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Toxicological information

Basic toxicokinetics

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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 Type:
publication
Title:
Kinetics of 3-(4-methylbenzylidene)camphor in rats and humans after dermal application
Author:
Schauer UMD, Völkel W, Heusener A, Colnot T, Broschard TH, von Landenberg F, Dekant W
Year:
2006
Bibliographic source:
Toxicology and Applied Pharmacology 216 (2006) 339–346

Materials and methods

Objective of study:
excretion
metabolism
toxicokinetics
Test guideline
Qualifier:
no guideline available
Principles of method if other than guideline:
- Principle of test: The toxicokinetics of 4-MBC after dermal administration were investigated in human subjects.
- Short description of test conditions: Humans (3 male and 3 female subjects) were exposed to 4-MBC by topical application of a commercial sunscreen formulation containing 4% 4-MBC (w/w), covering 90% of the body surface and resulting in a mean dermal 4-MBC dose of 22 mg/kg bw.
- Parameters analysed / observed: Concentrations of 4-MBC and its metabolites were monitored over 96 h in plasma and urine.
GLP compliance:
not specified
Remarks:
Published study from a peer-reviewed journal.

Test material

Reference
Name:
Unnamed
Type:
Constituent
Specific details on test material used for the study:
Composition of formulation (w/w):
4.00% 4-methylbenzylidene camphor
2.00% glyceryl stearate, ceteareth-15
2.00% stearyl alcohol
1.00% microwax
1.00% butyrospermum parkii (shea butter)
6.00% C12-15 alkyl benzoate
6.00% caprylic/capric triglyceride
3.00% dibutyl adipate
0.50% dimethicone
1.00% glycerin
0.25% xanthan gum
73.25% aqua (water)
Radiolabelling:
no

Test animals

Species:
other: human
Details on species / strain selection:
All subjects in the study had to refrain from alcoholic beverages and medicinal drugs 2 days before and throughout the experiment. Subjects did not abuse alcohol and were non-smokers. Subjects were healthy as judged by detailed medical anamnesis and had normal liver and kidney function based on clinical blood chemistry.
Sex:
male/female
Details on test animals and environmental conditions:
The study was carried out according to the Declaration of Helsinki, after approval by the Regional Ethical Committee of the University of Würzburg, Germany, and after written informed consent by the subjects. Information on the test subjects is available in "Any other information on materials and methods incl. tables".

Administration / exposure

Route of administration:
dermal
Vehicle:
unchanged (no vehicle)
Details on exposure:
TEST SITE
- % coverage: 90% of body surface

REMOVAL OF TEST SUBSTANCE
- Washing: Subjects were permitted to take showers 12 h after application of the formulation.
Duration and frequency of treatment / exposure:
Single application
Doses / concentrationsopen allclose all
Dose / conc.:
20.76 mg/kg bw (total dose)
Remarks:
Subject A
Dose / conc.:
21.41 mg/kg bw (total dose)
Remarks:
Subject B
Dose / conc.:
20.41 mg/kg bw (total dose)
Remarks:
Subject C
Dose / conc.:
23.58 mg/kg bw (total dose)
Remarks:
Subject D
Dose / conc.:
21.88 mg/kg bw (total dose)
Remarks:
Subject E
Dose / conc.:
24.16 mg/kg bw (total dose)
Remarks:
Subject F
No. of animals per sex per dose:
3
Control animals:
no
Positive control:
None used
Details on study design:
- Dose selection rationale: The application was intended to simulate a maximum exposure to 4-MBC.
Details on dosing and sampling:
TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine, blood, plasma
- Time and frequency of sampling: Plasma taken at 0, 0.5, 1, 2, 4, 6, 8, 12, 24, 36, 48, 60, 72, 84 and 96 h after application and urine taken in 8 h intervals.

METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled: urine, plasma
- Time and frequency of sampling: Plasma taken at 0, 0.5, 1, 2, 4, 6, 8, 12, 24, 36, 48, 60, 72, 84 and 96 h after application and urine taken in 8 h intervals.
- From how many animals: 6
- Method type for identification: LC–MS/MS with electrospray ionisation.
- Limits of detection and quantification: Limit of detection for 4-MBC and its metabolites 3-(4-carboxybenzylidene)-6-hydroxycamphor and 3-(4-carboxybenzylidene)camphor in plasma and urine were between 1 and 20 pmol/mL.
- Other: 4-MBC metabolites 3-(4-carboxybenzylidene)-6-hydroxycamphor and 3-(4-carboxybenzylidene)camphor were isolated by preparative HPLC with UV detection.

TREATMENT FOR CLEAVAGE OF CONJUGATES: Human urine samples were pretreated with glucuronidase to cleave glucuronides before analysis.
Statistics:
Standard deviations (mean ± SD), elimination half-lives and areas under the curve were calculated using Microsoft Excel. Polynoms given for best fit were transferred into “Functions” (Numerical-Mathematics.com) and AUCs were calculated from the mean of each time point.

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on absorption:
Peak plasma levels (Cmax) of 4-MBC were reached 6 h after dermal application. After the 6 h sampling point, 4-MBC concentrations decreased following 1st order kinetics to reach the limit of quantitation at 48 h (males) or 36 h (females) after the application. A precise number for the elimination half-lives could not be determined for the female participants due to insufficient data points for calculations, but are estimated to be similar to half-lives of male human subjects.
Details on excretion:
In urine samples, taken in 8 h intervals, concentrations of 4-MBC were below the limit of detection in all analysed samples.
Toxicokinetic parametersopen allclose all
Key result
Toxicokinetic parameters:
Cmax: 200 pmol/mL
Remarks:
males
Key result
Toxicokinetic parameters:
Cmax: 100 pmol/mL
Remarks:
females
Key result
Toxicokinetic parameters:
half-life 1st: 9 hours
Remarks:
males
Key result
Toxicokinetic parameters:
half-life 1st: 9 hours
Remarks:
females (estimated)
Key result
Toxicokinetic parameters:
AUC: 3884 pmol/mL h
Remarks:
males
Key result
Toxicokinetic parameters:
AUC: 1909 pmol/mL h
Remarks:
females

Metabolite characterisation studies

Metabolites identified:
yes
Remarks:
3-(4-carboxybenzylidene)-6-hydroxycamphor; 3-(4-carboxybenzylidene)-6-hydroxycamphor glucuronide; 3-(4-carboxybenzylidene)camphor; 3-(4-carboxybenzylidene)-camphor glucuronide
Details on metabolites:
Peak concentrations of 3-(4-carboxybenzylidene)-6-hydroxycamphor and 3-(4-carboxybenzylidene)camphor in plasma were reached within 12 to 24 h after application. These concentrations were 50–80 pmol/mL for 3-(4-carboxybenzylidene)-6-hydroxycamphor and 100– 200 pmol/mL for 3-(4-carboxybenzylidene)camphor. Concentrations of 3-(4-carboxybenzylidene)-6-hydroxycamphor thereafter decreased with apparent half-lives of 31 h in males and 20 h in females. Apparent half-lives of elimination from plasma of 3-(4-carboxybenzylidene) camphor were calculated as 26 h in males and 23 h in females. AUC values in plasma were 2657 pmol/mL h for males and 1615 pmol/mL h for females for 3-(4-carboxybenzylidene)-6-hydroxycamphor and for 3-(4-darboxybenzylidene)camphor were 5782 pmol/mL h for males and 3029 pmol/mL h for females. Low, but quantifiable concentrations of both metabolites were still present in plasma 96 h after 4-MBC application. Estimated concentrations of a glucuronide of 3-(4-carboxybenzylidene)camphor in plasma were low (<5% of the concentration of 3-(4-carboxybenzylidene) camphor in 12 h blood samples).

Excretion in urine of both 3-(4-carboxybenzylidene)-6- hydroxycamphor and 3-(4-carboxybenzylidene)camphor (present as glucuronide) peaked within 16–24 h after dermal application. Without pretreatment with glucuronidase, the concentrations of 3-(4-carboxybenzylidene) camphor were very low in urine samples. With glucuronidase pretreatment, the concentrations of 3-(4-carboxybenzylidene)camphor were significantly increased, whereas only minor increases in the peak areas for 3-(4-carboxybenzylidene)-6-hydroxycamphor were seen. Both metabolites were still present in low concentrations in urine samples collected 96 h after 4-MBC application. Elimination half-lives for 3-(4-carboxybenzylidene)-6-hydroxycamphor were 26 h in males and 23 h in females and for 3-(4-carboxybenzylidene)camphor were 23 h in males and 18 h in females. AUC values in urine were 205203 nmol h for males and 123544 nmol h for females for 3-(4-carboxybenzylidene)-6-hydroxycamphor and for 3-(4-carboxybenzylidene)camphor were 49479 nmol h for males and 25268 nmol h for females. Less than 1% of the applied dose of 4-MBC was recovered in human urine as metabolites. For 3-(4-carboxybenzylidene)-6-hydroxycamphor, 0.4 ± 0.15% and 0.3 ± 0.01% of the applied 4-MBC dose was recovered in urine of males and females, respectively, and for 3-(4-carboxybenzylidene)camphor 0.10 ± 0.02% and 0.07 ± 0.02% of the applied 4-MBC dose was recovered in urine of males and females, respectively.

The molecular weight of the glucuronides of both 4-MBC metabolites are below 500 and thus below the threshold for biliary elimination in humans; therefore, elimination of 4-MBC metabolites with faeces in humans is considered unlikely.

Applicant's summary and conclusion

Conclusions:
Peak plasma levels (Cmax) of 4-MBC were reached 6 h after dermal application (200 pmol/ml in males and 100 pmol/ml in females). After the 6 h sampling point, 4-MBC concentrations decreased following 1st order kinetics with a half-life of 9 h to reach the limit of quantitation at 48 h (males) or 36 h (females) after the application. The AUC values were 3884 and 1909 pmol/mL h in males and females, respectively. In plasma, 3-(4-carboxybenzylidene)camphor is the major metabolic product, whereas, in urine, 3-(4-carboxybenzylidene)-6-hydroxycamphor and a glucuronide of 3-(4-carboxybenzylidene) camphor are major metabolites. Less than 1% of the applied dose of 4-MBC was recovered in urine as metabolites.
Executive summary:

The toxicokinetics of 4-methylbenzylidene camphor after dermal administration were investigated in humans. Humans (3 male and 3 female subjects) were exposed to 4-MBC by topical application of a commercial sunscreen formulation containing 4% 4-MBC (w/w), covering 90% of the body surface and resulting in a mean dermal 4-MBC dose of 22 mg/kg bw. Concentrations of 4-MBC and its metabolites were monitored over 96 h in plasma and urine. Peak plasma levels (Cmax) of 4-MBC were reached 6 h after dermal application (200 pmol/ml in males and 100 pmol/ml in females). After the 6 h sampling point, 4-MBC concentrations decreased following 1st order kinetics with a half-life of 9 h to reach the limit of quantitation at 48 h (males) or 36 h (females) after the application. The AUC values were 3884 and 1909 pmol/mL h in males and females, respectively. In plasma, 3-(4-carboxybenzylidene)camphor is the major metabolic product, whereas, in urine, 3-(4-carboxybenzylidene)-6-hydroxycamphor and a glucuronide of 3-(4-carboxybenzylidene) camphor are major metabolites. Less than 1% of the applied dose of 4-MBC was recovered in urine as metabolites. This study is considered to be reliable with restrictions (Klimisch 2) as there are minor limitations in the reporting.