Bactrim vs. Zithromax
See how Bactrim and Zithromax compare on approved uses, dosing, side effects, and cost.
Key Takeaways
Bactrim and Zithromax treat different sets of bacterial infections, so the right choice depends on what is being treated.
Bactrim is typically far less expensive, while Zithromax offers shorter, more convenient treatment courses.
Bactrim carries a higher risk of severe skin reactions, while Zithromax carries a higher risk of heart rhythm problems.
Bactrim vs. Zithromax Drug Summary
Bactrim
Bactrim (sulfamethoxazole/trimethoprim) is a combination antibacterial that blocks two sequential steps in bacterial folate production. It treats urinary tract infections, Pneumocystis pneumonia, and several other bacterial infections. It comes as tablets, oral suspension, or IV injection and is usually taken twice a day.
Zithromax
Zithromax (azithromycin) is a macrolide antibiotic that stops bacteria from making the proteins they need to grow. It treats respiratory infections, skin infections, and certain sexually transmitted infections. It is usually taken as a short oral course, often the five-day 'Z-Pak,' or as a single dose for some infections.
Bactrim vs. Zithromax Side Effects
Bactrim
Zithromax
Bactrim vs. Zithromax Dosage
Bactrim
Zithromax
| STAGE | DOSE | WHEN |
| Starting dose | 800 mg/160 mg every 12h | At the start |
| Maximum dose | 8-10 mg/kg/day div q6-12h | If needed |
| Dose changes | 3 increases | As tolerated |
| STAGE | DOSE | WHEN |
| Starting dose | 500 mg once daily | Day 1 |
| Maximum dose | 30 mg/kg single dose | If needed |
| Dose changes | 5 increases | As tolerated |
Bactrim
| STAGE | DOSE | WHEN |
| Starting dose | 800 mg/160 mg every 12h | At the start |
| Maximum dose | 8-10 mg/kg/day div q6-12h | If needed |
| Dose changes | 3 increases | As tolerated |
Zithromax
| STAGE | DOSE | WHEN |
| Starting dose | 500 mg once daily | Day 1 |
| Maximum dose | 30 mg/kg single dose | If needed |
| Dose changes | 5 increases | As tolerated |
Bactrim vs. Zithromax Indications
Bactrim
Bactrim treats a range of bacterial infections by combining two drugs that block sequential steps in folate synthesis, which bacteria need to grow. It is FDA-approved for urinary tract infections, Pneumocystis pneumonia, and several other conditions, and is sometimes used off-label for MRSA skin infections.
Pneumocystis jirovecii pneumonia (treatment and prevention)
Shigellosis
Urinary tract infections
Acute otitis media in children
Acute exacerbations of chronic bronchitis
Zithromax
Zithromax treats many common bacterial infections by stopping bacteria from producing the proteins they need to survive. It is FDA-approved for respiratory infections, skin infections, certain sexually transmitted infections, and prevention of MAC disease in people with weakened immune systems.
Acute bacterial exacerbations of chronic bronchitis
Community-acquired pneumonia
Acute bacterial sinusitis
Skin and skin structure infections
Chlamydia and gonorrhea urethritis/cervicitis
Bactrim vs. Zithromax Pros and Cons
Bactrim
Bactrim has decades of clinical use and remains one of the most affordable antibiotics available, but it carries meaningful risks for certain patients. It is not appropriate for people with sulfa allergies, G6PD deficiency, or folate-related anemia.
Pros
Costs far less than Zithromax, often $10 to $30 per month
Effective for common infections like UTIs and traveler's diarrhea
Available as tablets, liquid, or IV injection
Used off-label for MRSA skin infections
Cons
Not safe for infants under 2 months old
Carries risk of severe skin reactions like Stevens-Johnson syndrome
Can cause hemolytic anemia in G6PD-deficient patients
Not effective for strep throat
Zithromax
Zithromax is valued for its short treatment courses, including the well-known five-day Z-Pak and single-dose regimens for some infections. It carries a boxed warning for heart rhythm risks and typically costs more than older antibiotics like Bactrim.
Pros
Short 3- to 5-day courses can improve treatment adherence
Single-dose option available for some sexually transmitted infections
Covers atypical respiratory pathogens Bactrim does not treat
Approved for MAC disease prevention in immunocompromised patients
Cons
Carries a boxed warning for QT prolongation and arrhythmia risk
Costs roughly $45 to $150 per treatment course, more than Bactrim
Risk of serious, sometimes fatal, liver toxicity
Can worsen myasthenia gravis symptoms
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