Orally administered indomethacin at 10-600 mu g per mouse per day has
been shown to inhibit UV radiation-induced erythema dose responsively,
At the higher doses tested (200-600 mu g) there was evidence of drug
toxicity. Indomethacin administered orally at 20 mu g per mouse daily
during photocarcinogenesis induction both increased the probability of
remaining tumour free and reduced the average tumour multiplicity. Wh
en indomethacin was administered only during the UV irradiation period
(initiation), a reduction in tumour multiplicity and in the progressi
on of tumours to malignant squamous cell carcinomas was observed; when
administered only during the post-irradiation promotion period, there
was a significant increase in the probability of remaining tumour fre
e. Thus both tumour initiation and promotion by UV radiation appear to
be indomethacin-sensitive, possibly affected by different mechanisms.