Distaclor Mechanism of Action



A. Menarini


Zuellig Pharma
Full Prescribing Info
Pharmacology: Cefaclor is well absorbed after oral administration to fasting subjects. Total absorption is the same whether the drugs is given with or without food, however, when it is taken with food, the peak concentration achieved is 50% to 75% of that observed when the drug is administered to fasting subjects and generally appears from three fourths to 1 hour later. Following administration of 250-mg, 500-mg, and 1-g doses to fasting subjects, average peak serum levels of approximately 7, 13, and 23 mg/L respectively were obtained within 30 to 60 minutes. Approximately 60% to 85% of the drug is excreted unchanged in the urine within 8 hours, the greater portion being excreted within the first 2 hours. During this 8-hour period, peak urine concentrations following the 250-mg, 500-mg, and 1-g doses were approximately 600, 900 and 1,900 mg/L respectively. The serum half-life in normal subjects is approximately 1 hour (range 0.6 to 0.9). In patients with reduced renal function, the serum half life of cefaclor is slightly prolonged. In those with complete absence of renal function, the plasma half-life of the intact molecule is 2.3 to 2.8 hours. Excretion pathways in patients with markedly impaired renal function have not been determined. Hemodialysis shortens the half-life by 25% to 30%.
Microbiology: In vitro tests demonstrate that the bactericidal action of the cephalosporins results from their inhibition of cell-wall synthesis. While in vitro studies have demonstrated the susceptibility of most strains of the following organisms to cefaclor, clinical efficacy for infections other than those included in the Indications and Dosage & Administration section is unknown.
Aerobes, Gram-positive: Staphylococci, including coagulase-positive, coagulase-negative and penicillinase-producing strains (when tested by in vitro methods), exhibit cross-resistance between cefaclor and methicillin; Streptococcus pneumoniae; Streptococcus pyogenes.
Aerobes, Gram-negative: Citrobacter diversus; Escherichia coli; Haemophilus influenzae, including β-lactamase-producing, ampicillin-resistant strains; Klebsiella spp; Moraxella (Branhamella) catarrhalis; Neisseria gonorrhoeae; Proteus mirabilis.
Anaerobes: Bacteroides spp (excluding Bacteroides fragilis); Peptococcus niger; Peptostreptococcus spp; Propionibacteria acnes.
Note: Methicillin-resistant staphylococci and most strains of enterococci [Enterococcus faecalis (formerly Streptococcus faecalium) and Enterococcus faecium (formerly Streptococcus faecium)] are resistant to cefaclor and other cephalosporins. Cefaclor is not active against most strains of Enterobacter spp, Serratia spp, Morganella morganii, Proteus vulgaris, and Providencia rettgeri. It has no activity against Pseudomonas spp or Acinetobacter spp.
Disk Susceptibility Tests: Diffusion techniques: Quantitative methods that require measurement of zone diameters give the most precise estimates of antibiotic susceptibility of bacteria to antimicrobial agents. One such standard procedure has been recommended for use with disks to test, susceptibility of organisms to cefaclor, using the 30 μg cefaclor disk. Interpretation involves the correlation of the diameters obtained in the disk test with the minimum inhibitory concentration (MIC) for cefaclor.
Reports from the laboratory giving results of the standard single-disk susceptibility tests with a 30 μg cefaclor disk should be interpreted according to the following criteria: (See Table 1.)

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When Testing *H. influenzae: (See Table 2.)

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Although the spectrum of activity of cefaclor is qualitatively similar to that of cephalothin and of the other first-generation cephalosporins, its activity against H. influenzae is considerably greater than that of the first-generation cephalosporins. For this reason, a disk containing 30μg of cefaclor may be used to determine the susceptibility of H. influenzae using the method described by NCCLS. In the testing of H. influenzae (on Mueller-Hinton agar supplemented with haemoglobin and a commercial VX supplement) or other organisms, zone diameter interpretive criteria, are identical to those used for the cephalothin disk: ≥18 mm, susceptible, 15-17 mm, moderately susceptible (intermediate for Haemophilus); and ≤14 mm, resistant.
A report of "Susceptible" indicates that the pathogen is likely to be inhibited by generally achievable blood levels. A report of "Intermediate" suggests that the organism would be susceptible if high dosage is used or if the infection is confined to tissue and fluids in which high antibiotic levels are obtained. A report of "Resistant" indicates that achievable concentration of the antibiotic are unlikely to be inhibitory and other therapy should be selected.
Standardized procedures require the use of laboratory control organisms. The 30μg cefaclor disk should give the following zone diameters: (See Table 3.)

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Dilution techniques: Use a standardized dilution method 2 (broth, agar, microdilution) or equivalent with cefaclor powder. The MIC values obtained should be interpreted according to the following criteria: (See Table 4.)

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As with standard diffusion techniques, dilution methods require the use of laboratory control organisms. Standard cefaclor powder should provide the following MIC values: (See Table 5.)

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