Cephalexin: What Is It For, Dosage, Side Effects

The  Cephalexin  is an antibiotic belonging to the class of first – generation cephalosporins. It is indicated for the treatment of skin and upper respiratory infections caused by bacteria resistant to other antibiotics or affecting patients allergic to penicillin and its derivatives.

It is currently the first-line treatment for these types of infections. Available only in oral presentation, this antibiotic has a narrow spectrum, although it is very effective in treating infections for which it is indicated.


Its greatest effect is against gram positive germs, including aggressive species such as staphylococcus and streptococcus , producers of beta-lactamase. Likewise, cephalexin has some action against some great negative germs such as E. coli, klebsiella and proteus mirabilis .

However, its use against these bacteria is reserved for selected cases where a more effective therapeutic option is not available.

Mechanism of action 

Like all other beta-lactam antibiotics (penicillins and cephalosporins), cephalexin inhibits the third step of bacterial wall synthesis by binding to Specific Penicillin-Binding Proteins (PBPs) present in the cell wall and critical in various processes of the synthesis of it.

By doing this they compromise the integrity of the wall, allowing the enzymes found in the wall (known as lysines) to come into contact with the cell membrane, ultimately lysis of the cell (autolysis).

The more PBPs in the cell wall, the more effective cephalexin will be. However, the total number of PBPs in the wall as well as their affinity in binding with the antibiotic varies from bacteria to bacteria, so its effectiveness as a bactericide varies depending on the characteristics of the bacterial strain that is being attacked.

Since the effect of cephalexin is mainly in the area of ​​the cell wall, its effect is more notable in gram positive bacteria (since its wall is thick and well developed), while in gram negative bacteria the effect is very scarce given that its cell wall is very thin.

What is it for?

This antibiotic is often used as prophylaxis in dental interventions, in minor outpatient surgeries as well as in minor invasive skin procedures. Likewise, cephalexin has an important role in the prophylaxis of recurrent infections secondary to cystic fibrosis.

On the other hand, it can be used in skin and soft tissue infections, including abscessed boils, although generally the first-line treatment in these cases is some type of semisynthetic penicillin.

Regarding the upper respiratory tract, cephalexin has been shown to be useful in cases of streptococcal pharyngitis, bacterial otitis media, chronic sinusitis and even in certain cases of lower respiratory infection.

Although it is true that for all these cases there are more effective first-line antibiotics, cephalexin will always be an option to consider, either in cases of bacterial resistance or in patients allergic to penicillin, for whom first-line antibiotics ( all derivatives of penicillin) are totally contraindicated.

How to use?

Cephalexin is an antibiotic exclusively for oral use; In this sense, there are solid presentations, capsules and tablets with a concentration of 250 and 500 mg respectively. Likewise, there is a presentation in the form of a syrup for pediatric patients.


The dose of cephalexin varies depending on the type of infection, its severity and the characteristics of the patient.

In general, a dose that ranges between 1 and 4 grams a day is used, divided into 4 daily doses. The final dose must be individualized according to each case.

Likewise, in pediatric patients it is estimated that the average weight dose is 25 to 50 mg / Kg / day divided into 4 daily intakes, although in very severe infections up to 100 mg / Kg / day can be administered. This administration must be under strict medical supervision.

Side effects

The side effects are many and varied, although fortunately most are infrequent and of low to moderate intensity. However, it is important to consider a detailed description of the most common side effects.

– Most of the undesirable effects are on the digestive system. Its administration is associated with nausea, vomiting, diarrhea and abdominal pain.

– Cases of pseudomembranous colitis due to proliferation of clostridium difficile have been described after treatment with cephalexin.

– This antibiotic can induce nephrotoxicity, especially when the treatments are for a long time (more than a week and a half).

– Elevations of transaminases have been reported, suggesting some degree of liver toxicity.

– From the immunological point of view, allergic reactions of varying intensity have been reported, ranging from urticaria to Stevens Johnson syndrome.

– In some cases anal and vaginal itching are reported, as well as the development of vaginal infections, probably in relation to changes in the local bacterial flora.


– The history of allergic reactions to cephalexin as well as to other cephalosporins is an absolute contraindication for its use. 

– Cases of cross reaction have been reported in patients allergic to penicillin, so in these cases one should proceed with caution.

– In cases of pregnancy and lactation, this drug is considered class B; that is, it has not been shown to have negative effects on the fetus. However, this possibility is not 100% excluded, so it is recommended to avoid its use unless there is no other safer option or the benefits far outweigh the potential risk.

– In patients with renal insufficiency, the dose should be adjusted and renal function monitored in order to detect any signs of nephrotoxicity in time.

– In cases of patients with peptic ulcer disease or any other functional disorder of the digestive tract, strict medical control is important since there is the possibility that adverse effects in the gastrointestinal area are more intense.


  1. Wick, WE (1967). Cephalexin, a new orally absorbed cephalosporin antibiotic. Applied microbiology15 (4), 765-769.
  2. Pfeffer, M., Jackson, A., Ximenes, J., & De Menezes, JP (1977). Comparative human oral clinical pharmacology of cefadroxil, cephalexin, and cephradine. Antimicrobial agents and chemotherapy11 (2), 331-338.
  3. Rajendran, PM, Young, D., Maurer, T., Chambers, H., Perdreau-Remington, F., Ro, P., & Harris, H. (2007). Randomized, double-blind, placebo-controlled trial of cephalexin for treatment of uncomplicated skin abscesses in a population at risk for community-acquired methicillin-resistant Staphylococcus aureus infection. Antimicrobial agents and chemotherapy51 (11), 4044-4048.
  4. Tritt, A., Langlois, A., Gabrielli, S., Lejtenyi, C., Eiwegger, T., Atkinson, AR,… & Ben-Shoshan, M. (2018). Immediate and Delayed Reactions to Cephalexin in Children with Confirmed Allergy to Amoxicillin. Journal of Allergy and Clinical Immunology141 (2), AB36.
  5. St-Amand, BF, Trottier, ED, Autmizguine, J., Vincent, M., Tremblay, S., Chevalier, I., & Gouin, S. (2017). LO26: The efficacy of high dose cephalexin in the outpatient management of moderate cellulitis for pediatric patients. Canadian Journal of Emergency Medicine19 (S1), S36-S36.
  6. Valent, AM, DeArmond, C., Houston, JM, Reddy, S., Masters, HR, Gold, A.,… & Warshak, CR (2017). Effect of post – cesarean delivery oral cephalexin and metronidazole on surgical site infection among obese women: a randomized clinical trial. Jama318 (11), 1026-1034.
  7. Banerjee, P., Maity, S., Bubna, A., & Das, M. (2017). A randomized controlled open label comparative clinical study of cephalexin versus doxycycline in patients with acne vulgaris in a hospital based population of South India. International Journal of Basic & Clinical Pharmacology6 (8), 1959-1964.

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