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.
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.
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.
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.
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.