text: Mecillinam (INN) or amdinocillin (USAN) is an extended-spectrum penicillin antibiotic of the amidinopenicillin class that binds specifically to penicillin binding protein 2 (PBP2), and is only considered to be active against Gram-negative bacteria. It is used primarily in the treatment of urinary tract infections, and has also been used to treat typhoid and paratyphoid fever. Because mecillinam has very low oral bioavailability, an orally active prodrug was developed: pivmecillinam.