HUMAN SKIN IRRITATION STUDIES OF A LECITHIN MICROEMULSION GEL AND OF LECITHIN LIPOSOMES

Soybean lecithin microemulsion gels offer promising features for the p ossible use as matrices in transdermal therapeutic systems. In order t o assess the skin irritancy potential of the gel, acute and cumulative irriation tests were performed in human subjects in vivo using as com parison an unilamellar soybean lecithin liposome preparation and the s olvent isopropyl palmitate (IPP), Acute irritation was tested in 151 v olunteers in a 48-hour patch test, whereas cumulative irritation was a ssessed in a 21-day human repeated insult patch test in 20 volunteers. In the acute irritation test, discrete irritation (erythema only) dev eloped with the gel in 2 subjects (1.3 %), with the liposomes in 3 sub jects (2.0 %), and with IPP in 2 subjects (1.3 %). For the assessment of cumulative irritation, the IT50 (irritation time of 50% of the test population) was calculated. IT50 was 13 days for the gel, 14 days for the liposomes and 17 days for IPP. This study shows a very low acute and a low cumulative irritancy potential for the soybean lecithin micr oemulsion gel making it a candidate matrix for transdermal therapeutic systems also under toxicological aspects.