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Trimethoprim, Oral try-METH-oh-prim

What are other names for this medicine?

Type of medicine: anti-infective

Generic and brand names: trimethoprim, oral; Primsol

What is this medicine used for?

This medicine is used to treat:

  • bacterial infections of the urinary tract
  • ear infections

It may be used to treat other infections as determined by your healthcare provider. It will not cure viral infections such as colds or the flu.

What should my healthcare provider know before I take this medicine?

Before taking this medicine, tell your healthcare provider if you have ever had:

  • an allergic reaction to any medicine
  • anemia or any blood disorder
  • liver or kidney disease

Females of childbearing age: Tell your healthcare provider if you are pregnant or plan to become pregnant. It is not known whether this medicine will harm an unborn baby. Do not breast-feed while taking this medicine without your healthcare provider's approval.

How do I take it?

You may take this medicine with or without food. Taking it with meals may lessen the chance the drug will upset your stomach.

Check the label on the medicine for directions about your specific dose. Take this medicine exactly as your healthcare provider prescribes. Do not take more or less or take it longer than prescribed. Do not stop taking this medicine without your healthcare provider's approval. If you stop taking it too soon the infection may return.

This medicine works best when taken in regularly spaced doses every day.

If you have the liquid form of this medicine, use the measuring device given to you by the pharmacist (not a common kitchen spoon) to make sure you get the right dose. The average household teaspoon may not hold the right amount of liquid.

What if I miss a dose?

If you miss a dose, take it as soon as you remember unless it is almost time for the next scheduled dose. In that case, skip the missed dose and take the next one as directed. Do not take double doses. If you are not sure of what to do if you miss a dose, or if you miss more than one dose, contact your healthcare provider.

What if I overdose?

If you or anyone else has intentionally taken too much of this medicine, call 911 or go to the emergency room right away. If you pass out, have seizures, weakness or confusion, or have trouble breathing, call 911. If you think that you or anyone else may have taken too much of this medicine, call the poison control center. Do this even if there are no signs of discomfort or poisoning. The poison control center number is 800-222-1222.

Symptoms of an acute overdose may include: nausea, vomiting, dizziness, headache, confusion.

What should I watch out for?

Do not use this medicine for other infections or give it to children unless your healthcare provider approves.

Contact your healthcare provider if your condition does not improve in a few days or if it gets worse.

If this medicine causes anemia, your healthcare provider may prescribe folic acid (a vitamin). Talk with your provider about this.

This medicine may make your skin more sensitive to the sun, which may lead to painful sunburns. While you are taking this medicine, avoid long exposure to the sun. Wear protective clothing, a hat, and sunscreen lotion when you need to be outdoors. Do not use a sunlamp. If you get a severe sunburn, contact your healthcare provider right away.

If you need emergency care, surgery, or dental work, tell the healthcare provider or dentist you are taking this medicine.

What are the possible side effects?

Along with its needed effects, your medicine may cause some unwanted side effects. Some side effects may be very serious. Some side effects may go away as your body adjusts to the medicine. Tell your healthcare provider if you have any side effects that continue or get worse.

Life-threatening (Report these to your healthcare provider right away. If you cannot reach your healthcare provider right away, get emergency medical care or call 911 for help): Allergic reaction (hives; itching; rash; trouble breathing; tightness in your chest; swelling of your lips, tongue, and throat).

Serious (report these to your healthcare provider right away): Sore throat; fever; pale skin; trouble breathing; bleeding gums; unusual tiredness or weakness; unusual bruising or bleeding; severe skin redness, peeling, or blistering.

Other: Headache, skin rash, nausea, vomiting, diarrhea, loss of appetite.

What products might interact with this medicine?

When you take this medicine with other medicines, it can change the way this or any of the other medicines work. Nonprescription medicines, vitamins, natural remedies, and certain foods may also interact. Using these products together might cause harmful side effects. Talk to your healthcare provider if you are taking:

  • ACE inhibitors such as benazepril (Lotensin), captopril, enalapril (Vasotec), fosinopril, lisinopril (Prinivil, Zestril), quinapril (Accupril), and ramipril (Altace)
  • antiseizure medicines such as carbamazepine (Tegretol, Carbatrol) and phenytoin (Dilantin)
  • dapsone
  • diabetes medicines such as pioglitazone (Actos), repaglinide (Prandin), rosiglitazone (Avandia), and tolbutamide
  • heart medicines such as digoxin (Lanoxin, Lanoxicaps), procainamide, and dofetilide (Tikosyn)
  • methotrexate (Rheumatrex)
  • rifampin (Rifadin)
  • warfarin (Coumadin)

If you are not sure if your medicines might interact, ask your pharmacist or healthcare provider. Keep a list of all your medicines with you. List all the prescription medicines, nonprescription medicines, supplements, natural remedies, and vitamins that you take. Be sure that you tell all healthcare providers who treat you about all the products you are taking.

How should I store this medicine?

Store this medicine at room temperature. Keep the container tightly closed. Protect it from heat, high humidity, and bright light.


This advisory includes selected information only and may not include all side effects of this medicine or interactions with other medicines. Ask your healthcare provider or pharmacist for more information or if you have any questions.

Ask your pharmacist for the best way to dispose of outdated medicine or medicine you have not used. Do not throw medicine in the trash.

Keep all medicines out of the reach of children.

Do not share medicines with other people.


Developed by RelayHealth.
Medication Advisor 2012.1 published by RelayHealth.
Last modified: 2010-07-16
Last reviewed: 2010-06-18
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
© 2012 RelayHealth and/or its affiliates. All rights reserved.
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