(Bactrim, Septra, co-trimoxazole)
Common Side Effects
Most patients taking sulfamethoxazole-trimethoprim experience no side effects at all. Occasionally, mild nausea may come if taking the medicine on an empty stomach. Rarely, a patient may become allergic to sulfamethoxazole-trimethoprim, experiencing a itchy rash on the body or hives; in this case, the drug should be discontinued and other “sulfa-drugs” should be avoided in the future as well.
Rare but Potentially Serious Side Effects
Unfortunately, there are rare and serious adverse effects that can occur with sulfamethoxazole-trimethoprim.
Drug Hypersensitivity Syndrome
Sulfamethoxazole-trimethoprim can cause a type of allergic reaction called drug hypersensitivity syndrome, also known as drug rash with eosinophilia and systemic symptoms (DRESS syndrome). This is a severe reaction that can result in damage to internal organs, such as the liver. Patients typically have a rash, fever, facial swelling, and they tend to feel very ill and therefore seek medical attention. Treatment is prompt withdrawal of the offending medicine as well as high dose steroids and close monitoring of the liver and other organs in hospital. Although the damage is potentially irreversible, most patients make a complete recovery with proper treatment if the offending drug is promptly discontinued. Rarely, potentially fatal liver failure or death can occur.
A rare type of allergic reaction to sulfamethoxazole-trimethoprim can be inflammation of the membranes surrounding the brain called aseptic meningitis: headache, neck pain, neck stiffness, and a decreased sharpness of the mind. The patient will feel unwell and will seek medical attention, typically requiring hospitalization. Most patient experience a full recovery with prompt drug discontinuation, but rarely permanent injury of the brain or nervous system can result.
Stevens–Johnson Syndrome & Toxic Epidermal Necrolysis
Another severe allergic reaction to sulfamethoxazole-trimethoprim is a rash in which the top layer of the skin (the epidermis) blisters and detaches from the underlying layer of the skin (the dermis). This requires prompt discontinuation of the drug and in many cases requires hospitalization for treatment. If less than 10% of the skin on the body is detached, the condition is called Stevens-Johnson syndrome. If greater than 30% of the skin on the body is detached, the condition is called Toxic Epidermal Necrolysis. However, the conditions are the same but with different severity. Death can occur.
Unlike the tetracycline family of antibiotics, sulfamethoxazole-trimethoprim is generally ineffective at killing anaerobic bacteria, and thus will probably not increase the risk of developing inflammatory bowel diseases such as ulcerative colitis and Crohn’s disease. This is in contrast to doxycycline and minocycline.
Sulfamethoxazole-trimethoprim is not safe for pregnant, conceiving, or breastfeeding women. Sulfamethoxazole-trimethoprim is appropriate for use in adolescents with acne; it comes in a liquid formulation for those who cannot swallow pills.
Patients taking spironolactone or certain blood pressure drugs of the ACE inhibitor or angiotensin receptor blocker classes should have their potassium level monitored carefully if taking sulfamethoxazole-trimethoprim. The combination can significantly raise potassium levels, leading to increased risk of sudden cardiac death.
Patients taking the drug methotrexate should not take sulfamethoxazole-trimethoprim, as the combination can be fatal.
Patients taking sulfamethoxazole-trimethoprim for an extended duration may consider supplementation with folic acid.
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