Stability and Blood Level Determinations of Cefaclor, a New Oral Cephalosporin Antibiotic

Abstract

Cefaclor solutions in pH 2.5 and 4.5 buffers contained at least 90% of their initial activity after 72 h at 40C. Samples in pH 6.0, 7.0, and 8.0 buffers contained 70, 46, and 34%, respectively, of their initial activity after 72 h at 4C. After 72 h at 250C, samples prepared with pH 2.5, 4.5, 6.0, 7.0, and 8.0 buffers contained 95, 69, 16, 5, and 3%, respectively, of their initial activity. After 72 h at 370C, cefaclor solutions in pH 2.5 buffer contained 80% of the initial activity, whereas samples prepared in pH 4.5, 6.0, 7.0, and 8.0 buffers contained less than 20%. Laboratory-prepared plasma and serum samples showed an 8% loss in activity when incubated for 6 h at 40C, a 51% loss when incubated for 6 h at 250C, and a 48% loss when incubated for 2 h at 370C. Clinical samples demonstrated a similar stability pattern. Degradation rates for cefaclor in commercially prepared serum increased from 4-to 10-fold in comparison to rates obtained when samples were made in human serum freshly prepared in our laboratory. Consequently, serum standards should be made in freshly prepared human serum.Cefaclor, 3-chloro-7-D-(2-phenylglycinamido)-3-cephem-4-carboxylic acid, is an orally effective, broad-spectrum cephalosporin derivative that has been shown by Sullivan et al. (3) to be quantitatively absorbed as the intact antibiotic from the gastrointestinal tract of mice, rats, and dogs. Cefaclor is structurally related to other cephalosporins, in particular cephalexin, but possesses stability characteristics different from those of cephalexin. This study describes the stability characteristics of cefaclor and outlines procedures for the proper handling and evaluation of clinical samples. MATERIALS AND METHODSStability of cefaclor in buffer. The stability of cefaclor in the following 0.1 M potassium phosphate buffers was examined: pH 2.5, 4.5, 6.0, 7.5, and 8.0. Samples were prepared at 1 mg of cefaclor activity per ml in the appropriate buffer and incubated at 37, 25, and 40C. Samples were assayed at 0-, 24-, 48-, and 72-h intervals by removing an appropriate amount of the sample, diluting it 100-fold with 0.1 M pH 4.5 potassium phosphate buffer, and assaying by the AUTOTURB System (2) against a standard curve prepared in 0.1 M pH 4.5 potassium phosphate buffer at concentrations of 2.0, 5.0, 10.0, 20.0, and 40.0 itg of cefaclor activity per ml. Staphylococcus aureus ATCC 9144 was used as the test organism.In vitro stability of cefaclor in plasma and serum. Samples were prepared at 10 Zg of cefaclor activity per ml in either pooled human serum obtained commercially or serum and plasma obtained from the same healthy volunteers. The fluids were tested before use to ensure that they were devoid of antimicrobial activity. The pH was adjusted to 7.45 by the addition of 2 N HCl. Samples were incubated at 4, 25, and 3700, and the pH was maintained at 7.45 by overlaying the sample with an atmosphere of 95% 02-5% C02. A 1-ml sample was removed at appropriate intervals up to 6 h, diluted 100-fold with pH 4.5 buffer, stored at 40C, and a...

Influence of storage and susceptibility test conditions on stability and activity of LY163892 and four other cephalosporins

“…Indeed, cefaclor activity (but not that of LY163892) diminished sharply at 4°C after 48 h in human serum and urine. Likewise, cefaclor deteriorated rapidly in serum, urine, and various culture media when exposed to 35°C for 8 to 18 h, as shown previously (1,5 Only subtle differences in antimicrobial activity were noted between LY163892 and cefaclor in this study, i.e., slightly greater activity of LY163892 against E. coli and H. influenzae and slightly less activity against Streptococcus pneumoniae strains with diminished penicillin susceptibility.…”

Comparison of cefprozil and cefaclor pharmacokinetics and tissue penetration

“…Since cefaclor is not very stable at neutral pH or in biological fluids (10), its lack of stability may be responsible for its accelerated disappearance from skin blister fluid and plasma. Concentrations of the two cephalosporins in urine greatly exceeded the MIC for 90% of most susceptible urinary tracer pathogens tested (MIC90) during the first 6 h after dosing.…”

Biliary Excretion of Cefaclor

“…1, pH adjusted to 6.5), with Bacillus subtilis (strain ATCC 6633) as test organism. With regard to the instability of cefac lor in biological fluids at room temperature [7], serum and biliary samples were immediately froz en after sampling and stored at -50 C until as sayed. Dilutions and standard reference curves were prepared using rabbit or human pooled ser um for serum assays, rabbit or human pooled bile for bile assays and phosphate buffer (pH 4.5, 0.1 M) for liver assays.…”