The ICH guidance in practice: stress decomposition studies on three piperazinyl quinazoline adrenergic receptor-blocking agents and comparison of their degradation behaviour

Stress degradation studies were carried out on three piperazinyl quinazoline alpha(1)-adrenergic receptor blockers, viz. prazosin, terazosin, and doxazosin, following the conditions prescribed in the parent drug stability testing guideline (Q1AR) issued by International Conference on Harmonization (ICH). All drugs showed significant decomposition at 80 °C in acidic conditions (0.1 M HCl) and complete degradation in alkaline conditions (0.1 M NaOH). Under both these conditions, 2-piperazinyl-6,7-dimethoxy-4-aminoquinazoline was formed as a major decomposition product in all three drugs. The degradation pattern under ICH-prescribed photolytic conditions in liquid and solid states was also similar for all the drugs. The light exposure resulted in the formation of a cluster of degradation products. No degradation was observed in neutral and oxidative conditions. In solid state, all drugs were stable at 50 °C in a 1-month study. In alkaline conditions, the order of sensitivity to degradation of the three drugs was doxazosin>terazosin>prazosin, while the same was terazosin>doxazosin>prazosin under acidic conditions. Mechanistic explanation is provided for the variable behaviour of decomposition