Topical chloroquine applied before irradiation protects against ultraviolet B (UVB)- and UVA-induced erythema but not against immediate pigment darkening.

Seventeen healthy volunteers were phototested with ultraviolet B (UVB) and UVA before and after topical treatment with chloroquine phosphate. The skin areas treated before but not after irradiation showed higher minimal erythema dose values for UVB and UVA than control skin. The effect was clearly spectral with greater protection afforded against UVB than UVA. The immediate pigment darkening after irradiation with UVA, however, was not affected by pretreatment with the drug. The mechanism of action for this protective effect did not seem to be related to merely absorption and screening, inhibition of the inflammatory reaction or a UV-induced effect on the stereo-isomerization of the drug.