How long does it take for Keflex to work on tooth infections? 

In this article, we will discuss the approximate time taken by Keflex (Cephalexin), a Cephalosporin antibiotic, to work on tooth infections. We will also discuss the dosage instructions and some potential side effects of this antibiotic when used for a tooth infection.

How long does it take for Keflex to work on tooth infections? 

Keflex (Cephalexin) can take around 3-10 days to work on tooth infections, depending on the severity of the infection. Most people begin to feel better on day 3 and may experience significant pain relief – especially people with a mild tooth infection (1). 

For more severe infections, Keflex might not be the best antibiotic and even if it is used, it can take up to 5 days to show symptomatic relief. However, it is important to know that getting better on day 2 or 3 of taking your antibiotic does not indicate that the infection has gone. 

That’s not how it works. You need to make sure that you take Keflex for as long as your doctor has advised you to. This ensures that your infection has been properly treated with complete eradication of the infection-causing bacteria. 

Sometimes, the infection might seem to get better way before your antibiotic course is completed, but that’s not true. 

Leaving your treatment at this stage can affect you, as the bacteria will start to multiply again, and soon your symptoms will start to come back – and they might come back even stronger. 

This is one of the main reasons why people develop resistance to antibiotics (2). So, never leave your antibiotic treatment halfway, no matter which one you’re taking.

What are the dosage recommendations of Keflex for a tooth infection?

For adults and teenagers aged 15 and above dealing with a tooth infection, the recommended dosage of Keflex typically falls within the range of 1000 to 4000 milligrams per day (3). This amount is usually divided into several doses throughout the day. 

Often, healthcare providers prescribe it as 250 milligrams to be taken four to six times a day, or alternatively, 500 milligrams can be taken two to three times a day (3). 

However, it’s important to note that the proper dose and duration of Keflex treatment should always be determined by a dentist. Keflex is also available in the form of liquid suspension for people who have difficulty swallowing the capsules. 

If you’re using Keflex suspension, make sure to keep it refrigerated to maintain its potency. In some cases, it might be okay to open the capsule and mix the contents in soft foods like pudding and applesauce for ease of administration. However, it’s important to discuss this with your doctor before you do it. 

What are the side effects of Keflex when used for a tooth infection?

Keflex is associated with some side effects, including: (3,4)

  • Stomach pain
  • Nausea
  • Vomiting
  • Diarrhoea
  • Heartburn
  • Rectal or genital itching
  • Dizziness
  • Headache
  • Joint pain
  • Extreme tiredness
  • Agitation
  • Confusion

Keflex may cause serious or rare side effects in some individuals – which should never be ignored. Seek medical attention in case of the following side effects: (3,4)

  • Skin reactions like a rash, itching, hives, etc.
  • Swelling of facial features including the face, throat, tongue, lips, and eyes.
  • Difficulty in breathing or swallowing.
  • Experiencing wheezing.
  • Watery or bloody stools, stomach cramps, or fever.
  • The resurgence of signs like fever, sore throat, chills, or other indications of infection.
  • Unusual sensory experiences, such as hallucinations, where you might perceive things or hear voices that aren’t real.

What are the alternative treatments to Keflex if it doesn’t help your tooth infection?

If Keflex doesn’t work for your tooth infection, there are some alternatives to try. In general, Amoxicillin and Penicillin, along with Co-Amoxiclav, are often the first-line agents for treating tooth infections. 

If you’re not allergic to these medications, they can be effective alternatives to Keflex (5). However, it’s important to note that some individuals may have allergies to these antibiotics, which is why a doctor might prescribe Keflex instead. 

However, some people allergic to Penicillins may also be allergic to Cephalosporins. 

Allergic reactions to medications can be serious and such meds should not be used. In cases where the first-line treatments like Amoxicillin or Penicillin aren’t suitable or effective, other antibiotics like Doxycycline and Clindamycin can be considered. 

These medications have their own mechanisms of action and can be effective against dental infections. Remember, never make changes to your treatment plan on your own. Always reach out to your dentist if you believe the initial treatment isn’t working as expected.


In this article, we have discussed the approximate time taken by Keflex to work for tooth infections. We have also discussed some side effects and what one should do if Keflex fails to work for the infection. 

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Herman TF, Hashmi MF. Cephalexin. 2023 Aug 17. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan–. PMID: 31747187. Available from:


Abushaheen MA, Muzaheed, Fatani AJ, Alosaimi M, Mansy W, George M, Acharya S, Rathod S, Divakar DD, Jhugroo C, Vellappally S, Khan AA, Shaik J, Jhugroo P. Antimicrobial resistance, mechanisms and its clinical significance. Dis Mon. 2020 Jun;66(6):100971. doi: 10.1016/j.disamonth.2020.100971. Epub 2020 Mar 20. PMID: 32201008. Available from:


The Food and Drug Administration (FDA). HIGHLIGHTS OF PRESCRIBING INFORMATION. KEFLEX® (cephalexin) capsules, for oral use. Available from:


National Library of Medicine. Cephalexin: MedlinePlus Drug Information [Internet]. Bethesda (MD): U.S. National Library of Medicine. Available from:


Ahmadi H, Ebrahimi A, Ahmadi F. Antibiotic Therapy in Dentistry. Int J Dent. 2021 Jan 28;2021:6667624. doi: 10.1155/2021/6667624. PMID: 33574843; PMCID: PMC7861949. Available from: