Cefaclor, like the penicillins, is a beta-lactam antibiotic. By binding to specific penicillin-binding proteins (PBPs) located inside the bacterial cell wall, it 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 cefaclor interferes with an autolysin inhibitor.
Cefaclor is a second generation cephalosporin antibiotic with a spectrum resembling first-generation cephalosporins. In vitro tests demonstrate that the bactericidal action of the cephalosporins results from inhibition of cell-wall synthesis. Cefaclor has been shown to be active against most strains of the following microorganisms, both in vitro and in clinical infections: Gram positive aerobes - Staphylococci (including coagulase-positive, coagulase-negative, and penicillinase-producing strains), Streptococcus pneumoniae, and Streptococcus pyogenes (group A _-hemolytic streptococci). Gram-negative aerobes - Escherichia coli, Haemophilus influenzae (including _-lactamase-producing ampicillin-resistant strains), Klebsiella sp, and Proteus mirabilis.
No appreciable biotransformation in liver (approximately 60% to 85% of the drug is excreted unchanged in the urine within 8 hours).
Symptoms of overdose include diarrhea, nausea, stomach upset, and vomiting.