Hey there,
I don't usually post on this forum as I have Crohn's but look on here anyway sometimes and your post caught my eye as last year I had a severe phototoxic reaction to the sun (I am on methotrexate) even with high strength sunscreen and I was prescribed Plaquenil (hydroxychloroquine) to take during the spring/summer months to prevent another reaction, even though I now avoid the sun it is impossible to avoid it completely, I went to Greece about a month after the reaction and on Plaquenil (very, very afraid I might add!) and although stayed in the shade still had to face sunlight to walk to the shop etc and didn't react.
From what I can gather its very effective in preventing sun/skin reactions as when I saw a skin specialist a few months later he wanted light testing done but said I had to have the Plaquenil well clear out of my system as otherwise the testing wouldn't show anything which helped reassure me that it works well! So just thought that may be something you might find worth looking into, nearly a year on and I still have pigment colour damage from the phototoxic reaction and it was horrific at the time, sunsensivity really isn't something to take lightly! Hope that may help.