Effect of fatty acid diesters on permeation of anti-inflammatory drugs through rat skin

Four fatty acid diesters (diethyl succinate, diethyl adipate, diethyl sebacate, and diisopropyl adipate) were used to study their, enhancement effect on the permeation of four non-steroidal anti-inflammatory drugs (NSAIDs: ketoprofen, indomethacin, diclofenac sodium, and ibuprofen) through rat abdominal skin. With the diester pretreatment, drug permeation increased and the lag times decreased. No relationship was observed between the solubilities of the drugs in the diesters and the diester enhancement effects. The enhancement effect decreased with an increase of the drug lipophilicity, but increased with an increase of the lipophilic index of the diester up to about 3.5, after which the enhancement effect decreased or remained constant. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) was employed to investigate the biophysical changes in the stratum corneum lipids caused by the diesters. The FTIR results showed that treatment of the skin with diesters did not produce a blue shift in the asymmetric and symmetric C-H stretching peak positions. However, all of the above diesters showed a decrease in peak heights and areas for both asymmetric and symmetric C-H stretching absorbances in comparison with water treatment. These results suggested that the diesters were more effective for enhancing the penetration of hydrophilic drugs than lipophilic drugs, and the enhancing effect of lipophilic diesters was more effective than that of hydrophilic diesters. The enhancement effects of diesters may be due to their causing lipid extraction in the skin.