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AHFS Consumer Medication Information [Internet]. Bethesda (MD): American Society of Health-System Pharmacists; 2000-2011.

AHFS Consumer Medication Information.

Trimethoprim(trye meth' oh prim)

Last reviewed: September 1, 2010.

Why is this medication prescribed?

Trimethoprim eliminates bacteria that cause urinary tract infections. It is used in combination with other drugs to treat certain types of pneumonia. It also is used to treat 'travelers' diarrhea.' Antibiotics will not work for colds, flu, or other viral infections.

This medication is sometimes prescribed for other uses; ask your doctor or pharmacist for more information.

How should this medicine be used?

Trimethoprim comes as a tablet to take by mouth. It usually is taken one or two times a day. Trimethoprim may be taken with or without food. Follow the directions on your prescription label carefully, and ask your pharmacist or doctor to explain any part you do not understand. Take trimethoprim exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

What special precautions should I follow?

Before taking trimethoprim,

  • tell your doctor and pharmacist if you are allergic to trimethoprim, sulfa drugs, diuretics ('water pills', oral diabetes medications, or any other drugs.

  • tell your doctor and pharmacist what prescription and nonprescription medications you are taking, especially phenytoin (Dilantin) and vitamins.

  • tell your doctor if you have or have ever had anemia or liver or kidney disease.

  • tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. If you become pregnant while taking trimethoprim, call your doctor immediately.

What special dietary instructions should I follow?

Take trimethoprim on an empty stomach, 1 hour before or 2 hours after meals. However, if you experience nausea, you may take trimethoprim with food.

Drink at least eight glasses of liquid (water, tea, coffee, soft drinks, milk, and fruit juice) every day.

What should I do if I forget a dose?

Take the missed dose as soon as you remember it. However, if it is almost time for your next dose, skip the missed dose and continue your dosing schedule. Do not take a double dose to make up for a missed one.

What side effects can this medication cause?

Trimethoprim may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

  • upset stomach

  • vomiting

  • diarrhea

If you experience any of the following symptoms, call your doctor immediately:

  • rash (hives)

  • itching

  • difficulty breathing or swallowing

  • sore throat

  • fever or chills

  • mouth sores

  • unusual bruising or bleeding

  • yellowing of the skin or eyes

  • paleness

  • joint aches

  • bluish-colored fingernails, lips, or skin

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online [at http://www.fda.gov/Safety/MedWatch] or by phone [1-800-332-1088].

What storage conditions are needed for this medicine?

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom). Throw away any medication that is outdated or no longer needed. Talk to your pharmacist about the proper disposal of your medication.

In case of emergency/overdose

In case of overdose, call your local poison control center at 1-800-222-1222. If the victim has collapsed or is not breathing, call local emergency services at 911.

What other information should I know?

Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests to check your response to trimethoprim.

Do not let anyone else take your medication. Your prescription is probably not refillable. If you still have symptoms of infection after you finish the trimethoprim, call your doctor.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.

This report on medications is for your information only, and is not considered individual patient advice. Because of the changing nature of drug information, please consult your physician or pharmacist about specific clinical use.

The American Society of Health-System Pharmacists, Inc. represents that the information provided hereunder was formulated with a reasonable standard of care, and in conformity with professional standards in the field. The American Society of Health-System Pharmacists, Inc. makes no representations or warranties, express or implied, including, but not limited to, any implied warranty of merchantability and/or fitness for a particular purpose, with respect to such information and specifically disclaims all such warranties. Users are advised that decisions regarding drug therapy are complex medical decisions requiring the independent, informed decision of an appropriate health care professional, and the information is provided for informational purposes only. The entire monograph for a drug should be reviewed for a thorough understanding of the drug's actions, uses and side effects. The American Society of Health-System Pharmacists, Inc. does not endorse or recommend the use of any drug. The information is not a substitute for medical care.

AHFS® Consumer Medication Information. © Copyright, 2011. The American Society of Health-System Pharmacists, Inc., 7272 Wisconsin Avenue, Bethesda, Maryland. All Rights Reserved. Duplication for commercial use must be authorized by ASHP.

The following brand names are from RxNorm, a standardized nomenclature for clinical drugs produced by the National Library of Medicine:

Brand names

  • Proloprim

  • Trimpex

Brand names of combination products

  • Bacter-Aid (containing Sulfamethoxazole and Trimethoprim)

  • Bactrim (containing Sulfamethoxazole and Trimethoprim)

  • Cofatrim Fort (containing Sulfamethoxazole and Trimethoprim)

  • Cotrim (containing Sulfamethoxazole and Trimethoprim)

  • Cotrim DS (containing Sulfamethoxazole and Trimethoprim)

  • Septra 400/80 (containing Sulfamethoxazole and Trimethoprim)

  • Septra 800/160 (containing Sulfamethoxazole and Trimethoprim)

  • Sulfatrim (containing Sulfamethoxazole and Trimethoprim)

  • Uroplus (containing Sulfamethoxazole and Trimethoprim)

What works?

  • Antibiotic treatment for the prevention of Pneumocystis pneumonia (PCP) in non‐HIV immunocompromised patients Antibiotic treatment for the prevention of Pneumocystis pneumonia (PCP) in non‐HIV immunocompromised patients
    Pneumocystis jiroveci is a fungus causing pneumonia mainly among patients with an impaired immune system, such as those infected with the human immunodeficiency virus (HIV), cancer patients, following organ transplantation, patients receiving immune suppressive medications, etc. Previous evidence showed that preventive antibiotic treatment (before the onset of the disease) could lower mortality and morbidity from PCP among patients with HIV. We assessed whether this is also true for immunocompromised non‐HIV patients. This review of randomised controlled trials (RCTs) found that prophylaxis with trimethoprim/sulfamethoxazole, an antibiotic effective against PCP, significantly reduced the occurrence of PCP by > 90%. The patients included in the 11 trials we identified were adults with acute leukemia or solid organ transplantation and children with acute leukemia. We found no evidence for reduction in all cause mortality.
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Conditions of interest

  • Pneumonia
    Pneumonia is a breathing (respiratory) condition in which there is an infection of the lung.
  • Flu
    The flu is an easily spread infection of the nose, throat, and lungs.
  • Urinary tract infection - adults
    A urinary tract infection, or UTI, is an infection that can happen anywhere along the urinary tract. Urinary tract infections have different names, depending on what part of the urinary tract is infected.
  • Urinary tract infection - children
    A urinary tract infection (UTI) is an infection of the urinary tract. This article discusses UTIs in children.
  • Cystitis - acute
    Acute cystitis is a bacterial infection of the bladder or lower urinary tract. Acute means sudden or severe.
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