You are right that mesalamine can stain toilet seats. I have used mesalamine enemas before and the stains were a hassle to deal with. However, I think it was more of a tan color. I don't remember peeing purple after using those either.
Sulfasalazine can definitely change the color of urine or stool since it's an AZO dye but mesalamine (Lialda and Pentasa) is not an AZO dye. Mesalamine is a light pinkish crystal so in and of itself it should not change the color of urine.
I called Shire and Warner Chilcott yesterday to get more information. Shire did mention that Pentasa could discolor stool but could not confirm that purple urine was a side effect with either Pentasa or Lialda. They took down my report of purple urine in their post marketing reporting process. Warner Chilcott is still getting back to me.
I looked at the package inserts to see the inactive ingredients and noticed that there were various food colorings added to Pentasa (D&C Yellow #1, FD&C Blue #1, FD&C Green #3) but these dyes are poorly absorbed by the intestines so they wouldn't be able to change the color of urine.
I know personally, that I have eaten foods that contain similar dyes and have not been able to observed a change in the color of my urine as a consequence, even after eating a whole bag of M&M's. So I can't attribute the purple stains on the toilet bowl from those dyes. I am trying very hard to tie the drug to these changes but I can't.
Then I also have to question the amount of purple staining that I noticed. At it's worst it was everywhere on the rim of the toilet bowl and it was a very deep indigo, who knows how much was in the pee I flushed down the toilet. When I was actually using the bathroom, I couldn't tell there were going to be purple stains because to me it just looked like concentrated urine at the time maybe slightly red, I actually thought it might have been peeing blood. There was no reason to suspect purple stains anywhere. I didn't see the purple until I came back later and it was everywhere on the rim of the toilet that was not drawn down by the flushed water. Unless something else is going on a drug can't make such huge and extremely noticeable color change in urine all of a sudden then stop after a week or two and leave no trace at all after that. I should be able to detect some purple staining now but I haven't seen any purple stains in weeks. Sometimes when I pee my urine is concentrated because I am a bit dehydrated but I don't even see a hint of purple.
Drugs can cause urine to change color, there is no doubt about that. The changes are predictable and well documented. There is nothing in the literature that indicates mesalamine causes purple pee. However, there is documentation in the literature that people with autoimmune disorders have been linked to porphyria which actually means purple pee in Greek.
