ROOSEWELT, C., et al. “Simultaneous Estimation of Drotaverine HCl and Mefenamic Acid in Tablet Dosage Form Using Spectrophotometric Method”. Asian Journal of Chemistry, vol. 22, no. 2, Mar. 2010, pp. 843-9, https://asianpubs.org/index.php/ajchem/article/view/11194.