Tetracyclines Calcium compounds

Because acid-pepsin disease rarely occurs in the absence of gastric acid and pepsin, antacids are highly effective in its overall management. Antacids consist of a mixture of magnesium, aluminum, and calcium compounds. Their efficacy is based on their inherent ability to react with and neutralize gastric acid. Sodium bicarbonate, which may leave the stomach rapidly, can cause alkalosis and sodium retention. Calcium salts may produce hypercalcemia, which can be detrimental in patients with impaired renal function. Aluminum salts may decrease the absorption of tetracyclines and anticholinergic drugs. 

Food, dairy products and calcium compounds markedly reduce the absorption of strontium ranelate, and administration should be separated by at least 2 hours. Aluminium and magnesium antacids only slightly reduce strontium ranelate absorption. Strontium ranelate is predicted to reduce the absorption of the quinolones and the tetracyclines, and strontium should be stopped during courses of these antibacterials. Vitamin D does not affect strontium ranelate bioavailability. 

Reduced absorption due to complex formation or other interactions between drugs and intestinal components leading to poor absorption has been described in a few cases. One example is the precipitation of cationic drugs as very poorly-soluble salts with bile acids, which has been reported for several compounds [62], Another well-known example is the complex formation between tetracycline together with calcium due to chelation after administration of the drug together... 

Despite the fact that a plethora of dietary factors could, and will, affect the absorption characteristics of phytochemicals, this area has not been systematically explored. One reason might be the complexity of dietary factors and their interactions that could affect absorption. A nonexhaustive list would include the volume and composition of the food consumed, pH, caloric density, viscosity, nutrients (carbohydrates, protein, fat, fibers), alcohol, caffeine, and the presence of other phytochemicals. Such dietary factors affect the functional status, motility, and acidity of the gastrointestinal tract in a complex manner and modify the physicochemical properties, formulation, and dissolution characteristics of the compound of interest. Calcium in dairy products, for example, has the potential to chelate tetracyclines and fluoroquinolones and, thereby, reduce their bioavailability and biological activity [31]. 

Adsorption of some drugs, especially vitamins, on diluents such as kaolin. Fuller s earth or hentonite can occur in capsule and tablet dosage forms. The physical adsorption can retard dissolution and, hence, hioavailahility. Some calcium salts (e.g. dicalcium phosphate) are extensively used as diluents in tablet and capsule dosage forms. The original use of dicalcium phosphate in a tetracycline capsule formation resulted in poor bioavailability. Lactose tends to react with amine compounds causing discoloration. 

Tetracyclines and fluoroquinolones form strong complexes with bivalent ions like calcium. Therefore, EDTA was added during milk extraction and EDTA-modified silica gel was selected as a layer material offering the best separation (free of tailing) of the target compounds and a signihcant fluorescence enhancement effect for a low limit of detection. The selected solvent system provided the complete separation of the seven antibiotics (Eigure 10.4), when a 10% EDTA solution for the layer modification was verified as optimal for the best separation of TCs and EQs [6]. 

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