Medically reviewed
Cephalexin and amoxicillin are common beta-lactam antibiotics. Both are broad-spectrum antibiotics, meaning they work against a wide range of bacteria.
They are often used to treat similar types of bacterial infections, but they are not the same.
One thing that is the same: Neither of these antibiotics is used for treating viral infections like colds, the flu, or COVID-19, since antibiotics do not treat viruses.
However, they may be given to address secondary infections in some patients.
In this article, I’ll explain more about what these two medications are—and their similarities and differences.
I’ll talk about the dosages, side effects, and uses of each, as well as other drugs that may interact with cephalexin and amoxicillin.
What is Cephalexin?
Cephalexin is a cephalosporin antibiotic sold under the brand name Keflex.
It’s a first-generation cephalosporin; there are now five generations of this type of antibiotic.
Later generations of cephalosporins are continuing to be developed to treat different kinds of bacteria and address the problem of antibiotic resistance.
Cephalexin is used to treat many common bacterial infections.
It works by disrupting bacterial cell wall growth, which stops them from replicating.
This prevents the infection from continuing.
Cephalexin may be prescribed as a tablet, capsule, or suspension liquid. It may be used in children or adults.
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What is Amoxicillin?
Amoxicillin is an antibiotic in the class of penicillin-like drugs that is sold under brand names including Amoxil and Moxatag.
Amoxicillin is very effective for many bacterial infections, but others may be resistant to it.
It is one of the most commonly prescribed of all medications: More than 50 million prescriptions for amoxicillin are filled in the United States each year.
Amoxicillin works by preventing bacterial growth by destroying the protective cellular exterior.
It is available as a tablet, chewable tablet, capsule, or suspension liquid. It may be given to children and adults.
Usage
Both amoxicillin and cephalexin are used for many common types of bacterial infections.
| Condition | Cephalexin | Amoxicillin |
| Respiratory tract infections | Yes | Yes |
| Sinusitis | Yes | Yes |
| Ear, nose, and throat infections | Yes | Yes |
| Urinary tract infections | Yes | Yes, but only when paired with clavulanate potassium |
| Skin and soft tissue infections | Yes | Yes, typically paired with clavulanate potassium |
| Oral infections | Yes | Yes |
| Lyme disease | No | Yes |
| Stomach ulcers caused by H. pylori bacteria | No | Yes |
| Anthrax exposure | No | Yes |
| Endocarditis prevention | Yes | Yes |
Your healthcare provider may use either of these medications for other purposes.
If you have a bacterial infection, your doctor will choose the antibiotic that is most effective for your medical history, your current infection, allergies, or other health-related factors.
Dosage
Because cephalexin and amoxicillin are different drugs, their dosages are not the same—and they aren’t comparable to each other.
Your doctor will prescribe an effective dosage for you based on your infection severity and type.
Both will typically start to work on your infection within a few days.
Even if you start feeling better, you should not stop taking your prescription until it is complete to avoid the development of bacterial resistance, and to make sure your infection fully clears.
Stopping your antibiotics too soon could also result in a recurrence of your infection.
Cephalexin
Dosages for cephalexin vary based on the type of infection being treated.
Prescriptions for cephalexin are typically for 7-14 days.
- Typical dosage for adults: 1-4 grams daily, divided between 2-4 doses
- Typical dosage for children: 25-50 mg per kilogram of body weight daily, divided between 2-4 doses
Amoxicillin
Dosages for amoxicillin will depend on the type of infection you are being treated for.
Prescriptions for amoxicillin may range from 7-10 days.
- Typical dosage for adults: 750-1750 mg daily, divided between 2-3 doses
- Typical dosage for children: 20-90 mg per kilogram of body weight daily, divided between 2-3 doses
Your doctor will prescribe the appropriate dose and duration to effectively treat your infection.
A dose too low or treatment too short may not completely clear your infection.
Side Effects
Both cephalexin and amoxicillin can cause side effects.
While most are mild, some may be severe or lead to allergic reactions that require emergency medical treatment.
Keep your doctor informed of how you are feeling when you are taking any type of drug.
Common, Mild Side Effects — Cephalexin vs. Amoxicillin
| Side effect | Cephalexin | Amoxicillin |
| Diarrhea | Yes | Yes |
| Abdominal pain | Yes | Less likely |
| Indigestion | Yes | Less likely |
| Vomiting | Yes | Yes |
| Nausea | Yes | Yes |
| Headache | Yes | Yes |
| Fatigue | Yes | Less likely |
| Vaginal discharge or itchiness | Yes | Yes |
| Increased creatinine levels | Yes | Yes |
| Changes in taste | Less likely | Yes |
Less Common, More Serious Side Effects — Cephalexin vs. Amoxicillin
| Side effect | Cephalexin | Amoxicillin |
| Anaphylaxis | Possible | Possible |
| Hives | Possible | Possible |
| Trouble breathing | Possible | Possible |
| Swelling of the face, lips, tongue, eyes, or throat | Possible | Possible |
| Trouble swallowing | Possible | Possible |
| Skin blisters | Possible | Possible |
| Severe diarrhea or bloody stools | Possible | Possible |
| Severe stomach cramps | Possible | Possible |
Drug Interactions
Most medications can interact with other drugs.
It’s important to understand how all of your medications can affect each other to avoid serious side effects or decreased effectiveness.
Your pharmacist will go over potential interactions.
Make sure your healthcare provider knows everything you take, including OTC medications, dietary supplements, and herbs.
Drug Interactions — Cephalexin vs. Amoxicillin
| Drug Interacts with: | Cephalexin | Amoxicillin |
| Metformin | Yes | No |
| Blood thinners | Yes | Yes |
| Furosemide | Possibly | No |
| Probenecid | Yes | Yes |
| Allopurinol | No | Yes |
| Other antibiotics | Yes | Yes |
| Oral contraceptives | No | No |
If you have kidney or liver diseases, talk to your healthcare provider about whether amoxicillin or cephalexin are safe for you to use.
Antibiotics online
Our physicians can prescribe antibiotics for various conditions, but only if necessary. Chat with a provider now.
When to See a Doctor
If you have any symptoms of a bacterial infection, including fever, burning during urination, bleeding gums, or if you are otherwise feeling unwell, check in with your healthcare provider for personalized medical advice.
If your symptoms are caused by a bacterial infection, you will most likely need antibiotics to recover.
If bacterial illnesses go untreated, they can result in more serious infections.
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Frequently Asked Questions
K Health has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical associations. We avoid using tertiary references.
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Review of the spectrum and potency of orally administered cephalosporins and amoxicillin/clavulanate. (2007).
https://pubmed.ncbi.nlm.nih.gov/17292577/ -
Cephalexin. (2016).
https://medlineplus.gov/druginfo/meds/a682733.html -
Keflex. (2018).
https://www.accessdata.fda.gov/drugsatfda_docs/label/2018/050405s107lbl.pdf -
Amoxicillin. (2020).
https://medlineplus.gov/druginfo/meds/a685001.html -
Amoxil. (2015).
https://www.accessdata.fda.gov/drugsatfda_docs/label/2015/50542s02950754s01950760s01950761s016lbl.pdf -
Comparative study of cefaclor and amoxicillin in treatment of urinary tract infection. (1979).
https://pubmed.ncbi.nlm.nih.gov/384643/
