The Score of Primary Irritation (SPI) was calculated
for each rabbit as the following. Scores for erythema and
edema at 24, 48 and 72 hours were summed and
divided by the number of the observations for the treated
sites.
13 The SPI for the control sites were calculated in
the same fashion. The differences between the summary
scores from the treated sites and the control sites were
calculated. The Primary Irritation Index (PII) was
calculated as the arithmetical mean of the SPI values of
the six animals. The irritation degree was categorized as
negligible, or slight, moderate or severe irritation based
on the PII (Table 3).