Augmentin vs. Keflex

See how Augmentin and Keflex compare on approved uses, dosing, side effects, and cost.

Key Takeaways

  • Augmentin adds a beta-lactamase inhibitor that lets it treat infections caused by resistant bacteria that amoxicillin alone cannot clear, while Keflex only works against bacteria that have not developed that resistance mechanism.

  • Both antibiotics are taken by mouth several times a day for one to two weeks, but Augmentin's clavulanate component makes stomach upset and diarrhea somewhat more common.

  • Keflex has a much longer track record, approved in 1971, more than a decade before Augmentin reached the market in 1984.

Augmentin vs. Keflex Drug Summary

Augmentin

Augmentin combines amoxicillin, a penicillin-class antibiotic, with clavulanate, which blocks the bacterial enzymes that would otherwise destroy amoxicillin. It treats bacterial infections of the sinuses, ears, lungs, skin, and urinary tract, including strains resistant to amoxicillin alone. It comes as a tablet, chewable tablet, or liquid suspension taken by mouth every 8 to 12 hours.

Keflex

Keflex is a first-generation cephalosporin antibiotic that stops bacteria from building their cell walls. It treats infections of the respiratory tract, ears, skin, bones, and urinary tract caused by susceptible bacteria. It is taken by mouth as a capsule, tablet, or liquid suspension, typically every 6 to 12 hours depending on the infection.

Augmentin vs. Keflex Side Effects

Augmentin

Most common
Diarrhea (up to 9%)
Nausea (up to 3%)
Vomiting (up to 1%)
Skin rash/urticaria (up to 3%)

Keflex

Most common
Diarrhea (most frequent reaction reported)
Nausea (rate not quantified in current label)
Vomiting (rate not quantified in current label)
Dyspepsia (rate not quantified in current label)

Augmentin vs. Keflex Dosage

Augmentin

Dosage
Dosage Table
STAGE DOSE WHEN
Starting dose 250 mg/125 mg every 8 hrs At the start
Maximum dose 2000 mg/125 mg every 12 hrs If needed
Dose changes 4 increases As tolerated

Keflex

Dosage
Dosage Table
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

Augmentin vs. Keflex Indications

Augmentin

Augmentin is FDA-approved for lower respiratory infections, ear infections, sinus infections, skin infections, and urinary tract infections. The added clavulanate lets it reach bacteria that produce beta-lactamase enzymes, which would otherwise destroy amoxicillin before it can work. It is not approved for viral infections or for patients with a history of penicillin anaphylaxis.

  • Lower respiratory tract infections

  • Acute bacterial otitis media

  • Acute bacterial sinusitis

  • Skin and skin structure infections

  • Urinary tract infections

Keflex

Keflex is FDA-approved for respiratory tract infections, ear infections, skin infections, bone infections, and genitourinary infections. It is also used off-label for surgical site infection prophylaxis, though this is not an FDA-approved indication. It is not effective against Pseudomonas or Acinetobacter species.

  • Respiratory tract infections

  • Otitis media

  • Skin and skin structure infections

  • Bone infections

  • Genitourinary tract infections

Augmentin vs. Keflex Pros and Cons

Augmentin

Augmentin covers a broader range of bacteria than plain amoxicillin because clavulanate disables the enzymes many resistant strains use to survive. This broader coverage comes with a tradeoff: more gastrointestinal side effects and stricter contraindications for people with prior liver reactions to the drug.

Pros

  • Effective against beta-lactamase-producing bacteria that resist amoxicillin alone

  • Available in chewable tablets and pediatric suspension formulations

  • FDA-approved for community-acquired pneumonia in an extended-release form

Cons

  • Higher rate of diarrhea and gastrointestinal upset than many oral antibiotics

  • Contraindicated in patients with prior amoxicillin/clavulanate-associated liver problems

  • Not recommended for anyone with a history of penicillin allergy or anaphylaxis

Keflex

Keflex has decades of clinical use behind it and tends to cause less stomach upset than penicillin-based combinations like Augmentin. Its narrower spectrum means it will not work against bacteria that produce beta-lactamase enzymes, and it requires extra caution in patients with kidney problems or diabetes.

Pros

  • Longer history of use, approved since 1971 with well-established safety data

  • Generally milder gastrointestinal side effect profile than penicillin combinations

  • Safe alternative for patients with penicillin allergy who are not cephalosporin-allergic

Cons

  • Not effective against beta-lactamase-producing resistant bacteria

  • Requires dose adjustment and monitoring in patients with kidney impairment to avoid seizures

  • Can raise metformin levels, requiring blood sugar monitoring in diabetic patients

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