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Optimization of a Quantitative Micro-neutralization Assay
10:09

Optimization of a Quantitative Micro-neutralization Assay

Published on: December 14, 2016

The quantification of the neutralization of the action of antibiotics by cationic iron

A A Miles, J P Maskell, S J Evans

    The Journal of Antimicrobial Chemotherapy
    |August 1, 1986
    PubMed

    Insights

    Iron can reverse antibiotic action, particularly with tetracyclines and aminoglycosides. The iron to antibiotic ratio varies, with tetracycline effectiveness depending on its concentration.

    Area of Science:

    • Pharmacology
    • Biochemistry
    • Microbiology

    Background:

    • Antibiotic efficacy is crucial for treating bacterial infections.
    • Interactions between metal ions and antibiotics can affect drug activity.
    • Iron's role in modulating antibiotic function requires further investigation.

    Purpose of the Study:

    • To investigate the reversal of antibiotic action by iron.
    • To determine the molar ratios of iron to various antibiotics at which reversal occurs.
    • To analyze the relationship between tetracycline concentration and iron's neutralizing effect.

    Main Methods:

    • Crude measurements of iron to antibiotic molar ratios for reversal.
    • Precise determination of the molar ratio using ferric iron (Fe+++) and tetracycline.
    • Testing across a range of tetracycline concentrations (1 to 625 mg/l).

    Main Results:

    • Low iron to antibiotic ratios (0.2-2.4) were observed for ampicillin, carbenicillin, and lincomycin.
    • Higher ratios were found for tetracyclines (average 46) and aminoglycosides (average 70).
    • The molar ratio for tetracycline neutralization by iron increased with tetracycline concentration, from 35 to 118.

    Conclusions:

    • Iron can antagonize the action of certain antibiotics, notably tetracyclines and aminoglycosides.
    • The concentration of tetracycline significantly influences the amount of iron required for reversal.
    • At therapeutic plasma concentrations (5 mg/l), a molar ratio of approximately 45 indicates substantial iron interference with tetracycline.

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