Tetracyclines pharmaceutical preparations

For identification of oxytetracycline in pharmaceutical preparations, USP 28 [1] describes Method II under identification of tetracycline <193> (see Table 1), BP 2003 [4] describes a TLC and color test. 

Paper partition chromatographic methods have been widely applied to the analysis of tetracyclines (128, 129). Pharmaceutical aqueous suspensions for oral use are acidified with HC1 and diluted with methanol. Crystalline formulations are dissolved only in methanol. A paper chromatographic method for TC determination in pharmaceutical preparations is based on the complexation of the antibiotic with a mixture of urea and disodium edetate on paper at pH 7.4. Urea helped in the separation of degradation products and led to the formation of well defined spots (130). Samples from fermentations must be acidified with oxalic acid to liberate TC from the mycelium. TC in filtrates may be precipitated in saturated solution of sodium tetraphenyl borate, precipitate dissolved in ethyl or butyl acetate and applied for paper chromatography. Various solvent systems and hRp values for paper chromatography are given in Table 4. 

Table 14.4 Determination of Chlorzoxazone and Ibuprofen in serum and pharmaceutical preparations using Eu-tetracycline complex optical sensor doped in sol-gel matrix.

Pharmaceutical preparations of the tetracyclines are mainly confined to capsules, tablets nd injections and the methods given above are usually applicable with little or no modification. For official purposes extensive use is made of microbiological assays. 

Several electrodes are used for the direct determination of pharmaceuticals. For example, an electrode is prepared using a polyvinyl chloride (PVC) membrane and bis(2-ethylhexyl)sebacate has been applied to tetracyclines in pharmaceutical formulations. The system has also been used to obtain the dissolution profile of some tetracycline formulations. A membrane for the determination of dopamine was synthesized using a CuS04-poly(ethylene-co-vinyl acetate) mixture in tetrahydrofuran, and the resulting solution was dropped into a tubular graphite-epoxy electrode. The drug was oxidized by Cu(II) immobilized on the membrane. 

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