Healthy Living

What Is Sulfamethoxazole?

What Is Sulfamethoxazole?

Generic Name: Sulfamethoxazole/Trimethoprim

Brand Name: Bactrim, Septra, Septra DS, Sulfatrim, Bactrim DS, SMZ-TMP Pediatric.

What Is Sulfamethoxazole?

In combination with trimethoprim, sulfamethoxazole is used for the treatment of certain infections such as middle ear infection, urinary tract infection, traveler’s diarrhea, bronchitis, and shigellosis. This drug is also used for both the treatment and prevention of pneumocystis carinii pneumonia (PCP) or pneumocystis jiroveci pneumonia (PJP).

This drug only works on bacterial infections, which means that it will not be effective against viral infections such as the flu or common cold.

Sulfamethoxazole is a medication that is only available by prescription. It is available in three forms; tablet, suspension, and injection.

Can Sulfamethoxazole Be Used by Anyone?

No. Sulfamethoxazole or trimethoprim should not be used by individuals who:

  • Have a history of low blood platelet count or immune thrombocytopenia.
  • Are allergic to any ingredients present in sulfamethoxazole or trimethoprim.
  • Are allergic to any other sulfonamide or sulfa medicines such as hydrochlorothiazide.
  • Are suffering from severe kidney or liver problems.
  • Are already taking methenamine or dofetilide.
  • Are younger than two months of age.
  • Have been diagnosed with anemia, which is caused by low levels of folic acid or folate in the blood.

Before Usage 

Certain medical conditions or drugs can interact negatively with sulfamethoxazole or trimethoprim. Before starting sulfamethoxazole, inform you doctor if you:

  • Are breastfeeding
  • Are pregnant or planning to conceive
  • Are taking any other prescription medications, over the counter medicines, or supplements.
  • Are allergic to any foods, medicines, or other substances.
  • Suffer from severe kidney damage, liver problems, blood related problems such as anemia or porphyria, thyroid gland issues, asthma, HIV, or G6PD deficiency.
  • Suffer from a folate deficiency in the blood.
  • Have a history of high potassium levels.

Apart from medical conditions, there are certain medications which tend to interact negatively with sulfamethoxazole or trimethoprim. The doctor should be aware of any other medications or supplements you are taking so as to avoid potential side effects. Inform your doctor if you are taking any of the following:

  • Anticoagulants
  • Pyrimethamine
  • Dofetilide
  • Methenamine
  • Tricyclic antidepressants
  • Cyclosporine
  • Amantadine, digoxin, sulfones or oral diabetic medicines.
  • ACE inhibitors such as enalapril, diuretics, or indomethacin.

What Is Sulfamethoxazole TMP Used For?

Sulfamethoxazole and trimethoprim should be used as directed by the doctor. Sulfamethoxazole and trimethoprim are given in the form of injection, in a hospital, under the guidance of a doctor or nurse. If you are using sulfamethoxazole at home, then ensure that you learn how to properly administer it.

Do not increase or decrease your dose of sulfamethoxazole without first consulting your doctor. Avoid taking it for more than the recommended duration. Sulfamethoxazole and trimethoprim should be taken with a glass of water. During the course of your treatment with this drug, ensure that you drink several glasses of water daily unless instructed otherwise by your doctor. Drinking plenty of water can help prevent unnecessary side effects which can be caused by this medication.

Sulfamethoxazole and trimethoprim should not be taken if it contains any kind of particles or if it is discolored or cloudy. Additionally, do not use the sulfamethoxazole and trimethoprim if the vial containing these medicines is damaged or cracked. Avoid reusing the needles or any of the other materials. Ensure that you follow all rules of disposal.

Those who are taking the liquid form of sulfamethoxazole and trimethoprim should use a specially marked measuring spoon, or any other measuring device, to properly measure their dose before consuming it. Household spoons may not hold the liquid properly; thus, it is best to have a special measuring device. Ensure that you complete the full course of treatment. Stopping the antibiotic early, even if you seem to be feeling better, can cause the symptoms to return and the infection to become drug resistant. The dosing of this medication varies from person to person. For the best results, follow the instructions given to you by your doctor.

Liquids or Tablets in Oral Form

Below are some of the commonly prescribed dosages of sulfamethoxazole and trimethoprim.

Bacterial Infection Treatment

For adults who weigh above 40kg:

  • 800mg of sulfamethoxazole every 12 hours.
  • 160mg of trimethoprim every 12 hours.

This should be taken for a period of 10 to 15 days. The doctor can adjust the dose based on the improvement of your condition.

The dose for children above the age of two months must be determined by the doctor. Usually, the doctor will structure the proper dose based on the child’s weight.

  • 40mg of sulfamethoxazole for every one kg of body weight.
  • 8mg of trimethoprim for every one kg of body weight.

The dosages should be divided into two doses in a gap of ten or twelve hours. This medication is not recommended for infants who are below two months of age.

Pneumocystis Jiroveci Pneumonia or Pneumocystis Carinii Pneumonia Treatment

For adults and children above the age of two months, the dose will be determined by the doctor based on your weight.

  • 80 to 100mg of sulfamethoxazole for every one kg of body weight
  • 15 to 20mg of trimethoprim for every one kg of body weight.

The dosages are divided equally to be taken every six hours for a duration of 14 to 20 days. This medication is not recommended for infants who are below two months of age.

Pneumocystis Jiroveci Pneumonia or Pneumocystis Carinii Pneumonia Prevention

For adults:

  • 800mg of sulfamethoxazole once daily.
  • 150mg of trimethoprim once daily.

For children above two months of age, the dose is determined by the body size and weight. The usual dose would be 750mg of sulfamethoxazole and 150mg of trimethoprim per square meter of the surface of the body. This dosing should be divided into equal doses twice daily at least 3 times a week.

Individuals Suffering from Traveler's Diarrhea

For adults:

  • 800mg of sulfamethoxazole every 12 hours.
  • 160mg of trimethoprim every 12 hours.

These doses should be taken for a period of five days.

The dose for children above the age of two months should be determined by the doctor. These medications are not recommended for infants below the age of two months.

If a dose is missed, ensure that you take the missed dose as soon as you remember. However, if it is already time for your next dose, then skip the missed dose and continue the regular dosing schedule. Do not take a double dose. Keep this medicine out of reach from children. It should be stored in a closed container at normal room temperature. It should also be kept out of light, heat, and moisture.

Side Effects of Sulfamethoxazole

If you come across any of the following side effects, inform your doctor before the symptoms can worsen. The common side effects of sulfamethoxazole include:

Severe allergic reaction side effects include:

When injecting this medication, it is possible to experience:

  • Redness at the injection site
  • Purple patches under the skin
  • Severe stomach pain
  • Chills
  • Seizures
  • Persistent diarrhea
  • Nausea
  • Vomiting
  • Tongue or mouth soreness
  • Low blood sugar symptoms such as excessive sweating, tremors, dizziness, increased heart rate, increased hunger, and vision changes.


Sulfamethoxazole and trimethoprim can cause you to burn more easily in the sun; thus, it is advisable to avoid direct sunlight or cover up while going out. Avoid sunlamps or tanning beds. Always make sure to apply sunscreen lotion before going outside.

Antibiotic can cause mild diarrhea; however, it is important to contact a doctor as soon as possible if this diarrhea worsens. Though rare, it is possible for an infection to become resistant against sulfamethoxazole or trimethoprim if the medications are discontinued early. This is why it is important to complete your course of treatment as instructed by the doctor.