Tetracyclines adsorption

Erythromycin, another macrolide, is rapidly transformed to anhydro-erythromycin in the environment (Hirsch et ah, 1999). A recent study by Chander et al. (2005) compared the sorption of tetracycline and tylosin in two soils that differ in clay and organic matter content. The adsorption of each of the antibiotics was higher in the soil that has a higher clay and organic matter content as these soil traits also provide greater exchange capacity (Fig. 3.8). Those workers speculated that the larger tylosin molecules (MW = 916.1) are adsorbed on the surface of the clay... 

Figure 3.8 Adsorption of tetracycline and tylosin on sandy loam Hubbard soil (10% clay and 2.2% organic matter) and a clay loam Webster soil (34% clay and 4.4% organic matter). (Based on data from Cbander et al., 2005.)...

Wang, J. Peng, T. Lin, M.S. Trace measurements of tetracyclines using adsorptive stripping voltammetry. Bioelec-trochem. Bioenerg. 1986,15, 147-156. 

Magnesium oxide is a basic compound and as such can react with acidic compounds in the solid state to form salts such as Mg(ibuprofen)2 or degrade alkaline-labile drugs. Adsorption of various drugs onto magnesium oxide has been reported, such as antihistamines, antibiotics (especially tetracyclines), salicylates, atropine sulfate, hyoscyamine hydrobromide, paracetamol, chloroquine, and anthranilic acid derivatives have been reported to adsorb onto the surface of magnesium... 

Magnesium silicate may decrease the oral bioavailability of drugs such as mebeverine hydrochloride, sucralfate, and tetracycline, via chelation or binding, when they are taken together. The dissolution rate of folic acid, erythromycin stearate, paracetamol, " and chloroquine phosphate, " may be retarded by adsorption onto magnesium silicate. Antimicrobial preservatives, such as parabens, may be inactivated by the addition of magnesium silicate. ... 

Divalent metal ion chelating agents (e.g. tetracyclines) and heavy metals accumulate in bone by adsorption onto the bone-crystal surface and eventual incorporation into the crystal lattice. 

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. 

The adsorbent properties of kaolin may influenee the adsorption of other orally administered drugs, ineluding cimetidine, lineomycin, tetracycline and digoxin. Since it is sometimes employed as a tablet diluent, it must never be used in tablets containing cardiac glycosides, alkaloids, estrogens and medicaments which may be adsorbed by kaolin. 

Dibasic calcium phosphate is only very slightly soluble in water. It is soluble in dilute hydrochlorie aeid and nitric acid, and slightly soluble in acetic acid. It is relatively stable, but should be stored in well closed containers in a cool dry place. It is incompatible with acids and interferes with the adsorption of tetracyclines. If used in tablet formulations containing inorganic acetate salts, the tablets are likely to develop an acetic odor on aging. An example of a typical tablet formulation eontaining dibasic calcium phosphate is as follows ... 

Tribasic calcium phosphate is soluble in dilute mineral aeids, very slightly soluble in water, and insoluble in aleohol. It is used in the pharmaceutical industry primarily as a tablet and eapsule diluent and as a flow and non-caking agent. Tribasic calcium phosphate provides a higher calcium load than dibasic calcium phosphate. It should not be used with strong acidie salts of weak organic bases or in the presenee of acetate salts. It influences the adsorption of vitamin D, and should not be used with water soluble B vitamins or with certain esters sueh as vitamin E or vitamin A acetate or palmitate. It forms a ealeium eomplex with tetracycline. A tablet formulation utilizing triealeium phosphate as a filler is shown below. 

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