An assessment of dose-uniformity of samples delivered from paediatric oral droppers

To assess the accuracy and precision of delivery from containers containing oral drops, both under optimal laboratory conditions and during use by volunteers using a variety of real pharmaceutical products and specially prepared fluids.

The effects of the physical properties (viscosity, surface tension, fluid density) of fluids and the angle of a dropper upon the accuracy and precision of dispensing were investigated under standard laboratory conditions. Dose delivery was then assessed using a number of volunteers who were either given no instructions on the use of containers or were instructed to hold the droppers vertically.

Viscosity, surface tension, fluid density and residual volume had little or no effect upon the volume of liquid delivered by a dropper clamped in the vertical position. However, when the angle of the dropper was moved towards 45 degrees from the vertical, the volume dispensed declined and became more variable to a point where the requirements of the European Pharmacopoeia were no longer fulfilled. This finding applied to a variety of products. When volunteers used the same droppers manually, the mean volumes dispensed were lower than when the droppers were vertically clamped and the variability was greater. It appeared that these problems were associated with volunteers failing to hold the dropper vertically and the precision and accuracy were indeed increased if the volunteers were instructed as to how the dropper should be held. The results from volunteers were more precise and accurate with the most viscous of the fluids tested and it was speculated that this may have been because the volunteers could more easily use the droppers vertically as there was less fear of dispensing too many drops.

The key factor in achieving satisfactory dispensing from droppers is to ensure that the dropper is held vertically and this should form the basis of instructions to patients. Formulators should consider increasing the viscosity of prepared dropper solutions to reduce further errors in dose.