The Medical Letter on Drugs and Therapeutics
In Brief: One Drop or Two
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Med Lett Drugs Ther. 2006 Jun 19;48(1237):49
 Select a term to see related articles  2006   Eye drops   issue 1237   June 19   One drop or two   ophthalmology   volume 48 

Many prescriptions for eye drops call for instillation of 1-2 drops. But Medical Letter consultants in ophthalmology seem to agree that all eye drops should generally be given in doses of only one drop.

The volume of a single drop can vary with the viscosity of the solution, the design of the dropper, and patient technique. The average volume of a drop is 35-50 microliters, but can be as high as 75 microliters. An eye brimming with fluid holds 30 microliters at best, so even one drop is often an overdose. A second either washes out the first or increases the possibility of systemic toxicity, and doubles the cost.

When two different drops are being used, they should be instilled at least 5 minutes apart.

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