Acetohydroxamic acid (also known as AHA or by the trade name Lithostat) is a drug that is a potent and irreversible enzyme inhibitor of the urease enzyme in various bacteria and plants; it is usually used for urinary tract infections and urinary stone disease. The molecule is similar to urea but is not hydrolyzable by urease; it thus disrupts the bacteria's metabolism through competitive inhibition. It is particularly effective for the prevention and treatment of infection stones (struvite stones).
In 1983 the US Food and Drug Administration approved acetohydroxamic acid (AHA) as an orphan drug for "prevention of so-called struvite stones" under the newly enacted Orphan Drug Act of 1983. AHA cannot be patented because it is a standard chemical compound.