Pharmacotherapeutic group: J01DB01, First generation Cephalosporins
Cefalexin monohydrate is bactericidal and has antimicrobial activity similar to that of cephaloridine or cephalothin against both gram-negative and gram-positive organisms. Chemically it is (6R, 7R)-7-[[(2R)-2-Amino-2-phenylacetyl] amino]-3-methyl-8-oxo-5-thia-1-azabicyclo [4.2.0] oct-2-ene-2-carboxylic acid monohydrate. The empirical formula is C6H17N3O4S1H2O representing a molecular weight of 365.4g/mol
| Image fro Wikipedia |
Pharmacodynamics
By binding to specific penicillin-binding proteins (PBPs) located inside the bacterial cell wall, Cefalexin inhibits the third and last stage of bacterial cell wall synthesis. Cell lysis is then mediated by bacterial cell wall autolytic enzymes such as autolysins; it is possible that cephalexin interferes with an autolysin inhibitor.
Therapeutic indication
Cephalexin is indicated in the treatment of the folloeing Infections due to susceptible micro-organisms: respiratory tract infections; otitis media; skin and soft tissue infections; bone and joint infections; genito-urinary tract infections, including prostatitis; dental infections.
Cephalexin is active against the following organisms in vitro: beta-haemolytic streptococci; staphylococci, including coagulase-positive, coagulase-negative and penicillinase-producing strains; streptococcus pneumonia; Escherichia coli; Proteus mirabilis; Krebsiella species, Haemophilus influenza; Branhamella cutarrhalis
Most strains of enterococci (Streptococcus faecalis) and a few strains of staphylococci are resistant to cephalexin. It is not active against most strains of Enterobacter species, Morganella morganii and Pr. Vulgaris. It has no activity against pseudomonas or Herellea species. When tested by in vitro methods, staphylococci exhibit cross-resistance between cephalexin and methicillin-type antibiotics
Interactions
Probenecid causes reduced excretion of cephalexin, leading to increased plasma concentration. Cephalosporins have an increased risk of nephrotoxicity in the presence of amphotericin, loop diuretics, aminoglycosides, capreomycin or vancomycin. Hypokalemia has been described in patients taking cytotoxic drugs for leukaemia when they were given gentamicin and cephalexin
Contraindications
Cephalexin is contraindicated in patients with known allergy to the cephalosporins group of antibiotics or any of the excipients. Cephalexin is contraindicated in patients with porphyria. Patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption should not take this medicine.
Posology and method of administration
Adults
The adult dosage ranges from 1-4g daily in divided doses; most infections will respond to a dosage of 500mg every 8 hours. For skin and soft tissue infections, streptococcal pharyngitis and mild, uncomplicated urinary tract infections, the usual dosage is 250 mg every 6 hours or 500mg every 12 hours. For more severe infections or those caused by less susceptible organisms, larger doses may be needed. If daily doses of cephalexin greater than 4g are required, parenteral cephalosporins, in appropriate doses, should be considered
Elderly
As for adults. Reduce dosage if renal function is markedly impaired
Children
The usual recommended daily dosage for children is 25-50mg/kg (10-20mg/lb) in divided doses. For skin and soft tissue infections, streptococcal pharyngitis and mild, uncomplicated urinary tract infections, the total daily dose may be divided and administered every 12 hours.
For severe infections, the dosage may be doubled. In the therapy of otitis media, clinical studies have shown that a dosage of 75-100 mg/kg/day in 4 divided doses is required. In the treatment of beta-haemolytic streptococcal infections, a therapeutic dose should be administered for atleast 10 days.
Pregnancy and lactation
Usage in pregnancy: although laboratory and clinical studies have shown no evidence of teratogenicity, cautions, should be exercised when prescribing for the pregnant patient.
Usage in nursing mothers: the excretion of cephalexin in human breast milk increased up to 4 hours following a 500mg dose. The drug reached a maximum level of 4 micrograms/ml then decreased gradually and had disappeared 8 hours after administration. Caution should be exercised when cephalexin is administered to a nursing woman
