
- Purity test date:
- Lot/batch No.: Y00035/030/001
- Expiration date of the lot/batch: n/a
- Radiochemical purity (if radiolabelling): >98%
- Specific activity (if radiolabelling): 21.7 mCi/mmol
- Locations of the label (if radiolabelling): U-14C
- Expiration date of radiochemical substance (if radiolabelling):
- Stability under test conditions:
- Storage condition of test material:
- Other: major impurity approximating to 1% of the total radio label was identified as 1,1,1,2,2-pentafluoro-2-chloroethane (CFC 115)

Radiolabelling:

yes

Remarks:

14C

Test animals

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Ltd, Kent, UK
- Age at study initiation:
- Weight at study initiation: 168 - 206g
- Fasting period before study:
- Housing:
- Individual metabolism cages: yes
- Diet (e.g. ad libitum): CTI diet, Special Diet Services Ltd, Witham, Essex given ad libitum except during exposure
- Water (e.g. ad libitum): ad libitum except during exposure
- Acclimation period:


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 3
- Humidity (%): 30 - 70
- Air changes (per hr):
- Photoperiod (hrs dark / hrs light): 12/12


IN-LIFE DATES: From: To:

Administration / exposure

Route of administration:

inhalation

Details on exposure:

Four male ratts (Numbered 1 -4) and four females (numbered 5-8) were exposed singly in the inhalation chamber for 1 hour to atmospheres of 1,1,1,2-tetrafluoroethane (HFC 134a). The HFC 134a was mixed with radiolabelled material using the following procedure to give an activity in the range 6.9 - 12.4uCi/mmol. The vial containing the radiolabelled material was opened inside an evacuated and sealed 5 litre Pedlar gas bag (SKC, Dorset). The bag was then filled with 5 litres of non-radio labelled HFC 134a. The contents were then drawn from the bag and mixed with silica gel dried laboratory air to give a concentration of 10000ppm HFC 134a which was passed through the chamber at a flow rate of 1L/min.
The atmosphere within the chamber was monitored by gas-chromatography at approximately 5 minute intervals throughout the exposure. Samples of the atmosphere (3x1ml) were removed at 30 minutes into exposure to check the specific activity of HFC 134a into the exposure to check the specific activity of the HFC 134a within the chamber.

Duration and frequency of treatment / exposure:

Single exposure of 1 hour

Doses / concentrations

Remarks:

Doses / Concentrations:
10000ppm

No. of animals per sex per dose / concentration:

4 males and 4 females

Control animals:

no

Details on dosing and sampling:

At the end of the exposure period the rats were rapidly transferred from the inhalation chamber to individual glass metabolism chambers equipped for the collection of urine, faeces, expired organic material and carbon dioxide. Air (silica gel dried) was drawn through the chamber at a rate of 1litre/min for the period of exposed air collection, after which the lid was replaced by a perforated perspex grid for the remaining duration of the study.
Urine and faeces were collected over dry ice and the traps changed at 6 hourly intervals up to 24 hours and then at 24 hour intervals up to 5 days. Samples were stored at -70°C prior to analysis.
Carbon dioxide was collected by dissolution in 2N sodium hydoxide (2X500ml) contained within two Nilox columns placed in sequence. The traps were changed 6, 12, 24 and 48 hours post-exposure. Samples were stored at 4°C prior to analysis.
Expired organic material was absorbed onto activated charcoal (Drager tubes, 4 x 1g). The traps were changed at 10 minute intervals for the first hour, at 15 minute intervals for the second hour and then hourly up to 10 hours post exposure. To effect efficient absorbtion the expired air was dried (Drierite 150 - 200g) prior to passage through the charcoal traps. Under these conditions > 95% of the radioactivity was trapped in the first pair of traps and the remainder in the second pair of traps. Samples were stored at room temperature (21°C) and analysed within 18 hours of collection.

At termination one male (rat 3) and one female (rat 6) were assayed for total carcass radioactivity. One further male (rat 1) and female (rat 8) were dissected and the following tissues removed and assayed for radioactivity: plasma, liver, kidney, heart, lungs, bone (femur), brain, muscle, spleen, renal fat, testes (male) and ovaries (female). The remaining two male (rats 2 and 4) and two female (rats 5 and 7) were stored at -70°C prior to dissection (as above) and tissue analysis. The residual carcasses from animals 1,2,4,5,7 and 8 were also assayed for radioactivity.

Statistics:

Exposure levels to HFC 134a and the amount of unchanged HFC 134a and metabolites eliminated in the urine, faeces and expired air of male and female rats are expressed as mean values ± standard deviation SD.

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on absorption:

1% of inhaled dose was absorbed (see Table 1).

Details on distribution in tissues:

There was no evidence for specific accumulation in any organ or tissue, including fat (see Table 2).

Details on excretion:

0.67% of the absorbed dose (1%) was excreted within one hour of cessation of exposure as unchanged HFC 134a.

Toxicokinetic parameters

Toxicokinetic parameters:

half-life 1st: ca. 20 minutes

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

Metabolism of HFC 134a was in the order of 0.37% of the dose (0.34 and 0.40% in males and females respectively) when measured as the sum of the amounts of radioactivity in urine and faeces and in expired air as carbon dioxide. Carbon dioxide was the major metabolite measured at 0.22 % (males) & 0.27% (females) of the inhaled dose (See Table 1). Other than carbon dioxide, trifluoroacetic acid (TFA) was the only other metabolite identified, which is consistent with oxidative metabolism by cytochrome P450, presumabley cytochrome P450IIEI.

Any other information on results incl. tables

Table 1. The Excretion of HFC 134a in Male and Female Rats Summary.

Rat No.	Weight (g)	Mean ± SD^d Exposure HFC 134a(ppm)	Specific ActivityuCi/mmol	Dose(umol)	Distribution of radiolable ^a (u mol equiv. HFC 134a)
					Urine		Faeces	Exhaled^c Organic Material	Carbon Dioxide	Carcass^b
Males
1	179	10800 ± 663	10.5	2709	1.61		0.83	19.13	11.00
2	168	10800 ± 760	9.9	2576	4.23		0.94	16.40	3.62
3	193	10200 ± 1338	10.4	2709	1.82		0.66	12.52	2.85	4.16 (0.154%)
4	206	10000 ± 840	12.4	2778	1.60		1.30	23.02	5.65
Mean ±SD				2693±84	2.32 ± 1.3 (0.086%)		0.93 ± 0.3 (0.035%)	17.77 ± 4.4 (0.660%)	5.78 ± 3.7 (0.215%)
Females
5	182	10900±264	11.6	2761	1.79		1.21	17.36	7.74
6	192	10600±1246	11.0	2789	2.52		0.71	24.17	16.91	3.77 (0.135%)
7	189	10500±776	8.3	2737	1.93		1.09	17.39	3.57
8	200	10500±1366	6.9	2866	3.63		1.16	17.18	4.87
Mean ± SD				2788 ±56	2.47 ± 0.8 (0.088%)		1.04±0.2 (0.037%)	19.03 ± 3.4 (0.682%)	7.52 ± 6.3 (0.027%)

a. Figures are % of inhaled dose

b. Values from individual tissues from the remaining animals are shown in Table 2

c. Radioactivity trapped in the charcoal and drierite traps

d. Population SD used for Exposure data.

Table 2. Tissue Distribution of Radioactivity in the Tissues of Male and Femal Rats Five Days Post-Exposure

	Tissue Digestion (nmol HFC 134a equiv/g tissue)
	MALE FEMALE
Tissue	Rat 1^*	Rat 2	Rat 4	Mean ± SD		Rat 5^*	Rat 7	Rat 8	Mean ± SD
Muscle	4.65	5.35	3.85	4.62 ± 0.75		6.81	5.55	7.30	6.55 ±0 .90
Liver	9.75	9.30	12.75	10.60 ± 1.88		10.13	25.00	11.5	15.54 ± 8.22
Brain	5.25	5.15	5.70	5.34 ± 0.29		7.46	5.55	7.2	6.74 ± 1.04
Renal fat	4.40	6.55	5.45	5.47 ± 1.08		6.25	7.15	10.9	8.10 ± 2.47
Lung	27.55	27.60	27.55	27.57 ± 0.03		31.29	18.40	30.45	26.71 ± 7.21
Kidney	9.00	11.31	11.80	10.70 ± 1.50		19.14	15.30	17.00	17.15 ± 1.92
Heart	14.05	17.45	23.60	18.37 ± 4.84		34.57	21.80	24.45	26.94 ± 6.74
Spleen	8.90	10.60	11.05	10.18 ± 1.13		10.00	14.70	13.05	12.58 ± 2.38
Femur bone	9.35	5.45	5.45	6.75 ± 2.25		6.34	7.25	8.00	7.20 ± 0.82
Testes / Ovaries	4.80	5.10	4.25	4.72 ± 0.43		5.56	4.90	10.65	7.04 ± 3.15
Carcass	5.80	6.85	5.70	6.12 ± 0.64		9.70	8.61	10.90	9.74 ± 1.15
Plasma	11.15	-	-			-	-	5.78	-

* Tissues were removed from Rat 1 (male) and Rat 8 (Female) at 5 days post-exposure. Carcasses for Rats 2 and 4 (males) and 5 and 7 (females) were stored at -70°C prior to tissue removal.

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): no bioaccumulation potential based on study results
There are no significant sex differences in the absorption, distribution, elimination and metabolism of HFC 134a in the rat. Absorption is low as might be expected for a heavily fluorinated molecule of this type and elimination of both unchanged chemical and metabolites is rapid when exposure ends. There are no significant residues remaining in the animal 5 days after cessation of exposure. Metabolism is minimal and accounts for approximately 0.37% of the dose. Carbon dioxide is the major metabolite, the only other metabolite identified being trifluoroacetic acid (TFA). Both these metabolites are consistent with a single metabolic pathway involving an oxidation which is catalysed by cytochrome P450.

Executive summary:

Male and female Wistar rats were exposed to atmospheres containing 10,000 ppm (41,700 mg/m3) 14C-labelled HFC-134a for a period of 1 hour. On cessation of exposure, the animals were removed from the inhalation chambers and housed individually in glass metabolism cages. Urine and faeces were collected, as well as expired organic material and carbon dioxide. The total radioactivity measured in expired air, urine and faeces amounted to approximately 1% of the inhaled dose in both male and female rats, which represented the amount of the inhaled dose of HFC-134a that had been absorbed. Of this 1% of radioactivity, approximately 0.67% was exhaled within 1 hour after cessation of exposure as unchanged HFC-134a. The half-life of excretion of HFC-134a was of the order of 20 minutes. The remaining radioactivity (approximately 0.33%) was excreted in the first 24 hours after cessation of exposure. Carbon dioxide, seen in exhaled air, was the major metabolite, accounting for 0.22% of the inhaled dose of HFC-134a for male and 0.27% for female rats. Urinary excretion accounted for 0.09% of the inhaled dose in both sexes and faecal excretion accounted for 0.04%. A single metabolite was detected in the urine by 19F-nuclear magnetic resonance (NMR) spectrometry; it was identified as trifluoroacetic acid (TFA). Total metabolism, measured as the sum of radioactivities in urine, faeces and as carbon dioxide was 0.34% and 0.40% of the inhaled dose of HFC-134a in males and females, respectively. Analyses of a range of tissues at the end of the study showed a relatively uniform distribution of radioactivity. There was no evidence for specific accumulation in any organ or tissue, including fat.