A tooth infection, also called a dental abscess, is a pocket of pus caused by bacteria invading the tissue around a tooth. It does not go away on its own. Without antibiotics, the bacteria can spread to your jaw, neck, or bloodstream. Cephalexin (the generic form of the now-discontinued brand Keflex) is one antibiotic a dentist or doctor may prescribe, though it is not the first choice for everyone.
Is Cephalexin a Good Antibiotic for a Tooth Infection?
Cephalexin is effective against many of the bacteria that cause dental abscesses, but it is not the first-line treatment for most patients. According to the American Dental Association (ADA) guidelines on antibiotic use for dental pain and swelling, amoxicillin or penicillin V potassium is prescribed first for patients without a penicillin allergy.
Cephalexin is specifically recommended by the ADA for patients with a mild penicillin allergy (such as a minor rash), as an alternative to the standard first-line drugs. It is a first-generation cephalosporin antibiotic that works by blocking bacteria from building cell walls, which causes the bacteria to die.
One important limitation: a 2024 study published in PMC found that cephalexin’s activity against some anaerobic oral bacteria is not well described, and clinicians are advised to have a low threshold to add metronidazole if a patient shows a slow response to cephalexin alone.
*Do not take cephalexin if you have a history of anaphylaxis or angioedema from penicillin.
In those cases, the ADA recommends azithromycin or clindamycin instead. Cephalexin shares structural similarities with penicillin and carries a risk of cross-reactivity in patients with severe penicillin allergy.
Cephalexin 500mg for Tooth Infection: The ADA-Recommended Dosage
The ADA-recommended dosage for cephalexin in adults with a mild penicillin allergy is:
500 mg taken four times per day, for 3 to 7 days.
This adds up to 2 grams per day. Most dentists prescribe this for 3 to 5 days, not 7 to 10 days. Research consistently shows that shorter courses deliver equivalent outcomes for dental infections while reducing the risk of antibiotic resistance and C. difficile diarrhea. Per updated ADA guidance reported by Coastal Periodontics, prescriptions exceeding five days should be the exception, not the rule.
Dosage by scenario:
| Patient Type | Dose | Frequency | Duration |
| Adult, mild penicillin allergy | 500 mg | 4 times daily | 3 to 5 days |
| Severe or complex infections | Discuss with your provider | May require a different antibiotic | Varies |
| Children | Based on body weight | As prescribed | As prescribed |
A few practical notes on taking it correctly:
- Cephalexin is available as capsules, tablets, and liquid suspension.
- You can take it with or without food. If it causes stomach upset, take it with food. Avoid spicy or acidic foods, which can worsen nausea.
- Take each dose at roughly the same time each day to maintain steady levels in your bloodstream.
- Stopping early can allow surviving bacteria to cause a rebound infection that is harder to treat.
The ADA also recommends that your dentist re-evaluate you within 3 days. If your symptoms have resolved, you can stop antibiotics 24 hours later, even if the original course was longer. Do not double up if you miss a dose. Take it as soon as you remember, unless the next dose is soon.
How Long Does Cephalexin Take to Work for a Tooth Infection?
Most patients begin noticing improvement within 2 to 3 days of starting cephalexin. Significant pain reduction and decreased swelling typically occur within the first 3 to 5 days of treatment.
A real-world study published in Drugs: Real World Outcomes confirmed a treatment window of 3 to 7 days for cephalexin in dental infections under standard dosing protocols.
Contact your dentist or doctor if:
- You see no improvement after 3 days of taking it correctly
- Your symptoms get noticeably worse at any point
- You develop difficulty swallowing, severe facial swelling, or fever above 101°F
These are signs the infection may be spreading and require immediate evaluation. Do not wait until the course finishes.
One critical point: antibiotics like cephalexin treat the bacterial infection, but they do not resolve the underlying dental problem. A tooth abscess requires drainage and dental treatment, such as a root canal, extraction, or surgical drainage, to permanently eliminate the source of infection. Antibiotics alone are not a cure.
Cephalexin Side Effects for Tooth Infection Treatment
Most side effects are mild and resolve once the course ends. The most common side effects include:
- Diarrhea
- Nausea
- Stomach pain
- Headache
- Fatigue or dizziness
- Vaginal yeast infection (in women)
Managing mild side effects: Taking cephalexin with food reduces nausea. Mild diarrhea typically clears up after finishing the course. Staying hydrated and eating regularly helps.
Serious side effects to watch for:
- Severe diarrhea with fever or stomach cramps: This can be a sign of C. difficile (C. diff) infection, a bacterial overgrowth triggered by antibiotics. Seek medical care immediately.
- Rash, hives, swelling of the face or throat, or difficulty breathing: These are signs of a serious allergic reaction. Go to the emergency room or call emergency services immediately.
- Seizures or unusual bleeding: These are rare but require urgent medical attention.
Drug interactions: Cephalexin can interact with metformin (commonly used for diabetes) and probenecid (used for gout). Tell your prescriber about all medications you are taking before starting cephalexin.
Avoid alcohol during treatment. It does not reduce the antibiotic’s effectiveness directly, but it can worsen nausea and make it harder for your body to recover.
Amoxicillin vs Cephalexin for Tooth Infection: Which is Better?
This is one of the most commonly searched questions about dental antibiotics, and the answer depends on your allergy history.
| Amoxicillin | Cephalexin | |
| ADA recommendation | First-line treatment | Alternative for mild penicillin allergy |
| Drug class | Penicillin antibiotic | Cephalosporin antibiotic |
| Standard dose (adult) | 500 mg, 3 times daily | 500 mg, 4 times daily |
| Duration | 3 to 7 days | 3 to 7 days |
| Suitable for penicillin allergy? | No | Yes, for mild allergy only |
| Suitable for severe penicillin allergy? | No | No (cross-reactivity risk) |
| Anaerobic coverage | Broader | Moderate (may need metronidazole added) |
| Cost (generic) | Very low | As low as $8.65 for a standard course |
The bottom line: if you have no penicillin allergy, amoxicillin or penicillin V potassium is the preferred choice because it has broader coverage against the specific bacteria found in dental infections. Cephalexin is the go-to alternative specifically for patients with a mild penicillin allergy who cannot take amoxicillin.
If you have a severe penicillin allergy (anaphylaxis, hives, or angioedema), neither amoxicillin nor cephalexin is appropriate. The ADA recommends azithromycin or clindamycin for those patients.
What Happens If a Tooth Infection Is Left Untreated?
A dental abscess will not resolve on its own. If you do not treat it, the bacterial infection can spread in stages, each more serious than the last.
According to Mayo Clinic’s overview of tooth abscess complications, an untreated abscess can spread to the jaw and other areas of the head and neck. It can also cause a sinus infection if the affected tooth sits near the maxillary sinus. In the most serious cases, bacteria enter the bloodstream and trigger sepsis, a life-threatening systemic response where the body’s immune system begins attacking its own tissues.
Warning signs that the infection is spreading and requires immediate emergency care:
- Fever above 101°F (38.3°C)
- Severe swelling in the face, jaw, or neck
- Difficulty swallowing or breathing
- Rapid heart rate or confusion
- Swollen lymph nodes under your jaw
These are emergency symptoms. Do not call a telehealth service for these. Go to an emergency room.
How Much Does Cephalexin Cost for a Tooth Infection?
Cephalexin is an affordable generic antibiotic. According to GoodRx pricing data (updated May 2026), the average retail price for a standard course of cephalexin is approximately $29.18, but with a free GoodRx coupon, you can pay as little as $8.65.
Prices vary by pharmacy, so comparing at your local pharmacies or using the GoodRx tool before picking up your prescription is worth the two minutes it takes.
Most Medicare and insurance plans cover generic cephalexin. All pricing reflects US figures as of May 2026. Verify current pricing with your pharmacist.
When to See a Doctor for a Tooth Infection
A tooth infection requires a prescription antibiotic. You cannot treat it with over-the-counter medications, and it will not go away on its own.
You need to see a dentist or doctor if you have:
- Persistent throbbing toothache that does not improve with OTC pain relievers
- Visible swelling in the gum, jaw, or face
- Sensitivity to hot or cold that lingers after the temperature source is removed
- Fever, even a mild one
- A bad taste in your mouth that suggests pus draining from the tooth
You can get a prescription for cephalexin or another dental antibiotic through an online doctor consultation if your symptoms do not suggest the emergency signs listed above. Talk to a doctor online at Your Doctors Online to get evaluated and receive a prescription without waiting for an in-person appointment.
Frequently Asked Questions
Yes, cephalexin is effective against many of the bacteria that cause dental abscesses and gum infections. However, it is not the first-choice antibiotic for most patients. The ADA recommends it specifically as an alternative for patients with a mild penicillin allergy. It may also need to be combined with metronidazole if you do not respond well to it alone, given its limited coverage of certain anaerobic oral bacteria.
The ADA-recommended dosage is 500 mg four times per day (every six hours), typically for 3 to 5 days. Take it at evenly spaced times throughout the day to maintain consistent antibiotic levels. Always follow the specific instructions your dentist or doctor gives you.
Most patients notice improvement within 2 to 3 days. Significant reduction in pain and swelling typically occurs within 3 to 5 days. If you see no improvement after 3 days, contact your provider rather than waiting.
No, this is the standard ADA-recommended dose for dental infections. It totals 2 grams per day, which is within the normal therapeutic range. It is not a high dose. The frequency (four times daily) is what allows cephalexin to maintain effective levels in your bloodstream throughout the day.
No. If you miss a dose, do not double up on your next dose to compensate. Taking two doses at once increases your risk of side effects without improving treatment outcomes. Simply take the missed dose as soon as you remember, or skip it if the next scheduled dose is approaching.
Typically 3 to 5 days. The ADA no longer recommends 7 to 10-day courses for most dental infections, as research shows shorter courses are equally effective and carry less risk of antibiotic resistance and side effects. Your dentist may prescribe up to 7 days for a severe infection.
Cephalexin can treat the bacterial infection associated with an abscess, but it cannot drain or remove the abscess itself. The abscess needs physical drainage by a dentist, followed by dental treatment (root canal or extraction) to eliminate the source. Antibiotics manage the bacteria, but dental intervention is required to prevent recurrence.
Yes. Keflex is generically known as cephalexin.
