Sulfamethoxazole and trimethoprim are two antibiotic medications which are often prescribed in combination. These two drugs are sometimes sold under the brand name Bactrim. Bactrim is useful for treating a variety of infections caused by bacteria. Although the combination of sulfamethoxazole and trimethoprim is generally safe for patients to use, there are some side effects that these two drugs can cause. Any patient experiencing bothersome or alarming side effects should call his doctor immediately or seek emergency medical help.
Gastrointestinal
Sulfamethoxazole and trimethoprim can cause a number of fairly mild side effects that affect the gastrointestinal system, Drugs.com explains. These include nausea, vomiting and a loss of appetite. Some patients may also develop diarrhea as a result of using these two antibiotics. In some cases the diarrhea may have blood in it, EMedTV notes, and the diarrhea may continue well after the two medications are no longer being used.
Nervous System
Bactrim can also affect the nervous system, RxList notes. Patients taking Bactrim may develop vertigo or become dizzy. They may also experience a headache or tinnitus, which is a ringing in the ear. Bactrim can also have some psychological side effects, including depression, nervousness, apathy and hallucinations.
Kidney
Trimethoprim and sulfamethoxzole can damage the kidneys. This can cause blood in the urine and flank pain. In more serious cases the kidneys can completely fail, which causes toxins to build up in the blood. Kidney failure is a dangerous medical problem which requires emergency medical attention.
Hyperkalemia
Sulfamethoxazole and trimethoprim can also cause potassium levels in the blood to become increased, which is also known as hyperkalemia. Hyperkalemia, according to EMedTV, can result in a slowed heart rate, weakness of the muscles and sensations of tingling, burning or pricking.
Hypersensitivity
Hypersensitivity describes several different side effects which occur as a result of the immune system reacting adversely with Bactrim. Hypersensitivity to this medication can result in an allergic reaction, which can cause an itchy rash, hives and swelling of the lips, face, tongue and fingers. Allergies can also result in a condition known as anaphylaxis, which is marked by swelling of the throat. This can make breathing and swallowing difficult and can also cause a condition known as anaphylactic shock, which is notable for leading to extremely low blood pressure and a slowed heart rate. Anaphylaxis is a medical emergency. Another serious hypersensitivity reaction that can be caused by taking sulfamethoxazole and trimethoprim is known as Stevens-Johnson syndrome. It begins as a red or purple rash that may extend over large parts of the body. Shortly after the rash appears, the top layer of the affected skin is shed. This causes the exposure of large tracts of immature skin to the environment, which can be extremely painful and lead to dangerous infections.
Hematologic
Bactrim can also affect the bone marrow, which is responsible for making red blood cells. Patients taking this medication can develop anemia, which causes pallor and chronic fatigue. Blood cells that are important for the immune system may also become depleted, causing the patient to be more susceptible to infection. Finally, platelet counts may go down, which can lead to easy bruising or bleeding.
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