Medically reviewed on September 3, 2018
Commonly used brand name(s)
In the U.S.
Available Dosage Forms:
Therapeutic Class: Antibiotic
Pharmacologic Class: Folic Acid Antagonist
Uses For trimethoprim
Trimethoprim is used to treat infections of the urinary tract. It may also be used for other problems as determined by your doctor. It will not work for colds, flu, or other virus infections.
Trimethoprim is available only with your doctor's prescription.
Before Using trimethoprim
In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For trimethoprim, the following should be considered:
Tell your doctor if you have ever had any unusual or allergic reaction to trimethoprim or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.
Trimethoprim has been used in a limited number of children 2 months of age or older, and tested in children 12 years of age or older. In effective doses, the medicine has not been shown to cause different side effects or problems in children than it does in adults.
Elderly people may be more sensitive to the effects of trimethoprim. Blood problems may be more likely to occur in elderly patients who are taking diuretics (water pills) along with trimethoprim.
|All Trimesters||C||Animal studies have shown an adverse effect and there are no adequate studies in pregnant women OR no animal studies have been conducted and there are no adequate studies in pregnant women.|
Studies in women suggest that this medication poses minimal risk to the infant when used during breastfeeding.
Interactions with Medicines
Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking trimethoprim, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using trimethoprim with any of the following medicines is not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.
Using trimethoprim with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Arsenic Trioxide
- Azilsartan Medoxomil
- Candesartan Cilexetil
- Chloral Hydrate
- Cholera Vaccine, Live
- Olmesartan Medoxomil
Using trimethoprim with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
Interactions with Food/Tobacco/Alcohol
Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using trimethoprim with any of the following is usually not recommended, but may be unavoidable in some cases. If used together, your doctor may change the dose or how often you use trimethoprim, or give you special instructions about the use of food, alcohol, or tobacco.
Other Medical Problems
The presence of other medical problems may affect the use of trimethoprim. Make sure you tell your doctor if you have any other medical problems, especially:
- Anemia—Patients with anemia may have an increased chance of side effects affecting the blood
- Kidney disease—Patients with kidney disease may have an increased chance of side effects
- Liver disease—Patients with liver disease may have an increased chance of side effects
Proper Use of trimethoprim
Do not give trimethoprim to infants or children under 12 years of age unless otherwise directed by your doctor.
Trimethoprim may be taken on an empty stomach or, if it upsets your stomach, it may be taken with food.
To help clear up your infection completely, keep taking trimethoprim for the full time of treatment even if you begin to feel better after a few days. If you stop taking trimethoprim too soon, your symptoms may return.
Trimethoprim works best when there is a constant amount in the body. To help keep the amount constant, do not miss any doses. Also, it is best to take the doses at evenly spaced times day and night. For example, if you are to take 2 doses a day, the doses should be spaced about 12 hours apart. If this interferes with your sleep or other daily activities, or if you need help in planning the best times to take your medicine, check with your health care professional.
The dose of trimethoprim will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of trimethoprim. If your dose is different, do not change it unless your doctor tells you to do so.
The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.
- For the treatment of urinary tract infections :
- Adults and children 12 years of age and older: 100 milligrams every twelve hours for ten days, or 200 milligrams once a day for ten days.
- Children up to 12 years of age: Dose must be determined by the doctor.
If you miss a dose of trimethoprim, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.
Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.
Keep out of the reach of children.
Do not keep outdated medicine or medicine no longer needed.
Precautions While Using trimethoprim
It is important that your doctor check your progress at regular visits if you will be taking trimethoprim for a long time. This will allow your doctor to check for any unwanted effects that may be caused by trimethoprim.
If your symptoms do not improve within a few days, or if they become worse, check with your doctor.
If trimethoprim causes anemia, your doctor may want you to take folic acid (a vitamin) every day to help clear up the anemia. If so, it is important to take folic acid every day along with trimethoprim; do not miss any doses.
Trimethoprim may cause blood problems. These problems may result in a greater chance of certain infections, slow healing, and bleeding of the gums. Therefore, you should be careful when using regular toothbrushes, dental floss, and toothpicks. Dental work should be delayed until your blood counts have returned to normal. Check with your medical doctor or dentist if you have any questions about proper oral hygiene (mouth care) during treatment.
Some people who take trimethoprim may become more sensitive to sunlight than they are normally. Exposure to sunlight, even for brief periods of time, may cause severe sunburn or skin rash, redness, itching, or discoloration. When you begin taking trimethoprim:
- Stay out of direct sunlight, especially between the hours of 10:00 a.m. and 3:00 p.m., if possible.
- Apply a sun block product that has a skin protection factor (SPF) of at least 15. Some patients may require a product with a higher SPF number, especially if they have a fair complexion. If you have any questions about this, check with your health care professional.
- Do not use a sunlamp or tanning bed or booth.
If you have a severe reaction from the sun, check with your doctor.
Trimethoprim Side Effects
Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.
Check with your doctor immediately if any of the following side effects occur:
- Skin rash or itching
- Black, tarry stools
- blood in urine or stools
- bluish fingernails, lips, or skin
- changes in facial skin color
- difficult breathing or shortness of breath
- fever with or without chills
- general feeling of discomfort or illness
- joint or muscle pain
- neck stiffness
- pale skin
- pinpoint red spots on skin
- redness, blistering, burning, tenderness, peeling, or loosening of skin or mucous membranes
- redness, swelling, or soreness of tongue
- red skin lesions, often with a purple center
- sore throat
- thickened or scaly skin
- unusual bleeding or bruising
- unusual tiredness or weakness
Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:
- loss of appetite
- nausea or vomiting
- stomach cramps or pain
Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.
Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.
See also: Side effects (in more detail)
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
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More about trimethoprim
- Trimethoprim Side Effects
- During Pregnancy or Breastfeeding
- Dosage Information
- Drug Images
- Drug Interactions
- Support Group
- Pricing & Coupons
- En Español
- 20 Reviews
- Drug class: urinary anti-infectives