Trimethoprim Brand names of trimethoprim Prior to taking trimethoprim let your health care provider know Usage How to use trimethoprim How trimethoprim works Side effects Possible interactions Storage instructions


Brand names of trimethoprim

  • Alti-Trimethoprim
  • Apo-Sulfatrim [CD]
  • Apo-Sulfatrim DS [CD]
  • Bactrim [CD]
  • Bactrim DS [CD]
  • Bethaprim [CD]
  • Comoxol {CD]
  • Coptin [CD]
  • Cotrim [CD]
  • Novo-Trimel [CD]
  • Novo-Trimel DS [CD]
  • Nu-Cotrimox
  • Polytrim
  • Proloprim
  • Protrin [CD]
  • Protrin DF [CD]
  • Roubac [CD]
  • Septra [CD]
  • Septra DS [CD]
  • SMZ-TMP [CD]
  • Sulfatrim D/S
  • Trimpex
  • Uroplus DS [CD]
  • Uroplus SS [CD]

Trimethoprim is a synthetically prepared antibiotic which acts against a wide range of bacteria causing several diseases. Bacterial as well as human cells need a chemical called tetrahydrofolic acid in order to produce proteins. Trimethoprim inhibits the enzymes responsible for converting dihydrofolic acid into tetrahydrofolic acid in bacterial as well as human cells, thereby interfering with the production of this chemical.

However, the inhibitive effect of trimethoprim is greater on bacterial enzymes than corresponding human enzymes. Therefore, it significantly prevents the production of tetrahydrofolic acid only in bacterial cells, not in human one.

Trimethoprim first received the FDA's approval to be used along with sulfamethoxazole (like Bactrim, Septra, etc.) in 1973. It received the FDA's approval as a stand-alone drug in 1980.

Prior to taking trimethoprim let your health care provider know

  • About your drug allergies, including allergies to trimethoprim, diuretics or "water pills", sulfa drugs, and oral diabetes medications.
  • About all the prescription or non-prescription medicines you are taking, including phenytoin (Dilantin) and vitamin or mineral supplements.
  • About the diseases you suffer from, or have ever suffered from in the past, including anemia, liver and kidney diseases.
  • About your pregnancy state, whether you are already pregnant, or plan to be pregnant shortly, or are breast feeding babies. If pregnancy occurs while you are on trimethoprim, immediately inform your doctor.


Trimethoprim is a broad spectrum antibiotic and finds use in the treatment of many conditions like urinary and respiratory tract infections, middle ear infections, traveler's diarrhea, and, in combination with sulfamethoxazole or dapsone, in pneumocystis infections.

Trimethoprim works by killing bacteria and stopping their growth. Like all antibiotics, it can treat only bacterial, and not viral infections. Therefore, it won't work in viral diseases like common cold, flu, etc. Unnecessarily using any antibiotic, or overusing it, may decrease its effectiveness and that is true of trimethoprim also.

How to use trimethoprim

Trimethoprim should be taken orally on an empty stomach, that is, at least one hour before or two hours after meal, as directed by the doctor. If it causes upset stomach, it can be taken with food. Dosage would be based on the severity of your condition and your body's response to the medicine.

Antibiotics are most effective when their amount in the body is kept constant. Therefore, take trimethoprim regularly at about the same time every day. Continue taking it till the full prescribed duration, even if symptoms subside early. Stopping an antibiotic too early may give breathing space to the bacteria to grow again, possibly with antibiotic resistant strains, and therefore the infection will be more difficult to treat the second time. Talk to the doctor if the condition persists or deteriorates even after a long period of time.

How trimethoprim works

Trimethoprim inhibits the enzymes responsible for converting dihydrofolic acid into tetrahydrofolic acid which is required by the bacteria to make necessary proteins. Thus the ability of the bacteria to make these proteins is disrupted and they are killed.

Side effects

Less common

Possible interactions

Other medicaments
Trimethoprim may precipitate the effects of these drugs, and combination may lead to various types of toxicity:The effect of trimethoprim may be decreased by:
Since homocysteine levels may be increased by this drug, taking a multivitamin supplement would be advisable.
Herbal medicines or minerals
Sometimes people use Echinacea in order to strengthen their immune system. However, Echinacea is not advisable to people who have already impaired immune system. In fact, it may actually weaken immune system further, if used indiscriminately.
Mistletoe herb, marshmallow root, oak bark and licorice extracts should not be taken with trimethoprim.
Pure cranberry juice, on the other hand, may help in preventing harmful bacteria from getting attached to the bladder and, in combination with antibiotics like trimethoprim, may be useful in preventing infections of the urinary tract.

Storage instructions

Keep the medicine tightly closed, in the container it originally came in. Store at room temperature, that is, 15 to 30�C, away from light, heat and moisture (not near fire place or in bathroom). All medicines should be kept away from children and pets and disposed of in the proper manner when expired or no longer required. Ask your pharmacist, or the local waste disposal company, about the proper method of disposal.

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