Amoxicillin vs. Keflex

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

Key Takeaways

  • Amoxicillin and Keflex (cephalexin) are both oral antibiotics used to treat many of the same bacterial infections, including ear, skin, and urinary tract infections.

  • Amoxicillin is usually dosed every 8 to 12 hours, while standard Keflex dosing is every 6 hours, which can make Amoxicillin easier to fit into a daily routine.

  • Amoxicillin generally costs less than Keflex, but Keflex is a useful option for patients with a penicillin allergy who are not also allergic to cephalosporins.

Amoxicillin vs. Keflex Drug Summary

Amoxicillin

Amoxicillin is an aminopenicillin antibiotic used to treat infections of the ear, nose, throat, lungs, skin, and urinary tract, as well as gonorrhea and, in combination regimens, H. pylori. It's taken orally as a capsule, tablet, chewable tablet, or liquid suspension, usually two to three times a day.

Keflex

Keflex (cephalexin) is a first-generation cephalosporin antibiotic used to treat infections of the respiratory tract, ears, skin, bones, and urinary system. It's taken orally as a capsule, tablet, or liquid suspension, typically every 6 to 12 hours depending on how severe the infection is.

Amoxicillin vs. Keflex Side Effects

Amoxicillin

Most common
Vomiting (greater than 1%)
Nausea (greater than 1%)
Diarrhea (greater than 1%)
Rash (greater than 1%)

Keflex

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

Amoxicillin vs. Keflex Dosage

Amoxicillin

Dosage
Dosage Table
STAGE DOSE WHEN
Starting dose 250 mg every 8 hours At the start
Maximum dose 1 g three times daily 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

Amoxicillin vs. Keflex Indications

Amoxicillin

Amoxicillin is FDA-approved for a wide range of common bacterial infections, from ear and sinus infections to urinary tract infections and gonorrhea. It's also used as part of combination therapy to eradicate H. pylori, the bacteria linked to stomach ulcers.

  • Ear, nose, and throat infections

  • Lower respiratory tract infections

  • Skin and skin structure infections

  • Urinary tract infections

  • Gonorrhea and H. pylori eradication (combination therapy)

Keflex

Keflex is FDA-approved for infections of the respiratory tract, skin, bones, and urinary system, and it's also used for middle ear infections. It's sometimes used off-label to help prevent infection during certain surgeries.

  • Respiratory tract infections

  • Middle ear infections (otitis media)

  • Skin and skin structure infections

  • Bone infections

  • Genitourinary tract infections

Amoxicillin vs. Keflex Pros and Cons

Amoxicillin

Amoxicillin has one of the broadest FDA-approved indication lists among oral antibiotics and is typically well tolerated with predictable, low side-effect rates. It's also one of the least expensive antibiotics available, though it's not an option for anyone with a penicillin allergy.

Pros

  • Approved for gonorrhea and H. pylori, unlike Keflex

  • Some regimens allow twice-daily dosing (every 12 hours)

  • Typically costs $11 to $25 per month, much less than Keflex

  • Long track record with well-quantified side effect rates

Cons

  • Not an option for patients with a penicillin allergy

  • Higher risk of rash if given during mono infection

  • Some regimens require dosing every 8 hours

  • Not effective against Pseudomonas or similar resistant bacteria

Keflex

Keflex offers an alternative for patients who can't take penicillins, as long as they don't also have a cephalosporin allergy. It's specifically approved for bone infections and is sometimes used off-label to help prevent surgical site infections.

Pros

  • Alternative for some patients with penicillin allergy

  • FDA-approved specifically for bone infections

  • Used off-label for surgical infection prevention

  • Higher max dose (up to 4 g/day) for severe infections

Cons

  • Typically costs $53 to $95 for a 20-capsule course

  • Standard dosing is every 6 hours, more frequent than Amoxicillin

  • Seizure risk if it accumulates in kidney impairment

  • Can raise metformin levels, requiring blood sugar monitoring

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