Trimethoprim and sulfamethoxazole, also known as bactrim or co-trimoxazole, is a combination of two antibiotics. It is approved by the FDA to treat acute bronchitis, pneumonia, ear infections, traveler's diarrhea and urinary tract infections. Co-trimoxazole is available for oral and intravenous administration, and acts by inhibiting the synthesis of the bacterial genetic material and proteins, thereby causing death. Although it is well tolerated in otherwise healthy individuals, trimethoprim and sulfamethoxazole can lead to adverse reactions in some cases.
Gastric Disturbances
Gastric disturbances such as nausea, vomiting, upset stomach and lack of appetite are the most common side effects associated with the use of co-trimoxazole. In fact, according to the John Hopkins Point of Care Information Technology Center, about 20 to 50 percent of the patients taking high doses of the drug develop gastric problems. Treatment should be continued if the problems are not debilitating, as most patients improve with time and the adverse reactions completely disappear once the treatment is withdrawn. However, it is important to talk to the doctor if gastric intolerance is severe or if the symptoms do not go away.
Skin Reactions
Most skin reactions due to trimethoprim and sulfamethoxazole are mild and include skin rashes itching. Skin reactions usually appear 7 to 14 days after starting therapy, and as with gastric disturbances, treatment should be continued unless the condition is debilitating.
In rare cases, the sulfamethoxazole componenet of co-trimoxazole has been associated with a potentially fatal reactions such as Stevens-Johnson syndrome, characterized by severe eruptions of the skin around the mouth, eyes or anus, and progressive degeneration of the outer layer of the skin. PubMed Health recommends contacting a physician immediately at the first sign of a skin reaction such as redness or rash.
Kidney Problems
High doses of trimethoprim and sulfamethoxazole can effect kidney function and lead to a condition known as reversible hyperkalemia, or the presence of high amounts of potassium in the blood. Hyperkalemia may or may not be associated with chronic renal insufficiency. A study published in the June 2010 edition of the "Archives of Internal Medicine" states that the use of trimethoprim and sulfamethoxazole leads to a seven-fold increase in the risk of hyperkalemia in older patients. Most cases of hyperkalemia get cured by themselves once the co-trimoxazole treatment is stopped.
Interstitial nephritis may also occur, though this is rare. This condition is characterized by inflammation of kidney tubules, thereby affecting the kidneys' function, including their ability to filter waste.
Bone Marrow Suppression
Suppression of the bone marrow can lead to decreased production of both white and red blood cells, leading to conditions such as anemia, leukocytopenia and thrombocytopenia. Lack of blood cells causes fatigue and makes the patient more susceptible to other infections. Treatment with growth factors may be required in some cases.
References
- John Hopkins POC-IT Center: Trimethoprim+Sulfamethoxazole
- PubMed Health: Co-trimoxazole (oral)
- "Archives of Internal Medicine"; Trimethoprim-Sulfamethoxazole-Induced Hyperkalemia in Patients Receiving Inhibitors of the Renin-Angiotensin System: A Population-Based Study; T. Antoniou, et al.; June 2010
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