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Dermal absorption

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Administrative data

Endpoint:
dermal absorption in vivo
Type of information:
experimental study
Adequacy of study:
key study
Study period:
Not reported
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study well documented, meets generally accepted scientific principles, acceptable for assessment
Cross-referenceopen allclose all
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to other study

Data source

Reference
Reference Type:
publication
Title:
Release and absorption of zinc from zinc oxide and zinc sulfate in open wounds
Author:
Agren MS, Krusell M & Franzen L
Year:
1991
Bibliographic source:
Acta. Derm. Venereol. (Stockh). 71: 330-333

Materials and methods

Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
The pharmacokinetic behaviour of zinc oxide was studied following application of a single dose to full-thickness excised rat skin wounds.
GLP compliance:
no

Test material

Constituent 1
Chemical structure
Reference substance name:
Zinc oxide
EC Number:
215-222-5
EC Name:
Zinc oxide
Cas Number:
1314-13-2
Molecular formula:
ZnO
IUPAC Name:
oxozinc
Details on test material:
- Name of test material (as cited in study report): Zinc oxide
Radiolabelling:
no

Test animals

Species:
rat
Strain:
Sprague-Dawley
Sex:
male
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: ALAB, Sweden
- Weight at study initiation: 210-250 g
- Housing: Kept in individual Makrolon cages
- Diet: Standard pellets containing 170 µg zinc/g (R3, AstracEwos, Sweden); ad libitum
- Water: Tap water (< 0.1 µg zinc/mL); ad libitum

Administration / exposure

Type of coverage:
semiocclusive
Vehicle:
unchanged (no vehicle)
Duration of exposure:
Up to 48 h
Doses:
250 µg zinc/cm2 (14 mg zinc/g of dressing)
No. of animals per group:
Nine animals both in control and treatment groups
Control animals:
yes
Details on study design:
DRESSING: Test material and binding agent (polyvinyl pyrrolidon, PVP) impregnated on absorbent gauze for application on test sites. Dressings were only impregnated with the binding agent for application on control sites. The PVP content of the dressings was 5 mg/g.

TEST SITE:
- Preparation of test site: Two circular full thickness skin wounds (each 11 cm2) were made on either side of the spine in the thoracic-lumbar region for application of dressings.
- Area of exposure: 15 cm2
- Type of cover / wrap if used: Dressings were covered with a semiocclusive polyurethane membrane and moistened with saline (1.5 µL at 37°C)

SITE PROTECTION: Yes: An adhesive tape was wrapped twice around the trunk to secure and protect the dressings.

SAMPLE COLLECTION AND PREPARATION
- Terminal procedure: 3 rats were killed from each group after 4, 24 and 48 h of treatment by heart puncture and exsanguination under anesthesia .
- Serum: Serum was obtained after centrifugation at 1000 x g for 10 min.
- Wound fluid: Dressings were put into a 5 mL plastic syringe with the plunger removed, then the plunger was inserted and the wound fluid ( ~ 0.5 mL) was squeezed out of the moist dressings. Finally, wound fluid samples were clarified through 0.22 µm filters mounted on the tip of the syringe
primarily to remove unsolubilized zinc oxide particles and thus leaving only solubilized zinc oxide.
- Wounded tissue: Wounded tissue, i.e. inflamed connective tissue, was dissected free from underlying fascia and rinsed with ice cold deionized water to remove superficial zinc contaminants (studies of the wounded tissue through a dissecting microscope showed no zinc oxide aggregates after treatment).

ANALYSIS
- Zinc estimation: Zinc analyses of diet, tap water, dressings, serum, wound fluid and wounded tissue was performed with atomic absorption
spectrophotometry.
- Protein estimation: Protein concentration of wound fluid and serum was determined according to Ohnishi & Barr.

OTHER: To get a rough estimate of the total quantity of zinc delivered to the wounds from dressings, the dressings were analyzed for their zinc content before and after 48 h of treatment.
Details on in vitro test system (if applicable):
Not applicable

Results and discussion

Signs and symptoms of toxicity:
not examined
Dermal irritation:
not examined
Absorption in different matrices:
- Wound fluid: Zinc concentration remained nearly constant over time in both the groups, although it increased to about 55 µg/mL at 48 h in treatment group. The levels were always higher in treatment group when compared to control group. Zinc concentration for control group was 0.8 at 4 h, 0.7 at 24 h and 1.1 µg/mL at 48 h (ref Fig. 2 in the attached full study report for details).

- Wounded tissue: The zinc concentration was almost at the same level in treatment group at 24 and 48 h, whereas, slightly increased for control group. The levels were always higher in treatment group when compared to control group (see Table 1).

- Serum: Zinc concentration remained nearly constant over time in the both the group, although slight increase was observed in the treatment group from 24 to 48 h. This increase was attributed to the increased wound fluid zinc level (could be due to increased protein concentration of the wound fluid and complex formation between zinc and proteins). The levels were always higher in treatment group when compared to control group showing absorption of zinc through the wounds (see Table 2).
Total recovery:
Not determined
Percutaneous absorption
Remarks on result:
other: Not determined
Conversion factor human vs. animal skin:
Not applied

Any other information on results incl. tables

Protein concentration: The protein concentration of the wound fluid increased over the experimental period (refer Fig. 1 in the attached full study report for details) and was about 70% of that of serum at 48 h.

Zinc release from dressing: About 45 µg zinc (12 % of the initial dosage) was delivered to each wound from the zinc oxide dressing.

Table 1. Zinc concentration (µg/g wet weight) of wounded tissue after 24 and 48 h of treatment

 

Treatment

Time (h)

 

24

48

Control

 

 

Median

6.9

10.4

Range

5.3-7.0

9.6-12.2

ZnO

 

 

Median

38

42

Range

36-48

38-53

 

Table 2. Serum zinc levels (µg/mL) after 4, 24 and 48 h of treatment

 

Treatment

Time (h)

 

4

24

48

Control

 

 

 

Median

1.1

1.2

1.2

Range

1.0-1.2

0.8-1.3

1.1-1.4

ZnO

 

 

 

Median

1.5

1.3

1.5

Range

1.4-1.7

0

1.4-1.6

Applicant's summary and conclusion

Conclusions:
In conclusion, zinc oxide was absorbed through the wounds by delivering zinc ions over an extended period of time, resulting in constant wound tissue zinc levels.
Executive summary:

The pharmacokinetic behaviours of zinc oxide when applied as single dose to full-thickness excised rat skin wounds were studied.

 

Zinc oxide (250 µg/cm2) or control dressings were applied semiocclusively to full-thickness excised skin wounds (11cm2) of nine rats (per group). 3 rats were killed from each group after 4, 24 and 48 h of treatment. Serum, wound fluid and wound tissue concentrations of zinc were determined.

In the treatment group, the wound fluid zinc concentration increased slightly over the 48 h postoperative period due to increased solubilization of zinc oxide, attributed to increased protein concentration of the wound fluid. The changes in the serum zinc level followed essentially the same kinetic pattern as that of the wound fluid zinc levels. The zinc concentration of the wounded tissue remained almost constant. The zinc concentration in all the studied matrices was always higher in the treatment group compared to the control group.

In conclusion, zinc oxide was absorbed through the wounds by delivering zinc ions over an extended period of time, resulting in constant wound tissue zinc cation levels due to its slow dissociation rate.