The objective of this study is to advice the number of eyedrops accessible per party of a variety of commonly prescribed glaucoma medications.

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Six bottles of every glaucoma medication to be tested: three each in the vertical and also horizontal orientations. Bottles were housed in a customized force gauge device designed to mimic ballpoint fingertip contact with a bottle. At a typical rate, all drops were expressed from each bottle and also counted v an automated autumn counter. Simultaneously, bottle volume was measured and also drop size and also number were likewise estimated. The key outcome measures were: total variety of drops, volume every bottle and also drops per milliliter (mL) the glaucoma medication.


A total of 192 party from 32 party designs and also manufacturers were tested. Twenty-two the the 32 bottle designs had actually a substantially different mean number of drops in the vertical and also horizontal positions, v 10 draft have an ext drops dispensed in the horizontal orientation and 12 in the upright orientation. 6 of the 32 party designs had a considerably different mean complete bottle volume in the vertical and also horizontal positions, v all design having better volume in the upright position. An changed ratio the mean variety of drops/mean party volume prove a variety from 20.9 drops/mL come 40.8 drops/mL.


There is significant variability in drops and also volume easily accessible per party of glaucoma medication depending on both the bottle position and also manufacturer. These data suggest to the need for circumspection in prescribing glaucoma medications and also caution in assessing therapeutic outcomes.

Peer testimonial reports


Although data demonstrate improved outcomes with lowered intraocular press from suitable pharmacotherapy <1, 2>, many patients with glaucoma battle to adhere to their prescribed regimens. Numerous studies indicate patients comply with 70% or fewer of your glaucoma medications <3,4,5>. Plenty of factors have actually been implicated <6>, but an obstacle instilling drops has garnered recent attention <7>. Appropriate eyedrop management requires eye-hand coordination and dexterity, linking intuitive acuity through a stable hand and also accurate proprioception <8>. Not surprisingly, videotape evidence demonstrated the glaucoma patient provided an mean of 1.4–1.8 drops when trying to instill a single eyedrop <9, 10>. A recent cross-sectional patient inspection revealed that 25% of patient reported problems with beforehand eyedrop bottle exhaustion and also associated compliance with therapy. One-third of patients reported the reason for early on bottle fatigue was as result of bottle related problems such together “more 보다 one drop come out” or “size of autumn is too large”. The last complaint is sustained by literary works that displayed the volume of an eyedrop in an ophthalmic solution might vary from 25 to 70 μl <11>. Offered the common tear film volume is 7 μl and also only qualified of include 30 μl without overflow, a significant portion of an eyedrop is wasted <12>. This data indicate that a significant number that glaucoma patients operation out of eyedrops prior to a reserved prescription refill and also that bottle connected mechanics play a role <13>.

Despite the importance of bottle style in suitable use of object therapeutics, over there exists no standardization of manufacture in regards to drop instillation dynamics <14>, and the only dosing necessity is to accurately label and also package medication volume <15>. Gift manufactured and sold top top the basis of volume, eyedrops are distinct from many other forms of pharmacotherapy, which room prescribed with a discrete number of doses to guide dispensing and also refill rates. If the minimum volume of medication consumers need to anticipate every container of medicine is available, this does no necessarily analyze to variety of applications, and without regulation, leads to the opportunity of inconsistency in the number of drops of medicine available per bottle. Numerous previous studies analyzing a smaller number of medications in a non-standardized fashion have found far-ranging variability in the number of drops in between both brands of medication and also position that the party <16,17,18>. Together such, the current study was designed to further evaluate this possibility by objectively and systematically measure up the number of eyedrops in each bottle of many common glaucoma medications.

The variety of eyedrops dispensed native various common glaucoma medications was measured. All medications were purchased at cost from the college of Kentucky research study Pharmacy and represented available regional brand and generic medications. A force gauge apparatus consisting that a Mecmesin M500E Motorised Tension and Compression check Stand, Mecmesin 100 N progressed Force Gauge (Mecmesin Corporation, Sterling, VA, USA) and also custom grips and compressors to be designed and calibrated by JA King & company (Whitsett, NC, USA) (Fig. 1). The compressors were designed to mimic ballpoint fingertip call with a bottle. Because that each medication, the bottle was housed in the apparatus and also clamps were adjusted until the ballpoint compressors were situated at mid bottle length. For bottles with a rectangular instead of ring shape, the thinner dimensions were chosen for compression, together this represents the technique most most likely to be utilized by patients once instilling drops. Starting at 0 kg-force (kgf) and 0 mm (mm) displacement, the gauge was progressed in 0.1 mm increments till a drop of liquid dropped from the bottle, together observed subjectively and confirmed v an automatically VCD-BTD drop respond to (Vernier Software and also Technology, Beaverton, OR, USA) and LabQuest 2 display screen (Vernier Software and Technology, Beaverton, OR, USA). At a rate of around one drop/s, 10 drops were expressed, then the apparatus to be retracted to 0 kgf. This was recurring until every drops were tired from the bottle.


Force Gauge Apparatus. A pressure gauge apparatus consisting that a Mecmesin M500E motorized Tension and Compression Stand, Mecmesin 100 N advanced Force Gauge and custom grips and compressors were designed and also calibrated through JA King & Company. a: The compressors to be designed to mimic ballpoint fingertip call with a party tip. b: for each medication, the bottle was housed in the apparatus and also clamps were changed until the ballpoint compressors were located at mid bottle length. The L-shaped compression clamp to be then changed until the force gauge sensor was centered on the crosshairs the the clamp at a 90-degree angle

Simultaneously, fall size and also number was also estimated making use of the densitometric method for volume decision <19>. In twenty drop increments, the complete volume of equipment expressed was measured with a 0.0001 g analytical balance (Ohaus Corporation, Parsippany, NJ, USA). This was recurring until all drops were tired from the bottle. A 200 uL pipette (Zhejiang Huawei clinical Instrument Co, LTD, Zhe Jiang, China) was provided to remove 4 100-uL aliquots of every bottle. The typical of the samples was divided by 0.1 mL to calculation the volume of every drop and also each bottle by separating the massive of each by the calculated density. For any type of bottles v residual liquid in the container lid, this was removed with the pipette and also volume to be measured separately.

Six bottles of every medication to be tested. 3 bottles were tested in the upright orientation through the bottle guideline at 180 degrees and also three bottles were tested in the close to horizontal orientation with the bottle pointer at 30 degrees. The vertical and also horizontal orientations to be the starting position for the bottle tip during each measurement, as compression of the bottle variably and slightly adjusted the pointer position.

Statistical analysis

Mean an answer was compared by constructing an analysis of variance because that a two way layout v factors: place (horizontal versus vertical) and also bottle (all combinations of medication name and formulation). A highly far-ranging interaction between position and also bottle was obtained (p 
Full size table
Full size table

The outcomes of this study suggest there is significant variability in the variety of drops and volume per party of glaucoma medications, both in regards to which party design and manufacturer is utilized and also the place the party is held when squeezed. Because that example, if a representative patient from this region is prescribed a 5 mL bottle of timolol 0.5%, there room 5 various generic and brand bottle designs that may be dispensed. The patient can anticipate a range of 123–209 and 147–166 typical drops per party in the horizontal and vertical positions, respectively. If instilled twice daily, this would suggest a difference in between 25.5 come 43 days of accessible medication relying on the manufacturer and bottle position.

This study is the an initial to our understanding to present an objective, automated and also reproducible technique to measure up the number of drops accessible per bottle of medication. Further, we measured countable drops rather of calculating the variety of drops based on volume, i beg your pardon was presented to be inaccurate. Number of previous studies have evaluated tiny samples of party formulations with similar, variable results. A 1994 examine of patient blinded to either use of a 5 mL party of timolol maleate versus levobunolol discovered a 21% greater length of usage of timolol (37 matches 29 days) <16>. Another study evaluate 45 versus 90 degree management of artificial tear bottles and found a considerably greater variety of drops per bottle making use of densitometric analysis and smaller sized drop volume for 4 out of 5 formulations at 45 compared to 90 degrees. The authors suggest administration at 45 levels would an outcome in as much as $1.93 savings per bottle compared to 90 levels <17>. A study examining 2.5 ml bottles of prostaglandin analogues held vertically, in ~ 45 degrees and horizontally uncovered that upright instillation resulted in much more drops per party for bimatoprost and latanoprost, if 45 levels was most efficient for travaprost. Presume 1 year that bilateral therapy at 2006 costs, the authors established use the the most effective instillation method would result in yearly savings of $109–192 <18>. Lastly, a current study found significant variability in the variety of eyedrops per party of 4 regionally available formulations the latanoprost as soon as measured through manually counting the variety of drops to express by hand, varying from 77.6 come 88.7 drops every bottle. The authors estimated a similarly far-reaching difference in estimated annual cost, ranging from $184 to $1198 per formulation <20>.

Currently, there exist no commonwealth guidelines to control bottle style or lot of drops obtainable per volume of medicine <14, 15>. It has been suggested that pharmacists frequently use a rough tip of 0.05 mL per eyedrop or 20 drops every mL (written personal communication, department of drug Information, FDA, march 27, 2015). Through that in mind, there space significantly much more eyedrops per party in this evaluation than recommended, varying from 10.4% to 45.8% more mean autumn per party tested. This may show that manufacturers “overfill” the bottles to enable for a margin that error throughout dispensing. If true, this serves an essential purpose, since it is recognized that countless patients require more than one eyedrop per application <9, 10>. However, this data suggests another problem has been developed by this practice: far-ranging variability in the variety of doses per bottle.

Aside from bottle volume, an additional factor affect the number of drops accessible per party is drop size. We found significant variability in the approximated drop dimension of learned formulations, varying from 0.024 come 0.221 mL. The size of fall dispensed native a bottle counts on three straightforward elements: the architecture of the dropper bottle and tip, nature of the consisted of solution and also the place of the bottle. The surface ar area around the bottle tip and surface stress of the solution space both manufacturer managed factors that influence drop size. Patience manipulations such together the angle and rate fall are developed are less predictable <11>. Further, the results of the current study and others indicate the many economical bottle place varies from one design to the next <17–19>. A final potential determinant that drop dimension is the pressure required to squeeze the bottle, which unfortunately is significantly variable in both the experimental and also clinical setting <21, 22>. With every one of these influences, it might be complicated to design suitable bottle for instillation. One skilled suggestion has been to utilize a dropper pointer with a smaller outer orifice diameter that provides continual surface area for a smaller-volume autumn to loss <11>.

This study has actually several limitations. The experimental architecture was novel, and also although measurements were automated, they have not been separately verified. Since the study was performed in an objective and reproducible manner, it may not correctly reflect numerous of the patience related determinants in dosing; that is most likely that our patient experience even greater variability in the variety of drops available per bottle. Just two bottle positions to be tested and most ophthalmic containers room not intended come be ceded in a strictly horizontal position. While 192 party from 32 bottle designs to be tested, they still represent a tiny sampling that all accessible brand and generic ophthalmic medications.

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In summary, this examine demonstrates the far-reaching variability in drops and also volume accessible per bottle of glaucoma medication depending on both the party position and manufacturer. This unregulated exercise leaves prescribing physicians and also pharmacists can not to accurately predict the quantity of medicine to dispense. This may bring about patients running the end of medication early on or being left with excess and associated costs. The variability indigenous one refill come the next could be a contributor to restricted compliance. The experimental architecture in this study shows an objective, reproducible an approach to determine drop number uniformly throughout different bottles and also designs. It have to compel additional evaluation and consideration of standardization in the industry.