Cephalexin vs. Zithromax
See how Cephalexin and Zithromax compare on approved uses, dosing, side effects, and cost.
Key Takeaways
Cephalexin and Zithromax are both antibiotics for bacterial infections, but they belong to different drug classes and target different bacteria.
Cephalexin usually requires multiple daily doses for 7 to 14 days, while Zithromax often works in a short 3 to 5 day course or a single dose.
Zithromax carries an FDA warning for heart rhythm problems that cephalexin does not, which may matter for people with cardiac risk factors.
Cephalexin vs. Zithromax Drug Summary
Cephalexin
Cephalexin is a first-generation cephalosporin antibiotic used to treat bacterial infections of the skin, respiratory tract, ears, bones, and urinary tract. It comes as a capsule, tablet, or oral liquid and is typically taken multiple times a day for 7 to 14 days.
Zithromax
Zithromax (azithromycin) is a macrolide antibiotic used to treat bacterial infections including pneumonia, sinusitis, skin infections, and certain sexually transmitted infections. It's usually taken as a short 5-day course or single dose, since it stays active in tissue long after the last pill.
Cephalexin vs. Zithromax Side Effects
Cephalexin
Zithromax
Cephalexin vs. Zithromax Dosage
Cephalexin
Zithromax
| STAGE | DOSE | WHEN |
| Starting dose | 25-50 mg/kg/day divided | At the start |
| Maximum dose | 1 to 4 g/day divided | If needed |
| Dose changes | 4 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 |
Cephalexin
| STAGE | DOSE | WHEN |
| Starting dose | 25-50 mg/kg/day divided | At the start |
| Maximum dose | 1 to 4 g/day divided | If needed |
| Dose changes | 4 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 |
Cephalexin vs. Zithromax Indications
Cephalexin
Cephalexin treats bacterial infections caused by susceptible strains of streptococci, staphylococci, and certain gram-negative bacteria. It is FDA-approved for a range of common outpatient infections affecting the skin, ears, respiratory tract, bones, and urinary tract.
Respiratory tract infections
Otitis media (ear infections)
Skin and skin structure infections
Bone infections
Genitourinary infections, including prostatitis
Zithromax
Zithromax treats bacterial infections caused by susceptible organisms, including atypical bacteria like Chlamydia. It is FDA-approved for respiratory and skin infections, certain sexually transmitted infections, and prevention of MAC disease in people with advanced HIV.
Community-acquired pneumonia
Acute bacterial sinusitis
Skin and skin structure infections
Chlamydia and gonorrhea urethritis/cervicitis
MAC disease prevention in advanced HIV
Cephalexin vs. Zithromax Pros and Cons
Cephalexin
Cephalexin has a decades-long safety record and doesn't carry the cardiac warnings seen with some newer antibiotics, though it requires more frequent dosing over a longer course. It remains one of the least expensive oral antibiotics available.
Pros
Long, well-established safety record since the early 1970s
No FDA warning for heart rhythm problems
Typically costs less: $10 to $65 per course, before insurance
Effective option for bone and joint infections
Cons
Requires dosing 2 to 4 times a day, harder to remember
Longer treatment courses, often 7 to 14 days
Not effective against atypical bacteria like Chlamydia
Dose must be adjusted for reduced kidney function
Zithromax
Zithromax's long tissue half-life allows shorter treatment courses, including single-dose options for some infections, but it carries FDA warnings for heart rhythm and liver risks. It offers dosing convenience at a higher price than many older antibiotics.
Pros
Short courses, often 3 to 5 days or a single dose
Effective against atypical bacteria like Chlamydia
Long-lasting tissue levels keep working after the last dose
Single-dose regimens available for certain STIs
Cons
FDA warning for QT prolongation and heart rhythm risk
Rare but serious risk of liver toxicity
Can worsen symptoms in people with myasthenia gravis
Typically costs more: $45 to $150 per course, before insurance
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