Keflex vs. Zithromax
See how Keflex and Zithromax compare on approved uses, dosing, side effects, and cost.
Key Takeaways
Keflex is a first-generation cephalosporin usually taken multiple times a day for one to two weeks, while Zithromax is a macrolide often given as a short five-day or single-dose course.
Both drugs can cause stomach upset, but Zithromax carries specific FDA warnings about heart rhythm changes and liver damage that Keflex does not share.
Keflex is commonly used for skin, bone, and urinary infections, while Zithromax is often chosen for respiratory infections and certain sexually transmitted infections.
Keflex vs. Zithromax Drug Summary
Keflex
Keflex (cephalexin) is a first-generation cephalosporin antibiotic used for infections like strep throat, ear infections, skin infections, and urinary tract infections. It works by weakening bacterial cell walls and is usually taken as a capsule, tablet, or liquid several times a day for one to two weeks.
Zithromax
Zithromax (azithromycin) is a macrolide antibiotic used for infections like pneumonia, sinusitis, skin infections, and certain sexually transmitted infections. It works by blocking bacterial protein production and is often taken as a short five-day course or a single dose because it stays in tissue longer than most antibiotics.
Keflex vs. Zithromax Side Effects
Keflex
Zithromax
Keflex vs. Zithromax Dosage
Keflex
Zithromax
| STAGE | DOSE | WHEN |
| Starting dose | 25-50 mg/kg/day divided | At the start |
| Maximum dose | up to 4 g/day divided | 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 |
Keflex
| STAGE | DOSE | WHEN |
| Starting dose | 25-50 mg/kg/day divided | At the start |
| Maximum dose | up to 4 g/day divided | 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 |
Keflex vs. Zithromax Indications
Keflex
Keflex is FDA-approved for common bacterial infections including respiratory tract infections, ear infections, skin infections, bone infections, and urinary tract infections. It is not effective against Pseudomonas or Acinetobacter bacteria, so doctors reserve it for infections caused by susceptible organisms.
Respiratory tract infections
Otitis media (ear infections)
Skin and skin structure infections
Bone infections
Genitourinary tract infections
Zithromax
Zithromax is FDA-approved for infections such as pneumonia, bronchitis flare-ups, sinusitis, skin infections, and certain sexually transmitted infections like chlamydia and gonorrhea. It is also used to prevent and treat MAC infections in people with advanced HIV, but it is not effective against viral illnesses.
Community-acquired pneumonia
Acute bacterial sinusitis
Skin and skin structure infections
Chlamydia and gonorrhea infections
MAC disease prevention and treatment
Keflex vs. Zithromax Pros and Cons
Keflex
Keflex has a long track record of safety and predictable dosing, and it does not carry the heart rhythm warnings seen with macrolides. It does require more frequent daily dosing and a longer overall course, and it isn't effective against certain resistant or atypical bacteria.
Pros
Long-established safety record since 1971
No FDA warning for heart rhythm effects
Effective against common skin and bone bacteria
No black-box-level liver toxicity warning
Cons
Requires dosing 2 to 4 times daily
Typical course runs 7 to 14 days
Not effective against atypical bacteria like chlamydia
Not effective against Pseudomonas or Acinetobacter
Zithromax
Zithromax's long tissue half-life allows short five-day or even single-dose treatment courses, which can improve adherence for some infections. It carries FDA warnings for heart rhythm changes and rare but serious liver toxicity that Keflex does not carry.
Pros
Short courses, often just 5 days or one dose
Covers atypical bacteria like chlamydia and mycoplasma
Convenient once-daily dosing
Effective for certain sexually transmitted infections
Cons
FDA warning for QT prolongation and arrhythmia risk
Rare but serious liver toxicity warning
Risk factor for cardiovascular death in some patients
Not first-line for skin or bone infections
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