Determination of Paracetamol in Commercial Suppositories Using Differential Scanning Calorimetry

Abstract

Paracetamol, also known as acetaminophen, has been commonly used as a major active pharmaceutical ingredient in numerous analgesics for over 30 years. This means that specific and reliable methods are crucial for quality control of its formulations. The purpose of this work was to show to what extent differential scanning calorimetry (DSC) can be useful for the determination of paracetamol in formulations intended for rectal use. Suppositories commonly available in Polish pharmacies were chosen for the study. In order to assess the impact of various suppository bases on active ingredient determination in the formulations analyzed, the selection was made from various producers and with varying doses of paracetamol. DSC scans were taken on a heat-flux instrument with a liquid nitrogen cooling system. To achieve the aim of this study, a well-defined endothermic DSC peak was used, assigned to the melting-point of paracetamol at 168.64 O C with the heat of transition of 183.99 J/g. A multiple standard addition method was chosen for the calibration. Except for one formulation containing 50 mg of paracetamol, the relative standard deviation for all the DSC determinations varied over the range of 0.27 to 2.64%, while the relative error varied between 0.24 and 12.50%. The study demonstrated that DSC could successfully be employed as a simple, specific and reliable method for the determination of paracetamol in rectal preparations based on the measurement of its heat of fusion. The results are consistent with the data obtained using UV spectrophotometry (pharmacopoeial method) as reference.