Force requirements in topical medicine use--the squeezability factor

Patient compliance is essential to ensure efficacious treatment. The ease of topical drop delivery is of paramount importance. At least 50% of patients report difficulty in self-administration of topical ocular medicine. The two most frequently reported causes of difficulty include aiming the bottle and squeezing the bottle.

The aims of this study were to identify (I) the force required to deliver a single drop from a bottle (the squeezability factor), (II) are some bottle designs easier to use than others? (III) Do compliance aids reduce the finger strength required to deliver an eye drop?

We measured the force required to deliver a single drop from a variety of commonly used ophthalmic preparations. Force was slowly applied at the midpoint along the bottle until a drop fell from the tip. Compliance aids were also tested with this technique.

We report a wide variation in the force requirements needed to use topical medicines. Three of the four compliance aids tested increased force requirements but may have had other beneficial effects by altering the grip on the medicine bottle.

This study highlights the large variability in force required to deliver a single drop using the ophthalmic preparations and compliance aids tested. We feel our results will be of interest and relevant to prescribing physicians and manufactures alike.