Abstract
Surface tension at the surface-to-air interface is a physico-chemical property of liquid pharmaceutical formulations that are often overlooked. To determine if a trend between surface tension and route of administration exists, a suite of oral, nasal, and ophthalmic drug formulations were analyzed. The surface tension at the surface-to-air interface of the oral formulations studied were in or above the range of the surface tension of gastric, duodenum, and jejunum fluids. The range of surface tensions for oral formulations were 36.6–64.7 dynes/cm. Nasal formulations had surface tensions below that of the normal mucosal lining fluid with a range of 30.3–44.9 dynes/cm. Ophthalmic OTC formulations had the largest range of surface tensions at the surface-to-air interface of 34.3–70.9 dynes/cm; however, all formulations indicated for treatment of dry eye had surface tensions higher than that of normal tears, while those for treatment of red eye had surface tensions below. Therefore, surface tension at the surface-to-air interface of liquid formulations is dependent on the route of administration, environment at site of introduction, and for ophthalmics, what the formulation is indicated for.
Highlights
Liquid drug delivery systems undergo extensive experimental testing beyond pharmacodynamic and pharmacokinetic studies, such as pH, viscosity, density, stability, leachable studies, isotonicity, etc
We hypothesized that the surface tension at the surface-to-air interface of oral formulations would have a large range, since, upon clinical administration of the medication, the liquids would be quickly distributed throughout the significantly large volume of the GI tract
Jejunal fluids have been reported to have a slightly lower surface tension of ~30.5 dynes/cm [5]. This lowering of surface tension has been hypothesized to be due to decreased secretion of bile salts from the gall bladder compared to the duodenum (~2.5 mM compared to ~3.3 mM, respectively) [5]
Summary
Liquid drug delivery systems undergo extensive experimental testing beyond pharmacodynamic and pharmacokinetic studies, such as pH, viscosity, density, stability, leachable studies, isotonicity, etc. We report our findings on the surface tensions at the surface-to-air interface for a range of oral, nasal, and ophthalmic over-the-counter (OTC) drug substances. Since the reported surface tension of the fluids in the GI tract were determined at room temperature, the oral OTC formulations were done at that temperature.
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