P09Comparison between mild irritant response in haired and hairless guinea pigs

The hairless guinea pig offers the possibility of performing irritant studies without the use of depilatory agents or clipping. Studies have shown a response to allergens and simple irritants comparable to that of the haired guinea pig. Histoanatomical studies have demonstrated differences in cutaneous structure in the two strains, differences that might influence the response to mild irritants such as topical drug vehicles. The purpose of this study was to compare the usability of hairless (HLGP) and shaved haired guinea pigs (SGP) in tolerability studies of complex topical formulations. The tolerability of 6 selected skin care formulations (SCF), known to cause a differentiated irritative response in HLGP, was studied in 15 male SGP and 15 male HLGP. All animals were treated on a 5 × 5 cm area on each flank twice daily for 4 consecutive days with SCF. The irritant effects of the SCF were quantified clinically and by measurement of transepidermal water loss (TEWL) and colorimetry (a*‐parameter). Both species were able to differentiate between SCF in relation to skin tolerance and although the response pattern was somewhat different in the two species the ranking of the SCF was essentially the same using TEWL and clinical scoring. However, colorimetry was found to be unsuited for the evaluation of cutaneous irritation in the SGP over a period of days as regrowth of fur obfuscated the underlying erythema. In conclusion the HLGP appears to be a more suitable model for tolerability testing of composite formulations.