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Equilibrium studies on tetracycline-metal ion systems
M Novák-Pékli1, M el-Hadi Mesbah, G Pethó
1Semmelweis University of Medicine, Department of Pharmaceutical Chemistry, Budapest, Hungary.
Journal of Pharmaceutical and Biomedical Analysis
|June 1, 1996
Summary
Oxytetracycline (OTC) and doxycycline (DOX) form different metal complexes. DOX binds fewer protons than OTC, potentially explaining its superior pharmacodynamic effect.
Area of Science:
- Coordination Chemistry
- Medicinal Chemistry
- Biochemistry
Background:
- Oxytetracycline (OTC) and doxycycline (DOX) are structurally similar tetracycline antibiotics.
- Understanding their metal ion interactions is crucial for their pharmacological activity and delivery.
Purpose of the Study:
- To determine the protonation and equilibrium constants of OTC and DOX with Zn2+, Ca2+, and Mg2+.
- To investigate the formation of binary and ternary complexes involving these antibiotics and metal ions.
- To correlate complexation differences with observed pharmacodynamic effects.
Main Methods:
- Calvin-type pH-metric titrations were employed.
- Experiments were conducted under physiological conditions (37°C, 0.15 M NaCl).
Main Results:
- Significant differences in complex composition and protonation states were observed between OTC and DOX.
- OTC generally formed species with fewer bound protons compared to DOX.
- These differences persisted in ternary complexes formed with ascorbic acid.
Conclusions:
- The distinct protonation behavior of OTC and DOX in metal complexes may underlie their differing pharmacodynamic profiles.
- Doxycycline's ability to bind fewer protons could contribute to its enhanced therapeutic efficacy over oxytetracycline.