Background: Analgesic therapy with the combinations of active ingredients having different mechanisms of action is beneficial for reducing the therapeutic dose and side effects. Therefore, multi-ingredients pharmaceutical preparations such as the combination of paracetamol and diclofenac are becoming more popular on the market.

Objectives: (1) Developing a capillary zone electrophoresis method for determining simultaneously paracetamol and diclofenac in pharmaceutical formulations (2) Applying this method on the products circulated on the market. Materials and methods: Paracetamol and diclofenac in Zengesic and Ripaigesic film-coated tablets were used in this research. The method was developed and validated according to AOAC 2016 and ICH 2005 guidelines.

Results: The procedure was developed using the Agilent 7100 CE electrophoresis system with the following electrophoresis conditions: uncoated fused-silica capillary column of a total length of 50 cm (effective length 41.5 cm), sodium tetraborate buffer solution 50 mM (pH = 9), the voltage applied to both capillary ends 30 kV, sample injection mode 35 mbar for 4s, detection with a PDA detector at 276 nm. The method was validated for the capillary zone electrophoresis system compatibility, specificity, linearity range, precision, and accuracy in accordance with AOAC standards.

Conclusions: The developed capillary zone electrophoresis method can be applied to simultaneously determine paracetamol and diclofenac in pharmaceutical formulations on the market.