Medically reviewed by Alan Lucks | MD, Alan Lucks MDPC Private Practice - New York on December 8th, 2025.
Sulfamethoxazole is commonly used in combination with trimethoprim to treat bacterial infections.
Dosage varies depending on the infection type, patient age, and kidney function.
Typical adult doses range from 800 mg sulfamethoxazole combined with 160 mg trimethoprim twice daily.
Children’s doses are carefully calculated based on weight and condition severity.
Missing doses or overdosing can lead to treatment failure or serious side effects.
Always consult with a healthcare provider for personalized dosing advice, including through telehealth services like Doctronic.ai.
Sulfamethoxazole is a sulfonamide antibiotic that stops bacteria from making folate, a nutrient they need to grow and multiply. It’s often paired with trimethoprim, which blocks folate production at a different step. Together, this combination is known as co-trimoxazole (sulfamethoxazole-trimethoprim), and it creates a stronger, more effective treatment while also helping reduce the chance of antibiotic resistance. Because of its broad coverage, co-trimoxazole is commonly used for urinary tract infections, respiratory infections, and certain gastrointestinal infections.
To get the best results, it’s important to follow the prescribed dosage exactly. Taking sulfamethoxazole with plenty of fluids can help prevent crystalluria, a condition where crystals form in the urine. Patients should also be mindful of drug interactions, especially with anticoagulants and certain anticonvulsants, since these combinations may increase side effects or reduce how well the medication works. Regular check-ins with a healthcare provider may be recommended to monitor kidney function and overall response to treatment.
Below, you will find a comprehensive dosage chart and detailed guidance on how to take sulfamethoxazole safely and effectively.
Form |
Strength |
Typical Adult Dose |
Typical Children’s Dose |
Frequency |
Route |
Maximum Daily Dose |
|---|---|---|---|---|---|---|
Tablet (co-trimoxazole) |
800 mg sulfamethoxazole / 160 mg trimethoprim |
1 tablet twice daily |
8 mg/kg sulfamethoxazole + 1.6 mg/kg trimethoprim twice daily |
Twice daily |
Oral |
3200 mg sulfamethoxazole / 640 mg trimethoprim |
Suspension (co-trimoxazole) |
200 mg sulfamethoxazole / 40 mg trimethoprim per 5 mL |
Not typically used in adults |
5-10 mL twice daily (based on weight) |
Twice daily |
Oral |
Based on weight, max varies |
For adults, the standard dose is one double-strength tablet (800 mg sulfamethoxazole / 160 mg trimethoprim) twice daily for 10 to 14 days. Children receive doses based on weight, typically 8 mg/kg sulfamethoxazole with 1.6 mg/kg trimethoprim twice daily for 10 days.
Adults usually take 1 to 2 double-strength tablets three times daily for treatment, or one tablet daily for prevention. Pediatric doses are adjusted similarly by weight and severity.
Doses vary widely depending on the infection. It’s essential to follow your healthcare provider’s instructions closely.
Adults typically take sulfamethoxazole combined with trimethoprim in double-strength tablets of 800 mg/160 mg twice daily. The duration depends on the infection type, but usually ranges from 7 to 14 days. For serious infections like PCP, doses may increase, and frequency may be adjusted.
Children’s doses are weight-based to ensure safety and effectiveness. The usual regimen is 8 mg/kg sulfamethoxazole with 1.6 mg/kg trimethoprim twice daily. Pediatric formulations like oral suspensions make dosing easier. Always use a precise measuring device and consult a healthcare provider for exact dosing.
If a dose is missed, take it as soon as remembered unless it is near the time for the next dose. Do not double up doses to catch up. Consistency is key in antibiotic therapy to prevent resistance and ensure the infection clears.
Since sulfamethoxazole is eliminated through the kidneys, patients with reduced kidney function may require dose adjustments to avoid toxicity. Your healthcare provider will determine the appropriate dose based on kidney tests.
Severe liver disease may also necessitate dose modification. Monitoring for side effects is important in these cases.
An overdose can cause symptoms like nausea, vomiting, dizziness, and in severe cases, kidney damage or blood disorders. Seek emergency medical attention immediately if overdose is suspected.
Be aware of potential allergic reactions, including rash, itching, or swelling. Sulfamethoxazole can interact with other medications, so always inform your healthcare provider about all drugs you are taking.
Take with a full glass of water to prevent kidney stones.
Complete the full prescribed course even if symptoms improve early.
Avoid excessive sun exposure as the medication can increase sensitivity.
Report any unusual side effects to your healthcare provider promptly.
For personalized advice on sulfamethoxazole dosing and to discuss your specific health needs, consider using Doctronic.ai. This AI-powered telehealth platform offers fast, smart, and personalized medical consultations 24/7. Whether you have questions about dosage adjustments, potential side effects, or need a second opinion, Doctronic’s AI doctor combines the latest peer-reviewed medical research with your personal health history to provide tailored guidance.
Doctronic also offers affordable video visits with licensed doctors across all 50 states, making it easy to get professional medical advice without leaving home. Over 10 million people have trusted Doctronic for their primary care needs, benefiting from its limitless patience and comprehensive medical knowledge.
Sulfamethoxazole is a valuable antibiotic when used correctly. Proper dosing based on your condition, age, and health status is essential to maximize benefits and minimize risks. Always follow your healthcare provider’s instructions and consult them if you have any doubts or experience side effects.
For quick, reliable answers about sulfamethoxazole dosing or to connect with a healthcare professional anytime, visit Doctronic.ai. Personalized care powered by advanced AI can help you manage your treatment confidently and safely.
Sulfamethoxazole is rarely used alone. It is almost always combined with trimethoprim to increase effectiveness and reduce resistance.
Improvement is often seen within 48 to 72 hours, but it is important to complete the full course as prescribed.
Use during pregnancy should be discussed with a healthcare provider, as risks and benefits vary depending on the stage of pregnancy.
Contact your healthcare provider immediately if you experience a severe rash, difficulty breathing, or swelling. For mild side effects, discuss options with your provider.
It is generally recommended to avoid alcohol as it may increase the risk of side effects and reduce antibiotic effectiveness.
Doctronic.ai offers AI-powered personalized medical advice and connects you with licensed doctors for tailored dosing guidance.
Key TakeawaysSulfamethoxazole is commonly used in combination with trimethoprim to treat bacterial infections.Dosage varies depending on the infection type, patient age, and [...]
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