Info

affinities of the tetracyclines for metal ions. One piece of evidence relating to the site of chelation is that isochlortetracycline, which lacks the C-11,C-12 enolic system, does not chelate with Ca2+ ions.

The highly coloured nature of the tetracycline complexes such as the uranyl ion-tetracycline complex may be utilised in analytical procedures.

Four criteria have been put forward for determining whether chelate formation has occurred:16 coloured product, decreased aqueous solubility, a drop in pH during chelate formation, and the absence of metal ions in solution after chelate formation. The decreased aqueous solubility of chelates suggests increased lipophilicity but, in the case of the tetracycline chelates, precipitation would decrease the biological activity of the drug as it would be less available for transport across membranes; the larger volume of the chelate would also prevent easy absorption in the intact form.

There is evidence for complex formation of a coumarin derivative with magnesium ions

Figure 10.10 Plasma levels of bishydroxycoumarin (BHC), also known as dicoumarol, in 6 subjects after a 300 mg oral dose with water (solid line), magnesium hydroxide (dotted line) or aluminium hydroxide (dashed line). Closed data points represent a significant difference from control.

Reproduced from reference 17.

Figure 10.10 Plasma levels of bishydroxycoumarin (BHC), also known as dicoumarol, in 6 subjects after a 300 mg oral dose with water (solid line), magnesium hydroxide (dotted line) or aluminium hydroxide (dashed line). Closed data points represent a significant difference from control.

Reproduced from reference 17.

0 0

Post a comment