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Sulfamethoxazole is a sulfonamide antibiotic. It is sold under the brand names Gantanol and Urobak. It is typically prescribed in combination with Trimethoprim, in which case it is referred to as co-trimoxazole[1] and sold under the brand names Bactrim, Bactrim DS, Cotrim, Cotrim DS, Septra, Septra DS, Sulfatrim, Sulfatrim-DS.[2]

Why It's Prescribed

Sulfamethoxazole and trimethoprim are given together to treat infections caused by bacteria including infections of the urinary tract, lungs (pneumonia), ears, and intestines.[3] Additionally, it is used to treat 'travelers' diarrhea.'

Labeled uses of Sulfamethoxazole combined with Trimethoprim include:[4] Acute Otitis Media Infection, Bacterial Urinary Tract Infection, Chronic Bronchitis with Bacterial Exacerbation, E. Coli Urinary Tract Infection, Enterobacter Cloacae Urinary Tract Infection, Gastroenteritis due to Shigella, Haemophilus Influenzae Acute Otitis Media, Haemophilus Influenzae Chronic Bronchitis, Klebsiella Urinary Tract Infection, Morganella Morganii Urinary Tract Infection, Pneumocystis Carinii Pneumonia, Pneumocystis Carinii Pneumonia Prevention, Proteus Urinary Tract Infection, Streptococcus Acute Otitis Media, Streptococcus Pneumoniae Chronic Bronchitis

Additionally, unlabeled uses include:[5] Acquired Immunodeficiency Syndrome with Toxoplasmosis, Bacterial Endocarditis, Bacterial Pneumonia, Bone Infections, Brucellosis, Chancroid, Chlamydial Infections, Cholera, Chronic Bacterial Prostatitis, Diabetic Foot Infection, Diverticulitis of Gastrointestinal Tract, Granuloma Inguinale, Listeria Meningitis, Lymphogranuloma Venereum, Meningococcus Carrier, Nocardiosis, Paracoccidioidomycosis, Paratyphoid Fever, Pertussis, Postexposure Plague Prophylaxis, Sinusitis, Skin and Skin Structure Infection, Toxoplasmosis Prevention, Typhoid Fever, Whipple's Disease

Form, Route, and Dosage

Sulfamethoxazole and trimethoprim come together either as tablets or a suspension (liquid). The branded sulfamethoxazole-trimethoprim tablet Bactrim contains 400mg sulfamethoxazole and 80mg trimethoprim.[6] Bactrim DS contains double the strength of each drug - 800mg sulfamethoxazole and 160mg trimethoprim. Patients are usually instructed to take it 2 times daily, but sometimes may be taken up to 4 times a day for severe lung infections.[7]


Side Effects

Some patients taking the combination of sulfamethoxazole and trimethoprim may experience side effects. These include:[8]

  • upset stomach
  • vomiting
  • loss of appetite
  • skin rash
  • itching
  • sore throat
  • fever or chills
  • mouth sores
  • unusual bruising or bleeding
  • yellowing of the skin or eyes
  • paleness
  • joint aches

As a Pollutant

Because humans and animals often do not fully metabolize pharmaceuticals in their body, they can excrete drugs or their breakdown products, which may the enter the environment.[9]

In Sewage Sludge

Sulfamethoxazole has been found in sewage sludge. In the Targeted National Sewage Sludge Survey, a 2009 test of 84 samples of sewage sludge from around the U.S., the EPA found sulfamethoxazole in 30 samples (36%) in concentrations ranging from 3.91 to 651 parts per billion.[10] There are no federal regulations governing how much of this drug may be present in sewage sludge applied to land as fertilizer.

Breakdown in the Environment

One study examined the biodegradability of the antibiotics cefotiam, ciprofloxacin, meropenem, penicillin G, and sulfamethoxazole as well as their toxicity to bacteria.[11] The study aimed to see how much of these drugs were breaking down in wastewater treatment plants as well as what effect they might have on creating antibiotic-resistance in bacteria. Of the drugs, only penicillin G biodegraded, and it did so only partially (35% in 40 days). The study concluded "Therefore, antibiotic drugs emitted into municipal sewage may affect the biological process in sewage treatment plants (STPs), and they may persist in the aquatic environment and contribute to the increasing resistance of pathogenic bacteria."

A 2004 study looked at the ability of 18 antibiotics to biodegrade in a closed bottle test.[12] The antibiotics tested were: Amoxicillin, Benzylpenicillin sodium salt, Ceftriaxone disodium, Cefuroxime sodium salt, Chlortetracycline hydrochloride, Clarithromycin, Clindamycin, Erythromycin, Gentamicin sulfate, Imipenem, Metronidazole, Monensin sodium salt, Nystatin, Ofloxacin, Sulfamethoxazole, Tetracycline, Trimethoprim naphthoate, and Vancomycin hydrochloride. The study concluded: "None of the antibiotics was readily biodegradable. Elimination in the environment by other mechanisms may happen, but will not completely mineralize the active compounds. The results of CFU determination showed that some of antibiotics have an inhibitory effect on the bacterial population. Our findings underline the need for more detailed investigating effects on antibiotics in the environment."

In Drinking Water

An Associated Press investigation found that, of 62 metropolitan areas in the U.S., only 28 tested for pharmaceuticals, and 24 found pharmaceuticals in the drinking water when they tested it.[13] The following cities tested positive for sulfamethoxazole:[14] Concord, CA, Philadelphia, Portland, OR, Tucson, AZ, and Washington, DC.

Articles and resources

Related SourceWatch articles


  1. Co-trimoxazole Oral: MedlinePlus Drug Information, Accessed September 2, 2010.
  2. List of Antibiotics, Accessed August 28, 2010
  3. Co-trimoxazole Oral: MedlinePlus Drug Information, Accessed September 2, 2010.
  4. Sulfamethoxazole-Trimethoprim Oral: Dosage, Uses, and Warnings, Accessed September 2, 2010.
  5. Sulfamethoxazole-Trimethoprim Oral: Dosage, Uses, and Warnings, Accessed September 2, 2010.
  6., Accessed September 2, 2010.
  7. Co-trimoxazole Oral: MedlinePlus Drug Information, Accessed September 2, 2010.
  8. Co-trimoxazole Oral: MedlinePlus Drug Information, Accessed September 2, 2010.
  9. O.A.H. Jones, N. Voulvoulis, and J.N. Lester, Human Pharmaceuticals in Wastewater Treatment Processes, Environmental Science and Technology, 2005.
  10. Targeted National Sewage Sludge Survey Report, US EPA website, Accessed August 28, 2010.
  11. Al-Ahmad A, Daschner FD, and Klaus Kümmerer, "Biodegradability of cefotiam, ciprofloxacin, meropenem, penicillin G, and sulfamethoxazole and inhibition of waste water bacteria", Environmental Contamination and Toxicology, August 1999.
  12. Radka Alexy, Tina Kümpel and Klaus Kümmerer, "Assessment of degradation of 18 antibiotics in the Closed Bottle Test", Chemosphere, November 2004.
  13. AN AP INVESTIGATION : Pharmaceuticals Found in Drinking Water, Associated Press, Accessed September 3, 2010.
  14. Pharmawater-Metros-By-Results, Associated Press, Accessed September 3, 2010.

External resources

External articles