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Sulfonamide Antibiotic Combination🔒 Prescription only

What Is Bactrim (Trimethoprim-Sulfamethoxazole) Used For?

Brand names: Bactrim, Septra, Co-trimoxazole

Trimethoprim-sulfamethoxazole (Bactrim, Co-trimoxazole) is a combination antibiotic that treats urinary tract infections, ear infections, and certain resistant bacterial infections.

What is Trimethoprim-Sulfamethoxazole used for?

Urinary tract infections (UTIs) — first-line treatment
Ear infections (otitis media)
MRSA skin infections
Pneumocystis pneumonia (PCP) in immunocompromised patients
Traveller's diarrhea
Shigellosis

How does Trimethoprim-Sulfamethoxazole work?

The two components block two sequential steps in bacterial folate synthesis — a nutrient bacteria must make themselves. By blocking both steps, the combination is more effective than either drug alone and bacteria find it harder to develop resistance.

Dosage information

💊Available forms

80mg/400mg (single strength) tablets
160mg/800mg (double strength DS) tablets
200mg/40mg per 5ml suspension

📏Typical dosage

UTI: 1 DS tablet (160/800mg) twice daily for 3–7 days. Dosing frequency and duration vary by infection. Take with a full glass of water.

⚠️ Dosage varies by individual. Always follow your doctor's or pharmacist's instructions — never self-dose based on general information.

Side effects

Common

Nausea and vomiting
Skin rash
Sun sensitivity
Loss of appetite
Diarrhea

⚠️ Serious — contact your doctor

Severe skin reactions — Stevens-Johnson syndrome (stop immediately for rash with blistering or peeling)
High potassium levels (especially in the elderly or those on ACE inhibitors)
Kidney damage
Blood disorders
Liver damage

Important warnings

Drink plenty of water throughout treatment — can cause kidney crystal formation

Stop immediately and seek care for any blistering skin rash

High potassium risk — avoid potassium supplements and salt substitutes

Avoid in severe kidney or liver disease

Use with caution in the elderly

Drug interactions

These substances may interact with Trimethoprim-Sulfamethoxazole. This is not a complete list — always tell your doctor and pharmacist ALL medications and supplements you take.

ACE inhibitors and ARBs (high potassium risk)Warfarin (greatly increases bleeding risk)Methotrexate (toxic levels)Phenytoin (increased phenytoin levels)Digoxin

Pregnancy & breastfeeding

🤰 Avoid in first trimester and near delivery — discuss with your doctor

Always consult your doctor or obstetrician before taking any medication during pregnancy or while breastfeeding.

Frequently asked questions

What is Bactrim (Co-trimoxazole) used for?

Bactrim treats bacterial infections including UTIs, ear infections, MRSA skin infections, and certain pneumonias in immunocompromised patients.

How much water should I drink with Bactrim?

Drink at least 6–8 glasses of water daily while taking Bactrim. It can form crystals in the kidneys if you're dehydrated.

Why did I get a rash on Bactrim?

Skin rashes are relatively common with Bactrim. A mild rash may be managed with antihistamines, but any rash involving blistering, peeling, or mucous membranes is an emergency — stop the medication and go to hospital immediately.

Can I take Bactrim for a UTI?

Bactrim is a first-line treatment for uncomplicated UTIs in many countries, though resistance rates vary by region. A 3-day course is typical for uncomplicated cases.

Is Bactrim safe during pregnancy?

Avoid Bactrim in the first trimester and at term (near delivery). It can interfere with folate which is critical in early pregnancy, and can cause newborn jaundice near delivery.

Related medications

💊AmoxicillinPenicillin-type Antibiotic 💊AzithromycinMacrolide Antibiotic 💊DoxycyclineTetracycline Antibiotic 💊IbuprofenNSAID

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This is an information resource — not medical advice.

🚨 If you are experiencing a medical emergency or think you may have taken too much of a medication, call emergency services (911 in the US) or go to your nearest emergency room immediately.

Information on this page is sourced from general pharmaceutical references and is provided for educational purposes only. Drug information may change — always verify with your pharmacist or prescriber. PillCodex.com is not affiliated with any pharmaceutical company.