Key takeaways:
Bactrim DS (sulfamethoxazole/trimethoprim) is a prescription antibiotic commonly used to treat bacterial infections of the ears, lungs, and more. It comes as a tablet and an oral liquid suspension.
A typical Bactrim DS dose for adults is 800 mg of sulfamethoxazole and 160 mg of trimethoprim every 12 hours for 5 to 14 days (depending on the type of infection that is being treated). The typical dose for children is based on their body weight.
Bactrim DS is available as a lower-cost generic. GoodRx can help you save over 70% off the average retail price at certain pharmacies.
Save on related medications
Bactrim DS is a combination antibiotic used to treat bacterial infections such as urinary tract infections (UTIs), ear infections, and certain types of pneumonia. It contains two medications, sulfamethoxazole and trimethoprim, which work together to kill bacteria.
Bactrim comes in different forms. Bactrim DS stands for “double strength” and contains 800 mg of sulfamethoxazole and 160 mg of trimethoprim per tablet. The single-strength version contains half that amount. Generic sulfamethoxazole / trimethoprim is also available as tablets and an oral liquid.
The right Bactrim dosage depends on factors such as the infection being treated, your age, and your kidney function. Below, we’ll cover typical Bactrim dosages for adults and children, along with tips for taking it safely.
Search and compare options
What’s the typical Bactrim DS dosage for adults?
In most cases, adults will take Bactrim DS for 5 to 14 days at a time. This can be longer or shorter depending on the type of infection that’s being treated and how severe your symptoms are.
In some cases, Bactrim DS can also be prescribed long-term to prevent complications in people who are at a higher risk for certain types of infections. This can be useful for people with weakened immune systems, such as those living with HIV or who are receiving high doses of chemotherapy. Prevention dosages are different from dosages used to treat an active infection.
Infection type | Adult Bactrim DS dosage |
|---|---|
Bronchitis | Take 1 tablet every 12 hours for 14 days |
Pneumocystis pneumonia (fungal infection of the lungs) | Prevention: Take 1 tablet once daily (or alternative dosing schedule) Treatment: Dosing depends on body weight. For example, if you weigh 64 kg (141 lbs), it’s recommended to take 2 tablets every 6 hours for up to 21 days. |
Shigellosis | Take 1 tablet every 12 hours for 5 days |
Take 1 tablet every 12 hours for 3 to 14 days | |
Take 1 tablet every 12 hours for 5 days |
In order to most effectively resolve an infection, it’s important to take all antibiotics exactly as they are prescribed. Bactrim DS is no different. You should take your entire course of Bactrim DS even if your symptoms start to improve and you feel better. This helps ensure the infection is cleared from your body and lowers your risk of having the infection come back.
What’s the typical Bactrim DS dosage for children?
Bactrim DS dosages for children ages 2 months or older are based on their body weight. Your child’s healthcare professional will calculate their dosage for them based on their body weight in kilograms (kg). Depending on their body weight, they may only be able to take a comparable single-strength tablet dose instead of Bactrim DS.
Like adults, Bactrim DS courses in children typically last 5 to 14 days depending on the type of infection being treated and how severe their symptoms are. However, you should give your child all of their prescribed doses even if they start to feel better.
Infection type | Bactrim DS dosage in children |
|---|---|
Take 40 mg/kg of sulfamethoxazole and 8 mg/kg of trimethoprim by mouth every 12 hours for 10 days | |
Pneumocystis pneumonia | Treatment dosage depends on body weight, and prevention dosage is based on body surface area. Example: If your child weighs 16 kg (35 lbs), they may be told to take 1 tablet every 6 hours for 14 to 21 days for treatment. |
Shigellosis infection | Take 40 mg/kg of sulfamethoxazole and 8 mg/kg of trimethoprim every 12 hours for 5 days |
UTI | Take 40 mg/kg of sulfamethoxazole and 8 mg/kg of trimethoprim every 12 hours for 10 days |
If your child is younger than 2 months old, they generally shouldn’t receive Bactrim DS. Speak with your healthcare provider about an alternative antibiotic for your child’s infection.
Are there any Bactrim DS dosage adjustments for medical conditions?
Yes, there are recommended dosage adjustments for people with substantial kidney problems. This is because Bactrim DS leaves your body through your kidneys. If your kidneys aren’t working properly, Bactrim DS could build up in your body. This can lead to unwanted side effects.
Dosage for people with kidney problems
If you have mild to moderate kidney problems, your prescriber most likely won’t need to adjust your dosage of Bactrim DS.
But if you have severe kidney problems, you’ll need to take a lower dosage. Your dose will likely be based on your “creatinine clearance” (CrCl). This is a lab test that helps your prescriber figure out how efficient your kidneys are working, and it determines the most appropriate Bactrim DS dosage based on your kidney health.
Kidney function (CrCl) | Recommended Bactrim DS dose |
|---|---|
Greater than 30 mL/min | No dosage adjustment necessary. |
15 to 30 mL/min | Take 50% (half) of the normal recommended dose. |
Less than 15 mL/min (or on hemodialysis) | Not recommended — unless otherwise advised by your healthcare team. In some cases, a lower dose may be recommended. If you're receiving hemodialysis, you should generally take your Bactrim DS dose on hemodialysis days after your hemodialysis session. Your kidney specialist can give you more information. |
What happens if you miss a dose of Bactrim DS?
Missing a dose of Bactrim DS may make your treatment less effective. If you miss a dose of Bactrim DS, you should take it as soon as you remember. But if you remember within a few hours before your next scheduled dose, you can skip the missed dose altogether and wait to take the next dose at your regular scheduled time.
Do not try to catch up by taking two doses of Bactrim DS at once. Taking too many doses at once can raise your risk of side effects.
What should you do if you take too much Bactrim DS?
At regular doses, Bactrim DS can cause side effects such as diarrhea, nausea, and vomiting. If you take too much Bactrim DS, these side effects may be worse. Taking too much can also lead to an overdose. Signs and symptoms of a Bactrim DS overdose may include:
Nausea and vomiting
Dizziness
Drowsiness
Headache
Confusion
Loss of consciousness
While less common, taking too much Bactrim DS over a prolonged period of time can also cause bone marrow suppression. This means your bone marrow makes fewer blood cells. It can lead to anemia (low red blood cells, low white blood cells, and low platelets).
If you think you or your child took too much Bactrim DS, contact a healthcare professional or call Poison Control at 1-800-222-1222 for guidance. But if your symptoms feel severe, it’s better to call 911 or go to the nearest ER.
How to save on Bactrim DS
There are ways to save on Bactrim DS, which is available as both a brand-name and generic medication. GoodRx can help you save over 70% off the average retail price of the generic version. Generic Bactrim’s price at certain pharmacies is as low as $2.10 with a free GoodRx discount.
Frequently asked questions
Bactrim DS tablets can generally be crushed or split if you have trouble swallowing them. However, the crushed tablets may have a bitter taste.
Check with your pharmacist before crushing Bactrim DS. They may recommend the liquid form of sulfamethoxazole / trimethoprim as an alternative.
It takes about 2 days for most of Bactrim DS to leave your system after your last dose. Its two active ingredients have half-lives of about 8 to 10 hours, meaning your body removes half of the medication during that time.
Bactrim DS may remain in your system longer if you have kidney problems, since the kidneys remove most of the medication. Your prescriber may adjust your dosage based on your kidney function.
Bactrim DS tablets can generally be crushed or split if you have trouble swallowing them. However, the crushed tablets may have a bitter taste.
Check with your pharmacist before crushing Bactrim DS. They may recommend the liquid form of sulfamethoxazole / trimethoprim as an alternative.
It takes about 2 days for most of Bactrim DS to leave your system after your last dose. Its two active ingredients have half-lives of about 8 to 10 hours, meaning your body removes half of the medication during that time.
Bactrim DS may remain in your system longer if you have kidney problems, since the kidneys remove most of the medication. Your prescriber may adjust your dosage based on your kidney function.
The bottom line
Bactrim DS is a prescription antibiotic that contains sulfamethoxazole and trimethoprim. Most people prescribed Bactrim DS take one tablet twice daily for 5 to 14 days. However, Bactrim DS dosages vary in adults and children depending on what it's being used to treat, symptom severity, and body weight. Your dosage may also be lowered if you have severe kidney problems. Speak with your prescriber or pharmacist about the best Bactrim DS dosage for you or your child’s situation.
Why trust our experts?
References
Amneal Pharmaceuticals of New York. (2025). Sulfamethoxazole and trimethoprim tablet [package insert]. DailyMed.
Centers for Disease Control and Prevention. (2021). Pneumocystis pneumonia.
Centers for Disease Control and Prevention. (2024). About shigella infection.
Centers for Disease Control and Prevention. (2024). Pneumocystis pneumonia basics.
Kemnic T. R., et al. (2026). Trimethoprim-sulfamethoxazole. StatPearls.
National Kidney Foundation. (n.d.). Dialysis.
Parajuli, P., et al. (2019). Trimethoprim-sulfamethoxazole induced pancytopenia: a common occurrence but a rare diagnosis. Cureus.
Shahbaz, H., et al. (2022). Creatinine clearance. StatPearls.
