Source: Υπουργείο Υγείας (CY) Revision Year: 2018 Publisher: MEDOCHEMIE LTD, 1-10 Constantinoupoleos street, 3011 Limassol, Cyprus
Pharmacotherapeutic group: First-generation cephalosporins
ATC code: J01DB01
In vitro tests demonstrate that cephalosporins are bactericidal because of their inhibition of cell-wall synthesis.
Cefalexin is active against the following organisms in vitro:
Beta-haemolytic streptococci
Staphylococci, including coagulase-positive, coagulase-negative, and penicillinase-producing strains
Streptococcus pneumoniae
Escherichia coli
Proteus mirabilis
Klebsiella species
Haemophilus influenzae
Branhamella catarrhalis
Most strains of enterococci (Streptococcus faecalis) and a few strains of staphylococci are resistant to cefalexin. It is not active against most strains of Enterobacter species, Morganella morganii, and Pr. vulgaris. It has no activity against Pseudomonas or Herellea species or Acinetobacter calcoaceticus. Penicillin-resistant Streptococcus pneumoniae is usually cross-resistant to beta-lactam antibiotics. When tested by in vitro methods, staphylococci exhibit cross-resistance between cefalexin and methicillin-type antibiotics.
Cefalexin is acid stable and may be given without regard to meals. It is rapidly absorbed after oral administration. Following doses of 250mg, 500mg, and 1g, average peak serum levels of approximately 9, 18, and 32mg/l, respectively, were obtained at 1 hour. Measurable levels were present 6 hours after administration. Cefalexin 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 250mg, 500mg, and 1g doses were approximately 1,000, 2,200, and 5,000mg/l, respectively.
Cefalexin is almost completely absorbed from the gastro-intestinal tract, and 75-100% is rapidly excreted in active form in the urine. Absorption is slightly reduced if the drug is administered with food. The half-life is approximately 60 minutes in patients with normal renal function. Haemodialysis and peritoneal dialysis will remove cefalexin from the blood.
Peak blood levels are achieved one hour after administration, and therapeutic levels are maintained for 6-8 hours. Approximately 80% of the active drug is excreted in the urine within 6 hours. No accumulation is seen with dosages above the therapeutic maximum of 4g/day.
The half-life may be increased in neonates due to their renal immaturity, but there is no accumulation when given at up to 50mg/kg/day.
The daily oral administration of cefalexin to rats in doses of 250 or 500mg/kg prior to and during pregnancy, or to rats and mice during the period of organogenesis only, had no adverse effect on fertility, foetal viability, foetal weight, or litter size.
Cefalexin showed no enhanced toxicity in weanling and newborn rats as compared with adult animals.
The oral LD50 of cefalexin in rats is 5,000mg/kg.
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