Registration Dossier

Administrative data

Endpoint:
dermal absorption in vivo
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Performed at lab with experts in field, GLP guidelines and international guideline.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1997
Report Date:
1998

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
Guideline:
other: EPA FIFRA 40 CFR, part 160 guideline
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Details on test material:
Test material (R-898) is the N,N'-di-tolyl component of p-benzenediamine composing ~20% of test material (SMILES Cc1ccccc1Nc2ccc(Nc3c(C)cccc3)cc2). It was used as surrogate for test material in this dermal absorption assessment. It was radiolabeled, making possible accurate quantitation of absorption kinetics using beta counting assay of test material. It is solid, and was radiolabeled with 14C with 94% chemical and radiochemical purities. Specific activity was 11.7 Ci/mole. The location of the 14C label was the center ring

Name of test material (as cited in study report) is R-898. Molecular formula is C20H20N2, and MW = 288.
Radiolabelling:
yes

Test animals

Species:
rat
Strain:
Fischer 344
Sex:
female
Details on test animals and environmental conditions:
Rats (females) were obtained from Charles River Breeding Labs, Michigan weighing 150 - 167 grams. They were housed 2 per cage until dosing at which time they were singly housed. Prior to dosing, rats were maintained in quarantine for 7 days. Drinking water & Purina Rodent Chow was provided ad libitum. Following dosing, animals were housed individually in metabolism cages to collect feces & urine separately. Temperatures in the lab were maintained at 23 +/- 6 degrees C, and relative humidity at 50 +/- 20%. The photoperiod was 14 hr light, 10 hr dark.

Administration / exposure

Type of coverage:
open
Vehicle:
acetone
Duration of exposure:
Single doses for both iv & dermal application.
Doses:
Dermal doses consisted of 350 ug C14 R-898 (10 uCi radioactivity) added to 1660 ug of DAPD in solution of acetone - total volume = 50 uL. The dosage for intravenous administration was 35 ug C14 R-898 (1 uCi radioactivity) added to 1660 ug of DAPD in solution of acetone - total volume = 20 uL. These levels of exposure were estimated to lack activity based upon acute toxicity test results.
No. of animals per group:
6 rats were employed for each of the two exposure groups.
Control animals:
no
Details on study design:
Dosing solutions were monitored for radioactivity counting by liquid scintillation prior to dosing.

Dermal sites were prepared by shaving the backs of test rats 24 hrs prior to chemical applications. The test area was 12 cm2 that was marked with black pen. Following application of the 50 uL volume of test chemical, the site remained open. An Elizabethan collar was afixed to each rat to avoid grooming of the test site for 7or a 24 hr period following application.

The iv dosing was conducted by placing rats in plexiglass cylinders that allowed access to tails. The tail was warmed to produce venous dilatation. Following occlusion of tail with rubbeand near its base, the injection was made in the lateral tail vein with 26G needle. Delivered doses were quantitated by weight difference of the syringe before and after dosing. No restraints were used in this test group.

Dermal application sites were undisturbed for 24 hrs. At that time, unabsorbed test chemical was removed from the 12 cm2 site by swabbing with cotton on sticks (Q-tips) soaked in, alternating, 50% soap solution and distilled water. In addition, the skin area surrounding the application site (1 cm outside the site) was washed in similar manner. This cotton was extracted with acetone which was then counted for radioactivity.

For the iv dosed rats, collections of urine, feces, & cage washes were made at 24, 48, 72, 96, 120, 144, & 168 hrs after dosing.
For dermal application group, the same collections were made as above PLUS skin and collar washes (24 hr), and at 168 hrs, tape stripping & whole skin of dosed skin & non-dosed skin.

Analyses of radioactivity was performed by liquid scintillation counting after suitable digestion or other prepartion of samples.
Details on in vitro test system (if applicable):
Not applicable

Results and discussion

Signs and symptoms of toxicity:
no effects
Dermal irritation:
no effects
Absorption in different matrices:
Data provided below
Total recovery:
Data provided below.
Conversion factor human vs. animal skin:
No quantitative values were given by investigators. Report indicates that the "percutaneous absorption in the rat is high relative to human".

Any other information on results incl. tables

Average % (S.Dev.) Distribution of 14C

Following R-898 Dosing to Rats*

Site/Parameter Monitored

IV Dose Group Dermal Application 
Urinary 1.4 (0.5) 0.7 (0.2)
Feces 68.4 (18.5) 38.2 (11.2)
Cage Washes 0.7 (0.2) 3.4 (1.5)
Skin site sample 0.07 (0.04)  -
Collar wash  - 0.03 (0.04)
Dosed skin wash  - 36.2 (10.7)
Non-dosed skin wash  - 0.16 (0.05)
Tape stripping of skin  - 3.6 ( (3.9)
Dosed skin site sample  - 6.3 (5.2)
Non-dosed skin site sample  - 0.20 (0.11)
TOTAL ACCOUNTABILITY 70.4 (18.6) 88.6 (11.5)
TOTAL Excretion 70.4 (18.6) 42.4 (12.8)
Bioavailability 100% 60.20%
Flux - ug equivalent/hr  - 1.62 (0.48)

* n = 6

Applicant's summary and conclusion

Conclusions:
Comparison of excreted radioactivity following adminstration of radioactive R-898 to groups of rats following dermal application versus iv dosing indicated 60% of the dermally-applied test chemical was absorbed during the 7-day study. The bulk (>95%) of absorbed test chemical was excreted via the feces.
Executive summary:

Radio-labelled (14C) dimethyl component of DAPD (R-898) was dermally and intravenously administered to female rats. The latter served as benchmark for 100% absorption of test material. Collection of urinary & fecal exretion demonstrated 70% recovery of radioactivity following iv dosing whereas recovery of 88% of dermally-applied test compound was achieved. The latter included skin site rinses, tape stripping and skin digestion samples to recover unabsorbed topically-applied residues. Comparison of excreted radioactivity from groups of rats following dermal application versus iv dosing indicated 60% of the dermally-applied test chemical was absorbed during the 7 -day study. The bulk (>95%) of absorbed test chemical was excreted via the feces. Percutaneous uptake of chemicals by rats is known to be substantially higher than that for primates including humans.