Development and validation of an LC-UV method for the simultaneous analyses of ciprofloxacin and metronidazole in tablet dosage forms: routine application and confirmation of falsifications

Poor quality medicines pose a threat to all health systems. It is obvious that they have harmful consequences not only from the public health point of view, but also from the economic and socio-economic as well [1].
In order to effectively combat this scourge, it is important to determine the quality of these medicines circulating on the pharmaceutical market. In general, this quality control is possible thanks to the methods listed in the pharmacopoeias. However, these methods are generally costly, not environmental friendly and often not easy to implement [2].
In this context and to overcome these disadvantages we undertook the development and validation of a rapid, less polluting and easy to implement HPLC/DAD method for the simultaneous analyses of two anti-infective very used and targeted by falsifiers, ciprofloxacin and metronidazole.
Retention times of 1.7min and 3.4min were obtained for metronidazole and ciprofloxacin respectively, using a mobile phase consisting of 0.025M orthophosphoric acid adjusted to pH3 with Triethylamin and Methanol (75:25) (v/v), an XBridge column C18 (2.1*100mm) 3.5µm and a flow rate of 0.3mL/min.
At first, this method was successfully validated to confirm its suitability following the total error approach with the accuracy profile as a decision tool in the laboratory of analytical pharmaceutical chemistry (LCAP) of the University of Liège and then transferred to the Laboratoire National de Contrôle des Médicaments et Expertise (LANACOME) in Cameroon to implement its usability. The acceptation limits were set at +/- 10% in total relative error and the tolerance intervals were built with a risk set at 5%.
The routine application of this method allowed the identification and quantification of ciprofloxacin and metronidazole in 96 samples collected in the framework of a prevalence study in Cameroon. On the other hand, it was used as a confirmatory method to identify and quantify metronidazole that has been previously detected in tablets by handheld vibrational spectroscopy methods in 4 falsified chloroquine samples seized on the Cameroonian market during the Covid-19 pandemic.