The doxycycline (DOX) is a broad-spectrum antibiotic used in several countries. This drug is part of the list of medicines to the SUS (Unified Health System), a model of health care in Brazil. This study describes the development and validation of a microbiological assay, applying the turbidimetric method for the determination of DOX, as well as the evaluation of the ability of the method in determining the stability of DOX in tablets against acidic and basic hydrolysis, photolytic and oxidative degradations, using Escherichia coli ATCC 10536 as micro-organism test and 3x3 parallel line assay design, with nine tubes for each assay, as recommended by the Brazilian Pharmacopoeia. The developed and validated method showed excellent results of linearity, selectivity, precision, accuracy and robustness. The assay is based on the inhibitory effect of DOX using Escherichia coli ATCC 10536. The results of the assay were treated by analysis of variance and were found to be linear (r= 0.9986) in the range from 4.0 to 9.0μg/mL, precise (repeatability R.S.D.= 0.99 and intermediate precision was confirmed by statistical analysis the mean values obtained from analysis by different analysts) and exact (97.73%). DOX solution exposed to direct UV light, alkaline and acid hydrolysis and hydrogen peroxide causing oxidation were used to evaluate the specificity of the bioassay. Comparison of bioassay and liquid chromatography showed differences in results between methodologies. The results showed that the bioassay is valid, simple and useful alternative methodology for DOX determination in routine quality control.
Hydrogen peroxide (H 2 O 2 ) is one of the most powerful oxidants used in many sectors. Analytical method such as titration by permanganometry is used to maintain the quality of products containing H 2 O 2 . Thus, the objective of this work was to evaluate commercial samples of H 2 O 2 10 V by permanganometry. A difference of almost 3 volumes was found in the analysis of the samples. These results can be real or assigned to the potassium permanganate solution, not automation of the results and/or instability of the H 2 O 2 solutions, for example. The main issue is, in addition to alerting the consumers to adequate storage of H 2 O 2 solutions, to alert the scientific community to the need for concomitant analysis methods for unstable products such as H 2 O 2 10 V solutions in order to avoid doubts on the results and make the manufacturers aware of these quality tests.
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