Cephalexin vs amoxicillin: antibiotics compared
Amoxicillin, a penicillin, and cephalexin (Keflex), a cephalosporin, are two of the most prescribed antibiotics. Amoxicillin is a first choice for ear, sinus and throat infections; cephalexin is a first choice for many skin infections and an option for some people with a penicillin allergy.
Updated October 4, 2026
At a glance
- Antibiotic family
- Cephalexin
- First-generation cephalosporin
- Amoxicillin
- Penicillin
- Common uses
- Cephalexin
- Skin infections, some urinary infections, strep throat
- Amoxicillin
- Ear, sinus and throat infections, some pneumonia, H. pylori treatment
- How often
- Cephalexin
- Two to four times a day
- Amoxicillin
- Two or three times a day
- Liquid storage
- Cephalexin
- Refrigerate; discard after 14 days
- Amoxicillin
- Refrigeration preferred; discard after 14 days
- Generic
- Cephalexin
- Yes
- Amoxicillin
- Yes
Cephalexin Keflex | Amoxicillin Amoxil | |
|---|---|---|
| Antibiotic family | First-generation cephalosporin | Penicillin |
| Common uses | Skin infections, some urinary infections, strep throat | Ear, sinus and throat infections, some pneumonia, H. pylori treatment |
| How often | Two to four times a day | Two or three times a day |
| Liquid storage | Refrigerate; discard after 14 days | Refrigeration preferred; discard after 14 days |
| Generic | Yes | Yes |
Matching the antibiotic to the infection
Each antibiotic covers particular bacteria. Amoxicillin works well against the usual causes of ear, sinus and throat infections, while cephalexin covers the staph and strep bacteria behind most simple skin infections. Neither treats viral infections such as colds or flu, and taking an antibiotic you do not need adds side effects without benefit.
Penicillin allergy
Many people with a penicillin allergy label can take cephalexin, because cross-reactions are uncommon, but the risk is not zero. If you have had a severe reaction to a penicillin, such as swelling of the throat, trouble breathing or a blistering rash, tell your prescriber, who may choose a different antibiotic. Many penicillin allergy labels turn out to be wrong when tested, which is worth discussing.
Side effects
Both commonly cause diarrhea and nausea. Severe or bloody diarrhea, during or even weeks after a course, can signal a serious bowel infection and needs prompt care. Stop and seek help for hives, facial swelling or breathing trouble. Finish the course as prescribed even if you feel better.
Cost
Both are inexpensive generics. Liquids for children usually cost more than capsules.
Missed doses
Take a missed dose as soon as you remember unless the next one is near, and never double up. Spacing doses evenly through the day keeps antibiotic levels steady, which matters more than the exact times you choose.
Questions for your prescriber
- Is this infection likely to be bacterial?
- Is my penicillin allergy label accurate, and does it matter for this antibiotic?
- What should I do if I feel no better in a few days?
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Sources
Written by the Script Unlock editorial team from the sources above. It is general information, not advice for you or your pet; your prescriber decides which medicine is right.
Script Unlock is a marketplace that lets licensed pharmacies quote a cash price on your prescription. It does not prescribe, dispense or sell medication, does not process patient payments, and does not give medical advice. Always follow the instructions of your prescriber and pharmacist and read the medication guide supplied with your medicine.