What is Cephalexin?

Cephalexin is a Generic name for a first-generation cephalosporin antibiotic that works by fighting bacteria in the body. It is usually prescribed to treat respiratory tract, skin, bone, middle ear and UTI – urinary tract infections. Cephalexin and other cephalosporin’s are broad-spectrum antibiotics are used to treat a various types of infections caused by many different bacteria.

It is effective against both gram-negative and gram-positive bacteria. This drug is also used to prevent infections that are caused by streptococcal bacteria, including rheumatic fever. However, cephalexin isn’t appropriate for sinus infections. Cephalexin should only be used when there’s strong evidence to support its use.

Misusing of cephalosporins can lead to serious infections from drug-resistant bacteria. Treating colds or flu symptoms with broad-spectrum antibiotics such as cephalexin can lead to antibiotic resistance and more severe infections that will be far harder to treat.

Cephalexin is available in the form of capsules, tablet, or liquid suspension to take by mouth. FDA approved cephalexin in 1971 and was first manufactured by Eli Lilly and Company under the brand name Keflex. Today Keflex is made and sold by Shionogi Inc.

cephalexin for sinus infection

Cephalexin molecular formula, weight and drug class


Chemical name: 7-(D-α-Amino-α-phenylacetamido)-3-methyl-3-cephem-4-carboxylic acid monohydrate

Molecular Formula: C16H17N3O4S•H2O

Weight: 365.41. Da

Cephalexin belongs to the class of organic compounds known as cephalosporins. These are beta lactams compounds containing a 1,2-thiazine fused to a 2-azetidinone to for a oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid moiety.

In what dosage forms is Cephalexin available on the market?

Cephalexin is available in following forms and doses: tablets 250 and 500 mg, capsules 250, 500 and 750 mg, and suspension 125 and 250 mg.

How Cephalexin capsules looks like?

250 mg Cepahlexin capsules: Dark green opaque/white size “2” hard gelatin capsule filled with off white granular powder and imprinted with “A 42” on dark green opaque cap and “250 mg” on white body with black ink.

500 mg Cephalexin capsules: Dark green opaque/light green opaque size “0” hard gelatin capsule filled with off white granular powder and imprinted with “A 43” on dark green opaque cap and “500 mg” on light green opaque body with black ink.

219 219 Pill - cephalexin 500 mg

What are different Brand names for Cephalexin?

Cephalexin is available on the market in following Brand names: Keflex, Cepol, Ceporex, Panixine, Biocef, Zartan, Ospexin, Felexin, Palitrex, Sanaxin, Tepaxin

What are FDA approved indications for Cephalexin?

FDA approved indications for cephalexin are following:

  1. Bone Infection
  2. Genitourinary tract infection
  3. Otitis Media (OM)
  4. Respiratory Tract Infections (RTI)
  5. Skin and skin structure infections
  6. Acute Prostatitis

What kind of bacteria can cephalexin fight?

  • Respiratory tract infections caused by: Streptococcus pneumoniae and Streptococcus pyogenes;
  • Otitis media caused by: Streptococcus pneumoniae, Staphylococcus aureus, Streptococcus pyogenes, Haemophilus influenzae and Moraxella catarrhalis;
  • Skin and skin structure infections caused by: Staphylococcus aureus and/or Streptococcus pyogenes;
  • Bone infections caused by: Staphylococcus aureus and/or Proteus mirabilis;
  • Genitourinary tract infections, including acute prostatitis, caused by: Escherichia coli, Proteus mirabilis and Klebsiella pneumonia

What bacteria cephalexin can’t fight?

Cephalexin has no efficacy against infections caused by MRSA – methicillin-resistant Staphylococcus aureus, Enterococcus or Pseudomonas. Cephalexin is also not active against most isolates of Enterobacter spp., Morganella morganii, Acinetobacter calcoaceticus and Proteus vulgaris. Penicillin-resistant Streptococcus pneumoniae is usually cross-resistant to beta-lactam antibacterial drugs. Like other antibiotics, cephalexin cannot treat viral infections, such as the flu, common cold or acute bronchitis.

How Cephalexin works in the body?

Cephalexin is bactericidal agent that works by inhibiting synthesis of the peptidoglycan layer of the bacterial cell wall. By binding to specific penicillin-binding proteins (PBPs) located inside the bacterial cell wall, cephalexin inhibits last stage of the synthesis of bacterial cell wall. After that, cell lysis is mediated by autolytic enzymes named autolysins located on bacterial cell wall.

It is most efficient against gram-positive cocci, but also has moderate activity against some gram-negative bacilli. However, some bacteria have the ability to produce the enzyme called β-lactamase which can hydrolyze the beta-lactam ring of cephalosporin, making the drug inactive. This contributes to antibacterial resistance to cephalexin.

Cephalexin for bone infections (osteomyelitis and septic arthritis)

Cephalexin is indicated for the treatment of bone infections such as osteomyelitis or septic arthritis caused by susceptible isolates of Staphylococcus aureus and Proteus mirabilis.

For osteomyelitis cephalexin should be used in doses of 500 mg orally every 6 hours. Therapy should last for about 4 to 6 weeks, depending on the nature and severity of the infection. However, chronic osteomyelitis infection may require an additional 1-2 months of antibiotic therapy and may benefit from surgical procedure.

Septic arthritis caused Staphylococcus aureus should be treated with antimicrobial regimens similar to those recommended for osteomyelitis, although generally a 2 – 3-week treatment is sufficient. Until the results of synovial fluid and blood culture are known, cephalexin may be given in doses of 25mg/kg (maximum 500mg) orally every 6 hours to complete the treatment course of 2 – 3 weeks.

Cephalexin for Respiratory tract infections

Cephalexin is effective in treatment of Infections of the upper respiratory tract caused by Streptococcus pneumoniae and Streptococcus pyogenes. 250 to 500 mg of cephalexin on orally every 6 hours for 7 to 10 days

However, majority of upper respiratory tract infections are caused by viruses and do not require treatment with antimicrobials. Because of the potential misuse of antimicrobials in these conditions, some agents are specifically not recommended.

Cephalexin for Otitis media infections

The bacterial pathogens that usually cause otitis media are most commonly Streptococcus pneumoniae and Haemophilus influenzae. Vaccination against the latter pathogen has significantly reduced the recurrence of H. influenzae. Cephalexin should be used 12.5 to 25 mg/kg orally every 6 hours for otitis media infections, as directed by the doctor. Therapy should be continued for approximately 7 to 21 days, depending on the nature and severity of the infection.

Cephalexin for Skin infections

Cephalexin can be used for the treatment of skin infections caused by Staphylococcus aureus and/or Streptococcus pyogenes. Cephalexin should be used in doses 12.5 to 25 mg/kg orally every 12 hours, as directed by the doctor, depending on infection nature and severity.

Cephalexin for Genitourinary tract infection

Cephalexin is effective against Escherichia coli, Proteus mirabilis and Klebsiella pneumonia genitourinary tract caused infections.

For the treatment of acute cystitis Cephalexin should be given in doses of 250 mg orally every 6 hours or 500 mg orally every 12 hours during 7 to 14 days.

For the treatment of acute prostatitis Cephalexin should be given in doses of 500 mg orally every 6 hours for 14 days.

Cephalexin side effects

Cephalexin is generally well-tolerated drug. Studies showed an overall 6% incidence of side effects, whereas some of them may not be related to cephalexin. Most commonly reported side effect caused by cephalexin is diarrhea. Other common side effects are irritation or inflammation of your stomach lining, indigestion, stomach pain.

Hypersensitivity side effects

Hypersensitivity side effects may include: fever, rash, urticaria, eosinophilia, anaphylaxis, contact dermatitis, angioedema, erythema multiforme, Stevens-Johnson syndrome, acute paronychia, toxic epidermal necrolysis and hepatitis. Up to 20% of patients with allergy to penicillin may be allergic to cephalexin.

Gastrointestinal side effects

Gastrointestinal side effects may include: diarrhea, dyspepsia, nausea, vomiting, abdominal pain, anorexia and anal pruritus. Diarrhea caused by Clostridium difficile colitis infection has been reported after cephalosporins use. If diarrhea occurs and is not resolved after discontinuation of the drug or after antidiarrheal therapy, serious condition called pseudomembranous colitis should be suspected.

Hepatic side effects

Hepatic side effects may include: transient hepatitis, transient elevations of liver function tests, and cholestatic jaundice.

Renal side effects

Renal side effects may rarely include interstitial nephritis. Reversible fever, pyuria, azotemia and eosinophiluria are main evidence of cephalosporin-induced interstitial nephritis. Acute tubular necrosis may also occur.

Hematologic side effects

Hematologic side effects have included neutropenia, eosinophilia, thrombocytopenia and hemolytic anemia.

Neurological side effects

Nervous system side effects may include: dizziness, headache, fatigue, agitation, confusion, and hallucinations.


Reversible ototoxicity and vertigo, because of provoked labyrinthine disease, have been reported in a few patients who uses cephalosporins and already have renal disease.

Genitourinary side effects

Genitourinary side effects may include: genital pruritus, vaginitis, vaginal discharge and genital moniliasis.

Musculoskeletal side effects

Musculoskeletal side effects are also described and may include: arthralgia, arthritis, and joint disorder

Dermatological side effects

Dermatologic side effects may include: urticaria, contact dermatitis, rash, erythema multiforme, and toxic epidermal necrolysis. Skin condition called acute generalized exanthematous pustulosis has been also reported.

Cephalexin dosage

Cephalexin dose that will be prescribed will depend on the nature and severity of infection and whether the patient is a child or an adult.

The general guidelines for cephalexin dosage are:

  • Adult dose ranges from 1 to 4 g per day, given in divided doses.
  • Typical adult doses of cephalexin are 250 mg every 6 hours or 500 mg every 12 hours.
  • The usual dose for a child is 25-50 mg/kg, given in divided doses.

Doses may be doubled for more severe infections.

Depending on the type of infection, treatment usually last from 7 to 14 days. However, some chronic and severe infections need to be treated for a longer period.

cephalexin 500 mg

Cephalexin overdose

Antibiotic overdoses are very rare and dangerous, but stomach upset and diarrhea may occur, especially if antibiotics are used for a long-term in high doses. Taking the wrong antibiotic could also be a life-threatening problem if patients are allergic to the drug.

Misuse of antibiotics is a general health problem for many reasons that infection may not be cured and antibiotic-resistant organisms can develop, or in situations where a specific antibiotic is needed, it might not be effective.

Symptoms of cephalexin overdose may include nausea, vomiting, diarrhea, stomach pain and blood in the urine. In such cases, patients should take extra fluids. Patients should also stay in touch with Poison Control to be sure that there are no unexpected effects.

Are there some precautions and warnings during Cephalexin use?

  • Patients who are allergic to penicillin have about a 10-20 % chance to be also allergic to cephalexin.
  • Patients with a history of liver, kidney, or colon disease are at greater risk of causing side effects after cephalexin use, so patients should tell their doctor about any of these conditions as well.
  • Like other antibiotics, cephalexin may also cause a growth of bacteria called Clostridium difficile in your colon. Toxins produced by C. difficile can cause diarrhea and a condition called pseudomembranous colitis.

Being on other antibiotics may also increase your risk for pseudomembranous colitis, so tell your doctor about any recent antibiotic use.

Cephalexin’s cross sensitivity with penicillins

Cephalosporins including cephalexin and penicillins both contain betalactam ring. So, they are chemically quite similar. Because of that it has been discovered that at least 10% of patients who are allergic to penicillin will be also allergic and have an adverse reaction to cephalosporins.

This potential cross-reactivity has very significant therapeutic implications because many serious infections that can’t be treated with penicillins are best treated with cephalosporins as first-line therapy.

Petz et al study showed a 4-fold increase in the incidence of cephalosporins cross sensitivity including cephalothin, cephaloridine and cephalexin in patients who are allergic to penicillins (8.1%) compared with patients not allergic to penicillins (1.9%).

When this incidence was compared with the overall incidence of allergic reactions to cephalosporins which is about 4%, there were 2-fold increases of reactivity in patients allergic to penicillins. The cross-sensitivity of first (such as cephalexin) and second-generation cephalosporins with penicillin is much higher than that of third-generation cephalosporins.

Cephalexin hypersensitivity reactions

Cephalexin can cause various allergic reactions such as: rash, urticaria, angioedema, anaphylaxis, Stevens-Johnson syndrome, erythema multiforme or toxic epidermal necrolysis. Before therapy with Cephalexin is started, patients should be asked if they have a history of hypersensitivity reactions to Cephalexin, cephalosporins, penicillins and other drugs.

Can cephalexin give you diarrhea?

Clostridium difficile-associated diarrhea has been described after use of nearly all antibiotics including Cephalexin and may vary in severity from mild diarrhea to even fatal colitis. Treatment with antibiotics modifies colon’s normal flora leading to overgrowth of C. difficile.

  1. difficile releases toxins A and B, which contribute to the development of Clostridium difficile-associated diarrhea. But some strains of C. difficile produce Hypertoxin that can cause increased morbidity and mortality. Such infections might be refractory to antibiotics therapy and may require colectomy. Clostridium difficile-associated diarrhea must be considered in all patients who with diarrhea following antibiotic use. Careful medical history is also necessary because this condition has been also reported to occur after 2 months of antibiotics administration. If this type of diarrhea is confirmed appropriate fluid and electrolyte therapy, protein supplementation, antibiotic treatment of C. difficile, and surgical assessment should be introduced.

Can I get Positive direct Coombs’ tests during cephalexin use?

Positive direct Coombs’ tests have been reported during treatment with Cephalexin but with other cephalosporins. Cephalexin’s induced acute intravascular hemolysis has been reported. If anemia develops during Cephalexin therapy diagnostic work-up for drug-induced hemolytic anemia should be performed and this drug should be discontinued.

Can Cephalexin provoke seizures?

In some rare cases seizure attacks have been described after cephalosporin use, specifically in patients with kidney diseases where doses of antibiotic was not reduced. If seizures occur, cephalexin should be discontinues and proper anticonvulsant therapy can be given.

Can Cephalexin prolong prothrombin time?

Cephalosporins including cephalexin may be related with prolonged prothrombin time. At highest risk are patients with renal or hepatic impairment, or those with poor nutritional state, as well as patients receiving a long-term course of antibacterial therapy, and patients receiving anticoagulant therapy. In such patients prothrombin time should be carefully monitored.

Can cephalexin give you a yeast infection?

In your gastrointestinal tract, antibiotics including cephalexin kill the good bacteria making the body vulnerable against harmful pathogens such yeast called Candida albicans, which in normal situations non-dominative in intestines. After antibiotic treatment, Candida albicans can rapidly come in position to dominate in small intestine, resulting in the disease that we know as Candida overgrowth.

Should I take probiotics during antibiotic therapy with cephalexin?

Using probiotics before, during, and after therapy with antibiotics can help to keep the balance in your digestive system. Studies have shown that probiotics are very effective during antibiotics.

Long-term therapy with high doses of strong antibiotics can kill practically all the bacteria in the digestive system, thus reducing the competition and clearing the path for fast-growing Candida albicans or for some other pathogen to fill the gap.

Probiotics can help to slow the growth of Candida by filling your gut with beneficial, healthful bacteria and they can also reduce the common side effects of the antibiotics. A 2008 study published in the “Journal of Clinical Gastroenterology” showed that probiotics significantly reduce diarrhea in patients taking antibiotics.

How should I take probiotics during antibiotic therapy with cephalexin?

Probiotics should be taken at least 2 hours apart from taken dose of antibiotics as this is the best way to avoid ‘good bacteria’ to be killed by the antibiotics in your intestines.

Researchers found that probiotics during antibiotics therapy survived best when taken during a meal, or in the 30 minutes before meal. So, when you take your probiotics, always take them during your meal or immediately before you start eating.

Can I take cephalexin while pregnant?

Cephalexin is listed in a pregnancy category B drug by the FDA. That means that animal studies have not shown risk to the fetus and that there aren’t adequate studies in pregnant women to show the drug poses a risk to the fetus. Because animal reproduction studies are not well and always predictive of human response, cephalexin should be used during pregnancy only if clearly needed.

Reproduction animal studies have been performed on mice and rats and mice using oral Cephalexin doses of 0.6 and 1.5 times the maximum daily human dose. Studies have failed to reveal evidence of impaired fertility or harm to the fetus.

Cephalexin can pass the human placenta. In one study of 30 pregnant women who used cephalexin 1g orally once a day, amniotic drug levels were 11.3 (4 hours after dosing) and 13.2 mcg/mL (6 hours after dosing).

Can Cephalexin be used during breastfeeding?

In small amounts Cephalexin is excreted into human milk, although adverse effects have not been observed in nursing infants. Other cephalosporins have been categorized as compatible with breast-feeding by the American Academy of Pediatrics.

How long does it take for Cephalexin to take effect?

Antibiotics such as cephalexin start to works as soon as they reach therapy concentrations in the infected area and this can be done between 10 and 24 hours after treatment initiation.

How long does Cephalexin stay in your system?

Cephalexin dose will be eliminated from the body after approximately 8 hours. However, after full therapy course, Cephalexin will stay in your system for about 72 hours after the therapy has been finished.

Can you take Cephalexin and alcohol together?

There is no direct interaction between cephalexin and alcohol. Alcohol doesn’t reduce the cephalexin’s effectiveness. Cephalexin’s data label doesn’t state that alcohol interacts with cephalexin. However, cephalexin is known to cause allergic reactions, nausea and vomiting. Taking alcohol together with cephalexin may increase the chance of provoking such side effects.

Chance of causing dizziness and drowsiness is also increased. Drinking alcohol can also have a direct effect on infections because it may decrease the ability of the body to fight urinary tract infection and increase the time it takes you to recover.

Drinking could also make you more prone to getting a new infection. It may be best to hold off on drinking alcohol until you have finished treatment. Patients should that some antibiotics such as metronidazole can cause serious adverse reactions if they are taken in combination with alcohol.

Can you give cephalexin to dogs and cats?

Cephalexin is an antibiotic of a broad spectrum that can be used in dogs and cats. It can be used for the management of some urinary tract infections, respiratory infections or skin and soft tissue infections such as wounds, abscesses and lacerations in dogs and cats. Cephalexin should be given in a dosage of 10-15 mg per lb body weight every 8-12 hours. It should be given to pets with meals.

What is the price of different Cephalexin products?

This cephalexin price guide is based on using the Drugs.com discount card which is accepted at most U.S. pharmacies. Prices are for cash paying customers only and are not valid with insurance plans.

The average price of Cephalexin 250 mg Oral Capsule is $ 7.77 for 4 capsules

The average price of Cephalexin 500 mg Oral Capsules is $ 7.36 for 4 capsules

The average price of Cephalexin 750 mg Oral capsules is $ 121.35 for 20 capsules

The average price of Cephalexin 125mg/5 ml powder for reconstitution is $ 12.70 for 100 ml

The average price of Cephalexin 250mg/5ml powder for reconstitution is $ 20.18 for 100 ml

The average price of Cephalexin 250 mg Oral tablets is $ 319.75 for 100 tablets

The average price of Cephalexin 500 mg Oral tablets is $ 622.55 for 100 tablets

How should I take cephalexin?

  • Always take medication exactly as it was prescribed by the doctor. Never use the medication in larger amounts, or for longer time than recommended by your doctor. Follow the instructions on your prescription label.
  • Take cephalexin with a full glass of water.
  • Cephalexin dispersible tables should be dissolvedin a small amount of water, about 2 teaspoonfuls. Mixing this and drink all of it right away. To make sure you get the full dose, pour a little more water to the same glass, mix and drink right away. Never swallow or chew a dispersible tablet.
  • Shake the oral suspension before you measure a dose. In order to get the precise dose, measure the liquid with a measuring spoon or medicine cup, not with a regular table spoon. If you do not have a dose-measuring device, ask your pharmacist for one.
  • Always take cephalexin for the entire length of treatment prescribed by your doctor. Your symptoms may eventually get better before the infection is completely treated.
  • Cephalexin will not treat a viral infection such as the common cold or flu.
  • Store the capsules and tabletsat room temperature away from moisture and heat.
  • Store the liquidin the refrigerator. Throw away any unused medication after 14 days.

Should I take cephalexin with food?

Cephalexin will be absorbed faster if it is taken on an empty stomach. However, cephalexin may be also taken with food and the overall effect won’t be changed. Patients, who have problems with gastrointestinal issues after taking cephalexin, should always take this drug with food.

Can I drink milk while taking cephalexin?

There is no interaction between milk and cephalexin. Cephalexin may cause an upset stomach and milk may easy these symptoms.

Can Cephalexin interact with Laboratory or Diagnostic Testing?

Cephalexin may give false-positive reaction when testing for the presence of glucose in the urine using Benedict’s solution or Fehling’s solution.

Can I take Cephalexin with Probenecid?

There is an interaction between these two drugs. Probenecid inhibits renal excretion of cephalexin. Cephalexin will stay in the body for more time in the body, increasing the chance of side effects to happen.

Can I take Cephalexin with Lasix?

Cephalosporin antibiotics such as cephalexin can in some cases cause kidney problems, and using it with strong diuretics such as furosemide (Lasix) may increase that risk. The exact mechanism of interaction is still unknown, although it has been shown that furosemide has a tendency to increase the plasma concentrations or reduce the clearance of several cephalosporins such as cephaloridine and ceftazidime.

The interaction is more likely to happen when cephalexin or other cephalosporins are given at high dosages by intravenously or when it is given to the elderly or to predisposed patients with preexisting kidney disease.

Signs and symptoms of kidney impairment may include: nausea, vomiting, increased or decreased urination, loss of appetite, sudden weight gain or weight loss, fluid retention, swelling, muscle cramps, shortness of breath, tiredness, weakness, dizziness, confusion, and irregular heart rhythm.

Can I take Cephalexin with Metformin?

The concomitant use of cephalexin and metformin may increase plasma concentrations and risk of side effects of metformin. Using cephalexin together with metformin may increase the risk of lowering blood sugar. The mechanism of this interaction is competitive inhibition of active renal tubular secretion.

Studies showed that after administration of cephalexin and metformin single doses of 500 mg, the maximum plasma concentration (Cmax) of metformin is increased by 34%, AUC parameter was increased by 24%, and metformin renal clearance decreased by 14%. However, adverse effects were not reported in this study.

Can I take Cephalexin with Warfarin?

Patients on anticoagulant therapy with warfarin, who also take antibiotics, may be at risk, because there are antibiotics that may interact with the anticoagulants and significantly increase the chance of serious bleeding events.

Studies noted alterations in INR are common among patients who receive antibiotics. Antibiotics that have most probable chance to interact with warfarin are: trimethoprim/sulfamethoxazole, metronidazole, ciprofloxacin, fluconazole, levofloxacin, azithromycin, and clarithromycin. Cephalexin and clindamycin have been showed to have minimal chances of interactions with warfarin, and are considered low-risk antibiotics.

Can I take Cephalexin with Advil?

Patients with no kidney problems can safely use these two drugs together. However, those with kidney impairment should avoid them, because both drugs are predominantly excreted via kidneys and have a tendency of competing for the same pathway through the kidney.

Can I take Cephalexin with Tylenol?

Since there are no major interactions between these two drugs, they can safely be taken together.

Can I take Cephalexin with Oral contraceptives?

Antibiotics such as cephalexin may interact with oral contraceptives and reduce the effects of ethinyl estradiol hormones in some women. If you are using oral contraceptives containing ethinyl estradiol for birth control, you may be at increased risk for pregnancy or breakthrough bleeding.

Most antimicrobials, with the exception of the rifamycins and possibly griseofulvin, do not induce hepatic enzymes and have not been shown to significantly increase the clearance of oral contraceptive estrogens. Talk to your doctor or pharmacist to determine if you should use an alternative or additional form of birth control during or after treatment with cephalexin.

Cephalexin and Carcinogenesis, Mutagenesis, Impairment of Fertility

Animal studies have not been performed in order to evaluate the carcinogenic potential of Cephalexin. Tests to define the mutagenic potential of Cephalexin have not been yet performed. In rats, fertility and reproductive toxicity performance were not affected by Cephalexin oral doses 1.5 times higher that doses recommended for humans.

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