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

Most common
nausea (up to 18%)
vomiting (up to 7%)
loose stools (up to 14%)
abdominal pain (up to 7%)

Keflex

Most common
nausea (rate not specified)
vomiting (rate not specified)
diarrhea (most frequent reported)
dyspepsia (rate not specified)

Azithromycin vs. Keflex Dosage

Azithromycin

Dosage
Dosage Table
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

Dosage
Dosage Table
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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