Brand name: Keflex
Drug class: First Generation Cephalosporins
CAS number: 23325-78-2

Medically reviewed by Drugs.com on Oct 2, 2023. Written by ASHP.

Introduction

Antibacterial; β-lactam antibiotic; first generation cephalosporin.

Uses for Cephalexin

Acute Otitis Media (AOM)

Treatment of AOM caused by susceptible Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, staphylococci, or streptococci.

When anti-infectives indicated, AAP recommends high-dose amoxicillin or amoxicillin and clavulanate as drugs of choice for initial treatment of AOM; certain cephalosporins (cefdinir, cefpodoxime, cefuroxime, ceftriaxone) recommended as alternatives for initial treatment in penicillin-allergic patients without a history of severe and/or recent penicillin-allergic reactions.

Pharyngitis and Tonsillitis

Treatment of pharyngitis and tonsillitis caused by S. pyogenes (group A β-hemolytic streptococci). Generally effective in eradicating S. pyogenes from nasopharynx; efficacy in prevention of subsequent rheumatic fever not established to date.

AAP, IDSA, AHA, and others recommend a penicillin regimen (10 days of oral penicillin V or oral amoxicillin or single dose of IM penicillin G benzathine) as treatment of choice for S. pyogenes pharyngitis and tonsillitis; other anti-infectives (e.g., oral cephalosporins, oral macrolides, oral clindamycin) recommended as alternatives in penicillin-allergic patients.

If an oral cephalosporin used, 10-day regimen of first generation cephalosporin (cefadroxil, cephalexin) preferred instead of other cephalosporins with broader spectrums of activity (e.g., cefaclor, cefdinir, cefixime, cefpodoxime, cefuroxime).

Bone and Joint Infections

Treatment of bone and joint infections caused by susceptible staphylococci or Proteus mirabilis.

Respiratory Tract Infections

Treatment of mild to moderate respiratory tract infections caused by susceptible S. pneumoniae.

Skin and Skin Structure Infections

Treatment of mild to moderate skin and skin structure infections caused by susceptible staphylococci or streptococci.

Urinary Tract Infections (UTIs)

Treatment of mild to moderate UTIs, including acute prostatitis, caused by susceptible Escherichia coli, Klebsiella pneumoniae, or P. mirabilis.

Prevention of Bacterial Endocarditis

Alternative for prevention of α-hemolytic (viridans group) streptococcal endocarditis^{† [off-label]} in penicillin-allergic individuals undergoing certain dental or upper respiratory tract procedures who have cardiac conditions that put them at highest risk. Should not be used in those with immediate-type penicillin hypersensitivity (see Cross-hypersensitivity under Cautions).

When selecting anti-infectives for prophylaxis of bacterial endocarditis, consult most recent AHA recommendations for specific information on which cardiac conditions are associated with highest risk of endocarditis and which procedures require prophylaxis.

Cephalexin Dosage and Administration

Administration

Oral Administration

Administer orally without regard to meals.

Reconstitution

Reconstitute oral suspension at time of dispensing by adding the amount of water specified on the container in 2 equal portions; shake after each addition.

Reconstituted suspensions contain 125 or 250 mg of cephalexin/5 mL.

Shake oral suspension well prior to administration of each dose.

Dosage

Available as cephalexin monohydrate; dosage expressed in terms of cephalexin.

Pediatric Patients

General Pediatric Dosage

Oral

25–50 mg/kg daily in divided doses. Manufacturers state these dosages may be doubled for severe infections.

Children beyond neonatal period: AAP recommends 25–50 mg/kg daily in 2 or 4 equally divided doses for treatment of mild or moderate infections and 75–100 mg/kg daily in 3 or 4 equally divided doses for treatment of severe infections.

Acute Otitis Media (AOM)

Oral

75–100 mg/kg daily in 4 divided doses.

Pharyngitis and Tonsillitis

Oral

25–50 mg/kg daily in 3–4 equally divided doses for ≥10 days. Daily dosage may be given in divided doses every 12 hours in those >1 year of age.

Children >15 years of age: 500 mg every 12 hours for ≥10 days.

Bone and Joint Infections

Oral

25–50 mg/kg daily in 3–4 equally divided doses for mild to moderate infections. Manufacturers state dosage may be doubled for severe infections.

Respiratory Tract Infections

Oral

25–50 mg/kg daily in 3–4 equally divided doses for mild to moderate infections. Manufacturers state dosage may be doubled for severe infections.

Skin and Skin Structure Infections

Oral

25–50 mg/kg daily in divided doses every 12 hours for mild to moderate infections.

Children >15 years of age: 500 mg every 12 hours for mild to moderate infections.

Manufacturers state dosage may be doubled for severe infections.

Urinary Tract Infections (UTIs)

Oral

25–50 mg/kg daily in 3–4 equally divided doses for mild to moderate infections.

Children >15 years of age with uncomplicated cystitis: 500 mg every 12 hours for 7–14 days.

Manufacturers state dosage may be doubled for severe infections.

Prevention of Bacterial Endocarditis† [off-label]

Patients Undergoing Certain Dental or Upper Respiratory Tract Procedures† [off-label]

Oral

50 mg/kg (up to 2 g) as a single dose given 0.5–1 hour prior to the procedure.

Adults

General Adult Dosage

Oral

Usual dosage ranges from 1–4 g daily given in divided doses. If dosage >4 g daily is required, consider initial therapy with a parenteral cephalosporin.

Acute Otitis Media (AOM)

Oral

250 mg every 6 hours. Higher dosage may be needed for severe infections or those caused by less susceptible bacteria.

Pharyngitis and Tonsillitis

Oral

500 mg every 12 hours for ≥10 days.

Bone and Joint Infections

Oral

250 mg every 6 hours. Higher dosage may be needed for severe infections or those caused by less susceptible bacteria.

Respiratory Tract Infections

Oral

250 mg every 6 hours for mild to moderate infections. Higher dosage may be needed for more severe infections or those caused by less susceptible bacteria.

Skin and Skin Structure Infections

Oral

500 mg every 12 hours for mild to moderate infections. Higher dosage may be needed for severe infections or those caused by less susceptible bacteria.

Urinary Tract Infections (UTIs)

Oral

500 mg every 12 hours for 7–14 days for mild to moderate infections. Higher dosage may be needed for severe infections or those caused by less susceptible bacteria.

Prevention of Bacterial Endocarditis† [off-label]

Patients Undergoing Certain Dental or Upper Respiratory Tract Procedures† [off-label]

Oral

2 g as a single dose given 0.5–1 hour prior to the procedure.

Special Populations

Renal Impairment

Use with caution in patients with markedly impaired renal function; close clinical observation and appropriate laboratory tests recommended because safe dosage may be lower than usual dosages.

Some clinicians suggest that the usual adult dosage be used for the initial dose. Then, for subsequent doses, use 500 mg every 8–12 hours if Cl_cr 11–40 mL/minute, 250 mg every 12 hours if Cl_cr 5–10 mL/minute, or 250 mg every 12–24 hours if Cl_cr <5 mL/minute.

Geriatric Patients

Cautious dosage selection because of age-related decreases in renal function. (See Renal Impairment under Dosage and Administration.)

Cautions for Cephalexin

Contraindications

• Known hypersensitivity to cephalexin or other cephalosporins.

Warnings/Precautions

Warnings

Superinfection/Clostridium difficile-associated Diarrhea and Colitis

Possible emergence and overgrowth of nonsusceptible bacteria or fungi with prolonged use. Careful observation of the patient is essential. Institute appropriate therapy if superinfection occurs.

Treatment with anti-infectives alters normal colon flora and may permit overgrowth of Clostridium difficile. C. difficile infections (CDI) and C. difficile-associated diarrhea and colitis (CDAD; also known as antibiotic-associated diarrhea and colitis or pseudomembranous colitis) reported with nearly all anti-infectives, including cephalexin, and may range in severity from mild diarrhea to fatal colitis. C. difficile produces toxins A and B which contribute to development of CDAD; hypertoxin-producing strains of C. difficile are associated with increased morbidity and mortality since they may be refractory to anti-infectives and colectomy may be required.

Consider CDAD if diarrhea develops during or after therapy and manage accordingly. Obtain careful medical history since CDAD may occur as late as 2 months or longer after anti-infective therapy is discontinued.

If CDAD is suspected or confirmed, discontinue anti-infectives not directed against C. difficile whenever possible. Initiate appropriate supportive therapy (e.g., fluid and electrolyte management, protein supplementation), anti-infective therapy directed against C. difficile (e.g., metronidazole, vancomycin), and surgical evaluation as clinically indicated.

Sensitivity Reactions

Hypersensitivity Reactions

Possible hypersensitivity reactions (e.g., urticaria, pruritus, rash, fever and chills, eosinophilia, joint pain or inflammation, edema, erythema, genital and anal pruritus, angioedema, shock, hypotension, vasodilatation, Stevens-Johnson syndrome, erythema multiforme, toxic epidermal necrolysis, exfoliative dermatitis, anaphylaxis).

If a hypersensitivity reaction occurs, discontinue cephalexin immediately and institute appropriate therapy as indicated (e.g., epinephrine, corticosteroids, maintenance of an adequate airway and oxygen).

Cross-hypersensitivity

Partial cross-sensitivity among cephalosporins and other β-lactam antibiotics, including penicillins and cephamycins.

Prior to initiation of therapy, make careful inquiry concerning previous hypersensitivity reactions to cephalosporins, penicillins, or other drugs. Cautious use recommended in patients with a history of hypersensitivity to penicillins: avoid use in those who have had an immediate-type (anaphylactic) hypersensitivity reaction and administer with caution in those who have had a delayed-type (e.g., rash, fever, eosinophilia) reaction.

General Precautions

History of GI Disease

Cephalosporins should be used with caution in patients with a history of GI disease, particularly colitis. (See Superinfection/Clostridium difficile-associated Diarrhea and Colitis under Cautions.)

Coombs’ Test Results

Positive direct Coombs’ test results reported with cephalosporins. This may interfere with certain hematologic studies or transfusion cross-matching procedures. May also cause positive Coombs’ tests in neonates whose mothers received a cephalosporin prior to delivery.

Selection and Use of Anti-infectives

To reduce development of drug-resistant bacteria and maintain effectiveness of cephalexin and other antibacterials, use only for treatment or prevention of infections proven or strongly suspected to be caused by susceptible bacteria.

When selecting or modifying anti-infective therapy, use results of culture and in vitro susceptibility testing. In the absence of such data, consider local epidemiology and susceptibility patterns when selecting anti-infectives for empiric therapy.

Specific Populations

Pregnancy

Category B.

Lactation

Distributed into milk. Use with caution.

Pediatric Use

Safety and efficacy in pediatric patients is based on clinical trials that used recommended dosages administered as capsules or oral suspension.

Use cephalexin capsules in children and adolescents only in those able to ingest capsules.

Geriatric Use

No overall differences in safety and efficacy in adults ≥65 years of age compared with younger adults, but the possibility of increased sensitivity in some geriatric individuals cannot be ruled out.

Substantially eliminated by kidneys; risk of toxicity may be greater in those with impaired renal function. Select dosage with caution and consider monitoring renal function because of age-related decreases in renal function. (See Renal Impairment under Dosage and Administration.)

Renal Impairment

Decreased clearance and increased plasma half-life.

Use with caution in those with markedly impaired renal function; close clinical observation and appropriate laboratory tests recommended.

Reduced dosage has been recommended in those with Cl_cr ≤ 40 mL/minute. (See Renal Impairment under Dosage and Administration.)

Common Adverse Effects

Adverse GI effects, including diarrhea, nausea, vomiting, dyspepsia, gastritis, abdominal pain.

Drug Interactions

Specific Drugs and Laboratory Tests

Cephalexin Pharmacokinetics

Absorption

Bioavailability

Rapidly and completely absorbed from the GI tract. Peak serum concentrations within 1 hour.

Food

Although peak serum concentrations are slightly lower and attained later when administered with food, total amount of drug absorbed is unchanged.

Distribution

Extent

Cephalosporins widely distributed into tissues and fluids.

Distributed into milk.

Plasma Protein Binding

6–15%.

Elimination

Metabolism

Not appreciably metabolized.

Elimination Route

Excreted in urine as unchanged drug by renal tubular secretion and glomerular filtration.

At least 70–90% of a dose eliminated in urine within 8–12 hours in adults with normal renal function.

Half-life

Adults with normal renal function: 0.5–1.2 hours.

Children: about 5 hours in neonates and 2.5 hours in children 3–12 months of age.

Special Populations

Decreased clearance and increased half-life in patients with renal impairment. Half-life is 7.7–13.9 in adults with Cl_cr <13.5 mL/minute.

Stability

Storage

Oral

Capsules

20–25°C (may be exposed to 15–30°C); tight, light-resistant container.

For Suspension

20–25°C. After reconstitution, refrigerate in a tight container; discard after 14 days.

Actions and Spectrum

• First generation cephalosporin with a limited spectrum of activity compared with second and third generation cephalosporins.

• Usually bactericidal.

• Like other β-lactam antibiotics, antibacterial activity results from inhibition of bacterial cell wall synthesis.

• In vitro spectrum of activity includes some gram-positive aerobic bacteria and some gram-negative aerobic bacteria. Inactive against anaerobic bacteria, fungi, and viruses.

• Gram-positive aerobes: active in vitro and in clinical infections against gram-positive aerobic bacteria including Staphylococcus aureus and S. epidermidis (including penicillinase-producing strains), Streptococcus pyogenes (group A β-hemolytic streptococci), and S. pneumoniae. Oxacillin-resistant (methicillin-resistant) staphylococci and most enterococci are resistant.

• Gram-negative aerobes: active in vitro and in clinical infections against some gram-negative aerobic bacteria including Haemophilus influenzae, Moraxella catarrhalis, Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis. Inactive against Acinetobacter, Citrobacter, Enterobacter, Listeria monocytogenes, Morganella morganii, Providencia, Pseudomonas, and Serratia.

Advice to Patients

• Advise patients that antibacterials (including cephalexin) should only be used to treat bacterial infections and not used to treat viral infections (e.g., the common cold).

• Importance of completing full course of therapy, even if feeling better after a few days.

• Advise patients that skipping doses or not completing the full course of therapy may decrease effectiveness and increase the likelihood that bacteria will develop resistance and will not be treatable with cephalexin or other antibacterials in the future.

• Advise patients that diarrhea is a common problem caused by anti-infectives and usually ends when the drug is discontinued. Importance of contacting a clinician if watery and bloody stools (with or without stomach cramps and fever) occur during or as late as 2 months or longer after the last dose.

• Importance of discontinuing therapy and informing clinician if an allergic reaction occurs.

• Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs as well as any concomitant illnesses.

• Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed.

• Importance of informing patients of other important precautionary information. (See Cautions.)

Preparations

Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

* available from one or more manufacturer, distributor, and/or repackager by generic (nonproprietary) name

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