Accuracy and precision of metered doses of nitroglycerin lingual spray.

Purpose: The accuracy and precision of nitroglycerin lingual spray are examined.

Methods: Two hundred and twenty-four bottles of nitroglycerin lingual spray product (0.4 mg nitroglycerin per dose, 75 doses per bottle) were collected from the hospital pharmacy at Vancouver General Hospital. Bottles were placed upright on a level surface. After three priming sprays, each bottle was weighed and an initial measurement was recorded. All measurements were recorded in grams to three decimal places and the bottles were weighed on an analytical balance. Three more sprays were made to simulate those in the patient instruction insert. The scale was set to zero before each measurement, and the bottles were then placed on the scale for five seconds before the final weight was recorded. The three spray weights were averaged to obtain a mean spray weight for each bottle.

Results: The manufacturer guarantees a minimum volume of 0.05-0.1 mL per spray. The lower value of 0.05 mL was used for comparison. The weight of 0.05 mL of preparation was calculated, and this was compared to the mean spray weight of all samples tested. A single sample t test revealed a significant difference between the value reported by the manufacturer and the mean of the sample (t((224)) = -23.42, p < 0.0005).

Conclusion: A significant difference was observed between the expected weight of nitroglycerin solution per metered dose and the mean weight of the study samples. Results of the study indicate that dose delivery may be inaccurate but is fairly precise.