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Systematic (IUPAC) name
Clinical data
AHFS/ Micromedex Detailed Consumer Information
  • AU: C
  • US: C (Risk not ruled out)
Legal status
Routes of
Oral, IV
Pharmacokinetic data
Protein binding 70%
Metabolism Hepatic acetylation and glucuronidation
Biological half-life 10 hours
Excretion Renal
CAS Registry Number 723-46-6 YesY
ATC code J01EC01 QJ01EQ11
PubChem CID: 5329
DrugBank DB01015 YesY
ChemSpider 5138 YesY
KEGG D00447 YesY
NIAID ChemDB 006897
Chemical data
Formula C10H11N3O3S
Molecular mass 253.279 g/mol
Physical data
Melting point 169 °C (336 °F)
 YesY (what is this?)  (verify)

Sulfamethoxazole (abbreviated SMZ or SMX)[1][2][3] 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 (abbreviated SMZ-TMP and SMX-TMP,[4] or TMP-SMZ and TMP-SMX), also known under trade names such as Bactrim, Septrin, or Septra; in Eastern Europe it is marketed as Biseptol. Its primary activity is against susceptible forms of Streptococcus, Staphylococcus aureus (including MRSA), Escherichia coli, Haemophilus influenzae, and oral anaerobes. It is commonly used to treat urinary tract infections. In addition it can be used as an alternative to amoxicillin-based antibiotics to treat sinusitis. It can also be used to treat toxoplasmosis and it is the drug of choice for Pneumocystis pneumonia, which affects primarily patients with HIV.

Other names include: sulfamethylisoxazol, sulfisomezole, MS 53, RO 4 2130[5][6] and sulfamethazole.[7]

Mechanism of action[edit]

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.[8] 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 is caused by mutations in the enzymes involved in folic acid synthesis that prevent the drug from binding to it.

Tetrahydrofolate synthesis pathway

A TMP-SMZ (also TMP-SMX or TMP-Sulfa) disk is a combination of trimethoprim and sulfamethoxazole(combination of both is known as cotrimoxazole) that acts synergistically for bactericidal action. A bacterial culture impregnated with a trimethoprim and sulfamethoxazole disk may be used to help identify an organism as Gardnerella vaginalis; it is sensitive to the TMP-SMZ disk.

Side effects[edit]

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. Sulfamethoxazole is also a Stevens–Johnson syndrome (SJS) inducing substance.[citation needed]

Sulfamethoxazole can also cause nausea or severe stomach or abdominal pain. Headaches commonly occur when taking sulfamethoxazole. Muscle pain sometimes occurs when taking this medication. If symptoms persist, one should contact his/her physician. If trouble breathing or swelling of the face, mouth, or tongue occurs, one should discontinue the medication and get emergency medical help. These are often symptoms of a severe allergic reaction (anaphylaxis).

Sulfamethoxazole/trimethoprim can lead to a megaloblastic anemia in some patients because it is a folate antagonist.[9]

See also[edit]


  1. ^ Ma, M.; Cheng, Y.; Xu, Z.; Xu, P.; Qu, H.; Fang, Y.; Xu, T.; Wen, L. (2007). "Evaluation of polyamidoamine (PAMAM) dendrimers as drug carriers of anti-bacterial drugs using sulfamethoxazole (SMZ) as a model drug". European journal of medicinal chemistry 42 (1): 93–8. doi:10.1016/j.ejmech.2006.07.015. PMID 17095123. 
  2. ^ Garg, S.K.; Ghosh, S.S.; Mathur, V.S. (1986). "Comparative pharmacokinetic study of four different sulfonamides in combination with trimethoprim in human volunteers". International journal of clinical pharmacology, therapy, and toxicology 24 (1): 23–5. PMID 3485584. 
  3. ^ SMZ in Abstract of "Rat model of concurrent Pneumocystis carinii (Pc), Toxoplasma gondii (Tg), and Mycobacterium avium complex (MAC) infections for assessment of multiple prophylaxis" at
  4. ^ SMZ-TMP in Abstract of "Cutaneous hypersensitivity to sulfamethoxazole-trimethoprim (SMZ TMP) in HIV infected patients" at
  5. ^ PubChem. "Sulfamethoxazole - Substance Summary", PubChem, National Center for Biotechnology Information (NCBI), National Library of Medicine (NLM), National Institutes of Health (NIH)
  6. ^ ChemDB. "Sulfamethoxazole", ChemDB, National Institute of Allergy and Infectious Diseases (NIAID), National Institutes of Health (NIH)
  7. ^ Sulfamethazole in "Clinical Diabetes: Case Study: A 90-Year-Old Man With Confusion and Night Sweats", and "Chronic Granulomatous Disease"
  8. ^ Martindale, The extra pharmacopoeia, 30th ed, p. 208
  9. ^ USMLE World Step1, Qbank Pharmacology, 2009, Q106

External links[edit]