Determination of Ranitidine in Human Plasma by SPE and ESI-LC-MS/MS for Use in Bioequivalence Studies

A method for determining ranitidine in human plasma by ESI-LC-MS/MS was validated, using propranolol as internal standard. The extraction method used was solid phase extraction (SPE). Chromatographic separation was performed in a Chromolith C18 (50？mm × 4.6？mm i.d.) analytical column, which provided good separation of ranitidine and propranolol peaks with an analysis time of 2.5 minutes. Extraction yields of 94.4% for ranitidine and 89.4% for the internal standard were obtained. The lower limit of quantification (LLOQ) was 3.00？ng/mL, and limit of detection (LOD) was 0.05？ng/mL, with linearity ranging from 3.00 to 500？ng/mL. The results, thus, showed that this method is suitable for application in bioequivalence studies of ranitidine in human plasma. 1. Introduction The chemical structure of ranitidine hydrochloride (Figure 1) consists of a five-membered furan heterocyclic ring and a nitroethenodiaminic group. The molecular mass of ranitidine hydrochloride is 350.9 daltons (g/mol), and its molecular formula is C13H22N4O3SHCl corresponding to hydrochloride N[2-[[[5-[(dimethylamine)methyl)-2-furan]methyl]thio]ethyl]-N′-methyl-nitro2-1,1-ethenodiamine. Ranitidine hydrochloride appears as a crystalline powder, practically odorless and white to light yellow. It is very soluble in water, somewhat soluble in alcohol, and slightly soluble in chloroform. Furthermore, it should be stored in hermetically sealed containers and protected from light [1]. Figure 1: Chemical structure of ranitidine hydrochloride. Ranitidine is widely used in the treatment of gastric pathologies, has a chemical structure that partially resembles histamine, and acts primarily as a competitive histamine inhibitor through the H2 receptors [2, 3]. Since around two thousand analyses are conducted before bioequivalence studies can be concluded, the search for quick and simple methods to determine drugs in biological matrices has been intense. Thus, several methods for determining ranitidine in human plasma have been reported. Zendelovska and Stafilov [4] developed a method for determining ranitidine and cimetidine in human plasma using HPLC with a diode array detector. In this study, the analysis time was 9 minutes, with a 50.0？ng/mL limit of detection for ranitidine. Famotidine was used as internal standard. In another study using the same detector, an analysis time of 6.5 minutes was obtained in a C18 column (300？mm 4.6？mm id, 5？μm), with a limit of quantification of 20.0？ng/mL [5]. Methods for analyzing ranitidine in plasma by LC-MS/MS have been reported in some studies [6–8]. The limits