Is cephalexin a powerful antibiotic?

Posted on  March 22, 2021, Edited by Jason, Category  

What is cephalexin?

1. Definition

Cephalexin (Cefalexin) is a semi-synthetic first-generation oral cephalosporin antibiotic drug that can inhibit the synthesis of cell walls, swell the cell contents until the cell ruptures and dissolves. The white crystalline solid has a bitter taste and slight odor. Cephalexin is slightly soluble in water, but insoluble in ethanol, chloroform or ether.

Cephalexin has a high concentration in urine and pus. It is especially suitable for urogenital infections. It is effective for bacteremia, bacterial endocarditis, meningitis, acute palatine tonsillitis, pharyngitis, pneumonia, bronchitis lobar pneumonia and soft tissue infections caused by streptococcus.

Cefadroxil and cephalexin are two different drugs, belonging to the same class of antibiotics. And their indications and therapeutic effects are roughly the same. Cefadroxil and cephalexin can be used interchangeably in most cases. The antibacterial strength of cephalexin is greater than that of cephalexin. The adverse reactions of cefadroxil are less and lighter, with a total incidence of about 4%. The adverse reactions of cephalexin are more, with a total incidence of about 8%.

2. Pharmacological effects

Cephalexin is a semi-synthetic first-generation oral cephalosporin. Its mechanism of action is to inhibit bacterial cell wall synthesis by combining with one or more penicillin binding proteins (PBPs) of bacteria (cephalexin mainly binds to PBP-3), thereby playing an antibacterial effect. The antibacterial spectrum of cephalexin is similar to that of cephalothin, but its antibacterial activity is worse than the latter.

Except for enterococci and methicillin-resistant staphylococci, gram-positive cocci are sensitive to cephalexin. Cephalexin has a good antibacterial effect on Neisseria spp. and is less sensitive to influenza bacilli. It has certain antibacterial effects on some Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae, Salmonella, and other Enterobacter spp. Acinetobacter, Pseudomonas aeruginosa and Bacteroides fragilis are resistant to cephalexin.

3. Pharmacokinetics

Cefalexina is well absorbed, and the peak blood concentration (Cmax) is reached 1 hour after taking 0.5 g of the product on an empty stomach, with an average of 18 mg/L. Taking the drug after a meal prolongs the absorption and reduces the peak plasma concentration, but the absorption amount does not decrease. The absorption of the product can be increased in infants with celiac disease and small intestinal diverticulum, and it can be delayed and reduced in patients with Crohn's disease and pulmonary cystic fibrosis.

Although there is no decrease in gastrointestinal absorption in the elderly, the blood drug concentration remains longer than that in the young. The blood elimination half-life (t1/2b) of this product is 0.6-1.0 hours. Adding probenecid can increase the blood concentration, t1/2b can be extended to 1.8 hours; t1/2b can be extended to 5-30 hours in renal failure; The newborn t1/2b is 6.3 hours.

After being absorbed, cefalexina is widely distributed in various tissues and body fluids. The average concentration in sputum after oral administration of 0.5g every 6 hours is 0.32mg/L, and the concentration in purulent sputum is higher. The drug concentration in pus is basically equal to the blood drug concentration, and the drug concentration in the joint cavity exudate is 50% of the blood drug concentration.

Cefalexina can enter the blood circulation of the fetus through the placenta; the milk concentration of the lactating mother after oral 0.5g is 5mg/L. About 5% of the oral dose is excreted from the bile, and the concentration of the drug in the bile is 1 to 4 times the concentration of the blood drug. The serum protein binding rate is 10% to 15%. The product is not metabolized in the body, and the accumulated excretion in the urine within 24 hours is 80% to 90% of the dose. The peak concentration of the urine after oral administration of 0.5g can reach 2.2g/L. Cephalexin can be removed by hemodialysis and peritoneal dialysis.

Its antibacterial spectrum is basically the same as that of cefalotin and ceftazidime, and its antibacterial effect is weaker than the two. However, the product is characterized by acid resistance and good oral absorption. It has a good antibacterial effect on resistant Staphylococcus aureus.

Cefalexina is mainly used for respiratory tract infections, urinary tract infections, obstetrics and gynecology infections, skin and soft tissue infections, gonorrhea caused by sensitive bacteria.

Cephalexin uses


1. Indications

Cephalexin is a broad-spectrum antibiotic, mainly used for Gram-positive and negative bacterial infections, such as influenza, hemorrhagic sepsis, streptococcal disease, erysipelas, anthrax, emphysema gangrene, malignant edema, and actin Septic hyperthermia (41~43℃) or continuous low temperature (below 37℃) caused by mycosis, necrotosis, leptospirosis, etc., indigestion, like drinking cold water, lethargy, lameness when walking, blue ears, weep, etc.

At the same time, keflex is used to treat various inflammatory diseases, such as: infectious pleuropneumonia, pulmonary pneumonia, atrophic rhinitis, PRRS, mastitis, metritis, stomatitis, urethritis, cough, asthma, dyspnea, low pregnancy, stillbirths or piglet death 7-10 days after birth, breast swelling, milk deterioration, decreased milk production, foot and mouth ulcers, salivation, sores and pus.

Keflex is indicated for acute tonsillitis, angina, otitis media, sinusitis, bronchitis, pneumonia and other respiratory tract infections, urinary tract infections and skin and soft tissue infections caused by sensitive bacteria. Keflex is an oral preparation and should not be used for severe infections.

2. Cephalexin dosage

  • Adult dose: oral. Usually 0.25~0.5g (1~2 capsules) once, 4 times a day, the highest dose is 4g (16 capsules) a day. Patients with impaired renal function should reduce the medication according to the degree of impaired renal function. 0.5g (4 tablets) every 12 hours for patients with simple cystitis, skin and soft tissue infections and streptococcal angina.
  • Child dose: Oral. Daily weight 25-50 mg/kg, 4 times a day. Patients with skin and soft tissue infections and streptococcal angina take 12.5-50 mg/kg orally every 12 hours.

3. Veterinary uses

Cephalexin is an antibiotic used in dogs and cats. It belongs to cephalosporin drugs and is related to penicillin drugs in killing bacteria. Cephalosporins have a broader antibacterial activity than penicillin. Keflex is also one of the most commonly used antibiotics for cats and dogs.

The antibacterial mechanism of cephalosporins is similar to that of other beta lactam drugs, that is, it exerts an antibacterial effect by competing for the central binding site of the active structure of the cell wall and hindering the synthesis of the peptidoglycan structure of the bacterial cell wall. At present, cephalosporins are widely used in the field of human medicine, but their use in veterinary medicine is restricted.

Many countries have gradually separated human and veterinary cephalosporins in order to reduce the resistance caused by the common use of cephalosporins by humans and animals and the emergence of cross-resistance between the two. The cephalosporin family members are classified according to the development time, the stability of beta lactamase, and the difference in antibacterial activity against gram-negative bacilli. At present, there are hundreds of cephalosporin products, but most of them are human products and few veterinary products.

Cephalexin prevents bacteria from forming adequate and protective cell walls. This can lead to instability and subsequent death of bacteria. Cephalexin is a prescription medicine and can only be obtained by prescription by a veterinarian. The U.S. Food and Drug Administration (FDA) has not approved the drug for animals, but veterinarians have prescribed it as an additional prescription drug by law.

Cephalexin can be used to treat various bacterial infections in cats and dogs, including: skin infections, wound infections, bone infections, pneumonia and bladder infections. Cephalexin is similar to the veterinary drug cefadroxil, and veterinarians often use the two drugs interchangeably because they have the same effect. Cephalexin has no therapeutic effect on infections caused by parasites (such as intestinal worms), mites, viruses or fungi.

Cephalexin Side Effects


1. Adverse Reactions

  • Allergic reaction symptoms such as skin rash, urticaria, erythema, and drug fever are common, and occasionally anaphylactic shock is seen.
  • Gastrointestinal reactions: gastrointestinal symptoms such as nausea, vomiting, diarrhea and abdominal discomfort are common. Pseudomembranous enteritis is occasionally seen.
  • Nervous system reactions: A few patients may have nervous system reactions such as dizziness, diplopia, tinnitus, and convulsions.
  • Hepatotoxicity: A few patients may have transient liver dysfunction after medication (transient increase of serum alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase).
  • Nephrotoxicity: A few patients may experience temporary increases in urea nitrogen, creatine, and creatinine after medication, and occasionally proteinuria and oliguria are seen.
  • Blood system: occasionally decreased hemoglobin, thrombocytopenia, neutropenia, eosinophilia, etc. after medication.
  • Others: Long-term medication can cause flora imbalance and double infection; vitamin K and vitamin B deficiency may also occur.
  • Two cases of disulfide reaction caused by cephalexin were reported. The patient drank beer a few days after taking cephalexin and developed general malaise, chest tightness, shortness of breath, sweating, irritability, etc. The electrocardiogram showed atrial premature contraction, which recovered after symptomatic treatment. Drinking beer at the next day, the above symptoms appeared again. The disulfiram-like reaction caused by drinking liquor is more severe and even fatal. Many drugs such as cephalosporin antibiotics and furazolidine with alcohol can easily lead to disulfide reaction. So cephalexin and alcohol should not be taken both during a few days.

2. Cephalexin warnings

  • Before using cephalexin, you must ask the patient in detail about the history of allergy to cephalosporins, penicillins and other drugs. People with a history of anaphylactic shock from penicillin drugs should not use this product. Other patients must pay attention to cephalosporins when using this product. The chance of cross-allergic reaction between penicillins and cephalosporins is about 5% to 7%, and should be used with caution under close observation. In the event of an allergic reaction, the drug should be discontinued immediately. In the event of anaphylactic shock, immediate rescue on the spot must be performed including measures such as keeping the airway open, inhaling oxygen, adrenaline, and glucocorticoids.
  • Patients with a history of gastrointestinal diseases, especially those with ulcerative colitis, localized enteritis, or antibiotic-related colitis (cephalosporins rarely produce pseudomembranous enteritis), and those with impaired renal function should use it with caution.
  • Interference with diagnosis: Direct Coombs test positive reaction and urine glucose false positive reaction (copper sulfate method) may occur when using cephalexin; alkaline phosphatase, serum alanine aminotransferase and aspartate in a few patients Aminotransferase can be increased.
  • When the daily oral dose exceeds 4g (anhydrous cephalexin), consider switching to cephalosporins for injection.
  • Cephalexin is mainly excreted through the kidneys, and patients with impaired renal function should use this product to reduce the dose.
  • The product passes through the placenta, so pregnant women should use it with caution; the product can also be excreted through milk. Although there are no reports of problems with cephalosporins used by breastfeeding women, it is still necessary to weigh the pros and cons before using it.

3. Cephalexin Interactions

  • The simultaneous use of probenecid and cephalexin can delay the renal excretion of cephalexin and increase the blood concentration of cephalexin. However, there are also reports that probenecid can increase the excretion of cephalexin in the bile.
  • The simultaneous use with cholestyramine can reduce the average peak blood concentration of cephalexin.
  • The simultaneous use with aminoglycoside drugs can increase nephrotoxicity.
  • The simultaneous use of live typhoid vaccine may reduce the immune effect of live typhoid vaccine. The possible mechanism is that cephalexin has antibacterial activity against Salmonella typhi.


Cephalexin is a beta lactam antibiotic, a semi-synthetic penicillin antibiotic, and a broad-spectrum antibiotic. It has a broad antibacterial spectrum, with no cross-resistance, low residue, low side effects and other good characteristics.

It has been widely used in medicine and veterinary circles. It mainly inhibits the synthesis of the cell wall, so that the cell content swells to rupture and dissolve, thereby achieving a bactericidal effect. It has antibacterial effect on both gram-positive bacteria and gram-negative bacteria, and the absorption is rapid and complete after injection with high bioavailability.

BALLYA provides a betalactam-cefalexin-combo-test to tell you if there are beta lactam residues and cephalexin residues in dairy products you eat every day.


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