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Dr. Lloyd's blog has now been retired. We appreciate all the wisdom and support Dr. Lloyd has brought to the WebMD community throughout the years.

Friday, September 28, 2007

How Many Drops Are in That Eyedrop Bottle?

“Doctor, you better write me for two bottles, there’s no way that will last a full month!”

It’s a common response when patients receive a new eyedrop prescription, especially for a long-term condition like glaucoma. There doesn’t appear to be much fluid inside.

Most eyedrop containers are designed to last a month or more. As a result, most insurers will only pay for one bottle per month; patients cover any extras at $30 – $150 per bottle!

The core issue, of course, is the volume of a single drop of medication. Try and guess:

A. 0.0005 ml

B. 0.0050 ml

C. 0.0500 ml

D. 0.5000 ml

E. 5.0000 ml

The correct answer is C. Did you guess correctly? A standard eyedropper dispenses 0.05 ml per drop, meaning there are 20 drops in 1 milliliter of medication.

Let’s do the math: a 5 ml bottle has 100 doses and a 10 ml bottle has 200 doses. (Most eyedrop prescriptions are dispensed in either 5 or 10ml bottles.) Evaporation is not a big problem so long as the cap is replaced after every application.

Calculating for a 30-day month, once-a-day drops and twice-a-day drops in a 5ml bottle will easily last a month. A 10ml bottle will usually accommodate higher doses.

Here’s one last tip. If you cannot recall whether or not the instructions called for shaking the bottle before use, go ahead and shake away – it will not hurt the medicine! Conversely, failure to shake certain prescription eyedrop solutions will likely lead to inadequate dosing.

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Posted by: Bill Lloyd MD at 10:50 pm


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