Identification and characterization of urapidil stress degradation products by LC-Q-TOF-MS and NMR: Toxicity prediction of degradation products

Urapidil, an antihypertensive drug is subjected to various stress conditions (acidic, basic, neutral, oxidative and photolytic) as per ICH guidelines. A stability indicating HPLC method was developed using InertSustain C8 (250 × 4.6 mm; 5 µm) column and 10 mM ammonium formate (pH 3.5) with gradient elution at a flow rate of 1 mL/min to separate all the DPs. The drug was susceptible to acidic and basic hydrolysis, oxidative and photolytic stress conditions in the solution phase and stable in neutral solution phase and photolytic solid state conditions. A total of five DPs were detected under different stress conditions including DP4 which was previously reported in the literature. An extensive fragmentation pattern of drug and DPs were established using LC-Q-TOF-MS which aided the characterization of DPs. The ambiguity in the position of N-oxide formation in DP5 was confirmed by NMR studies. In silico toxicity of the drug and its DPs were also evaluated. The plausible mechanism of DPs formation was explained.