Generic name: trimethoprim [ trye-METH-oh-prim ]
Brand names: Primsol, Trimpex, Proloprim
Dosage form: oral tablet (100 mg)
Drug class: Urinary anti-infectives

Medically reviewed by Drugs.com on Aug 4, 2023. Written by Cerner Multum.

What is trimethoprim?

Trimethoprim is an antibiotic that is used to treat bladder or kidney infections, or ear infections caused by certain bacteria.

Trimethoprim may also be used for purposes not listed in this medication guide.

Trimethoprim side effects

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Trimethoprim may cause serious side effects. Call your doctor at once if you have:

• severe stomach pain, diarrhea that is watery or bloody (even if it occurs months after your last dose);

• pale, gray, or bluish skin;

• fever, weakness;

• sore or swollen tongue;

• easy bruising, purple or red spots under your skin;

• a skin rash, no matter how mild; or

• high potassium level--nausea, weakness, tingly feeling, chest pain, irregular heartbeats, loss of movement.

Common side effects of trimethoprim may include:

• vomiting, diarrhea, stomach pain;

• rash, itching; or

• swelling in your tongue.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Related/similar drugs

amoxicillin, doxycycline, azithromycin, cephalexin, ciprofloxacin, clindamycin, ceftriaxone

Warnings

You should not use trimethoprim if you have anemia caused by a folate (folic acid) deficiency.

Before taking this medicine

You should not use trimethoprim if you are allergic to it, or if you have:

• anemia (low red blood cells) caused by a folate (folic acid) deficiency.

Trimethoprim is not approved for use by anyone younger than 2 months old. Trimethoprim should not be used to treat an ear infection in a child younger than 6 months old.

Tell your doctor if you have ever had:

• a folate deficiency;

• liver or kidney disease; or

• a blood disorder.

Tell your doctor if you are pregnant. Trimethoprim can interfere with your body's ability to metabolize folic acid, a form of vitamin B important in the development of the unborn baby's brain and spinal cord.

It may not be safe to breastfeed while using this medicine. Ask your doctor about any risk.

How should I take trimethoprim?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.

Measure liquid medicine carefully. Use the dosing syringe provided, or use a medicine dose-measuring device (not a kitchen spoon).

Use trimethoprim for the full prescribed length of time, even if your symptoms quickly improve. Skipping doses can increase your risk of infection that is resistant to medication. This medicine will not treat a viral infection such as the flu or a common cold.

This medicine can affect the results of certain medical tests. Tell any doctor who treats you that you are taking trimethoprim.

Store at room temperature away from moisture, heat, and light.

Trimethoprim dosing information

Usual Adult Dose for Urinary Tract Infection:

100 mg orally every 12 hours or 200 mg orally every 24 hours
Duration of therapy: 10 days

Use: For the treatment of initial episodes of uncomplicated urinary tract infections due to susceptible strains of Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae, Enterobacter species, and coagulase-negative Staphylococcus species (including Staphylococcus saprophyticus)

Usual Pediatric Dose for Urinary Tract Infection:

12 years or older: 100 mg orally every 12 hours or 200 mg orally every 24 hours
Duration of therapy: 10 days

Use: For the treatment of initial episodes of uncomplicated urinary tract infections due to susceptible strains of E coli, P mirabilis, K pneumoniae, Enterobacter species, and coagulase-negative Staphylococcus species (including S saprophyticus)

Usual Pediatric Dose for Otitis Media:

6 months or older: 5 mg/kg orally every 12 hours for 10 days
Maximum dose: 200 mg/dose

Comments:
-This drug is not indicated for prophylactic or prolonged use in otitis media at any age.
-When infection with Moraxella catarrhalis suspected, use of alternative antimicrobial agents should be considered.

Use: For the treatment of acute otitis media due to susceptible strains of Streptococcus pneumoniae and Haemophilus influenzae

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose symptoms may include nausea, vomiting, headache, dizziness, confusion, depression, fever, chills, or flu-like symptoms.

Overdose can occur slowly over a long period of time if your daily doses are too high.

What should I avoid while taking trimethoprim?

Antibiotic medicines can cause diarrhea, which may be a sign of a new infection. If you have diarrhea that is watery or bloody, call your doctor before using anti-diarrhea medicine.

What other drugs will affect trimethoprim?

Other drugs may affect trimethoprim, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all your current medicines and any medicine you start or stop using.

Popular FAQ

More FAQ

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Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Medical Disclaimer

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