Sulfonamides inhibit competitively a bacterial enzyme which is responsible for entering Paraminobenzoic acid to dihydrofolate reductase structure. Trimethoprime by connecting bacterial dihydrofolate reductase enzyme inhibits it reversely. Son mox is a choice medicine in the treatment and prevention of pneumonia caused by Pneumocystis carinii and toxoplasmosis, Nocardiosis, urinary tract infections and acute exacerbation of chronic bronchitis is used. Also Sonmox is useful in treatment of infections of the middle ear caused by microorganisms in children.