Composition :

Each 1 gm contains:
Trimethoprim 125 mg
Sulfadiazine Sodium 625 mg

Properties:

Alone, sulfonamides are bacteriostatic agents and trimethoprim is bacteriostatic, but in combination, the potentiated sulfas are bactericidal. Potentiated sulfas sequentially inhibit enzymes in the folic acid pathway, thereby inhibiting bacterial thymidine synthesis. The sulphonamide blocks the conversion of para-aminobenzoic acid (PABA) to dihydrofolic acid (DFA), and trimethoprim blocks the conversion of DFA to tetrahydrofolic acid by inhibiting dihydrofolate reductase.
The in vitro optimal ratio for most susceptible bacteria is approximately 1:20 (trimethoprim : sulfa), but synergistic activity can reportedly occur with ratios of 1:1 – 1:40. The serum concentration of the trimethoprim component is considered to be more important than the sulfa concentration. For most susceptible bacteria, the MIC’s for TMP are generally above 0.5 micrograms/ml. The potentiated sulfas have a fairly broad spectrum of activity. Gram positive bacteria that are generally susceptible include most streptococci, many strains of staphylococcus and Nocardia. Many gram negative organisms of the family Enterobacteriaceae are susceptible to the potentiated sulfas, but not Pseudomonas aeruginosa. Some protozoa (Pneumocystis carinii, Coccidia and Toxoplasma) are also inhibited by the combination. Potentiated sulfas reportedly have little activity against most anaerobes, but opinions on this vary. Resistance will develop slower to the combination of drugs than to either one alone. In gram negative organisms, resistance is usually plasmid-mediated.