Dose quantification of topical drug delivery to the paranasal sinuses by fluorescein luminosity calculation

Background: Our group has previously described a novel method of objectively quantifying the temporospatial distribution of sinonasal irrigation in a nonanesthetized patient. The purpose of this study is to refine this technique to provide an accurate method of determining concentration of dose delivery as well.

Methods: An endoscope at a fixed position within 2 dissected cadaveric heads was used to image 4 subsites under blue light. Each site was dosed with 3 mL of successively increasing concentrations of fluorescein-labeled saline. In vitro images of the labeled saline were also captured over a range of depths. Images were exported into a graphics editing program that was used to calculate luminosity at 3 regions per subsite. The relationship between luminosity and fluorescein concentration was calculated using a Pearson product-moment correlation coefficient. Significance was determined using a 2-tailed Student t test.

Results: Luminosity of the irrigation delivered to the maxillary sinus, lamina papyracea, ethmoid roof, and frontal sinus positively correlated with fluorescein concentration over a range of 0.1 to 0.01 mg/mL (n = 6; r = 0.95, p < 0.001; r = 0.94, p < 0.001; r = 0.92, p < 0.001; and r = 0.94, p < 0.001; respectively). There was no significant difference between luminosities of a 0.01 mg/mL irrigation layer subtending a range of depths up to 6.6 mm.

Conclusion: The described method is capable of determining the concentration of fluorescein delivery to a mucosal surface via objective luminosity quantification. Our data suggest that this method will remain accurate regardless of the potential for heterogeneous pooling of irrigation. This method may be used to optimize delivery strategies of a variety of topical sinonasal therapies.