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

Most common
Vomiting (rate not quantified)
Nausea (rate not quantified)
Anorexia (rate not quantified)
Rash (rate not quantified)

Zithromax

Most common
Vomiting (2% to 7%)
Nausea (3% to 18%)
Diarrhea (5% to 14%)
Abdominal pain (3% to 7%)

Bactrim vs. Zithromax Dosage

Bactrim

Dosage
Dosage Table
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

Dosage
Dosage Table
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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