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Basic toxicokinetics

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Administrative data

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
key study
Study period:
6 October 1997 to 28 August 1998
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Although no specific test guideline was identified, the study was conducted according to valid and internationally recognized test procedures that followed recognized GLP standards.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1998
Report Date:
1998

Materials and methods

Objective of study:
other: disposition and pharmacokinetics
Test guideline
Qualifier:
no guideline followed
Guideline:
other: equivalent to an OECD Guideline 417 study
Principles of method if other than guideline:
Rats and mice were dosed by oral gavage with 14C-tetrahydrofuran at dose levels of 50 and 500 mg/kg. Total radioactivity was quantitated in expired air, plasma, urine and feces at various time points up to 168 hours post-dosing.
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material: tetrahydrofuran- Physical state: liquid- Analytical purity: 99%- Impurities: not supplied by Sponsor- Purity test date: not supplied- Lot/batch No.: HR00360ER (Lot. No.)- Expiration date of the lot/batch: not supplied- Radiochemical purity: not supplied (purity of labeled material 99%)- Specific activity: not supplied- Locations of the label: 3,4-14C-tetrahydrofuran (3302-029, Supplier: New England Nuclear, Lot. No.)- Expiration date of radiochemical substance: not supplied- Stability under test conditions: The test substance was stable under the conditions of the study; no evidence of instability was observed.- Storage condition of test material: not supplied
Radiolabelling:
yes

Test animals

Species:
rat
Strain:
Fischer 344
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS- Source: Charles River Laboratories, Inc., Raleigh, North Carolina, USA- Age at study initiation: at least 63 days old- Weight at study initiation: males, 150-200 g; females, 100-150 g- Fasting period before study: yes, overnight before dosing- Housing: appropriate cages- Individual metabolism cages: yes, glass metabolism cages- Diet (ad libitum): PMI Nutrition International Inc., Certified Rodent LabDiet(TM) 5002- Water (ad libitum): tap water- Acclimation period: animals quarantined six days, after which selected for studyENVIRONMENTAL CONDITIONS- Temperature (°C): 23 +/- 1- Humidity (%): 50 +/- 10- Air changes (per hr): not supplied- Photoperiod (hrs dark / hrs light): 12/12IN-LIFE DATES: From: 6 October 1997 To: 31 October 1997

Administration / exposure

Route of administration:
oral: gavage
Vehicle:
water
Details on exposure:
PREPARATION OF DOSING SOLUTIONS:Dose solutions were prepared one day prior to dosing and were frozen at -20 deg C until the time of dosing. The dose vehicle was reagent grade water. The radiolabeled and unlabeled test compounds were dissolved together in the vehicle. The dose volume was targeted at 4 ml/kg. Each animal in the high dose group received a single 500 mg/kg bwt dose by gavage. Each animal in the low dose received 50 mg/kg bwt.VEHICLE- Concentration in vehicle: not given- Amount of vehicle (if gavage): dose volume of 4 ml/kgHOMOGENEITY AND STABILITY OF TEST MATERIAL:Dose solutions were quantitatively diluted with water and analyzed by gas chromatography for concentration against a standard curve of non-labeled tetrahydrofuran standards. Standards were prepared fresh on the day of analysis by dissolving a weighed amount of tetrahydrofuran in water and preparing serial dilutions over a range suitable for the expected diluted dose solution concentration.
Duration and frequency of treatment / exposure:
Single gavage dose
Doses / concentrations
Remarks:
Doses / Concentrations:50 and 500 mg/kg bwt (nominal)
No. of animals per sex per dose:
5
Control animals:
no
Details on study design:
Three male and female rats from each dose group were cannulated and used for blood collections. The remaining 2 male and female rats in each dose group were used for the collection of CO2 and volatile organics.
Details on dosing and sampling:
The high dose animals were administered the test compound by gavage at a target tetrahydrofuran dose of 500 mg/kg bwt and at least 25 microCuries/animal of radioactivity. For the low dose, rats were administered the test compound at a target tetrahydrofuran dose of 50 mg/kg bwt and at least 25 microCuries/animal of radioactivity. Rats were housed individually in glass metabolism units.Urine and feces were collected on dry ice at approximately 12 and 24 hours, and each 24 hours post-dosing until sacrifice at 168 hours.Expired air from metabolism chambers was passed through two traps connected in series for the collection of CO2 and volatile organics. The first trap contained 2 N sodium hydroxide and the second ethylene glycol. For the high dose rats, solvent traps were collected and replaced every 24 hours post-dosing throughout the study. The solvent traps for low dose rats were collected and replaced at approximately 12 and 24 hours and each 24 hour post-dosing until sacrifice at 168 hours.Three jugular-vein cannulated rats of each sex were used to determine the plasma pharmacokinetics of each rat. They were administered 14C-tetrahydrofuran. Blood (approx. 0.2 ml) was drawn from the cannula and placed into Microtainer(TM) tubes containing EDTA at the following post-dosing times: 15 and 30 minutes, 1, 1.5, 2, 4, 8, 12 and 24 hours and every subsequent 24-hour period until sacrifice.Tissues collected at sacrifice were the following:blood (for plasma and RBCs) fat liverkidney muscle heartlung testes ovaries/uterusbone and bone marrow brain spleenG.I. tract and contents adrenals skinAfter collection, tissue samples were stored at approximately -20 deg C until processing and analysis. Because only a portion of the muscle, skin, fat, and bone were collected, the values were adjusted to account for total weight by multiplying the sample weight by a percentage of body weight (muscle: 40%, skin: 19%, fat: 7%, bone: 7.3%). The remaining carcass was homogenized and assayed so that total material balance could be determined.Rats were sacrificed by CO2 asphyxiation. Blood was collected via cardiac puncture into heparinized tubes and kept on ice until processing. In order to separate plasma from red blood cells, whole blood was centrifuged at 4 deg C for 15 min at approx. 2500 x g. Plasma was stored at approx. -20 deg C.Radioactivity AnalysisAliquots of plasma were assayed for radioactivity by liquid scintillation counting (LSC). Radioactive residues in red blood cells was determined by sample oxidation and LSC.Each urine sample was thawed and 0.05 to 1.0 ml aliquots were assayed in duplicate or triplicate by LSC.Feces from each collection interval were homogenized and aliquots were combusted. The CO2 liberated from the combustion was assayed by LSC to determine total fecal radioactivity for individual animals.Tissues and carcasses were analyzed by complete combustion with trapped 14CO2 assayed by LSC. Each sample was analyzed induplicate or triplicate.For expired CO2 and volatile organics, aliquots from NaOH and ethylene glycol traps were assayed in duplicate or triplicate for 14CO2 content by LSC.Cage washes were assayed in duplicate or triplicate by LSC.The total recovery of radioactivity was determined by adding total amounts of radioactivity from all samples and dividing by the amount of 14C administered to the animals.For LSC determinations, samples were counted for 10 minutes or until 160,000 disintegrations (0.5% 2-alpha) were accumulated, whichever came first. Low radioactivity samples may have been counted for up to 75 minutes or until 6500 disintegrations (2.5% 2-alpha) were accumulated.
Statistics:
Results were reported as the mean and standard deviation.The following plasma pharmacokinetic parameters were determined: plasma half-life (t 1/2), maximum concentration in plasma (Cmax), time to Cmax (Tmax), and area under the curve (AUCinf) for plasma concentration versus time. Pharmacokinetic parameters were determined with WinNonLin (Scientific Consulting Inc.). The same pharmacokinetic parameters were determined for red blood cells. Concentration-time curves were graphed in semilog format. The terminal elimination rat constant (beta, days-1) was calculated from the slope (beta = -2.303 x slope) of the terminal elimination phase that was determined from linear regression. Half-life (t1/2) was calculated using the following equation: t1/2 = 0.693/beta. Area under the concentration-time curve (AUCinf) was determined by integration.

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on absorption:
Male rats at the 500 mg/kg bwt dose level received actual doses 428.7 +/- 30.5 mg/kg bwt and 45.0 microCuries/subject. Female rats received 478.3 +/- 36.7 mg/kg bwt and 33.9 microCuries/subject.Male rats at the 50 mg/kg bwt dose level received actual doses 40.3 +/- 3.4 mg/kg bwt and 44.1 microCuries/subject. Female rats received 30.9 +/- 1.4 mg/kg bwt and 45.9 microCuries/subject.
Details on distribution in tissues:
For male rats at the 500 mg/kg bwt dose level, all tissues combined represented an average of 6.0 +/- 1.7% of the dose. The carcasses contained the most radioactivity (2.5 +/- 0.8%), followed by muscle (1.1 +/- 0.2%), liver (0.7 +/- 0.2%), and skin (0.7 +/- 0.2%). For female rats at the 500 mg/kg bwt dose level, all tissues combined represented an average of 3.7 +/- 0.4% of the dose. As with male rats, the carcasses contained the most radioactivity (1.6 +/- 0.2%), followed by muscle (0.9 +/- 0.0%), liver (0.4 +/- 0.1%), and skin (0.3 +/- 0.2%).For male rats at the 50 mg/kg bwt dose level, all tissues combined represented an average of 10.3 +/- 3.7% of the dose. The carcasses contained the most radioactivity (4.2 +/- 1.6%), followed by muscle (1.8 +/- 0.4%), liver (1.7 +/- 0.9%), and skin (1.0 +/- 0.5%). For female rats at the 50 mg/kg bwt dose level, all tissues combined represented an average of 7.5 +/- 1.7% of the dose. As with male rats, the carcasses contained the most radioactivity (3.0 +/- 0.8%), followed by muscle (1.5 +/- 0.4%), liver (1.2 +/- 0.3%), and skin (0.7 +/- 0.3%).In terms of micrograms equivalent/g of tissue, the liver stands out with respect to both dose levels and sexes of rats, having a range of 11.0 microg equiv/g in the low dose female rats to 60.5 microg equival/g in the high dose male rats. Fat was high relative to all other tissues, having a range of 3.0 microg equiv/g in the low dose females and 31.3 microg equival/g in the high dose male rats. The adrenals contained almost as much material/g as the fat, with a range of 3.9 microg equival/g in the low dose females to 30.2 microg equival/g in the high dose males. Kidney and bone marrow also contained relatively large concentrations.
Details on excretion:
The high dose rats had overall low total material balance (33.0% in males; 25.5% in females). The low dose rats also had low total material balance (67.5% males; 61.3% females).Male rats at the 500 mg/kg bwt dose level expired an average of 21.9% of the dose as 14CO2 after 168 hours, with the majority expired within the first 24 hours. Female rats at this dose level expired an average of 18.8% of the dose as 14CO2 after 168 hours, with the majority expired within the first 24 hours.Male rats at the 50 mg/kg bwt dose level expired an average of 47.8% of the dose as 14CO2 after 168 hours, with the majority expired within the first 24 hours. Female rats at this dose level expired an average of 47.5% of the dose as 14CO2 after 168 hours, with the majority expired within the first 24 hours.Male rats at the 500 mg/kg bwt dose level excreted 2.1 +/- 0.5% of the dose in the urine, and 0.9 +/- 0.3% in the feces. Female rats at the 500 mg/kg bwt dose level excreted 2.0 +/- 0.4% of the dose in the urine, and 0.5 +/- 0.0% in the feces. In both sexes, the majority of urinary radioactivity was excreted within the first 24 hours.Male rats at the 50 mg/kg bwt dose level excreted 3.4 +/- 1.3% of the dose in the urine, and 1.4 +/- 0.6% in the feces. Female rats at the 50 mg/kg bwt dose level excreted 3.5 +/- 0.4% of the dose in the urine, and 0.8 +/- 0.3% in the feces. In both sexes, the majority of urinary radioactivity was excreted within the first 24 hours.There was no significant radioactivity (< limit of detection) found in the volatile organic traps for either male or female rats. There was also no significant radioactivity found in cage wash or residual feed for either male or female rats.
Toxicokinetic parametersopen allclose all
Test no.:
#2
Toxicokinetic parameters:
Tmax: 3.0 +/- 1.7 hr, females, 50 mg/kg bwt
Test no.:
#2
Toxicokinetic parameters:
Cmax: 13.8 +/- 1.5 microg equiv/g plasm, females, 50 mg/kg bwt
Test no.:
#2
Toxicokinetic parameters:
AUC: 319.6 +/- 10.3 microg equiv-hr/g plasm, females, 50 mg/kg bwt
Test no.:
#2
Toxicokinetic parameters:
half-life 1st: 50.5 +/- 2.8 hr, females, 50 mg/kg bwt
Test no.:
#2
Toxicokinetic parameters:
Tmax: 4.0 +/- 0.0 hr, males, 50 mg/kg bwt
Test no.:
#2
Toxicokinetic parameters:
Cmax: 19.8 +/- 2.0 microg equiv/g plasma, males, 50 mg/kg bwt
Test no.:
#2
Toxicokinetic parameters:
AUC: 535.8 +/- 63.5 microg equiv-hr/g plasm, males, 50 mg/kg bwt
Test no.:
#2
Toxicokinetic parameters:
half-life 1st: 52.1 +/- 0.2 hr, males, 50 mg/kg bwt
Test no.:
#1
Toxicokinetic parameters:
Tmax: 3.2 +/- 4.2 hr, females, 500 mg/kg wt
Test no.:
#1
Toxicokinetic parameters:
Cmax: 89.2 +/- 44/2 microg equiv/g plasm, females, 500 mg/kg bwt
Test no.:
#1
Toxicokinetic parameters:
AUC: 1998.0 microg equiv-hr/g plasm, females, 500 mg/kg bwt
Test no.:
#1
Toxicokinetic parameters:
half-life 1st: 59.0 +/- 0.9 hr, females, 500 mg/kg bwt
Test no.:
#1
Toxicokinetic parameters:
Tmax: 8.0 +/- 0.0 hr, males, 500 mg/kg bwt
Test no.:
#1
Toxicokinetic parameters:
Cmax: 71.6 +/- 11.3 microg equiv/g plasm, males, 500 mg/kg bwt
Test no.:
#1
Toxicokinetic parameters:
AUC: 2825.5 microg equiv-hr/g plasma, males, 500 mg/kg bwt
Test no.:
#1
Toxicokinetic parameters:
half-life 1st: 48.0 +/- 4.3 hr, males, 500 mg/kg bwt

Metabolite characterisation studies

Metabolites identified:
yes
Details on metabolites:
Urine and feces accounted for only a small portion of the percentage recoveries from rats. An attempt was made to analyze the urine by HPLC, but significant loss of radioactivity during th concentration and clean-up made the radioactivity in the samples too low to detect. Radioactivity in urine was completely unretained on a C-18 HPLC column, as well as a variety of solid phase extraction reverse phase columns, indicating that the metabolite(s) were polar in nature. Radioactivity was retained on a polymeric ion exchange column designed for organic acid separations, suggesting that metabolites may be acidic in nature.No attempt was made to analyze the feces for metabolites given the low percent of recovery and the problems encountered with the analysis of urine metabolites.

Applicant's summary and conclusion

Conclusions:
Interpretation of results (migrated information): no bioaccumulation potential based on study resultsThe major route of elimination of tetrahydrofuran from both male and female rats was as expired 14CO2. The exhalation of volatile organics, perhaps as unchanged tetrahydrofuran, was also significant. The urine and feces were not significant routes of elimination. Urinary metabolites were not isolated or identified, but they were characterized as very polar, and perhaps acidic in nature.The Tmax for tetrahydrofuran from rat plasma was approximately 4 hours at the 50 mg/kg bwt dose level for both male and female rats. This value nearly doubled in male rats (8 hours) at the high dose level. The average Tmax value for female rats at the high dose level was 3.2 hours but individual subjects varied from 0.5 to 8 hours. The Cmax averages for male and female rats at the 500 mg/kg bwt dose level were within the standard deviation of each other. The Cmax for the 50 mg/kg bwt rats was approximately 4-fold lower than at the high dose. The half-life for tetrahydrofuran in plasma from male and female 500 mg/kg bwt dosed rats was 53.5 +/- 4.4 hours, comparable to the half-life of 51.3 +/- 2.8 hours observed at the lower dose level.Red blood cell analyses indicated an increase in the observed concentration of radioactivity between the 24 and 48 hour samples. This elevated concentration remained until sacrifice reaching a plateau value of 8-11 microg equivalents/g in the 500 mg/kg bwt dosed rats. At the 50 mg/kg bwt dose level, this plateau value was 2 microg equivalents/g. These concentrations in red blood cells made it difficult to reliably calculate a half-life.The carcasses contained the largest percentage of the dose at 168 hours at both dose levels in rats. The muscle, skin, and liver were the three tissues with highest concentrations of activity, although each was less than 1% of the administered dose. In terms of concentration, the liver had the highest levels at both dose levels and sexes of rat. Fat was high relative to other tissues. The adrenals contained almost as much material per gram as fat. Kidney and bone marrow also contained relatively larger concentrations.
Executive summary:

Male and female rats were administered 14C-tetrahydrofuran by oral gavage at nominal dose levels of 50 or 500 mg/kg bwt. Total radioactivity was quantitated in expired air, plasma, urine, and feces samples collected at various times after dose administration. Tissue radioactivity was determined for a number of tissues at 168 hours post dose.

The major route of elimination of tetrahydrofuran in both sexes of rat was as expired 14CO2 (20.3% of dose, 500 mg/kg bwt; 47.6% of dose, 50 mg/kg bwt). Volatile organics were not trapped efficiently but it is probable that this elimination route represented a significant percentage of the dose.

Based on plasma samples for low dose male and female rats, a Tmax of approximately 4 hours was obtained for both sexes. The Tmax value for male rats in the high dose group was 8 hours, about twice that of the low dose. Female rats at the high dose level had an average Tmax value of 3.2 hours but individual female rat values varied widely. The average Cmax values for high dose male and female rats were within one standard deviation of each other. The Cmax values for the 50 mg/kg bwt dose level rats were approximately 4-fold lower than for the high dose group. The half-life for total radioactivity in the 500 mg/kg bwt dose rats was 53.5 +/-6.6 hours, comparable to the half-life value for the low dose rats of 51.3 +/- 2.8 hours.

Rats were sacrificed at 168 hours and tissue samples collected, oxidized and analyzed for radioactivity by liquid scintillation counting. At both dose levels and in both male and female rats, the average of all tissues combined represented an average of 6.8% of the dose. The carcasses contained the most radioactivity, followed by muscle, liver and skin.

The urine and feces accounted for only small portions of the percentage recoveries for both dose levels and sexes or rat. Urine never accounted for more than 5% of the dose and feces never more than 2%. An attempt was made to analyze urine by HPLC, but significant loss of radioactivity during concentration and clean up made the radioactivity in the samples too low to analyze. The radioactivity in urine was not retained on a C-18 reverse-phase HPLC column, as well as on a variety of solid phase extraction columns, indicating the polar nature of the metabolites. Radioactivity was retained on a polymeric ion exchange column designed for organic acid separations, but column recovery experiments indicated irreversible binding of approximately 50% of the sample. These results indicate the possible acidic nature of the metabolites.

No attempt was made to analyze feces for metabolites based on the problems encountered with urine samples.

There was no significant radioactivity found in cage wash or residual feed for either males or females.