Development and validation of a rapid turbidimetric assay to determine the potency of norfloxacin in tablets

Norfloxacin is one of the first commercially available (and most widely used) fluoroquinolone antibiotics. This paper reports the development and validation of a simple, sensitive, accurate and reproducible turbidimetric assay method to quantify norfloxacin in tablets formulations in only 4 hours. The bioassay is based on the inhibitory effect of norfloxacin upon the strain ofStaphylococcus epidermidis ATCC 12228 IAL 2150 used as test microorganism. The assay was performed 3x3 parallel lines like, three tubes for each concentration of reference substance and three tubes for each sample concentration. The results were treated statistically by analysis of variance and were found to be linear (r2 = 0.9999) in the selected range of 25-100 μg mL-1; precise (intra-assay: relative standard deviation (RSD) = 1.33%; inter-assay: RSD = 0.21%), accurate (100.74%) and robust with RSD lower than 4.5%. The student's t-test showed no statistically significant difference between the proposed turbidimetric method and an HPLC method previously validated. However the turbidimetric assay can be used as a valuable alternative methodology for the routine quality control of this medicine, complementary to other physical-chemical methods.

诺氟沙星（Norfloxacin）是首批实现商业化应用且应用最为广泛的氟喹诺酮类（fluoroquinolone）抗生素之一。本研究报道了一种简便、灵敏、准确且重现性良好的比浊测定法的开发与验证，该方法可在仅4小时内完成片剂制剂中诺氟沙星的定量分析。该生物测定法基于诺氟沙星对作为试验菌株的表皮葡萄球菌（Staphylococcus epidermidis）ATCC 12228 IAL 2150的抑制作用。本次测定采用3×3平行线设计：对照品各浓度设置3支试管，供试品各浓度同样设置3支试管。所得结果经方差分析（analysis of variance）进行统计学处理，在25~100 μg·mL⁻¹的选定范围内呈良好线性关系（决定系数r²=0.9999）；精密度良好（批内相对标准偏差（relative standard deviation, RSD）=1.33%；批间相对标准偏差（RSD）=0.21%），准确度达100.74%，且稳健性优异，相对标准偏差低于4.5%。t检验（Student's t-test）结果显示，本研究提出的比浊法与此前已验证的高效液相色谱（High Performance Liquid Chromatography, HPLC）法之间无统计学显著性差异。该比浊测定法可作为该药品常规质量控制的可靠替代方法，作为其他物理化学检测方法的补充。