Generic name: sulfamethoxazole and trimethoprim (oral) [ SUL-fa-meth-OX-a-zole-and-trye-METH-oh-prim ]
Brand names: Septra, Septra DS
Dosage form: tablets (80mg/400 mg​​), DS tablets (160mg/800 mg)
Drug class: Sulfonamides

Medically reviewed by Melisa Puckey, BPharm. Last updated on Jul 31, 2024.

What is Septra and Septra DS?

Septra and Septra DS (double strength) is a combination antibiotic used to treat ear infections, urinary tract infections, bronchitis, traveler's diarrhea, shigellosis, and Pneumocystis jiroveci pneumonia. Septra and Septra DS contains sulfamethoxazole and trimethoprim.

Sulfamethoxazole is a sulfonamide antibiotic that prevents the growth of susceptible bacteria by interfering with their ability to make folic acid. Trimethoprim is an antifolate antibiotic that works by inhibiting an enzyme, resulting in bacteria's inability to make DNA and survive. Sulfamethoxazole and trimethoprim are combined because they are complementary and have a greater effect when used together. 

Other brands of sulfamethoxazole and trimethoprim are Bactrim, Bactrim DS, and it is also available as a generic medicine.

Septra and Septra DS side effects

Common Septra side effects

Common Septra side effects may include nausea, vomiting, loss of appetite, or skin rash.

Serious Septra and Septra DS side effects

Get emergency medical help if you have signs of an allergic reaction to Septra (hives, cough, chest pain, shortness of breath, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).

Seek medical treatment if you have a serious drug reaction that can affect many parts of your body. Symptoms may include skin rash, fever, swollen glands, joint pain, muscle aches, severe weakness, pale skin, unusual bruising, or yellowing of your skin or eyes.

Call your doctor at once if you have:

• severe stomach pain, diarrhea that is watery or bloody (even if it occurs months after your last dose);
• a skin rash, no matter how mild;
• yellowing of your skin or eyes;
• a seizure;
• new or unusual joint pain;
• increased or decreased urination;
• swelling, bruising, or irritation around the IV needle;
• increased thirst, dry mouth, fruity breath odor;
• new or worsening cough, fever, trouble breathing;
• high potassium level - nausea, weakness, tingly feeling, chest pain, irregular heartbeats, loss of movement;
• low sodium level - headache, confusion, slurred speech, severe weakness, vomiting, loss of coordination, feeling unsteady; or
• low blood cell counts - fever, chills, mouth sores, skin sores, easy bruising, unusual bleeding, pale skin, cold hands, and feet, feeling light-headed or short of breath.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Warnings

You should not use Septra if you have severe liver disease, kidney disease that is not being monitored, anemia caused by folic acid deficiency, if you take dofetilide, or if you have had low platelets caused by using trimethoprim or a sulfa drug.

You should not take Septra if you are pregnant or breastfeeding.

Before taking this medicine

You should not use Septra if you are allergic to sulfamethoxazole or trimethoprim, or if you have:

• severe liver disease;
• kidney disease that is not being treated or monitored;
• anemia (low red blood cells) caused by folic acid deficiency;
• a history of low blood platelets after taking trimethoprim or any sulfa drug; or
• if you take dofetilide (Tikosyn).

Do not use Septra if you are pregnant. This medicine could harm the unborn baby or cause birth defects. Use effective birth control, and tell your doctor if you are pregnant or if you become pregnant.

Do not breastfeed while using this medicine.

This medicine should not be given to a child younger than 2 months old.

To make sure this meidicne is safe for you, tell your doctor if you have:

• kidney or liver disease;
• a folate (folic acid) deficiency;
• asthma or severe allergies;
• a thyroid disorder;
• malnourishment;
• alcoholism;
• high levels of potassium in your blood;
• porphyria, or glucose-6-phosphate dehydrogenase (G6PD) deficiency; or
• if you use a blood thinner (such as warfarin) and you have routine "INR" or prothrombin time tests.

How should I use Septra and Septra DS?

Take Septra and Septra DS exactly as prescribed by your doctor. Follow all directions on your prescription label and read all medication guides or instruction sheets.

Drink plenty of fluids to prevent kidney stones while you are using this medicine.

Septra doses are based on weight in children. Use only the recommended dose when giving this medicine to a child.

Use this medicine for the full prescribed length of time, even if your symptoms quickly improve. Skipping doses can increase your risk of infection that is resistant to medication. This medicine will not treat a viral infection such as the flu or a common cold.

You may need frequent medical tests.

This medicine can affect the results of certain medical tests. Tell any doctor who treats you that you are using this medicine.

Store at room temperature away from moisture, heat, and light.

Related/similar drugs

prednisone, amoxicillin, doxycycline, ciprofloxacin, cephalexin, azithromycin, metronidazole, triamcinolone, ceftriaxone, clindamycin

What happens if I miss a dose?

Use the medicine as soon as possible, but skip the missed dose if it is almost time for your next dose. Do not use two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose symptoms may include loss of appetite, vomiting, fever, blood in your urine, yellowing of your skin or eyes, confusion, or loss of consciousness.

What should I avoid while using Septra and Septra DS?

Antibiotic medicines can cause diarrhea, which may be a sign of a new infection. If you have diarrhea that is watery or bloody, call your doctor before using anti-diarrhea medicine.

Sulfamethoxazole and trimethoprim could make you sunburn more easily. Avoid sunlight or tanning beds. Wear protective clothing and use sunscreen (SPF 30 or higher) when you are outdoors.

What other drugs will affect Septra and Septra DS?

You may need more frequent check-ups or medical tests if you also use medicine to treat depression, diabetes, seizures, or HIV.

Tell your doctor about all your current medicines. Many drugs can affect sulfamethoxazole and trimethoprim, especially:

• amantadine, digoxin, cyclosporine, indomethacin, leucovorin, methotrexate, procainamide, pyrimethamine;
• an "ACE inhibitor" heart or blood pressure medication (benazepril, enalapril, lisinopril, quinapril, ramipril, and others); or
• a diuretic or "water pill" (chlorthalidone, hydrochlorothiazide, and others).

This list is not complete and many other drugs may affect sulfamethoxazole and trimethoprim. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

Popular FAQ

More FAQ

• Can I drink alcohol when taking sulfamethoxazole / trimethoprim DS?
• What dose of co-trimoxazole is used in a patient with a UTI?

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Medical Disclaimer