Public domain "acetylsalicylic acid" (2-acetoxybenzoic acid) is better known as "aspirin" in the United States—a generic term. In Canada, however, "Aspirin", with an uppercase A, is still a trademark of the German company Bayer, while aspirin, with a lowercase "a", is not. Bayer lost the trademark in the United States, the UK and France after World War I, as part of the Treaty of Versailles. So many copycat products entered the marketplace during the war that it was deemed generic just three years later. Bayer also lost the trademark in the same jurisdictions for "Heroin" which it trademarked a year before it
4-Aminosalicylic acid because aminosalicylic acid inhibits the synthesis of thyroid hormones. Drug interactions include elevated phenytoin levels. When taken with rifampicin, the levels of rifampicin in the blood fall by about half. The U.S. FDA assigned PAS to pregnancy category C, indicating that it is not known whether it will harm an unborn baby. With heat, aminosalicylic acid is decarboxylated to produce CO and 3-aminophenol. PAS has been shown to be a pro-drug and it is incorporated into the folate pathway by dihydropteroate synthase (DHPS) and dihydrofolate synthase (DHFS) to generate a hydroxyl dihydrofolate antimetabolite, which in turn inhibits dihydrofolate reductase (DHFR)