Studies on 6-acetylmethylenepenicillanic acid (Ro 15-1903). III. Relationship between in vitro activity and chemical stability.
To resolve discrepancies between its enzymological activity and its in vitro or in vivo activity, 6-acetylmethylenepenicillanic acid (Ro 15-1903), a potent beta-lactamase inhibitor, was investigated for its chemical stability and its ability to penetrate the bacterial cell envelope. Although Ro 15-1903 was fairly stable in water or saline, it was found to be unstable in a rich medium, in mouse plasma and in human serum. Decomposition half-lives in Tryptic Soy Broth (TSB) and mouse plasma were determined by spectrometry to be 1.3 hours and 12 minutes respectively. These values were confirmed by a biochemical method for determination of Ro 15-1903. Furthermore, a large enhancement of the in vitro activity was noticed when the assay medium was changed from TSB to a synthetic medium in which Ro 15-1903 was more stable. The ampicillin-potentiating activity marginally increased if a permeability mutant harboring the R6K plasmid, which codes for TEM-1 beta-lactamase production, was used instead of the wild-type strain. These results prove that the chemical instability of Ro 15-1903 is the main cause of its disproportionally low activity in vitro and in vivo. Ro 15-1903 is not nonspecifically inactivated by proteins, since it did not lose its activity after incubation with bovine serum albumin (50 mg/ml) for 2 hours at 37 degrees C. It seems to react specifically with beta-lactamase.
D000667:Ampicillin / Q000633:toxicity; D000818:Animals; D000900:Anti-Bacterial Agents / Q000097:blood*; D004355:Drug Stability; D004926:Escherichia coli / Q000187:drug effects; D006207:Half-Life; D006801:Humans; D007700:Kinetics; D051379:Mice; D008826:Microbial Sensitivity Tests; D010397:Penicillanic Acid / Q000097:blood* / Q000633:toxicity / Q000031:analogs & derivatives; D013056:Spectrophotometry, Ultraviolet
D000900:Anti-Bacterial Agents; D000667:Ampicillin; C036977:6-acetylmethylenepenicillanic acid; D010397:Penicillanic Acid