A spoonful of what helps the medicine go down? Improving the reliability of voluntary ingestion for oral dosing in rats and mice

Voluntary ingestion is a refined method for substance administration that can replace oral gavage in rats and mice. It requires no physical restraint and has no associated risks of adverse effects, resulting in improved welfare and reduced distress for both animals and research staff. This method has been shown to be effective for a variety of compounds but is still not widely used due to concerns about accuracy and reliability. One potential issue is aversion to the taste of the compound being administered, including a common issue of bitter taste. In this study we tested compounds used in oral preparations for human medicines to mask bitter tasting drugs, including a commercial formulation designed for this purpose, Bitter Drug Powder (BDP). The masking agents were given in combination with a palatable vehicle (10% condensed milk) and the amount consumed and time to consume recorded. Animals were first habituated to the vehicle with reliable ingestion achieved within a few days. In the first studies, only BDP was fully effective at masking the bitter taste of quinine and preventing the progressive reduction in reliability of intake of the antidepressant, venlafaxine in mice and rats. We were able to replicate these effects using a combination of two different artificial sweeteners, saccharine and acesulfame K, and a thickening agent xanthan gum. These studies demonstrate that using a masking agent can improve the reliability of voluntary oral dosing in mice and rats and provide evidence to support a formulation which is readily available for researchers.