Efficacy of Red Glass in Protecting 1,4-Dihydropyridine Antihypertensive Drugs in Liquid Formulations

A series of different-colored glasses were tested to evaluate their ability to protect dihydropyridine antihypertensives in solution from light. The work aims to define a primary packaging capable of guaranteeing photoprotection for this class of drugs in liquid formulations as an alternative to the current formulations, which are dispensed almost exclusively in solid form. The photostability tests were performed according to international rules by exposing 11 dihydropyridine drugs in ethanol and PEG-ethanol solution to stressing light, shielded by quartz, transparent, amber, or red glass. The transparent glass proved to be completely ineffective, recording a dramatic degradation of all compounds, some of which by 10% in less than 1 min, and with complete disappearance in just 1 h. The amber glass showed a valid photoprotection for almost all compounds, apart from nifedipine and nisoldipine, which degraded by 10% in less than 20 min. The adoption of red glass in filtering the light led to a satisfactory photoprotection for these two drugs, detecting concentrations above 90% for all drugs after 1 h under forced light. The results obtained can help to define safe dispensing systems of liquid formulations of dihydropyridine drugs, which are necessary for those patients who cannot take tablets.