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Pronunciation: SEF-a-LEX-in
Class: Antibiotic, Cephalosporin

Trade Names

- Tablets 250 mg
- Tablets 500 mg
- Powder for oral suspension 125 mg per 5 mL
- Powder for oral suspension 250 mg per 5 mL

- Capsules 250 mg
- Capsules 500 mg
- Capsules 750 mg

APO-Cephalex (Canada)
Novo-Lexin (Canada)
Nu-Cephalex (Canada)


Inhibits mucopeptide synthesis in bacterial cell wall.

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Cephalexin is rapidly absorbed. C max is about 9 to 32 mcg/mL (250 mg to 1 g doses). T max is 1 h.


Cephalexin is 10% protein bound.


More than 90% is excreted unchanged in the urine within 8 h. The half-life is 50 to 80 min.

Indications and Usage

Treatment of infections of respiratory tract, urinary tract, skin and skin structures, and bone; treatment of otitis media caused by susceptible strains of specific microorganisms.


Hypersensitivity to cephalosporins.

Dosage and Administration


PO 1 to 4 g/day in divided doses (max, 4 g/day).


PO 25 to 50 mg/kg/day in divided doses.

General Advice

  • Administer with food or milk if GI upset occurs. Food slows but does not decrease absorption.
  • Shake oral suspension well before measuring and administering. Space doses evenly around the clock.


Oral suspension is stable up to 14 days after reconstitution when refrigerated. Store capsules and tablets at room temperature (59° to 86°F).

Drug Interactions


May increase metformin plasma C max and AUC.


Inhibition of renal excretion of cephalexin.

Laboratory Test Interactions

May cause false-positive urine glucose test results with Benedict solution, Fehling solution, or Clinitest tablets, but not with enzyme-based tests (eg, Clinistix , Tes-Tape ); false-positive test results for proteinuria with acid and denaturization-precipitation tests; false-positive direct Coombs test results in certain patients (eg, those with azotemia); false elevations in urinary 17-ketosteroid values.

Adverse Reactions


Agitation, confusion, dizziness, fatigue, hallucinations, headache.


Anorexia; abdominal pain or cramps; colitis, including pseudomembranous colitis; diarrhea; dyspepsia; flatulence; gastritis; nausea; vomiting.


Genital moniliasis, genital pruritus, reversible interstitial nephritis, vaginitis and vaginal discharge.


Eosinophilia, hemolytic anemia, neutropenia, thrombocytopenia.


Cholestatic jaundice, elevated AST and ALT, hepatitis.


Arthralgia, arthritis, joint disorder.


Anal pruritus; anaphylaxis; candidal overgrowth; hypersensitivity, including rash, Stevens-Johnson syndrome, angioedema, erythema multiforme, toxic epidermal necrolysis, and urticaria.



Monitor patient's response to therapy. Instruct patient to notify health care provider if infection does not appear to improve or worsens. Monitor prothrombin time in patients on anticoagulants. Monitor patient for adverse reactions and signs of superinfection.


Category B .


Excreted in breast milk.


Cephalosporins may accumulate in newborns.


Reactions range from mild to life-threatening. Administer drug with caution to penicillin-sensitive patients because of possible cross-reactivity.

Renal Function

Use drug with caution in patients with renal function impairment. Dosage adjustment based on renal function may be required.


May result in bacterial or fungal overgrowth of nonsusceptible microorganisms.

GI disease

Use with caution, particularly colitis.

Pseudomembranous colitis

Consider in patients in whom diarrhea develops.



Diarrhea, epigastric distress, hematuria, nausea, vomiting.

Patient Information

  • Instruct patient to complete full course of therapy.
  • Advise patient to take with food or milk if GI distress occurs.
  • Remind patient to check body temperature daily. Advise patient to notify health care provider immediately if fever persists for more than a few days or if high fever (more than 102°F) or shaking chills are noted.
  • Advise patient to maintain normal fluid intake while using this medication.
  • Advise diabetic patient to use enzyme-based tests (eg, Clinistix , Tes-Tape ) for monitoring urine glucose because drug may give false results with other tests.
  • Instruct patient to report the following symptoms to health care provider: diarrhea, hives, muscle or joint pain, nausea, skin rash, vomiting.
  • Instruct patient to report signs of superinfection: black “furry” tongue, white patches in mouth, foul-smelling stools, vaginal itching or discharge.
  • Warn patient that diarrhea that contains blood or pus may be a sign of serious disorders. Tell patient to seek medical care and not to treat at home.
  • Instruct patient to seek emergency care immediately if wheezing or difficulty breathing occurs.

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