Mariappan T T, Jindal K C, Singh Saranjit
Department of Pharmaceutical Analysis, National Institute of Pharmaceutical Education and Research, Sector 67, S.A.S. Nagar, Punjab, India.
J Pharm Biomed Anal. 2004 Nov 19;36(4):905-8. doi: 10.1016/j.jpba.2004.08.005.
When present together in fixed-dose combinations (FDC) of anti-tuberculosis drugs, rifampicin (R) and isoniazid (H) interact with each other to form isonicotinyl hydrazone (HYD). In a preliminary study, this product was found to possess similar colorimetric spectrum to that of rifampicin. Therefore, an investigation was undertaken to determine interference of HYD during analysis of rifampicin in FDC products by colorimetry. For the purpose, standard plots were constructed for rifampicin and HYD at 475 nm, the wavelength maximum for both the compounds. The plots were linear in the range of 10-100 microg/ml. Molar absorptivity values for rifampicin and HYD were 15279 and 5034, respectively. It indicated that HYD possessed one-third absorptivity to that of rifampicin. The analysis of combinations of rifampicin and HYD revealed that rifampicin could be overestimated to a maximum extent of 33%, while interference varied at other relative ratios of the two compounds. This was also confirmed by colorimetric and HPLC analysis of a degraded marketed product and samples from a dissolution study. Thus this investigation suggests that any method devoid of interference of HYD should be preferred for analysis of rifampicin, whenever it is present along with isoniazid.
当抗结核药物以固定剂量组合（FDC）形式同时存在时，利福平（R）和异烟肼（H）会相互作用形成异烟腙（HYD）。在一项初步研究中，发现该产物具有与利福平相似的比色光谱。因此，开展了一项研究以确定在通过比色法分析FDC产品中的利福平时异烟腙的干扰情况。为此，在475nm（两种化合物的最大波长）处构建了利福平和异烟腙的标准曲线。曲线在10 - 100μg/ml范围内呈线性。利福平和异烟腙的摩尔吸光系数值分别为15279和5034。这表明异烟腙的吸光率是利福平的三分之一。对利福平和异烟腙组合的分析表明，利福平可能被高估至最大33%的程度，而在两种化合物的其他相对比例下干扰情况有所不同。这也通过对一种降解的市售产品和溶出度研究样品的比色法和高效液相色谱分析得到了证实。因此，这项研究表明，只要利福平与异烟肼同时存在，在分析利福平时应优先选择任何不受异烟腙干扰的方法。
