Ceruminal diffusion activities and ceruminolytic characteristics of otic preparations - an in-vitro study

Abstract

Background: An in-vitro setup was established in order to determine a) the diffusion activities of eight otic preparations (Aurizon®, Eas Otic®, Epi Otic®, Otifree®, Otomax®, Panolog®, Posatex®, Surolan®) through synthetic cerumen, and b) the ceruminolytic capacity and impregnation effects of these products. The main lipid classes of canine cerumen produced with moderate, non-purulent otitis externa were determined by thin layer chromatography and were subsequently used to produce a standardised synthetic cerumen (SCC). SCC was filled into capillary tubes, all of which were loaded with six commercially available multipurpose otic medications and two ear cleaners, each mixed with two markers in two experimental setups. These two marker compounds (Oil red O and marbofloxacin) were chosen, since they exhibit different physicochemical drug characteristics by which it is possible to determine and verify the diffusion activity of different types of liquids (i.e. the otic preparations). A synthetic cerumen described in the literature (JSL) was also used for comparison as its lipid composition was different to SCC. The diffusion activities of the otic preparations through both types of synthetic cerumen were studied over 24 hours. A second in-vitro experiment determined both the ceruminolytic activity and impregnation effect of the otic preparations by comparing the weight loss or weight gain after repeated incubation of JSL.

Results: Canine cerumen is mainly composed of triglycerides, sterol esters, fatty acid esters and squalene. The diffusion experiments showed a high diffusion efficacy along with a high impregnation effect for one test product. All the other products exhibited a lower diffusion activity with a mild to moderate impregnation effect. A mild ceruminolytic activity was observed for the two ear cleaners but not for any of the otic medications.

Conclusions: The present study demonstrates that there are significant differences in the diffusion characteristics and ceruminolytic properties of the eight tested otic preparations.

Figure 1

Diffusion of Oilred O supplemented to eight otic preparations through synthetic canine cerumen (SCC), means ± standard deviations, n = 6, asterisks (***) indicate p < 0.001 after 1440 h (Aurizon® vs. seven other formulations and control).

Figure 2

Mean diffusion of Oilred O supplemented to eight otic preparations through synthetic canine cerumen (JSL), n = 6, asterisks (***) indicate p < 0.001 after 1440 h (Aurizon® vs. seven other preparations and control).

Figure 3

Oil red O diffusion through synthetic canine cerumen (SCC) after 24 hours, 1 = control (SCC), 2 = Aurizon®, 3 = Epi Otic®, 4 = Eas Otic®, 5 = Panolog®, 6 = Posatex®, 7 = Otomax®, 8 = Surolan®, 9 = Otifree®. The yellow box indicates the approximate area of SCC sampling for the HPLC analysis of supplemented marbofloxacin.

Figure 4

Mean percentage of standardised synthetic cerumen (JSL) removed after Tests 1–3, n = 4 loadings; positive values indicate ceruminolysis, negative values indicate that there has been impregnation of the product.

Figure 5

Mean percentage of standardised synthetic cerumen (JSL) removed after Test 4; weighing was performed after washing with cold water in order to remove all product residues, n = 4 loadings per Test. Positive values indicate ceruminolysis; negative values indicate that there has been impregnation of the product.

Figure 6

Thin layer chromatography presenting the composition of canine cerumen in comparison to lipid standards.