How it is administered
Trimethoprim is most commonly given by mouth in combination with sulfamethoxazole as a tablet. It is available in two strengths: a regular tablet (containing 80 mg trimethoprim and 400 mg sulfamethoxazole) and a double-strength tablet (containing 160 mg trimethoprim and 800 mg sulfamethoxazole). There is also an intravenous (IV) formulation for hospital use, especially when oral administration is not possible.
How it works
Trimethoprim works by blocking the production of tetrahydrofolic acid from dihydrofolic acid in bacteria. It does this by binding to and reversibly inhibiting the enzyme dihydrofolate reductase. This step is essential for bacteria to make nucleic acids and proteins, which are needed for their growth and survival. When combined with sulfamethoxazole, which blocks an earlier step in the same pathway, the two drugs work together to stop bacteria from multiplying. This combination is more effective than either drug alone and helps prevent the development of bacterial resistance.
In patients with blood cancers such as Large Granular Lymphocytic Leukemia, trimethoprim (with sulfamethoxazole) is often used to prevent or treat infections, especially those caused by Pneumocystis jirovecii, a type of pneumonia that can affect people with weakened immune systems.
Common side effects
- Nausea
- Vomiting
- Loss of appetite (anorexia)
- Rash or hives (urticaria)
- Diarrhea
- Headache
- Allergic skin reactions
- Serious but less common side effects include severe skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis), blood disorders (anemia, low white blood cells, low platelets), liver problems, and kidney problems.
- Some patients may experience cough, shortness of breath, or other respiratory symptoms.
If you experience a rash, fever, sore throat, or signs of an allergic reaction, contact your healthcare provider immediately.
Who Should take it
Trimethoprim (with sulfamethoxazole) is indicated for treating and preventing infections proven or strongly suspected to be caused by susceptible bacteria. In the context of blood cancers or immunosuppression, it is especially important for preventing and treating Pneumocystis jirovecii pneumonia (PJP), a serious lung infection. It may also be used for urinary tract infections, certain types of ear infections, and other bacterial infections when appropriate.
For people with Large Granular Lymphocytic Leukemia or other blood cancers, your doctor may prescribe this medication to prevent infections if your immune system is weakened due to the disease or its treatment.
Who should not take it
You should not take trimethoprim (with sulfamethoxazole) if you:
- Are allergic to trimethoprim or sulfonamides
- Have a history of drug-induced immune thrombocytopenia with use of trimethoprim and/or sulfonamides
- Have documented megaloblastic anemia due to folate deficiency
- Are a pediatric patient less than 2 months of age
- Have marked hepatic damage or severe renal insufficiency when renal function status cannot be monitored
- Are taking dofetilide (a heart rhythm medication)
If you have impaired kidney or liver function, possible folate deficiency, or severe allergies or asthma, you should use this medication with caution and only under close medical supervision.
Commonly used with
Trimethoprim is almost always used in combination with sulfamethoxazole. This combination is known as co-trimoxazole and is much more effective than either drug alone for most infections.
It may also be used alongside other medications in people with blood cancers, such as antifungal or antiviral drugs, depending on your risk of infection and your doctor's recommendations.
Commonly tested with
Trimethoprim (with sulfamethoxazole) is often tested with other antibiotics to determine the best treatment for specific bacterial infections. In the context of blood cancers, it may be part of a broader infection prevention or treatment protocol that includes antifungals (like fluconazole) or antivirals (like acyclovir) if you are at risk for multiple types of infections.