Trimethoprim (TMP) is an antibiotic is used for the treatment of initial episodes of uncomplicated urinary tract infections due to susceptible strains of the following organisms: Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae, Enterobacter species, and coagulase-negative Staphylococcus species, including S. saprophyticus. Cultures and susceptibility tests should be performed to determine the susceptibility of the bacteria to trimethoprim. Therapy may be initiated prior to obtaining the results of these tests. Trimethoprim is rapidly absorbed following oral administration. It exists in the blood as unbound, protein-bound, and metabolized forms. Ten to twenty percent of trimethoprim is metabolized, primarily in the liver; the remainder is excreted unchanged in the urine. The principal metabolites of trimethoprim are the 1- and 3-oxides and the 3'- and 4'-hydroxy derivatives. The free form is considered to be the therapeutically active form. Approximately 44% of trimethoprim is bound to plasma proteins. Trimethoprim blocks the production of tetrahydrofolic acid from dihydrofolic acid by binding to and reversibly inhibiting the required enzyme, dihydrofolate reductase. This binding is very much stronger for the bacterial enzyme than for the corresponding mammalian enzyme

Sulfamethoxazole is a synthetic antibacterial drug,which is used in combination with trimethoprim (Bactrim, Septra) for the treatment or prevention of infections that are proven or strongly suspected to be caused by bacteria. Sulfamethoxazole acts by inhibiting folic acid synthesis via enzyme called dihydropteroate synthase.

Sulfacetamide is a synthetic sulfonamide antibiotic, which exerts its effect through inhibition of bacterial dihydrofolate synthetase, an enzyme responsible for the conversion of p-aminobenzoic acid into folic acid in bacterias. The topical formulation of the drug is prescribed for the treatment of acne vulgaris and the ophtalmic formulation is used in patients with eye infections.

Sulfadiazine is a sulfonamide antibiotic. The sulfonamides are synthetic bacteriostatic antibiotics with a wide spectrum against most gram-positive and many gram-negative organisms. However, many strains of an individual species may be resistant. Sulfonamides inhibit multiplication of bacteria by acting as competitive inhibitors of p-aminobenzoic acid in the folic acid metabolism cycle. Bacterial sensitivity is the same for the various sulfonamides, and resistance to one sulfonamide indicates resistance to all. Most sulfonamides are readily absorbed orally. However, parenteral administration is difficult, since the soluble sulfonamide salts are highly alkaline and irritating to the tissues. The sulfonamides are widely distributed throughout all tissues. High levels are achieved in pleural, peritoneal, synovial, and ocular fluids. Although these drugs are no longer used to treat meningitis, CSF levels are high in meningeal infections. Their antibacterial action is inhibited by pus. Sulfadiazine is a competitive inhibitor of the bacterial enzyme dihydropteroate synthetase. This enzyme is needed for the proper processing of para-aminobenzoic acid (PABA) which is essential for folic acid synthesis. The inhibited reaction is necessary in these organisms for the synthesis of folic acid. Used for the treatment of rheumatic fever and meningococcal meningitis.

Sulfatroxazole is a sulfamide derivative patented by Swiss multinational healthcare company F. Hoffmann-La Roche & Co., A.-G. as an antibacterial agent and bacteriostatic antibiotic. Sulfatroxazole competitively inhibits dihydropteroate synthase preventing the formation of dihydropteroic acid, a precursor of folic acid which is required for bacterial growth. Sulfatroxazole is a component present in various veterinary drugs.

Sulfazamet is a sulfanilamide derivative that exhibits antibacterial activity against Streptococci sepsis

Sulfadoxine is an antimalarial agent which, together with pyrimethamine, composes an FDA-approved drug, Fansidar. Sulfadoxine acts by inhibiting dihydropteroate synthase; it crosses the blood-brain barrier and achieves 30% to 60% of the plasma concentration.

Sulfaphenazole is an oral antibiotic, which was used for the treatment of bacterial infections under the name Sulfabid. The drug was found to block folate synthesis in bacterias by inhibiting the enzyme dihydropteroate synthase. Sulfaphenazole is also known to inhibit CYP2C9 with high potency and specificity. Sulfabid is no longer marketed in the USA.

Sulfachlorpyridazine is a broad spectrum antibacterial compound which is effective in the treatment of infections caused by gram-positive and gram-negative organisms that are commonly susceptible to sulfonamide therapy and which has been proven by laboratory and field experiments to be highly effective against diseases caused by Escherichia coli. Sulfachlorpyridazine has a rapid onset of action in several species of animals following both oral and parenteral administration. Sulfachlorpyridazine (brand name Vetisulid) is especially indicated for the treatment of diarrhea caused or complicated by E. coli (colibacillosis) in calves under 1 month of age: Vetisulid powder is also indicated for the treatment of colibacillosis in swine. Sulfachlorpyridazine is a dihydropteroate synthase inhibitor.

Sulfadimethoxine is a sulfonamide antibacterial used to treat many infections including treatment of respiratory, urinary tract, enteric, and soft tissue infections. It is most frequently used in veterinary medicine, although it is approved in some countries for use in humans. Sulfadimethoxine inhibits bacterial synthesis of folic acid (pteroylglutamic acid) from para-aminobenzoic acid. Sulfadimethoxine is approved in Russia for use in humans, including children, and has been successfully used there for more than 35 years and is available as an over-the-counter drug manufactured by a number of Russian pharmaceutical companies. In USA and Europe sulfadimethoxine is approved in a veterinary medicinal products. ANADA was approved by FDA in US in 1997 as an Over the Counter medicine for treatment of bovine respiratory disease complex (shipping fever complex) and bacterial pneumonia associated with Pasteurella Spp. Sensitive to sulfadimethoxine; necrotic pododermatitis (foot rot) and calf diphtheria caused by Fusobacterium necrophorum (Sphaerophorus necrophorus) sensitive to sulfadimethoxine. Bioequivalence for this generic animal drug, Sulfadimethoxine Injection 40%, was established by demonstration of chemical equivalence to the pioneer product, Hoffmann-La Roche's Albon® Injection 40% (NADA 041-245).