Open-Label Study of the Stability of Sublingual Nitroglycerin Tablets in Simulated Real-Life Conditions

Contemporary practice favors refilling sublingual nitroglycerin (SL NTG) every 3 to 6 months. This recommendation is based on antiquated data that does not consider the reformulated tablet and the improved manufacturing process. Our objective was to investigate the stability of SL NTG over time using simulated real-life scenarios in comparison to controlled storage conditions. This was an open-label study of 100- and 25-count commercial SL NTG bottles stored in either controlled temperature and relative humidity conditions, or carried in a pocket or purse. SL NTG potency (chemical stability) was assessed using high performance liquid chromatography and physical stability was assessed by changes in tablet weights over time through the labeled expiration date. Both chemical and physical stability of SL NTG were affected by environmental and physical factors. High temperature storage resulted in the most rapid loss of potency. Tablets carried in a pant pocket lost potency faster than those carried in a purse. Potency was also dependent on headspace of the bottle. Tablets stored in the original bottle in a temperate environment could be expected to maintained potency for more than 2 years when carried in a purse, irrespective of package size. When carried in a pant pocket, potency of a 25-count bottle was maintained for 2 years, whereas potency of a 100-count bottle fell below acceptable limits at 12 months. In conclusion, since potency is dependent on temperature, headspace, and carrying practices, frequency of SL NTG refills should be based on individual patient behavior.