Sulfamethoxazole and trimethoprim are two different antibiotics sometimes referred to as co-trimoxazole. These antibiotics kill bacteria using different mechanisms and are often prescribed together because they are much more powerful when used in combination. The most common reasons for prescribing these antibiotics are ear infections, traveler's diarrhea, bronchitis, urinary infections and certain kinds of pneumonia.
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Mild Side Effects
Because sulfamethoxazome and trimethoprim are antibiotics, they are prone to causing certain side effects. Some of these adverse effects include painful swelling of the tongue, insomnia and pain in the joints. Some patients also experience problems with the ears, which include a ringing sensation in their ears or abnormalities that cause dizziness or a sensation of spinning. These side effects are not considered to be serious or life-threatening, so you should continue taking sulfamethoxazome and trimethoprim unless they become unbearable.
Allergic Side Effects
Because both of these antibiotics come from outside of the body, there is the potential that one or both of sulfamethoxazole and trimethoprim can cause an allergic reaction (especially true for sulfamethoxazole, because it is known as a "sulfa" drug, which is a class of drugs to which many people are allergic). Symptoms of an allergic reaction include the development of a rash or hives, as well as pruritus (itching of the skin). Other patients may experience swelling of their feet, hands, tongue, lips or face. In severe cases, patients may experience difficulty swallowing or breathing, as well as tightness in the chest and hoarseness. If you experience any symptoms of an allergic reaction, stop taking sulfamethoxazole/trimethoprim immediately and contact your doctor.
Serious Side Effects
Although rare, in some cases sulfamethoxazole and trimethoprim can cause serious side effects that are fatal, often by triggering a specific reaction called Stevens-Johnson syndrome or by causing serious damage to the skin and liver. Symptoms of these adverse effects can include a rash, especially if the rash blisters and is combined with a headache and sore throat. Other serious side effects include severe pallor of the skin as well as easy bruising and bleeding (indicative of liver damage), and bloody or watery diarrhea. Some patients also develop hallucinations, paranoia or severe agitation. Contact your doctor immediately if you have any of these side effects.