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Is the permeability coefficient Kp a reliable tool in percutaneous absorption studies?
Gintautas Korinth1, Karl Heinz Schaller, Hans Drexler
1Institute and Out-Patient Clinic of Occupational, Social and Environmental Medicine, University Erlangen-Nuremberg, Schillerstrasse 25/29, 91054, Erlangen, Germany. Gintautas.Korinth@rzmail.uni-erlangen.de
Archives of Toxicology
|January 1, 2005
Summary
The permeability coefficient (Kp) did not accurately reflect the concentration-dependent percutaneous absorption of 2-butoxyethanol (BE). Flux measurements showed less variability than Kp, but Kp failed to normalize for concentration differences in BE absorption studies.
Area of Science:
- Dermatology
- Toxicology
- Pharmacokinetics
Background:
- Percutaneous absorption studies utilize the permeability coefficient (Kp) to describe chemical penetration potency.
- Kp is theoretically derived from Fick's first law of diffusion (Kp=Flux/C) and should remain constant regardless of concentration.
- This study investigates the reliability of Kp and flux for 2-butoxyethanol (BE) at different concentrations.
Purpose of the Study:
- To evaluate the percutaneous absorption parameters, flux and Kp, for neat and 50% aqueous solutions of 2-butoxyethanol (BE).
- To determine if Kp accurately reflects concentration-dependent absorption as predicted by theory.
- To compare the variability and specificity of flux versus Kp in describing BE percutaneous absorption.
Main Methods:
- Excised human skin from two donors was used in static diffusion cells.
- Infinite doses of neat and 50% aqueous solutions of non-radiolabeled BE were applied.
- Flux and Kp values were measured for each test setting with n=21 replicates.
Main Results:
- The flux of 50% aqueous BE (0.704 mg/cm²/h) was approximately 15-fold higher than that of neat BE (0.045 mg/cm²/h).
- The Kp values for 50% aqueous BE (1.563 x 10⁻³ cm/h) were about 31-fold higher than for neat BE (0.050 x 10⁻³ cm/h).
- Kp values did not normalize for the concentration difference, failing to remain constant as theory suggests.
Conclusions:
- The permeability coefficient (Kp) did not adequately adjust the flux of 2-butoxyethanol (BE) to its concentration.
- Flux, while showing smaller differences between concentrations, remains a non-specific parameter for describing percutaneous absorption.
- Experimental findings contradict the theoretical expectation of Kp as a constant, concentration-independent parameter in this context.