**Trimethoprim: An Overview**  

**Definition:**  

Trimethoprim is a synthetic antibacterial agent belonging to the diaminopyrimidine class. It is widely used for its ability to inhibit bacterial folate synthesis, making it effective against a range of bacterial infections.  

**Function:**  

Trimethoprim works by blocking the enzyme dihydrofolate reductase, which is essential for the production of tetrahydrofolic acid, a key component in bacterial DNA and protein synthesis. This action effectively halts bacterial growth and replication.  

**Applications:**  

Trimethoprim is primarily used to treat urinary tract infections (UTIs), respiratory tract infections, and gastrointestinal infections. It is often combined with sulfamethoxazole (as co-trimoxazole) to enhance its antibacterial spectrum and efficacy. Additionally, it is used in veterinary medicine for similar purposes.