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In vitro effect on group A streptococci of loracarbef versus cefadroxil, cefaclor and penicillin V.

The in vitro activity of loracarbef, penicillin V, cefaclor and cefadroxil against log and stationary phase cultures of group A streptococci was compared. MICs and MBCs were determined with the broth dilution method and by a modified agar plate dilution technique where the beta-lactams were inactivated after the MICs were determined allowing inhibited but not killed organisms to grow on further incubation. The MICs of loracarbef and the two cephalosporins were 16-32 times higher than those of penicillin V. In plate dilution the MBC/MIC ratios of all agents were < or = 2 for log phase cultures. With stationary phase cultures, especially in the broth dilution test, the MBC/MIC ratios of loracarbef and the two cephalosporins were > or = 32 for a large number of strains. The phenotype response of stationary phase cultures to beta-lactam antibiotics may not only be related to the physiological status of the streptococci, to the culture conditions and to the beta-lactam under test. The present investigation indicated that the phenotypic response was also an intrinsic property of certain strains.

Anti-Bacterial Agents↗

Hydrolysis of 3-chloro-3-cephems. Intramolecular nucleophilic attack in cefaclor.

The chemical reactivity of 3-chloro-3-cephems was found to be similar to that of the correspondingly substituted 7-aminocephalosporanic acids and 12-13 times greater than that of the correspondingly substituted 7-aminode-acetoxycephalosporanic acids. Cefaclor, 7-(D-2-amino-2-phenylacetamido)-3-chloro-3-cephem-4-carboxylic acid, was found to undergo intramolecular nucleophilic attack at the beta-lactam. Loss of chlorine from 3-chloro-3-cephem may be a general reaction subsequent to beta-lactam opening.

Bacteria↗

In vitro activity of cefaclor against aerobic and anaerobic bacteria.

Cefaclor (CCL), a new cephalosporin, was tested in vitro against 602 (271 anaerobic and 331 aerobic) clinical isolates in comparison with cephalothin, cefazolin, cephradine, and cefamandole. Sixteen micrograms of CCL per ml inhibited 68% of all aerobes tested and 80% of the 211 enteropathogenic organisms (Escherichia coli, Salmonella, and Shigella) isolated from cases of infantile diarrhoea. CCL inhibited 88% of gram-positive anaerobic cocci and 72% of Bacteroides other than B. fragilis at a concentration of 16 mug/ml. B. fragilis and Clostridia were resistant to CCL. Increased inoculum of E. coli from 10(5) to 10(9) increased the minimal inhibitory concentration of CCL and cefamandole by fourfold against 7 of the 64 strains tested. All seven were beta-lactamase negative. No antimicrobial synergism was noted between CCL and penicillin. The in vitro efficacy of CCL, an oral cephalosporin, against enteropathogenic E. coli, if proven safe, may be tested in vivo against such infections.

Aerobiosis↗

Pharmacokinetics of cefaclor in patients with end stage renal disease and during hemodialysis.

A single 1.0-g dose of cefaclor administered to patients with stable end stage renal disease whose creatinine clearances were <5 ml/min produced a mean peak serum concentration of 48.3 +/- 19.8 mug/ml. The half-life was 2.3 +/- 0.3 h. Hemodialysis shortened the half-life of a similar dose to 1.6 +/- 0.3 h. Approximately one-third (340 mg) of the administered drug was recovered in the dialysate. Multiple doses of 500 mg every 6 h between hemodialysis sessions produced effective serum concentrations and no bioassay evidence of drug accumulation.

Aged↗

Susceptibilities of beta-lactamase-producing and -nonproducing ampicillin-resistant strains of Haemophilus influenzae to ceftibuten, cefaclor, cefuroxime, cefixime, cefotaxime, and amoxicillin-clavulanic acid.

In in vitro studies we evaluated the susceptibilities of beta-lactamase-producing and -nonproducing, ampicillin-resistant strains of Haemophilus influenzae and compared them with those of ampicillin-susceptible strains. Ampicillin, amoxicillin-clavulanic acid, ceftibuten, cefaclor, cefuroxime, cefixime, and cefotaxime were evaluated by broth microdilution tests and disk diffusion tests. The disk diffusion tests accurately categorized beta-lactamase-producing strains and ampicillin-susceptible strains as being susceptible to the study drugs other than ampicillin. Ampicillin-resistant, beta-lactamase-nonproducing strains were relatively resistant to all seven study drugs, but the disk diffusion test did not always predict that resistance. The clinical relevance of the decreased susceptibility to various agents remains unclear, but to be conservative, all ampicillin-resistant, beta-lactamase-nonproducing strains might be assumed to be resistant to other beta-lactams. After excluding that small group of isolates, reliable susceptibility test results were obtained with lots of Haemophilus Test Medium that met quality assurance criteria.

Amoxicillin↗

Antimicrobial action of Nitens mouthwash (cetyltrimethylammonium naproxenate) on multiple isolates of pharyngeal microbes: a controlled study against chlorhexidine, benzydamine, hexetidine, amoxicillin, amoxicillin-clavulanate, clarithromycin, and cefaclor.

BACKGROUND: Acute oropharyngeal and respiratory tract infections are due to a wide spectrum of microorganisms. The aim of this study was to compare and evaluate the in vitro activity of four antiseptics (cetyltrimethylammonium naproxenate, chlorhexidine, benzydamine, hexetidine) to four antibiotics (amoxicillin, amoxicillin-clavulanate, clarithromycin, cefaclor) on strains of Haemophilus influenzae, Moraxella catarrhalis, Streptococcus pyogenes and Streptococcus pneumoniae. METHODS: Susceptibility tests were performed on 90, aerobic and anaerobic, bacterial strains, isolated from nasopharyngeal swabs and sputum. Minimum inhibitory concentrations (by microdilution) and minimum bactericidal concentrations were determined and compared. RESULTS: Our selected panel of bacteria was highly susceptible to the antiseptics, particularly to chlorhexidine and naproxenate, even more so than two of the most frequently used antibiotics. Data were statistically significant (p < 0.005). CONCLUSIONS: In view of their bactericidal and anti-inflammatory properties, these antiseptics may be effective in controlling the transitory colonization of the oral cavity by microbes that cause or worsen disease in patients with mild infections.

Anti-Bacterial Agents↗

[Prevalence of Haemophilus influenzae resistant to ampicillin, cefaclor, cefotaxime, chloramphenicol and cotrimoxazol isolated from laboratories in the city of São Paulo, Brazil].

OBJECTIVE: To determine Haemophilus influenzae resistant to ampicillin and other antibiotics isolated from different clinical specimens. METHODS: Isolates of H. influenzae were identified by culture with V and X factors and the aminolevulinic test. Nitrocefin was used to detect beta-lactamase (betaLac) production isolates were tested for antimicrobial susceptibility by disc diffusion and agar dilution methods. Serotype b was assessed by slide co-agglutination. RESULTS: From 245 H. influenzae identified, 155 were tested for serotype b, 28% (43/155) of which were positive. The global rate of beta-lactamase-positive isolates was 9% (22/245). Resistance was similar among serotype b (11.6%) and non-type b H. influenzae (9.8%) (p>0.05). No difference on betaLac production was found according to specimen's origin or the patients' age. Resistances to other antibiotics (by agar dilution and disc diffusion method, respectively) were: chloramphenicol 3.3 to 7.1%; cefaclor: 1.6 to 3.9% and cotrimoxazol: 9.1 to 10.5%. No resistance to cefotaxime has been detected; 63% (5/8) beta-Lac-positive isolates by agar dilution showed also resistance to chloramphenicol, compared to 3% (4/118) in the ss-Lac-negative group (p<0.001). CONCLUSIONS: H. influenzae ampicillin-resistance has shown to be lower than other hospital-based-studies in São Paulo, and comparable to rates found in healthy carriers. The association between ampicillin and chloramphenicol resistance was significant: where this pattern is frequently found, the initial therapy for severe H. influenzae infections - like meningitis - should include a third generation cephalosporin.

English Abstract↗