Pharmacology: Cefalexin is a bactericidal and has antimicrobial activity against both Gram-positive and Gram-negative organisms.
Pharmacokinetics: Cefalexin is completely absorbed after oral administration either with or without food and rapidly excreted in the urine. Recovery in the urine of 70-100% of the drug given orally indicates virtually complete absorption. After an oral dose of 250 mg, Cefalexin (Zeporin) achieves the therapeutic urine concentrations. Therefore, increased doses are not required unless high plasma levels are considered necessary. It provides more than adequate antibacterial activity in body fluids and tissues. Taken orally, the serum concentration of this drug is found to be equal or greater than those resulting from comparable intramuscular doses of cephalotin or cephaloridine. It allows a wider margin of safety. Doses of 250-500 mg administered every 6 hours do not produce evidence of accumulation of the drug or signs of toxicity.
Microbiology: In vitro tests demonstrate that the cephalosporins are bactericidal because they inhibit cell wall synthesis. Cefalexin is active against the following organisms in vitro beta hemolytic Streptococci, including coagulase negative and penicillinase-producing strains, Streptococcus pneumoniae, Escherichia coli, Proteus mirabilis, Klebsiella sp., Neiserria catarrhalis, some strains of Haemophilus influenzae. Note: 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 sp., Pr. morganil and Pr. vulgaris. It has no activity against Pseudomonas or Herella species. When tested by in vitro methods, staphylococci exhibit cross resistance between cefalexin and methicillin type antibiotics.