Azithromycin vs. Keflex
See how Azithromycin and Keflex compare on approved uses, dosing, side effects, and cost.
Key Takeaways
Azithromycin is a macrolide usually taken for 3 to 5 days, while Keflex is a cephalosporin typically taken for 7 to 14 days.
Both treat respiratory and skin infections, but azithromycin also covers atypical bacteria and certain sexually transmitted infections that Keflex does not treat.
Azithromycin carries an FDA warning for heart rhythm changes, while Keflex requires dose adjustments in kidney disease and is unsafe for patients allergic to cephalosporins.
Azithromycin vs. Keflex Drug Summary
Azithromycin
Azithromycin is a macrolide (azalide) antibiotic used to treat bacterial infections such as pneumonia, sinusitis, and certain skin and sexually transmitted infections. It comes as a tablet, oral suspension, or IV infusion, and its long tissue half-life allows short courses, often just 3 to 5 days or a single dose.
Keflex
Keflex (cephalexin) is a first-generation cephalosporin antibiotic used for respiratory, skin, bone, and urinary tract infections. It is taken as an oral capsule, tablet, or suspension, usually several times a day for 7 to 14 days depending on the infection.
Azithromycin vs. Keflex Side Effects
Azithromycin
Keflex
Azithromycin vs. Keflex Dosage
Azithromycin
Keflex
| STAGE | DOSE | WHEN |
| Starting dose | 500 mg once | Day 1 |
| Maximum dose | 5 mg/kg once daily | Days 2-5 |
| Dose changes | 4 increases | As tolerated |
| STAGE | DOSE | WHEN |
| Starting dose | 25-50 mg/kg/day | At the start |
| Maximum dose | 25-50 mg/kg/day | Same as starting |
| Dose changes | None | Fixed dose |
Azithromycin
| STAGE | DOSE | WHEN |
| Starting dose | 500 mg once | Day 1 |
| Maximum dose | 5 mg/kg once daily | Days 2-5 |
| Dose changes | 4 increases | As tolerated |
Keflex
| STAGE | DOSE | WHEN |
| Starting dose | 25-50 mg/kg/day | At the start |
| Maximum dose | 25-50 mg/kg/day | Same as starting |
| Dose changes | None | Fixed dose |
Azithromycin vs. Keflex Indications
Azithromycin
Azithromycin is FDA-approved for a range of bacterial infections, including community-acquired pneumonia, sinusitis, and pharyngitis. It also treats certain sexually transmitted infections and pelvic inflammatory disease, and is sometimes used off-label for traveler's diarrhea.
Community-acquired pneumonia
Acute bacterial sinusitis
Pharyngitis and tonsillitis
Urethritis, cervicitis, and chancroid
Pelvic inflammatory disease
Keflex
Keflex is FDA-approved for respiratory tract infections, ear infections, and skin infections. It also treats bone and genitourinary tract infections, and is sometimes used off-label to prevent surgical site infections.
Respiratory tract infections
Otitis media
Skin and skin structure infections
Bone infections
Genitourinary tract infections
Azithromycin vs. Keflex Pros and Cons
Azithromycin
Azithromycin's short 3-to-5-day or single-dose regimens are easier for many patients to complete than longer antibiotic courses. It also covers atypical bacteria that Keflex cannot treat, though it carries a heart-rhythm warning that Keflex does not share.
Pros
Short 3-to-5-day or single-dose regimens
Covers atypical bacteria like Chlamydia and Mycoplasma
Effective for chancroid and pelvic inflammatory disease
Generic course often costs less than Keflex ($15 to $50 vs $53 to $95)
Cons
QT prolongation and heart rhythm risk warning
Risk of serious, sometimes fatal liver injury
Serious hypersensitivity reactions including anaphylaxis
Rare pyloric stenosis risk reported in infants
Keflex
Keflex has been used safely for decades and is a reliable choice for skin, bone, and urinary infections. It requires more frequent daily dosing over a longer course than azithromycin, and it is not an option for patients with a cephalosporin allergy.
Pros
Long track record of safety since 1971
Effective for bone and urinary tract infections
No QT-prolongation warning on its label
Lower risk of serious liver toxicity
Cons
Requires dosing multiple times per day
Longer 7-to-14 day treatment course
Contraindicated in patients with cephalosporin allergy
Typical course costs $53 to $95, more than generic azithromycin ($15 to $50)
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