Re: An unsolved riddle.....

The most common adverse effects are gastrointestinal disturbances (nausea, vomiting, anorexia) and allergic skin reactions such as hives.

It is also capable in rare circumstances in people very sensitive to the drug to cause, FULMINANT HEPATIC NECROSIS; a fancy name for liver unidentified liver failure.

It is official recorded as rarely causing gastrointestinal problems.

Here is the link to the official drug information page:

http://www.fda.gov/cder/foi/label/2003/17377slr057_Bactrim_lbl.pdf