General Administration Information
For storage information, see the specific product information within the How Supplied section.
-All dosage forms may be administered without regard to meals.
Oral Solid Formulations
-Capsules and Tablets: Swallow whole. May be taken without regard to meals.
Oral Liquid Formulations
-Cephalexin oral suspension may be taken without regard to meals.
-Shake well prior to each use.
-To ensure accurate dosage, measure dose with a calibrated oral syringe, spoon, or measuring cup.
-Review the manufacturer's reconstitution instructions for the particular product and package size as the amount of water used for reconstitution may vary between manufacturers.
-Follow the manufacturer's directions for mixing; the water volume is usually added in 2 aliquots, shaking well after each addition.
-Storage: After mixing, store under refrigeration for up to 14 days.
Gastrointestinal adverse reactions (nausea, vomiting, diarrhea) are some of the most common adverse reactions to cephalexin and occur in < 5% of patients receiving cephalexin in the general population. Other gastrointestinal effects include abdominal pain, gastritis, and dyspepsia. Colitis has been reported with the cephalosporin class.
Allergic reactions (i.e., rash (unspecified), pruritus, angioedema, and urticaria) have been observed with cephalexin. Erythema multiforme, Stevens-Johnson syndrome or toxic epidermal necrolysis have been reported rarely. Approximately 1-3% of treatment courses in the general population result in some kind of dermatologic allergic reaction. These reactions usually resolve upon discontinuation of the drug. Anaphylaxis or anaphylactoid reactions have also been reported and are likely to occur in 0.0001-0.1% of patients.
Cephalexin has been associated with acute generalized exanthematous pustulosis (AGEP). The non-follicular, pustular, erythematous rash starts suddenly and is associated with fever above 38 degrees C. Drugs are the main cause of AGEP. A period of 2-3 weeks after an inciting drug exposure appears necessary for a first episode of AGEP. Unintentional reexposure may cause a second episode within 2 days.
Nephrotoxicity occurs very rarely during therapy with cephalexin, but patients with renal dysfunction and patients receiving other nephrotoxic drugs may be more susceptible. Interstitial nephritis, a hypersensitivity reaction, has been reported with many of the cephalosporins, including rarely (< 1%) with cephalexin. Renal dysfunction, increased BUN and creatinine (i.e., azotemia), and toxic nephropathy have been reported with the cephalosporin class.
Seizures are a rare (< 1%), but serious, complication of cephalosporin therapy. More commonly associated with penicillins, the epileptogenic properties of both penicillins and cephalosporins are thought to be related to their beta-lactam ring. High doses and administration to patients with renal impairment (without an appropriate dosage reduction) are associated with an increased risk of seizures. Discontinue the drug if seizures occur; if clinically indicated, anticonvulsant therapy can be used.
Eosinophilia, neutropenia, thrombocytopenia, acute intravascular hemolysis, and hemolytic anemia have been reported in patients receiving cephalexin. Agranulocytosis, aplastic anemia, hemorrhage (bleeding), leukopenia, pancytopenia, and prolonged prothrombin time (hypoprothrombinemia) have been reported with cephalosporin-class antibiotics. Positive direct Coombs' tests have been reported in patients receiving cephalosporins. If hematological testing is performed in patients receiving cephalosporins, a positive Coombs' test should be considered as being possibly due to the antibiotic.
As with other cephalosporins, a transient rise in AST and ALT (elevated hepatic enzymes) concentrations has been observed with patients receiving cephalexin. Elevated transaminases have been noted in 1-7% of patients in the general population receiving cephalosporins. Other adverse events associated with the cephalosporin class include hepatic dysfunction (including transient hepatitis, cholestasis, and jaundice), hyperbilirubinemia, and elevated alkaline phosphatase and LDH.
Prolonged antibiotic use can result in an overgrowth of non-susceptible organisms such as Candida sp. and Clostridium difficile, which may cause superinfection. Local candidiasis infections, such as genital candidiasis, genital and anal pruritus (pruritus ani), vaginitis, and vaginal discharge have been reported with cephalexin. Diarrhea may be indicative of an antibiotic-associated colitis, and the possible development of pseudomembranous colitis from toxins produced by Clostridium difficile should be considered. Clostridium difficile associated diarrhea (CDAD) may range in severity from mild diarrhea to fatal colitis. If CDAD is suspected or confirmed, ongoing antibiotic use not directed against C. difficile may need to be discontinued. Appropriate fluid and electrolyte management, protein supplementation, antibiotic treatment of C. difficile, and surgical evaluation should be instituted as clinically indicated.
Generalized adverse events associated with cephalexin include dizziness, fatigue, headache, agitation, confusion, hallucinations, arthralgia, arthritis, and joint disorder. Fever has been reported with cephalosporin-class antibiotics.
A false-positive reaction for glucose in the urine has been observed in patients receiving cephalosporins and using Benedict's solution, Fehling's solution, or Clinitest tablets for urine glucose testing. However, this reaction has not been observed with glucose oxidase tests (e.g., Tes-tape, Clinistix, Diastix). Patients with diabetes mellitus who test their urine for glucose should use glucose tests based on enzymatic glucose oxidase reactions while on cephalexin treatment.
A positive direct Coombs test may develop in some patients receiving cephalosporins. In hematologic studies or in transfusion cross-matching procedures when antiglobulin tests are performed on the minor side or in Coombs' testing of newborns whose mothers received cephalexin before delivery, clinicians should keep in mind that a positive Coombs' test may be due to the drug.
Cephalexin is contraindicated in patients with cephalosporin hypersensitivity or cephamycin hypersensitivity. Cephalexin should be used cautiously in patients with hypersensitivity to penicillin. The structural similarity between cephalexin and penicillin causes these patients to be more susceptible to hypersensitivity reactions. Penicillins can cause a variety of hypersensitivity reactions ranging from mild rash to fatal anaphylaxis. Patients who have experienced severe penicillin hypersensitivity should not receive cephalexin. While the FDA-approved product label states that cross-hypersensitivity among beta-lactam antibiotics may occur in up to 10% of patients with a history of penicillin allergy, other experts report an incidence of cross-reactivity of approximately 3 to 7% of patients with a documented history to penicillin.
Because cephalexin is renally eliminated, use it with caution in patients with significant renal disease, renal impairment (CrCl < 30 mL/min, with or without dialysis) or renal failure. The degree of renal impairment and the severity of the infection will determine whether dose or dosing interval adjustments are required. Careful clinical observation and renal function monitoring should be conducted in these patients. Rarely, cephalexin may worsen renal function; pre-existing renal impairment may increase the risk of drug-induced renal toxicity.
Almost all antibacterial agents, including cephalexin, have been associated with pseudomembranous colitis (antibiotic-associated colitis), which may range in severity from mild to life-threatening. In the colon, overgrowth of Clostridia may occur when normal flora is altered subsequent to antibacterial administration. The toxin produced by Clostridium difficile is a primary cause of pseudomembranous colitis. Consider pseudomembranous colitis as a potential diagnosis in patients presenting with diarrhea after antibacterial administration. Systemic antibiotics should be prescribed with caution to patients with inflammatory bowel disease such as ulcerative colitis or other GI disease. If diarrhea develops during therapy, discontinue the drug. After a diagnosis of pseudomembranous colitis, institute therapeutic measures. Practitioners should be aware that antibiotic-associated colitis can occur over 2 months or more after discontinuation of systemic antibiotic therapy; a careful medical history should be taken.
All cephalosporins, including cephalexin, may rarely cause hypothrombinemia and have the potential to cause bleeding. Cephalosporins that contain the NMTT side chain (e.g., cefoperazone, cefamandole, cefotetan) have been associated with an increased risk for bleeding. Those at risk include patients with renal or hepatic impairment, patients with poor nutritional status, patients receiving a prolonged course of antimicrobial therapy, and patients previously stabilized on anticoagulant therapy. Prothrombin time should be monitored in at risk patients with a preexisting coagulopathy (e.g., vitamin K deficiency) because these patients are at a higher risk for developing bleeding complications; exogenous vitamin K should be administered as indicated.
Description: Cephalexin is an oral, first-generation cephalosporin antibiotic with activity against most gram-positive bacteria. Cephalexin is used primarily in children for the treatment of infections of the respiratory tract (e.g., pharyngitis, tonsillitis), skin infections, bone and joint infections, and urinary tract infections caused by susceptible staphylococci, Streptococcus pneumoniae, and group A beta-hemolytic streptococci. Cephalexin is considered one of the recommended agents for group A streptococcal (GAS) pharyngitis in patients with penicillin allergy. Cephalexin is FDA-approved for use in pediatric patients older than 1 year of age.
Per the manufacturer, this drug has been shown to be active against most strains of the following microorganisms either in vitro and/or in clinical infections: Escherichia coli, Haemophilus influenzae (beta-lactamase negative), Klebsiella pneumoniae, Moraxella catarrhalis, Proteus mirabilis, Staphylococcus aureus (MSSA), Staphylococcus epidermidis, Streptococcus pneumoniae, Streptococcus pyogenes (group A beta-hemolytic streptococci)
NOTE: The safety and effectiveness in treating clinical infections due to organisms with in vitro data only have not been established in adequate and well-controlled clinical trials.
This drug may also have activity against the following microorganisms: Streptococcus agalactiae (group B streptococci)
NOTE: Some organisms may not have been adequately studied during clinical trials; therefore, exclusion from this list does not necessarily negate the drug's activity against the organism.
For the treatment of skin and skin structure infections (e.g., cellulitis, impetigo):
Infants*, Children, and Adolescents: 25 to 50 mg/kg/day PO in 2 to 4 divided doses (Max: 2 g/day for most SSTIs, Max: 1 g/day for impetigo). In general, a treatment duration of 7 to 14 days is recommended for most indications. Clinical practice guidelines recommend cephalexin as a treatment option for the management of mild nonpurulent SSTIs (e.g., cellulitis) and for moderate purulent SSTIs (e.g., furuncle, carbuncle, abscess) caused by methicillin susceptible Staphylococcus aureus (MSSA). Cephalexin is not recommended for the treatment of severe infections. For impetigo, a treatment duration of 7 days is recommended. Unless cultures have yielded streptococci alone, antibiotic therapy for ecthyma or impetigo should cover S. aureus. Because S. aureus isolates from ecthyma or impetigo are usually methicillin susceptible, cephalexin or dicloxacillin is recommended. If methicillin resistance is suspected or confirmed, doxycycline, clindamycin, or sulfamethoxazole-trimethoprim is recommended.
For the treatment of upper respiratory tract infections, including tonsillitis and/or pharyngitis secondary to Streptococcus pyogenes (i.e., primary rheumatic fever prophylaxis):
Infants*: 20 mg/kg/dose PO twice daily for 10 days is recommended by guidelines for group A streptococcal pharyngitis as an alternative for those with non-immediate type penicillin allergy.
Children and Adolescents: 20 mg/kg/dose PO twice daily (Max: 500 mg/dose) for 10 days is recommended by guidelines for group A streptococcal pharyngitis as an alternative for those with non-immediate type penicillin allergy. The FDA-approved dosage range is 25 to 50 mg/kg/day PO in 2 to 4 divided doses (Max: 2 g/day). In general, a treatment duration of 7 to 14 days is recommended for most indications. Cephalexin given twice daily has been shown to achieve comparable bacteriologic and clinical cure rates as cephalexin given 3 or 4 times daily in clinical studies of children with group A beta-hemolytic streptococcal tonsillopharyngitis.
For the treatment of lower respiratory tract infections (LRTIs), including community-acquired pneumonia (CAP):
-for the treatment of nonspecific lower respiratory tract infections (LRTIs):
Infants*, Children, and Adolescents: 25 to 50 mg/kg/day PO divided in 2 to 4 doses (Max: 2 g/day) for mild to moderate infections or 50 to 100 mg/kg/day PO divided in 3 to 4 doses (Max: 4 g/day) for severe infections.
-for the treatment of community-acquired pneumonia (CAP):
Infants 4 to 11 months*, Children, and Adolescents: 75 to 100 mg/kg/day PO divided in 3 or 4 doses (Max: 4 g/day) for 10 days. Guidelines recommend cephalexin as initial therapy for mild infections or oral step-down therapy for infections due to methicillin-sensitive S. aureus (MSSA).
For the treatment of bone and joint infections (i.e., osteomyelitis, infectious arthritis):
Infants*, Children, and Adolescents: 100 mg/kg/day PO in 4 divided doses is commonly used in clinical practice and is recommended in guidelines for septic arthritis. 75 to 100 mg/kg/day PO in 3 to 4 divided doses (Max: 4 g/day) is recommended by the American Academy of Pediatrics (AAP) for bone and joint infections. The FDA-approved dosage for severe infections in pediatric patients older than 1 year is 50 to 100 mg/kg/day PO in 3 to 4 divided doses (Max: 4 g/day).
For the treatment of genitourinary infection (i.e., urinary tract infection (UTI), cystitis, prostatitis):
NOTE: There is substantial geographical variability in susceptibility to cephalexin; consider local susceptibility patterns before prescribing cephalexin for empiric therapy.
Infants* and Children 2 months to 2 years: 50 to 100 mg/kg/day PO in 4 divided doses for 7 to 14 days is recommended by the American Academy of Pediatrics (AAP) for the treatment of initial UTI in febrile infants and young children. The general FDA-approved dosage in pediatric patients older than 1 year is 25 to 50 mg/kg/day PO in 2 to 4 divided doses. For severe infections, 50 to 100 mg/kg/day PO in 3 to 4 divided doses may be used. In general, a treatment duration of 7 to 14 days is recommended for most indications.
Children and Adolescents 3 to 17 years: 25 to 50 mg/kg/day PO in 2 to 4 divided doses (Max: 2 g/day). For severe infections, 50 to 100 mg/kg/day PO in 3 to 4 divided doses (Max: 4 g/day) may be used. In general, a treatment duration of 7 to 14 days is recommended for most indications.
For urinary tract infection (UTI) prophylaxis* in infants with hydronephrosis or vesicoureteral reflux:
NOTE: Guidelines from the Pediatric Vesicoureteral Reflux (VUR) Panel recommend antibiotic prophylaxis for all grades of vesicoureteral reflux in all children younger than 1 year. The American Academy of Pediatrics (AAP) states that routine antimicrobial prophylaxis for patients aged 2 to 24 months with vesicoureteral reflux is not supported by currently available data; however, antimicrobial prophylaxis is still utilized and has biological plausibility. Further research is needed.
Neonates and Infants younger than 2 months: 10 to 15 mg/kg/dose PO once daily.
Infants 2 months and older: Cephalexin is not generally used. Sulfamethoxazole; trimethoprim or nitrofurantoin are preferred agents for UTI prophylaxis in infants aged 2 months or older.
For bacterial endocarditis prophylaxis*:
Children and Adolescents: 50 mg/kg PO as a single dose (Max: 2 g/dose) given 30 to 60 minutes before procedure as an alternative for patients allergic to penicillin. Prophylaxis is recommended for at-risk cardiac patients who are undergoing dental procedures that involve manipulation of gingival tissue, manipulation of the periapical region of teeth, or perforation of the oral mucosa. Cardiac patients that are considered to be at highest risk include those with prosthetic cardiac valves or prosthetic material used for cardiac valve repair, previous infective endocarditis, select types of congenital heart disease (CHD), and cardiac transplantation with valvulopathy.
For the treatment of otitis media:
Children and Adolescents: 75 to 100 mg/kg/day PO in 3 to 4 divided doses (Max: 2 to 4 g/day). Although cephalexin is FDA-approved for the treatment of otitis media, it is not recommended as a treatment option in the guidelines by the American Academy of Pediatrics (AAP). Second- or third-generation oral cephalosporins (i.e., cefdinir, cefuroxime, and cefpodoxime) are the recommended agents for patients allergic to amoxicillin.
Maximum Dosage Limits:
Safety and efficacy have not been established; however, doses up to 15 mg/kg/day PO have been used for UTI prophylaxis.
100 mg/kg/day PO.
100 mg/kg/day PO (Max: 4 g/day).
100 mg/kg/day PO (Max: 4 g/day).
Patients with Hepatic Impairment Dosing
No dosage adjustments are necessary.
Patients with Renal Impairment Dosing
The following dosage adjustments are based on a usual dose in pediatric patients of 25 to 50 mg/kg/day PO divided every 6 hours :
CrCl > 50 mL/min/1.73 m2: No dosage adjustment needed.
CrCl 30 to 50 mL/min/1.73 m2: 5 to 10 mg/kg/dose PO every 8 hours.
CrCl 10 to 29 mL/min/1.73 m2: 5 to 10 mg/kg/dose PO every 12 hours.
CrCl < 10 mL/min/1.73 m2: 5 to 10 mg/kg/dose PO every 24 hours.
FDA-approved dosage adjustments (adolescents at least 15 years of age):
CrCl >= 60 mL/min: No dosage adjustment needed.
CrCl 30 to 59 mL/min: No dosage adjustments; maximum daily dose should not exceed 1 gram PO.
CrCl 15 to 29 mL/min: 250 mg PO every 8 hours or 12 hours.
CrCl 5 to 14 mL/min (not yet on dialysis): 250 mg PO every 24 hours.
CrCl 1 to 4 mL/min (not yet on dialysis): 250 mg PO every 48 hours or 60 hours.
NOTE: Although the FDA product label states there is insufficient information to make dosage adjustment recommendations in patients on hemodialysis, some experts recommend the following regimens:
5 to 10 mg/kg/dose PO every 24 hours, after hemodialysis.
For mild infections: 5 to 10 mg/kg/dose PO every 24 hours.
For exit-site and tunnel infections: 10 to 20 mg/kg/day given in 1 or 2 doses (Max: 1000 mg/day).
Monograph content under development
Mechanism of Action: Cephalexin, a beta-lactam antibiotic similar to penicillins, inhibits the third and final stage of bacterial cell wall synthesis by preferentially binding to specific penicillin-binding proteins (PBPs) that are located inside the bacterial cell wall. Penicillin-binding proteins are responsible for several steps in the synthesis of the cell wall and are found in quantities of several hundred to several thousand molecules per bacterial cell. Penicillin-binding proteins vary among different bacterial species. Thus, the intrinsic activity of cephalexin, as well as the other cephalosporins and penicillins, against a particular organism depends on its ability to gain access to and bind with the necessary PBP. Like all beta-lactam antibiotics, cephalexin's ability to interfere with PBP-mediated cell wall synthesis ultimately leads to cell lysis. Lysis is mediated by bacterial cell wall autolytic enzymes (i.e., autolysins). The relationship between PBPs and autolysins is unclear, but it is possible that the beta-lactam antibiotic interferes with an autolysin inhibitor.
Beta-lactams, including cephalexin, exhibit concentration-independent or time-dependent killing. In vitro and in vivo animal studies have demonstrated that the major pharmacodynamic parameter that determines efficacy for beta-lactams is the amount of time free (non-protein bound) drug concentrations exceed the minimum inhibitory concentration (MIC) of the organism (free T above the MIC). This microbiological killing pattern is due to the mechanism of action, which is acylation of PBPs. There is a maximum proportion of PBPs that can be acylated; therefore, once maximum acylation has occurred, killing rates cannot increase. Free beta-lactam concentrations do not have to remain above the MIC for the entire dosing interval. The percentage of time required for both bacteriostatic and maximal bactericidal activity is different for the various classes of beta-lactams. Cephalosporins require free drug concentrations to be above the MIC for 35% to 40% of the dosing interval for bacteriostatic activity and 60% to 70% of the dosing interval for bactericidal activity.
Considering site of infection and appropriate cephalexin dosing, oxacillin-susceptible Staphylococcus sp. can be considered susceptible to cephalexin. Breakpoints for cefazolin are used to predict results for cephalexin for treatment of uncomplicated urinary tract infections due to E. coli, K. pneumoniae, and P. mirabilis.
Pharmacokinetics: Cephalexin is administered orally. Approximately 10 to 15% of the circulating drug is protein-bound. Cephalexin is distributed into most body tissues and fluids but does not reach therapeutic concentrations within the CSF or aqueous humour. Cephalexin is largely excreted unchanged (90%) in the urine via glomerular filtration and tubular secretion, which leads to high urinary concentrations. The elimination half-life is approximately 1 hour in adults with normal renal function.
Affected cytochrome P450 isoenzymes: none
Cephalexin is rapidly absorbed after oral administration. Peak concentrations are reached approximately 30-60 minutes after administration in infants and children. In a pharmacokinetic study in 20 infants and children, peak concentrations at 30 minutes were higher when cephalexin was given in the fasting state (23.4 mg/L) compared to the fed state (8.7 mg/L). However, the FDA-approved labeling states that cephalexin may be given without regard to meals.
Infants and Children
The elimination half-life of cephalexin in infants and children is approximately 1 hour, which is similar to the half-life in adults.
The pharmacokinetics of cephalexin in pediatric patients with renal impairment have not been extensively studied. However, cephalexin is primarily excreted by the kidneys and clearance is decreased in patients with renal impairment. In adults with renal impairment, the elimination half-life of cephalexin is prolonged to 4-6 hours in patients with a CrCl of 15-30 ml/min, 6-10 hours in patients with a CrCl of 5-15 ml/min, and 30-40 hours in patients with a CrCl < 5 ml/min. Cephalexin is moderately dialyzable (20-50%).