Thymol

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

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

Data source

Reference

Reference 1

Reference Type:

publication

Title:

Unnamed

Year:

1987

Reference 2

Reference Type:

review article or handbook

Title:

The biochemistry of foreign compounds, Internat. series of monographs in pure and applied biology 5

Author:

Parke DV

Year:

1968

Bibliographic source:

Oxford; Pergamon Press, p. 147-148

Materials and methods

Objective of study:

metabolism

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Thymol was dissolved in propylene glycol (1-2 ml) and given 6 male albino rats per stomach tube at a dose level of 1 mmol/kg bw (ca. 150 mg/kg bw). Similar animals receiving solvent only served as controls. Urine samples were collected at -10°C at 24 hours intervals and anaylsed by chromatography after conjugate hydrolysis.

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

Thymol

EC Number:

201-944-8

EC Name:

Thymol

Cas Number:

89-83-8

Molecular formula:

C10H14O

IUPAC Name:

5-methyl-2-(propan-2-yl)phenol

Test material form:

solid

Radiolabelling:

no

Test animals

Species:

rat

Strain:

Wistar

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Mollegaards Breeding Centre Ltd., Ejby, Denmark
- Weight at study initiation: 250 - 350 g
- Diet (e.g. ad libitum): ad libitum. They were switched from a standard pellet diet to a purified diet two days before dosing and during the experiments in order to reduce the number of normal chromatographic peaks in the urine extracts.

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

propylene glycol

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
The test compounds was dissolved in propylene glycol (1-2 mL) and given by stomach tube at a dose level of 1 mmol/kg.

Duration and frequency of treatment / exposure:

Single application

Doses / concentrations

Dose / conc.:

150.22 mg/kg bw/day

Remarks:

1 mmol = 150.22 mg/kg bw

No. of animals per sex per dose / concentration:

6

Control animals:

yes, concurrent vehicle

Details on dosing and sampling:

METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled: urine
- Time and frequency of sampling: 24 h intervals
- From how many animals (samples pooled or not) : 6 animals, not pooled
- Method type(s) for identification: GLC-MS

TREATMENT FOR CLEAVAGE OF CONJUGATES (if applicable): conjugate hydrolysis using a glucuronidase + sulphatase preparation

ANALYTICAL METHOD
- Complete description including: The capillary GLC columns employed were prepared in using SE-54 (bonded phase), OV-1701 (bonded phase), Pluronic 64 and Emulphor. TMS-derivatives were chromatographed using 20 m SE-54 column (0.32 mm x 20 m) at 100°C for 2 min., then increasing at 8°C/min to 260°C. Methyl ester-derivatives chromatographed using OV-1701 column (0.29 mm x 30 m) at 100°C, then increasing at 8°C/min to 250°C. Mass spectra recorded from > m/z 80 (TMS-derivatives) or > m/z 50 (methyl ester-derivatives).

Results and discussion

Main ADME results

Type:

metabolism

Results:

Oxidation of the methyl and isopropyl groups occurred. This resulted in the formation of derivatives of benzyl alcohol and 2-phenylpropanol and their corresponding carboxylic acids. In contrast, ring hydroxylation of the two phenols was a minor reaction.

Toxicokinetic / pharmacokinetic studies

Details on excretion:

The urinary excretion of metabolites were rapid. Only very small amounts were excreted after 24 h.

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

In the 24 h rat urine the following metabolites were identified:
2.5-Dihydroxy-p-cymene, 2-(2-hydroxy-4-methylphenyl)propan-1-ol, 5-Hxdroxymethyl)-2-(1-methylethyl)phenol, 2-(4-Hydroxymethyl-2-hydroxyphenyl)propan-1-ol, 2-(2-Hydroxy-4-methylphenyl)propionic acid, 3-Hydroxy-4-(1-methylethyl)benzoic acid (please refer to attached figure)

Any other information on results incl. tables

The urinary excretion of metabolites were rapid. Only very small amounts were excreted after 24 h. Although large quantities of thymol was excreted unchanged (or as their glucuronide and sulfate conjugates), extensive oxidation of the methyl and isopropyl groups also occurred. This resulted in the formation of derivatives of benzyl alcohol and 2-phenylpropanol and their corresponding carboxylic acids. In contrast, ring hydroxylation of the two phenols was a minor reaction.

The following metabolites were identified: 2.5-Dihydroxy-p-cymene, 2-(2-hydroxy-4-methylphenyl)propan-1-ol, 5-Hxdroxymethyl)-2-(1-methylethyl)phenol, 2-(4-Hydroxymethyl-2-hydroxyphenyl)propan-1-ol, 2-(2-Hydroxy-4-methylphenyl)propionic acid, 3-Hydroxy-4-(1-methylethyl)benzoic acid (please refer to attached figure).

Applicant's summary and conclusion

Conclusions:

The urinary excretion of metabolites were rapid. Only very small amounts were excreted after 24 h. Although large quantities of thymol was excreted unchanged (or as their glucuronide and sulfate conjugates), extensive oxidation of the methyl and isopropyl groups also occurred. This resulted in the formation of derivatives of benzyl alcohol and 2-phenylpropanol and their corresponding carboxylic acids. In contrast, ring hydroxylation of the two phenols was a minor reaction.

Executive summary:

Thymol was dissolved in propylene glycol (1-2 mL) and given 6 male albino rats per stomach tube at a dose level of 1 mmol/kg bw (ca. 150 mg/kg bw). Similar animals receiving solvent only served as controls. Urine samples were collected at -10°C at 24 hours intervals and analysed by chromatography after conjugate hydrolysis.

The urinary excretion of metabolites were rapid. Only very small amounts were excreted after 24 h. Although large quantities of thymol was excreted unchanged (or as their glucuronide and sulfate conjugates), extensive oxidation of the methyl and isopropyl groups also occurred. This resulted in the formation of derivatives of benzyl alcohol and 2-phenylpropanol and their corresponding carboxylic acids. In contrast, ring hydroxylation of the two phenols was a minor reaction. The following metabolites were identified: 2.5-Dihydroxy-p-cymene, 2-(2-hydroxy-4-methylphenyl)propan-1-ol, 5-Hxdroxymethyl)-2-(1-methylethyl)phenol, 2-(4-Hydroxymethyl-2-hydroxyphenyl)propan-1-ol, 2-(2-Hydroxy-4-methylphenyl)propionic acid, 3-Hydroxy-4-(1-methylethyl)benzoic acid.