Abstract
BackgroundThe purpose of this study is to evaluate the number of eyedrops available per bottle of a variety of commonly prescribed glaucoma medications.MethodsSix bottles of each glaucoma medication were tested: three each in the vertical and horizontal orientations. Bottles were housed in a customized force gauge apparatus designed to mimic ballpoint fingertip contact with a bottle. At a standard rate, all drops were expressed from each bottle and counted with an automated drop counter. Simultaneously, bottle volume was measured and drop size and number were also estimated. The main outcome measures were: total number of drops, volume per bottle and drops per milliliter (mL) of glaucoma medication.ResultsA total of 192 bottles from 32 bottle designs and manufacturers were tested. Twenty-two of the 32 bottle designs had a significantly different mean number of drops in the vertical and horizontal positions, with 10 designs have more drops dispensed in the horizontal orientation and 12 in the vertical orientation. Six of the 32 bottle designs had a significantly different mean total bottle volume in the vertical and horizontal positions, with all designs having greater volume in the vertical position. An adjusted ratio of mean number of drops/mean bottle volume demonstrated a range from 20.9 drops/mL to 40.8 drops/mL.ConclusionsThere is significant variability in drops and volume available per bottle of glaucoma medication depending on both the bottle position and manufacturer. These data point to the need for circumspection in prescribing glaucoma medications and caution in evaluating therapeutic outcomes.
Highlights
The purpose of this study is to evaluate the number of eyedrops available per bottle of a variety of commonly prescribed glaucoma medications
Being manufactured and sold on the basis of volume, eyedrops are distinct from most other forms of pharmacotherapy, which are prescribed with a discrete number of doses to guide dispensing and refill rates
Comparing mean number of drops per bottle using observed measurements versus the densitometric method to calculate number of drops in the bottle, there was no difference in the vertical (p = 0.35, paired t-test), but a significant difference between measurements in the horizontal (p = 0.02, paired t-test) position
Summary
The purpose of this study is to evaluate the number of eyedrops available per bottle of a variety of commonly prescribed glaucoma medications. Despite the importance of bottle design in proper use of topical therapeutics, there exists no standardization of manufacture in regards to drop instillation dynamics [14], and the only dosing requirement is to accurately label and package medication volume [15]. Several previous studies evaluating a smaller number of medications in a non-standardized fashion have found significant variability in the number of drops between both brands of medication and position of the bottle [16,17,18]. The current study was designed to further evaluate this possibility by objectively and systematically measuring the number of eyedrops in each bottle of many common glaucoma medications
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