Sulfamethoxazole-trimethoprim is a commonly-prescribed combination antibiotic that fights off a wide spectrum of bacterial infections. Most people know it as Bactrim, the brand-name version. Healthcare professionals often just call it TMP-SMX or co-trimoxazole. For most infections, twice-daily doses for a few days to a couple of weeks are usually enough to eliminate the infection.
Check our best Sulfamethoxazole-Trimethoprim prices
Sulfamethoxazole-Trimethoprim overview
BRAND NAMES:
Bactrim, Bactrim DS, Sulfatrim
Generic Names:
Sulfamethoxazole-trimethoprim
Uses:
Treats or prevents infections.
Therapeutic Classes:
Antibiotic, sulfonamide combination
Forms:
Tablet, oral suspension (liquid)
How it’s taken:
By mouth
What is Sulfamethoxazole-Trimethoprim used for?
Sulfamethoxazole-trimethoprim treats bacterial infections in adults and children 2 years of age and older.
What form(s) does Sulfamethoxazole-Trimethoprim come in
Tablet
400 mg sulfamethoxazole/80 mg trimethoprim (regular strength)
800 mg sulfamethoxazole/160 mg trimethoprim (double strength)
Oral suspension (liquid)
200 mg sulfamethoxazole/40 mg trimethoprim/5 mL
What are common Sulfamethoxazole-Trimethoprim doses?
For urinary tract infections in adults and children weighing more than 88 pounds: Two regular strength tablets OR one double-strength tablet OR 20 mL oral suspension every 12 hours for 10–14 days
For children weighing between 22 and 44 pounds: 5 mL oral suspension every 12 hours for 10 days
For children weighing between 44 and 66 pounds: One regular strength tablet OR 10 mL oral suspension every 12 hours for 10 days
For children weighing between 66 and 88 pounds: One and one-half regular strength tablets OR 15 mL oral suspension every 12 hours for 10 days
For ear infections (otitis media) in children:
Weighing between 22 and 44 pounds: 5 mL oral suspension every 12 hours for 10–14 days
Weighing between 44 and 66 pounds: One regular strength tablet OR 10 mL oral suspension every 12 hours for 10–14 days
Weighing between 66 and 88 pounds: One and one-half regular strength tablets OR 15 mL oral suspension every 12 hours for 10–14 days
Weighing more than 88 pounds: Two regular strength tablets OR one double-strength tablet OR 20 mL oral suspension every 12 hours for 10 days
For shigellosis in adults and children weighing 88 pounds or more: Two regular strength tablets OR one double-strength tablet OR 20 mL oral suspension every 12 hours for five days
For children weighing between 22 and 44 pounds: 5 mL oral suspension every 12 hours for five days
For children weighing between 44 and 66 pounds: One regular strength tablet OR 10 mL oral suspension every 12 hours for five days
For children weighing between 66 and 88 pounds: One and one-half regular strength tablets OR 15 mL oral suspension every 12 hours for five days
For exacerbations of chronic bronchitis in adults: Two regular strength tablets OR one double-strength tablet OR 20 mL oral suspension every 12 hours for 14 days
For Pneumocystis jirovecii pneumonia in adults and children:
Weighing between 18 and 35 pounds: 5 mL oral suspension every six hours for 14–21 days
Weighing between 35 and 53 pounds: One regular strength tablet OR 10 mL oral suspension every six hours for 14–21 days
Weighing between 53 and 70 pounds: One and one-half regular strength tablets OR 15 mL oral suspension every six hours for 14–21 days
Weighing between 70 and 88 pounds: Two regular-strength tablets OR one double-strength tablet OR 20 mL oral suspension every six hours for 14–21 days
Weighing between 88 and 106 pounds: Two and one-half regular strength tablets OR 25 mL oral suspension every six hours for 14–21 days
Weighing between 106 and 141 pounds: Three regular strength tablets OR one and one-half double strength tablets OR 30 mL oral suspension every six hours for 14–21 days
Weighing between 141 and 176 pounds: Four regular strength tablets OR two double strength tablets OR 40 mL oral suspension every six hours for 14–21 days
Weighing 176 pounds or more: Five regular strength tablets OR two and one-half double strength tablets OR 50 mL oral suspension every six hours for 14–21 days
For prevention of Pneumocystis jirovecii pneumonia in adults: One double-strength tablet OR 20 mL oral suspension tablet daily
For children with a body surface area of 0.26 m2 to 0.53 m2: 2.5 mL oral suspension given twice per day for three consecutive days per week
For children with a body surface area of 0.53 m2 to 1.06 m2: One-half regular strength tablet OR 5 mL oral suspension given twice per day for three consecutive days per week
For children with a body surface area greater than 1.06 m2: One regular strength tablet OR 10 mL oral suspension given twice per day for three consecutive days per week
For traveler’s diarrhea in adults: Two regular strength tablets OR one double-strength tablet OR 20 mL oral suspension every 12 hours for five days.
Common Sulfamethoxazole-Trimethoprim prescriptions
Sulfamethoxazole-Trimethoprim
473ml of 200-40mg/5ml bottleSulfamethoxazole-Trimethoprim
400-80mg tabletSulfamethoxazole-Trimethoprim
800-160mg tabletSulfamethoxazole-Trimethoprim
10ml of 400-80mg/5ml vialSulfamethoxazole-Trimethoprim
30ml of 400-80mg/5ml vialSulfamethoxazole-Trimethoprim
5ml of 400-80mg/5ml vial
How to take Sulfamethoxazole-Trimethoprim
Your doctor will tell you how much medicine to use. Do not use more than directed.
Take all the medicine in the prescription, even if you feel better in the first few days.
Sulfamethoxazole-trimethoprim can be taken with food or on an empty stomach. Try taking doses with food if you have problems with stomach upset or nausea.
How to take sulfamethoxazole-trimethoprim tablets:
Swallow the tablet whole with a drink of water.
Both regular-strength and double-strength tablets are scored so that they can be divided into half-tablets. A pharmacist or prescriber can demonstrate the correct procedure for breaking tablets in half.
Store the medicine in a light-resistant, closed container at room temperature.
How to take sulfamethoxazole-trimethoprim oral suspension:
Shake the bottle well before measuring a dose.
Measure doses with a calibrated oral syringe to ensure accurate doses.
Do not use a kitchen measuring spoon to measure out doses unless the prescriber says it’s okay. Conversions from milliliters to teaspoons are printed on the drug information sheet that comes with the medicine.
Store the oral suspension in a light-resistant, tightly closed container at room temperature protected from light.
What to do if you miss a dose of Sulfamethoxazole-Trimethoprim
Take a missed dose when it’s remembered unless it’s almost time for the next dose. In that case, forget the missed dose and take the next regular dose as scheduled.
Do not take extra medicine to make up for a missed dose.
Sulfamethoxazole-Trimethoprim contraindications
This medicine is not right for everyone.
It is not safe to take sulfamethoxazole-trimethoprim during pregnancy because it can harm an unborn baby. Immediately tell the prescribing doctor if you become pregnant.
Sulfamethoxazole-trimethoprim is contraindicated in children 2 months of age or younger
Sulfamethoxazole should not be used by anyone who has:
Allergies to trimethoprim, sulfamethoxazole, or sulfa drugs
Any history of drug-induced blood-clotting problems
Anemia due to low folic acid levels
Significant liver impairment
Severe, unmonitored kidney problems
Sulfamethoxazole-Trimethoprim warnings
Tell any doctor, dentist, or other healthcare professional who treats you that you are taking sulfamethoxazole-trimethoprim.
The prescriber may need regular check-ups and blood tests to ensure the medicine is working and not causing side effects. Keep all appointments.
Tell the prescribing doctor if you are breastfeeding, pregnant, or have:
Asthma
Severe allergies
Diabetes
Malnutrition
Folate deficiency
Malabsorption syndrome
Underactive thyroid
HIV/AIDS
Porphyria
A hereditary disorder called G6PD deficiency
Sulfamethoxazole-trimethoprim can cause serious side effects including:
Liver problems
Kidney problems
Breathing problems
Fast or irregular heartbeats
Blood disorders
Low blood sugar
Low sodium
High potassium
Severe muscle damage
Severe allergic reactions
To avoid kidney problems or kidney damage, drink plenty of extra fluids when taking TMP-SMX.
People on TMP-SMX may bleed or bruise more easily. Try to avoid injuries.
This medicine can cause diarrhea that can occur weeks to months after TMP-SMX has been discontinued. Call a healthcare professional immediately if you experience severe, watery, or bloody diarrhea even after treatment has stopped. Do not take any medicine to stop the diarrhea until you have talked to your doctor.
Sulfamethoxazole-trimethoprim can cause serious problems in people with folate deficiency. Most people don't know if they have low folic acid, but it’s likely in:
Elderly people
Chronic alcoholics
Malnourished people
People taking anticonvulsants
Sulfamethoxazole-Trimethoprim interactions
Sulfamethoxazole should never be taken by someone who is also taking the heart rhythm drug Tikosyn (dofetilide).
People being treated for Pneumocystis jirovecii cannot take TMP-SMX if they’re also taking leucovorin, a cancer drug.
Before taking TMP-SMX, tell the prescribing doctor about all the prescription drugs, over-the-counter medications, and supplements being taken, including:
Blood pressure drugs called ACE inhibitors or angiotensin receptor blockers (ARBs)
Oral diabetes drugs
Drugs that make you pee (diuretics)
Drugs that treat depression, especially tricyclic antidepressants
Amantadine, cyclosporine, digoxin, indomethacin, memantine, methotrexate, phenytoin, procainamide, pyrimethamine, warfarin, zidovudine
Tell all other healthcare professionals that you are taking sulfamethoxazole-trimethoprim before they prescribe new medications.
Find more information about sulfamethoxazole-trimethoprim interactions to avoid here.
Sulfamethoxazole-Trimethoprim side effects
Serious side effects
Talk to a healthcare provider if you notice any signs or symptoms of a possible serious side effect, including:
Racing heartbeats, chest pain
Change in how much or how often you urinate, painful urination, lower back or side pain
Dark urine or pale stools, nausea, vomiting, loss of appetite, stomach pain, yellow skin or eyes
Chest pain, cough, or trouble breathing
Cough, shortness of breath, trouble breathing
Severe diarrhea, stomach pain, cramps, bloating
Unusual bleeding or bruising
Severe muscle pain, dark urine
Severe abdominal pain
Confusion, weakness, muscle twitching, seizures
Lack of energy, numbness or tingling, loss of appetite, problems walking, smooth tongue
Skin rash, purple spots on your skin, pale skin
Blistering, peeling, red skin rash, fever, pus-filled nodules
Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing
Less serious side effects
Skin rash
Light sensitivity
Loss of appetite
Nausea
Vomiting
Stomach upset and stomach pain
Dizziness
Ringing in the ears
Fatigue
Trouble sleeping
Sources:
Bactrim DS, Bactrim sulfamethoxazole and trimethoprim tablet prescribing information, DailyMed (NIH National Library of Medicine)
Bactrim DS drug summary, Prescriber’s Digital Reference (PDR)
Sulfamethoxazole and trimethoprim suspension, DailyMed (NIH National Library of Medicine)
Sulfamethoxazole and trimethoprim tablet, DailyMed (NIH National Library of Medicine)
Trimethoprim and sulfamethoxazole, StatPearls
Subscribe to our savings newsletter
Health education, drug info, wellness & more
By clicking 'Subscribe', I agree to SingleCare's Terms & Conditions.
