1 INDICATIONS AND USAGE

1.1 Respiratory Tract Infections

Cephalexin is indicated for the treatment of respiratory tract infections caused by susceptible isolates of Streptococcus pneumoniae and Streptococcus pyogenes.

1.2 Otitis Media

Cephalexin is indicated for the treatment of otitis media caused by susceptible isolates of Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, Streptococcus pyogenes, and Moraxella catarrhalis.

1.3 Skin and Skin Structure Infections

Cephalexin is indicated for the treatment of skin and skin structure infections caused by susceptible isolates of the following Gram-positive bacteria: Staphylococcus aureus and Streptococcus pyogenes.

1.4 Bone Infections

Cephalexin is indicated for the treatment of bone infections caused by susceptible isolates of Staphylococcus aureus and Proteus mirabilis.

1.5 Genitourinary Tract Infections

Cephalexin is indicated for the treatment of genitourinary tract infections, including acute prostatitis, caused by susceptible isolates of Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae.

1.6 Usage

To reduce the development of drug-resistant bacteria and maintain the effectiveness of cephalexin capsules, and cephalexin for oral suspension and other antibacterial drugs, cephalexin capsules, and cephalexin for oral suspension should be used only to treat infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information is available, this information should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy.

7 DRUG INTERACTIONS

7.1 Metformin

Administration of cephalexin with metformin results in increased plasma metformin concentrations and decreased renal clearance of metformin.

Careful patient monitoring and dose adjustment of metformin is recommended in patients concomitantly taking cephalexin and metformin [see Clinical Pharmacology (12.3)].

7.2 Probenecid

The renal excretion of cephalexin is inhibited by probenecid. Co- administration of probenecid with cephalexin is not recommended.

7.3 Interaction with Laboratory or Diagnostic Testing

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

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Cephalexin is a cephalosporin antibacterial drug [see Microbiology (12.4)].

12.3 Pharmacokinetics

Absorption: Cephalexin is acid stable and may be given without regard to meals. Following doses of 250 mg, 500 mg, and 1 g, average peak serum levels of approximately 9, 18, and 32 mcg/mL, respectively, were obtained at 1 hour. Serum levels were detectable 6 hours after administration (at a level of detection of 0.2 mcg/mL).

Distribution: Cephalexin is approximately 10% to 15% bound to plasma proteins.

Excretion: Cephalexin is excreted in the urine by glomerular filtration and tubular secretion. Studies showed that over 90% of the drug was excreted unchanged in the urine within 8 hours. During this period, peak urine concentrations following the 250 mg, 500 mg, and 1 g doses were approximately 1000, 2200, and 5000 mcg/mL respectively.

Drug Interactions
In healthy subjects given single 500 mg doses of cephalexin and metformin, plasma metformin mean Cmax and AUC increased by an average of 34% and 24%, respectively, and metformin mean renal clearance decreased by 14%. No information is available about the interaction of cephalexin and metformin following multiple doses of either drug.

12.4 Microbiology

Mechanism of Action

Cephalexin is a bactericidal agent that acts by the inhibition of bacterial cell-wall synthesis.

Resistance

Methicillin-resistant staphylococci and most isolates of enterococci are resistant to cephalexin. Cephalexin is not active against most isolates of Enterobacter spp., Morganella morganii, and Proteus vulgaris. Cephalexin has no activity against Pseudomonas spp., or Acinetobacter calcoaceticus. Penicillin-resistant Streptococcus pneumoniae is usually cross-resistant to beta-lactam antibacterial drugs.

Antimicrobial Activity

Cephalexin has been shown to be active against most isolates of the following bacteria both in vitro and in clinical infections [see Indications and Usage (1)].

Gram-positive bacteria

Staphylococcus aureus (methicillin-susceptible isolates only) Streptococcus pneumoniae (penicillin-susceptible isolates)

Gram-negative bacteria

Escherichia coli

Haemophilus influenzae

Klebsiella pneumoniae

Moraxella catarrhalis

Proteus mirabilis

Susceptibility Testing

For specific information regarding susceptibility test interpretive criteria and associated test methods and quality control standards recognized by FDA for this drug, please see: https://www.fda.gov/STIC**.**