Cefaclor 375 mg (MR) · Tablets

The cefaclor extended-release tablet formulation of cefaclor is pharmacokinetically different from the cefaclor immediate-release capsule formulation of cefaclor. (See TABLE 1.) No direct comparisons with the suspension formulation of cefaclor have been conducted; therefore, there are no data with which to compare the pharmacokinetic properties of the extended-release tablet formulation and the suspension formulation. Until further data are available, the pharmacokinetic equivalence of the extended-release tablet and the suspension formulations should NOT be assumed.

Mechanism of Action — As with other cephalosporins, the bactericidal action of cefaclor results from inhibition of cell-wall synthesis.

Mechanism of Resistance — Resistance to cefaclor is primarily through hydrolysis of ß-lactamases alteration of penicillin-binding proteins (PBPs) and decreased permeability. Pseudomonas spp., Acinetobacter calcoaceticus and most isolates of Enterococci (Enterococcus faecalis, group D streptococci), Enterobacter spp., indole-positive Proteus, Morganella morganii (formerly Proteus morganii), Providencia rettgeri (formerly Proteus rettgeri) and Serratia spp. are resistant to cefaclor. Cefaclor is inactive against methicillin-resistant staphylococci, ß-lactamase-negative, ampicillin-resistant isolates of H. influenzae should be considered resistant to cefaclor despite apparent in vitro susceptibility to this agent.

List of Microorganisms — Cefaclor has been shown to be active against most isolates of the following microorganisms both in vitro and in clinical infections as described in the INDICATIONS AND USAGE section.

Gram-negative Bacteria — Haemophilus influenzae (excluding β-lactamase-negative, ampicillin-resistant isolates)

Moraxella catarrhalis — The following in vitro data are available, but their clinical significance is unknown. At least 90 percent of the following bacteria exhibit in vitro minimum inhibitory concentrations (MICs) less than or equal to the susceptible breakpoint for cefaclor against isolates of similar genus or organism group. However, the efficacy of cefaclor in treating clinical infections caused by these bacteria has not been established in adequate and well-controlled trials.

Propionibacterium acnes — For specific information regarding susceptibility test interpretive criteria and associated test methods and quality control standards recognized by FDA for this drug, please see: https://www.fda.gov/STIC.