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

Most common
Abdominal pain (not specified)
Vomiting (not specified)
Nausea (not specified)
Diarrhea (not specified)

Zithromax

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

Cephalexin vs. Zithromax Dosage

Cephalexin

Dosage
Dosage Table
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

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

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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