Sulfamethoxazole
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Sulfamethoxazole
Systematic (IUPAC) name
4-amino-N-(5-methylisoxazol-3-yl)-benzenesulfonamide
Identifiers
CAS number	723-46-6
ATC code	J01EC01
PubChem	5329
DrugBank	APRD00076
Chemical data
Formula	C10H11N3O3S
Mol. mass	253.279 g/mol
SMILES	eMolecules & PubChem
Physical data
Melt. point	3 °C (37 °F)
Pharmacokinetic data
Bioavailability	?
Protein binding	70%
Metabolism	Hepatic acetylation and glucuronidation
Half life	10 hours
Excretion	Renal
Therapeutic considerations
Pregnancy cat.	C (Au, U.S.)
Legal status	Prescription Only (S4)(AU) ℞-only
Routes	Oral

Sulfamethoxazole is a sulfonamide bacteriostatic antibiotic. It is most often used as part of a synergistic combination with trimethoprim in a 5:1 ratio in co-trimoxazole, which is also known as Bactrim, Septrin, or Septra (also abbreviated SMX/TMP). Its primary activity is against susceptible forms of Streptococcus, Staphylococcus aureus, Escherichia coli, Haemophilus influenzae, and oral anaerobes. It is commonly used to treat urinary tract infections. In addition can be used as an alternative to amoxicillin-based antibiotics to treat sinusitis.

Mechanism of action

Sulfonamides are structural analogs and competitive antagonists of para-aminobenzoic acid (PABA). They inhibit normal bacterial utilization of PABA for the synthesis of folic acid, an important metabolite in DNA synthesis.^[1] The effects seen are usually bacteriostatic in nature. Folic acid is not synthesized in humans, but is instead a dietary requirement. This allows for the selective toxicity to bacterial cells (or any cell dependent on synthesizing folic acid) over human cells. Bacterial resistance to sulfamethoxazole are caused by mutations in the folic acid enzyme that do the drugs from binding and blocking folic acid synthesis.

Tetrahydrofolate synthesis pathway

Side effects

The most common side effect of sulfamethoxazole/trimethoprim is gastrointestinal upset. Allergies to sulfa-based medications typically cause skin rashes, hives, or trouble breathing or swallowing and warrant immediate discontinuation of the medication and contact with doctor immediately. Sulfamethoxazole/trimethoprim is also known to increase blood concentrations of the drug warfarin (U.S. brand name: Coumadin) and can cause an unexpected increase in clotting time and uncontrolled bleeding. Neutropenia and thrombocytopenia also are rare adverse effects to be monitored if a patient is placed on long-term therapy.

Gardnerella

A TM-SXT (or simply SXT) disk impregnated with trimethoprim and sulfamethoxazole may be used to help identify an organism as Gardnerella vaginalis; it is sensitive to the TM-SXT disk.

References

1. ^ Martindale, The extra pharmacopoeia, 30th ed, p. 208

External links

See also

• trimethoprim