Cefalin Capsule Mechanism of Action

Pharmacology: Pharmacodynamics: Cefalexin is a semi-synthetic, first generation cephalosporin which exerts its bactericidal activity by interfering with the bacterial cell wall synthesis. It binds to specific penicillin-binding proteins responsible for the synthesis of peptidoglycan, a heteropolymeric structure that gives the cell wall its mechanical stability. The final stage of peptidoglycan synthesis involves completion of the cross-linking of the terminal glycine residue of the pentaglycine bridge to the fourth residue of the pentapeptide. The transpeptidase that catalyzes this step is inhibited by cephalosporins. As a result, the bacterial cell wall is weakened, the cell swells and then ruptures.
ANTIMICROBIAL SPECTRUM OF ACTIVITY: Cefalexin  is active in vitro and in clinical infections against most strains of the following microorganisms: (See Table 1.)

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Cefalexin is inactive against methicillin-resistant staphylococci and most strains of enterococci (e.g., Enterococcus faecalis), Enterobacter spp., Morganella morganii, and Proteus vulgaris. It has no activity against Pseudomonas spp. or Acinetobacter calcoaceticus. Penicillin-resistant Streptococcus pneumoniae is usually cross-resistant to beta-lactam antibiotics.
It is suggested to carry out susceptibility tests.
Pharmacokinetics: Cefalexin is acid stable and is rapidly absorbed from gastrointestinal (GI) tract. After single oral doses of 250 and 500 mg in healthy, fasting adults with normal renal function, the mean peak serum concentrations (Cmax) are 9 and 18 mcg/mL respectively, and are achievedd within 1 hour of administration. Serum concentrations are still detectable after 6 hours.
When Cefalexin is administered with food, peak serum concentrations are slightly lower and are attained later, although the total amount of drug absorbed remains unchanged.
Cefalin readily diffuses into tissues, including bone, joints, and the pericardial as well as pleural cavities. It reaches therapeutic levels in the blood, urine, bile, synovial fluis, pus, tonsillar tissue, amniotic fluid, cord blood, and fetal blood. Cefalexin does not enter the cerebrospinal fluid (CSF) in significant quantities. The drug crosses the placenta and small quantities are found ub breast milk.
The serum half-life (t_½) of Cefalexin is 0.5 to 1.2 hours in adults with normal renal function. In adults with creatinine clearance of 13.5, 9.2 and 4 mL/minute, the serum t_½ were 7.7, 10.8, and 13.9, respectively.
Cefalexin is not metabolized in the body. It is excreted in the urine by both glomerular filtration and tubular secretion. About 70 to 90% of a single oral dose of cefalexin 250 or 500 is excreted within 8 - 12 hours in adults with normal renal function. Peak urine concentrations average about 2 mg/mL and occur 2 hours after a single 500 mg oral dose of cefalexin.