Tetracyclines stability constants

I = 0.01 (KCl) NB Metal-free solutions of die tetracycline were titrated with N2 atmosphere standard NaOH solution and ttie pH measured. No details were given of the pH meter calibration. Metal stability constants were determined from identical titrations in the presence of varying concentrations of nickel(II), zinc(II) or copper(II) ions. 

Benet LZ and Goyan JE, Determination of the stability constants of tetracycline complexes,/. Pharm. Sci, 54,983-987 (1965). NB Used carbonate-free KOH to titrate die hydrochloride salt and measured pH with a high quality pH meter (Beckman Research Model) that had been calibrated at pH 4.01. Activity corrections were applied. 

The thermodynamic proton-ligand (pJ a) metal-ligand stability constants of clioquinol, clofibrate, nitrofurazone, and tetracycline with Cu", Zn, Mn", Mg" and Ca" have been determined at 35 °C in 50% ethanol-water media. An empirical pH correction for... 

Benet LZ and Goyan JE, Determination of the stability constants of tetracycline complexes, /. Pharm. ScL, 54,983-987 (1965). 

That the tetracyclines were effective chelating agents was first demonstrated by Albert and Rees, 1956. Their stability constants were found to be similar to those for glycine (see Table 11.2). 

That tetracycline and its derivatives such as chlorotetracycline and ox5Ttetracycline were chelating agents was found by determination of their stability constants (Albert and Rees, 1956), which showed that their avidity for divalent metals was similar to that of glycine. Stability constants of tetracycline are given in Table 11.2. 

Tetracyclines have the tendency to form chelates with bivalent metal ions. As a consequence of their affinity to calcium, tetracyclines tend to accumulate in the bones of treated animals. Although their chelates with calcium show considerable stability, tetracyclines can be extracted from bones containing these drugs and, therefore, may be present in soups and meals when bones from treated animals are cooked (80, 81). The extractability of chlortetracycline from bone tissue is strongly pH-dependent, being higher at low pH values. This can be easily explained by the dependence of the dissociation constant of the chelate from the pH value. 

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